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Sample records for annihilation operators

  1. Two photon annihilation operators and squeezed vacuum

    NASA Technical Reports Server (NTRS)

    Roy, Anil K.; Mehta, C. L.; Saxena, G. M.

    1993-01-01

    Inverses of the harmonic oscillator creation and annihilation operators by their actions on the number states are introduced. Three of the two photon annihilation operators, viz., a(sup +/-1)a, aa(sup +/-1), and a(sup 2), have normalizable right eigenstates with nonvanishing eigenvalues. The eigenvalue equation of these operators are discussed and their normalized eigenstates are obtained. The Fock state representation in each case separates into two sets of states, one involving only the even number states while the other involving only the odd number states. It is shown that the even set of eigenstates of the operator a(sup +/-1)a is the customary squeezed vacuum S(sigma) O greater than.

  2. Number-operator-annihilation-operator uncertainty as an alternative for the number-phase uncertainty relation

    SciTech Connect

    Urizar-Lanz, Inigo; Toth, Geza

    2010-05-15

    We consider a number-operator-annihilation-operator uncertainty as a well-behaved alternative to the number-phase uncertainty relation, and examine its properties. We find a formulation in which the bound on the product of uncertainties depends on the expectation value of the particle number. Thus, while the bound is not a constant, it is a quantity that can easily be controlled in many systems. The uncertainty relation is approximately saturated by number-phase intelligent states. This allows us to define amplitude squeezing, connecting coherent states to Fock states, without a reference to a phase operator. We propose several setups for an experimental verification.

  3. Nuclear annihilation by antinucleons

    DOE PAGESBeta

    Lee, Teck-Ghee; Wong, Cheuk-Yin

    2016-01-25

    We examine the momentum dependence ofmore » $$\\bar p$$$p$ and $$\\bar n$$$p$ annihilation cross sections by considering the transmission through a nuclear potential and the $$\\bar p p$$ Coulomb interaction. Compared to the $$\\bar n p$$ annihilation cross section, the $$\\bar p p$$ annihilation cross section is significantly enhanced by the Coulomb interaction for projectile momenta below $$p_{\\rm lab} <$$ 500 MeV/$c$$, and the two annihilation cross sections approach the Pomeranchuk's equality limit [JETP {\\bb 30}, 423 (1956)] at $$p_{\\rm lab}\\sim 500$ MeV/$c$. Using these elementary cross sections as the basic input data, the extended Glauber model is employed to evaluate the annihilation cross sections for $$\\bar n$$ and $$\\bar p$$ interaction with nuclei and the results compare well with experimental data.« less

  4. Attraction and mortality of Bactrocera dorsalis (Diptera: Tephritidae) to STATIC Spinosad ME weathered under operational conditions in California and Florida: a reduced-risk male annihilation treatment.

    PubMed

    Vargas, Roger I; Souder, Steven K; Hoffman, Kevin; Mercogliano, Juan; Smith, Trevor R; Hammond, Jack; Davis, Bobbie J; Brodie, Matt; Dripps, James E

    2014-08-01

    Studies were conducted in 2013-2014 to quantify attraction, feeding, and mortality of male oriental fruit flies, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), to STATIC Spinosad ME a reduced-risk male annihilation treatment (MAT) formulation consisting of an amorphous polymer matrix in combination with methyl eugenol (ME) and spinosad compared with the standard treatment of Min-U-Gel mixed with ME and naled (Dibrom). Our approach used a behavioral methodology for evaluation of slow-acting reduced-risk insecticides. ME treatments were weathered for 1, 7, 14, 21, and 28 d under operational conditions in California and Florida and shipped to Hawaii for bioassays. In field tests using bucket traps to attract and capture wild males, and in toxicity studies conducted in 1-m(3) cages using released males of controlled ages, STATIC Spinosad ME performed equally as well to the standard formulation of Min-U-Gel ME with naled for material aged up to 28 d in both California and Florida. In laboratory feeding tests in which individual males were exposed for 5 min to the different ME treatments, mortality induced by STATIC Spinosad ME recorded at 24 h did not differ from mortality caused by Min-U-Gel ME with naled at 1, 7, 14, and 21 d in California and was equal to or higher for all weathered time periods in Florida during two trials. Spinosad has low contact toxicity, and when mixed with an attractant and slow release matrix, offers a reduced-risk alternative for eradication of B. dorsalis and related ME attracted species, without many of the potential negative effects to humans and nontargets associated with broad-spectrum contact insecticides such as naled. PMID:25195423

  5. Attraction and mortality of Bactrocera dorsalis to STATIC Spinosad ME weathered under operational conditions in California and Florida: A reduced-risk male annihilation treatment

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Studies were conducted in 2013 in Hawaii, USA, to quantify attraction, feeding, and mortality of male oriental fruit flies, Bactrocera dorsalis (Hendel)(Diptera: Tephritidae), to a reduced risk male annihilation treatment(MAT)formulation consisting of an amorphous polymer matrix in combination with...

  6. Positron-Annihilation Lifetime Spectroscopy using Electron Bremsstrahlung

    NASA Astrophysics Data System (ADS)

    Wagner, A.; Anwand, W.; Butterling, M.; Cowan, T. E.; Fiedler, F.; Fritz, F.; Kempe, M.; Krause-Rehberg, R.

    2015-06-01

    A new type of an intense source of positrons for materials research has been set up at the superconducting electron linear. The source employs hard X-rays from electron- bremsstrahlung production generating energetic electron-positron pairs inside the sample under investigation. CW-operation allows performing experiments with significantly reduced pile-up artefacts in the detectors compared to pulsed mode operation in conventional accelerators. The high-resolution timing of the accelerator with bunch lengths below 10 ps full width at half maximum (FWHM) allows positron annihilation lifetime spectroscopy (PALS) measurements with high time resolution. A single-component annihilation lifetime of Kaptonhas been measured as (381.3 ± 0.3) ps. Employing segmented detectors for the detection of both annihilation photons allows for the first time to perform a 4D tomographic reconstruction of the annihilation sites including the annihilation lifetime.

  7. Annihilation of strained vortices

    NASA Astrophysics Data System (ADS)

    Kimura, Yoshifumi

    2014-11-01

    As an initial stage of vortex reconnection, approach of nearly anti-parallel vortices has often been observed experimentally and studied numerically. Inspired by the recent experiment by Kleckner and Irvine on the dynamics of knotted vortices, we have studied the motion of two anti-parellel Burgers vortices driven by an axisymmetric linear straining field. We first extend the Burgers vortex solution which is a steady exact solution of the Navier-Stokes equation to a time-dependent exact solution. Then by superposing two such solutions, we investigate the annihilation process analytically. We can demonstrate that during the annihilation process the total vorticity decays exponentially on a time-scale proportional to the inverse of the rate of strain, even as the kinematic viscosity tends to 0. The analytic results are compared with the numerical simulations of two strained vortices with the vortex-vortex nonlinear interaction by Buntine and Pullin.

  8. Some Annihilating Particle Systems.

    NASA Astrophysics Data System (ADS)

    Balding, David

    Available from UMI in association with The British Library. Requires signed TDF. Systems of annihilating and coalescing particles on both infinite and periodic one-dimensional state spaces are studied. These systems have various applications in the physical sciences, in particular they are useful as simple models of diffusion-limited reactions. A unified approach to computing properties of the systems using duality methods is presented and it is shown that many results in the scientific literature, derived using diverse techniques, are readily obtained in this general framework. The transition distributions of the processes with arbitrary initial configurations are characterized in terms of two-particle annihilation processes. Further, a concise expression for the distribution of the cardinality of the processes with finite initial configurations is given and particular cases of interest from the applications perspective are described in detail. Asymptotic site occupancies, previously known for certain classes of initial configurations, are derived for all spatially stationary configurations. The asymptotic spatial structure is described for many cases by showing convergence to point processes whose properties are given.

  9. Brane annihilations during inflation

    SciTech Connect

    Battefeld, Diana; Battefeld, Thorsten; Firouzjahi, Hassan; Khosravi, Nima E-mail: tbattefe@princeton.edu E-mail: nima@ipm.ir

    2010-07-01

    We investigate brane inflation driven by two stacks of mobile branes in a throat. The stack closest to the bottom of the throat annihilates first with antibranes, resulting in particle production and a change of the equation of state parameter w. We calculate analytically some observable signatures of the collision; related decays are common in multi-field inflation, providing the motivation for this case study. The discontinuity in w enters the matching conditions relating perturbations in the remaining degree of freedom before and after the collision, affecting the power-spectrum of curvature perturbations. We find an oscillatory modulation of the power-spectrum for scales within the horizon at the time of the collision, and a slightly redder spectrum on super-horizon scales. We comment on implications for staggered inflation.

  10. Annihilation in Gases and Galaxies

    NASA Technical Reports Server (NTRS)

    Drachman, Richard J. (Editor)

    1990-01-01

    This publication contains most of the papers, both invited and contributed, that were presented at the Workshop of Annihilation in Gases and Galaxies. This was the fifth in a biennial series associated with the International Conference on the Physics of Electronic and Atomic Collisions. Subjects covered included the scattering and annihilation of positrons and positronium atoms in various media, including those of astrophysical interest. In addition, the topics of antimatter and dark matter were covered.

  11. Weak annihilation and new physics in charmless decays

    NASA Astrophysics Data System (ADS)

    Bobeth, Christoph; Gorbahn, Martin; Vickers, Stefan

    2015-07-01

    We use currently available data of nonleptonic charmless 2-body decays () that are mediated by QCD- and QED-penguin operators to study weak annihilation and new-physics effects in the framework of QCD factorization. In particular we introduce one weak-annihilation parameter for decays related by quark interchange and test this universality assumption. Within the standard model, the data supports this assumption with the only exceptions in the system, which exhibits the well-known " puzzle", and some tensions in . Beyond the standard model, we simultaneously determine weak-annihilation and new-physics parameters from data, employing model-independent scenarios that address the " puzzle", such as QED-penguins and current-current operators. We discuss also possibilities that allow further tests of our assumption once improved measurements from LHCb and Belle II become available.

  12. Apparatus for photon activation positron annihilation analysis

    DOEpatents

    Akers, Douglas W.

    2007-06-12

    Non-destructive testing apparatus according to one embodiment of the invention comprises a photon source. The photon source produces photons having predetermined energies and directs the photons toward a specimen being tested. The photons from the photon source result in the creation of positrons within the specimen being tested. A detector positioned adjacent the specimen being tested detects gamma rays produced by annihilation of positrons with electrons. A data processing system operatively associated with the detector produces output data indicative of a lattice characteristic of the specimen being tested.

  13. Photon spectra from WIMP annihilation

    SciTech Connect

    Cembranos, J. A. R.; Cruz-Dombriz, A. de la; Dobado, A.; Maroto, A. L.; Lineros, R. A.

    2011-04-15

    If the present dark matter in the Universe annihilates into standard model particles, it must contribute to the fluxes of cosmic rays that are detected on the Earth and, in particular, to the observed gamma-ray fluxes. The magnitude of such a contribution depends on the particular dark matter candidate, but certain features of the produced photon spectra may be analyzed in a rather model-independent fashion. In this work we provide the complete photon spectra coming from WIMP annihilation into standard model particle-antiparticle pairs obtained by extensive Monte Carlo simulations. We present results for each individual annihilation channel and provide analytical fitting formulas for the different spectra for a wide range of WIMP masses.

  14. Annihilation of defects in liquid crystals

    NASA Astrophysics Data System (ADS)

    Svetec, M.; Ambrožič, M.; Kralj, S.

    The annihilation of defect is studied theoretically in liquid crystals (LCs). We consider the annihilation of point disclinations in nematic and line edge dislocations in smectic A LC phase, respectively. We stress qualitative similarities in these processes. The whole annihilation regime is taken into account, consisting of the pre-collision, collision, and post-collision stage.

  15. INSTRUMENTS AND METHODS OF INVESTIGATION: Positron annihilation spectroscopy in materials structure studies

    NASA Astrophysics Data System (ADS)

    Grafutin, Viktor I.; Prokop'ev, Evgenii P.

    2002-01-01

    A relatively new method of materials structure analysis — positron annihilation spectroscopy (PAS) — is reviewed. Measurements of positron lifetimes, the determination of positron 3γ- and 2γ-annihilation probabilities, and an investigation of the effects of different external factors on the fundamental characteristics of annihilation constitute the basis for this promising method. The ways in which the positron annihilation process operates in ionic crystals, semiconductors, metals and some condensed matter systems are analyzed. The scope of PAS is described and its prospects for the study of the electronic and defect structures are discussed. The applications of positron annihilation spectroscopy in radiation physics and chemistry of various substances as well as in physics and chemistry of solutions are exemplified.

  16. Sensitivity of HAWC to high-mass dark matter annihilations

    NASA Astrophysics Data System (ADS)

    Abeysekara, A. U.; Alfaro, R.; Alvarez, C.; Álvarez, J. D.; Arceo, R.; Arteaga-Velázquez, J. C.; Ayala Solares, H. A.; Barber, A. S.; Baughman, B. M.; Bautista-Elivar, N.; Becerra Gonzalez, J.; Belmont, E.; BenZvi, S. Y.; Berley, D.; Bonilla Rosales, M.; Braun, J.; Caballero-Lopez, R. A.; Caballero-Mora, K. S.; Carramiñana, A.; Castillo, M.; Cotti, U.; Cotzomi, J.; de la Fuente, E.; De León, C.; DeYoung, T.; Diaz Hernandez, R.; Diaz-Cruz, L.; Díaz-Vélez, J. C.; Dingus, B. L.; DuVernois, M. A.; Ellsworth, R. W.; Fiorino, D. W.; Fraija, N.; Galindo, A.; Garfias, F.; González, M. M.; Goodman, J. A.; Grabski, V.; Gussert, M.; Hampel-Arias, Z.; Harding, J. P.; Hui, C. M.; Hüntemeyer, P.; Imran, A.; Iriarte, A.; Karn, P.; Kieda, D.; Kunde, G. J.; Lara, A.; Lauer, R. J.; Lee, W. H.; Lennarz, D.; León Vargas, H.; Linares, E. C.; Linnemann, J. T.; Longo, M.; Luna-Garcia, R.; Marinelli, A.; Martinez, H.; Martinez, O.; Martínez-Castro, J.; Matthews, J. A. J.; McEnery, J.; Mendoza Torres, E.; Miranda-Romagnoli, P.; Moreno, E.; Mostafá, M.; Nellen, L.; Newbold, M.; Noriega-Papaqui, R.; Oceguera-Becerra, T.; Patricelli, B.; Pelayo, R.; Pérez-Pérez, E. G.; Pretz, J.; Rivière, C.; Rosa-González, D.; Ryan, J.; Salazar, H.; Salesa, F.; Sanchez, F. E.; Sandoval, A.; Schneider, M.; Silich, S.; Sinnis, G.; Smith, A. J.; Sparks Woodle, K.; Springer, R. W.; Taboada, I.; Toale, P. A.; Tollefson, K.; Torres, I.; Ukwatta, T. N.; Villaseñor, L.; Weisgarber, T.; Westerhoff, S.; Wisher, I. G.; Wood, J.; Yodh, G. B.; Younk, P. W.; Zaborov, D.; Zepeda, A.; Zhou, H.; Abazajian, K. N.; Milagro Collaboration

    2014-12-01

    The High Altitude Water Cherenkov (HAWC) observatory is a wide field-of-view detector sensitive to gamma rays of 100 GeV to a few hundred TeV. Located in central Mexico at 19° North latitude and 4100 m above sea level, HAWC will observe gamma rays and cosmic rays with an array of water Cherenkov detectors. The full HAWC array is scheduled to be operational in Spring 2015. In this paper, we study the HAWC sensitivity to the gamma-ray signatures of high-mass (multi-TeV) dark matter annihilation. The HAWC observatory will be sensitive to diverse searches for dark matter annihilation, including annihilation from extended dark matter sources, the diffuse gamma-ray emission from dark matter annihilation, and gamma-ray emission from nonluminous dark matter subhalos. Here we consider the HAWC sensitivity to a subset of these sources, including dwarf galaxies, the M31 galaxy, the Virgo cluster, and the Galactic center. We simulate the HAWC response to gamma rays from these sources in several well-motivated dark matter annihilation channels. If no gamma-ray excess is observed, we show the limits HAWC can place on the dark matter cross section from these sources. In particular, in the case of dark matter annihilation into gauge bosons, HAWC will be able to detect a narrow range of dark matter masses to cross sections below thermal. HAWC should also be sensitive to nonthermal cross sections for masses up to nearly 1000 TeV. The constraints placed by HAWC on the dark matter cross section from known sources should be competitive with current limits in the mass range where HAWC has similar sensitivity. HAWC can additionally explore higher dark matter masses than are currently constrained.

  17. Flavor dependence of annihilation parameters in QCD factorization

    NASA Astrophysics Data System (ADS)

    Wang, Kai; Zhu, Guohuai

    2013-07-01

    For Bd,s→π∓K± and K(*)K(*) decays, the flavor symmetry-breaking effects may be particularly small since the final-state interactions should be the same between the corresponding Bd and Bs decays due to the charge conjugation symmetry of the final states. This is consistent with the newly measured direct CP asymmetry of Bs→π+K-. These decays are thus supposed to be important in testing the Standard Model and in probing new physics effects. However, the observation of pure annihilation decay Bs→π+π- appears to imply a large annihilation scenario with ρA˜3, in contrast to the case of ρA˜1 in Bu,d decays in the framework of QCD factorization. This seems to indicate unexpectedly large flavor symmetry-breaking effects between the annihilation amplitudes of Bs and Bu,d decays. This apparent contradiction could be resolved by noticing that there is a priori no reason to justify the common practice of assuming the universality of annihilation parameters for different Dirac structures of effective operators. We then argue that, for Bd,s→π∓K± decays, the flavor symmetry-breaking effects of annihilation amplitudes have all been included in the initial-state decay constants and are thus small. But the flavor symmetry-breaking effects in Bd,s→K(*)K(*) decays are likely to be much larger, as part of the annihilation topologies of Bs→KK decay could be related to Bs→π+π- decay. Therefore when new physics effects are searched for in these decay channels, care must be taken to consider the potentially large flavor symmetry-breaking effects in more detail.

  18. Annihilation of Quantum Magnetic Fluxes

    NASA Astrophysics Data System (ADS)

    Gonzalez, W. D.

    After introducing the concepts associated with the Aharonov and Bohm effect and with the existence of a quantum of magnetic flux (QMF), we briefly discuss the Ginzburg-Landau theory that explains its origin and fundamental consequences. Also relevant observations of QMFs obtained in the laboratory using superconducting systems (vortices) are mentioned. Next, we describe processes related with the interaction of QMFs with opposite directions in terms of the gauge field geometry related to the vector potential. Then, we discuss the use of a Lagrangian density for a scalar field theory involving radiation in order to describe the annihilation of QMFs, claimed to be responsible for the emission of photons with energies corresponding to that of the annihilated magnetic fields. Finally, a possible application of these concepts to the observed variable dynamics of neutron stars is briefly mentioned.

  19. Monopole annihilation in cosmic necklaces

    SciTech Connect

    Blanco-Pillado, Jose J.; Olum, Ken D. E-mail: kdo@cosmos.phy.tufts.edu

    2010-05-01

    A sequence of two symmetry breaking transitions in the early universe may produce monopoles whose flux is confined into two strings each, which thus assemble into ''necklaces'' with monopoles as beads. Such ''cosmic necklaces'' have been proposed as a source of ultra-high-energy cosmic rays. We analyze the evolution of these systems and show that essentially all monopoles annihilate or leave the string at early times, after which cosmic necklaces evolve in a similar way to a network of ordinary cosmic strings. We investigate several modifications to the basic picture, but in nearly all cases we find that too few monopoles remain on the necklaces to produce any observable cosmic rays. There may be a small window for superconducting condensates to prevent annihilations, but only if both the string and the condensate scale are very high.

  20. Positron annihilation in the interstellar medium

    NASA Technical Reports Server (NTRS)

    Guessoum, Nidhal; Ramaty, Reuven; Lingenfelter, Richard E.

    1991-01-01

    Positronium formation and annihilation are studied in a model for the interstellar medium consisting of cold cloud cores, warm partially ionized cloud envelopes, and hot intercloud gas. The gamma-ray spectra resulting from positron annihilation in these components of the interstellar medium are calculated. The spectra from the individual components are then combined, using two limiting assumptions for the propagation of the positrons, namely, that the positrons propagate freely throughout the interstellar medium, and that the positrons are excluded from the cold cloud cores. In the first case, the bulk of the positrons annihilate in the cloud cores and the annihilation line exhibits broad wings resulting from the annihilation of positronium formed by charge exchange in flight. In the second case, the positrons annihilate mainly in the warm envelopes, and the line wings are suppressed.

  1. Positron annihilation induced Auger electron emission

    SciTech Connect

    Weiss, A.; Jibaly, M.; Lei, Chun; Mehl, D.; Mayer, R.; Lynn, K.G.

    1988-01-01

    We report on measurements of Auger electron emission from Cu and Fe due to core hole excitations produced by the removal of core electrons by matter-antimatter annihilation. Estimates are developed of the probability of positrons annihilating with a 3p electron in these materials. Several important advantages of Positron annihilation induced Auger Electron Spectroscopy (PAES) for surface analysis are suggested. 10 refs., 2 figs.

  2. Positron annihilation in gamma-ray bursts

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.

    1990-01-01

    Emission features appear at energies of 350 to 450 keV in the spectra of a number of gamma ray burst sources. These features were interpreted as electron-positron annihilation lines, redshifted by the gravitational field near the surface of a neutron star. Evidence that gamma ray bursts originate at neutron stars with magnetic field strengths of approx. 10(exp 12) Gauss came from recent observations of cyclotron scattering harmonics in the spectra of two bursts. Positrons could be produced in gamma ray burst sources either by photon-photon pair production or by one-photon pair production in a strong magnetic field. The annihilation of positrons is affected by the presence of a strong neutron star magnetic field in several ways. The relaxation of transverse momentum conservation causes an intrinsic broadening of the two-photon annihilation line and there is a decrease in the annihilation cross section below the free-space value. An additional channel for one-photon annihilation also becomes possible in high magnetic fields. The physics of pair production and annihilation near strongly magnetized neutron stars will be reviewed. Results from a self-consistent model for non-thermal synchrotron radiation and pair annihilation are beginning to identify the conditions required to produce observable annihilation features from strongly magnetized plasmas.

  3. Positron Annihilation in the Bipositronium Ps2

    SciTech Connect

    Bailey, David H.; Frolov, Alexei M.

    2005-07-01

    The electron-positron-pair annihilation in the bipositronium PS2 is considered. In particular, the two-, three-, one- and zero-photon annihilation rates are determined to high accuracy. The corresponding analytical expressions are also presented. Also, a large number of bound state properties have been determined for this system.

  4. Gas Permeations Studied by Positron Annihilation

    NASA Astrophysics Data System (ADS)

    Yuan, Jen-Pwu; Cao, Huimin; Jean, X.; Yang, Y. C.

    1997-03-01

    The hole volumes and fractions of PC and PET polymers are measured by positron annihilation lifetime spectroscopy. Direct correlations between the measured hole properties and gas permeabilities are observed. Applications of positron annihilation spectroscopy to study gas transport and separation of polymeric materials will be discussed.

  5. Skyrmion creation and annihilation by spin waves

    SciTech Connect

    Liu, Yizhou Yin, Gen; Lake, Roger K.; Zang, Jiadong; Shi, Jing

    2015-10-12

    Single skyrmion creation and annihilation by spin waves in a crossbar geometry are theoretically analyzed. A critical spin-wave frequency is required both for the creation and the annihilation of a skyrmion. The minimum frequencies for creation and annihilation are similar, but the optimum frequency for creation is below the critical frequency for skyrmion annihilation. If a skyrmion already exists in the cross bar region, a spin wave below the critical frequency causes the skyrmion to circulate within the central region. A heat assisted creation process reduces the spin-wave frequency and amplitude required for creating a skyrmion. The effective field resulting from the Dzyaloshinskii-Moriya interaction and the emergent field of the skyrmion acting on the spin wave drive the creation and annihilation processes.

  6. Fermionic semi-annihilating dark matter

    NASA Astrophysics Data System (ADS)

    Cai, Yi; Spray, Andrew

    2016-01-01

    Semi-annihilation is a generic feature of dark matter theories with symmetries larger than Z_2 . We investigate two examples with multi-component dark sectors comprised of an SU(2) L singlet or triplet fermion besides a scalar singlet. These are respectively the minimal fermionic semi-annihilating model, and the minimal case for a gauge-charged fermion. We study the relevant dark matter phenomenology, including the interplay of semi-annihilation and the Sommerfeld effect. We demonstrate that semi-annihilation in the singlet model can explain the gamma ray excess from the galactic center. For the triplet model we scan the parameter space, and explore how signals and constraints are modified by semi-annihilation. We find that the entire region where the model comprises all the observed dark matter is accessible to current and planned direct and indirect searches.

  7. Multiple gamma lines from semi-annihilation

    SciTech Connect

    D'Eramo, Francesco; McCullough, Matthew; Thaler, Jesse E-mail: mccull@mit.edu

    2013-04-01

    Hints in the Fermi data for a 130 GeV gamma line from the galactic center have ignited interest in potential gamma line signatures of dark matter. Explanations of this line based on dark matter annihilation face a parametric tension since they often rely on large enhancements of loop-suppressed cross sections. In this paper, we pursue an alternative possibility that dark matter gamma lines could arise from ''semi-annihilation'' among multiple dark sector states. The semi-annihilation reaction ψ{sub i}ψ{sub j} → ψ{sub k}γ with a single final state photon is typically enhanced relative to ordinary annihilation ψ{sub i}ψ-bar {sub i} → γγ into photon pairs. Semi-annihilation allows for a wide range of dark matter masses compared to the fixed mass value required by annihilation, opening the possibility to explain potential dark matter signatures at higher energies. The most striking prediction of semi-annihilation is the presence of multiple gamma lines, with as many as order N{sup 3} lines possible for N dark sector states, allowing for dark sector spectroscopy. A smoking gun signature arises in the simplest case of degenerate dark matter, where a strong semi-annihilation line at 130 GeV would be accompanied by a weaker annihilation line at 173 GeV. As a proof of principle, we construct two explicit models of dark matter semi-annihilation, one based on non-Abelian vector dark matter and the other based on retrofitting Rayleigh dark matter.

  8. Positron annihilation in transparent ceramics

    NASA Astrophysics Data System (ADS)

    Husband, P.; Bartošová, I.; Slugeň, V.; Selim, F. A.

    2016-01-01

    Transparent ceramics are emerging as excellent candidates for many photonic applications including laser, scintillation and illumination. However achieving perfect transparency is essential in these applications and requires high technology processing and complete understanding for the ceramic microstructure and its effect on the optical properties. Positron annihilation spectroscopy (PAS) is the perfect tool to study porosity and defects. It has been applied to investigate many ceramic structures; and transparent ceramics field may be greatly advanced by applying PAS. In this work positron lifetime (PLT) measurements were carried out in parallel with optical studies on yttrium aluminum garnet transparent ceramics in order to gain an understanding for their structure at the atomic level and its effect on the transparency and light scattering. The study confirmed that PAS can provide useful information on their microstructure and guide the technology of manufacturing and advancing transparent ceramics.

  9. Positron scattering and annihilation in hydrogenlike ions

    NASA Astrophysics Data System (ADS)

    Green, D. G.; Gribakin, G. F.

    2013-09-01

    Diagrammatic many-body theory is used to calculate the scattering phase shifts, normalized annihilation rates Zeff, and annihilation γ spectra for positron collisions with the hydrogenlike ions He+, Li2+, B4+, and F8+. Short-range electron-positron correlations and longer-range positron-ion correlations are accounted for by evaluating nonlocal corrections to the annihilation vertex and the exact positron self-energy. The numerical calculation of the many-body theory diagrams is performed using B-spline basis sets. To elucidate the role of the positron-ion repulsion, the annihilation rate is also estimated analytically in the Coulomb-Born approximation. It is found that the energy dependence and magnitude of Zeff are governed by the Gamow factor that characterizes the suppression of the positron wave function near the ion. For all of the H-like ions, the correlation enhancement of the annihilation rate is found to be predominantly due to corrections to the annihilation vertex, while the corrections to the positron wave function play only a minor role. Results of the calculations for s-, p-, and d-wave incident positrons of energies up to the positronium-formation threshold are presented. Where comparison is possible, our values are in excellent agreement with the results obtained using other, e.g., variational, methods. The annihilation-vertex enhancement factors obtained in the present calculations are found to scale approximately as 1+(1.6+0.46ℓ)/Zi, where Zi is the net charge of the ion and ℓ is the positron orbital angular momentum. Our results for positron annihilation in H-like ions provide insights into the problem of positron annihilation with core electrons in atoms and condensed matter systems, which have similar binding energies.

  10. AC quantum efficiency harmonic analysis of exciton annihilation in organic light emitting diodes (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Giebink, Noel C.

    2015-10-01

    Exciton annihilation processes impact both the lifetime and efficiency roll-off of organic light emitting diodes (OLEDs), however it is notoriously difficult to identify the dominant mode of annihilation in operating devices (exciton-exciton vs. exciton-charge carrier) and subsequently to disentangle its magnitude from competing roll-off processes such as charge imbalance. Here, we introduce a simple analytical method to directly identify and extract OLED annihilation rates from standard light-current-voltage (LIV) measurement data. The foundation of this approach lies in a frequency domain EQE analysis and is most easily understood in analogy to impedance spectroscopy, where in this case both the current (J) and electroluminescence intensity (L) are measured using a lock-in amplifier at different harmonics of the sinusoidal dither superimposed on the DC device bias. In the presence of annihilation, the relationship between recombination current and light output (proportional to exciton density) becomes nonlinear, thereby mixing the different EQE harmonics in a manner that depends uniquely on the type and magnitude of annihilation. We derive simple expressions to extract different annihilation rate coefficients and apply this technique to a variety of OLEDs. For example, in devices dominated by triplet-triplet annihilation, the annihilation rate coefficient, K_TT, is obtained directly from the linear slope that results from plotting EQE_DC-EQE_1ω versus L_DC (2EQE_1ω-EQE_DC). We go on to show that, in certain cases it is sufficient to calculate EQE_1ω directly from the slope of the DC light versus current curve [i.e. via (dL_DC)/(dJ_DC )], thus enabling this analysis to be conducted solely from common LIV measurement data.

  11. Quark dynamics of N anti N annihilation

    SciTech Connect

    Dover, C.B.

    1985-01-01

    It is argued that recent observations of strong L dependence and approximate selection rules in certain N anti N annihilation modes necessitate a description of the reaction mechanism in terms of quark-gluon degrees of freedom.

  12. Accelerating an iterative process by explicit annihilation

    NASA Technical Reports Server (NTRS)

    Jespersen, D. C.; Buning, P. G.

    1983-01-01

    A slowly convergent stationary iterative process can be accelerated by explicitly annihilating (i.e., eliminating) the dominant eigenvector component of the error. The dominant eigenvalue or complex pair of eigenvalues can be estimated from the solution during the iteration. The corresponding eigenvector or complex pair of eigenvectors can then be annihilated by applying an explicit Richardson process over the basic iterative method. This can be done entirely in real arithmetic by analytically combining the complex conjugate annihilation steps. The technique is applied to an implicit algorithm for the calculation of two dimensional steady transonic flow over a circular cylinder using the equations of compressible inviscid gas dynamics. This demonstrates the use of explicit annihilation on a nonlinear problem.

  13. Accelerating an iterative process by explicit annihilation

    NASA Technical Reports Server (NTRS)

    Jespersen, D. C.; Buning, P. G.

    1985-01-01

    A slowly convergent stationary iterative process can be accelerated by explicitly annihilating (i.e., eliminating) the dominant eigenvector component of the error. The dominant eigenvalue or complex pair of eigenvalues can be estimated from the solution during the iteration. The corresponding eigenvector or complex pair of eigenvectors can then be annihilated by applying an explicit Richardson process over the basic iterative method. This can be done entirely in real arithmetic by analytically combining the complex conjugate annihilation steps. The technique is applied to an implicit algorithm for the calculation of two dimensional steady transonic flow over a circular cylinder using the equations of compressible inviscid gas dynamics. This demonstrates the use of explicit annihilation on a nonlinear problem.

  14. Antiproton constraints on dark matter annihilations from internal electroweak bremsstrahlung

    SciTech Connect

    Garny, Mathias; Ibarra, Alejandro; Vogl, Stefan E-mail: alejandro.ibarra@ph.tum.de

    2011-07-01

    If the dark matter particle is a Majorana fermion, annihilations into two fermions and one gauge boson could have, for some choices of the parameters of the model, a non-negligible cross-section. Using a toy model of leptophilic dark matter, we calculate the constraints on the annihilation cross-section into two electrons and one weak gauge boson from the PAMELA measurements of the cosmic antiproton-to-proton flux ratio. Furthermore, we calculate the maximal astrophysical boost factor allowed in the Milky Way under the assumption that the leptophilic dark matter particle is the dominant component of dark matter in our Universe. These constraints constitute very conservative estimates on the boost factor for more realistic models where the dark matter particle also couples to quarks and weak gauge bosons, such as the lightest neutralino which we also analyze for some concrete benchmark points. The limits on the astrophysical boost factors presented here could be used to evaluate the prospects to detect a gamma-ray signal from dark matter annihilations at currently operating IACTs as well as in the projected CTA.

  15. Positron annihilation gamma rays from novae

    NASA Technical Reports Server (NTRS)

    Leising, Mark D.; Clayton, Donald D.

    1987-01-01

    The potential for observing annihilation gamma rays from novae is investigated. These gamma rays, a unique signature of the thermonuclear runaway models of novae, would result from the annihilation of positrons emitted by beta(+)-unstable nuclei produced near the peak of the runaway and carried by rapid convection to the surface of the nova envelope. Simple models, which are extensions of detailed published models, of the expansion of the nova atmospheres are evolved. These models serve as input into investigations of the fate of nearby Galactic fast novae could yield detectable fluxes of electron-positron annihilation gamma rays produced by the decay of N-13 and F-18. Although nuclear gamma-ray lines are produced by other nuclei, it is unlikely that the fluxes at typical nova distances would be detectable to present and near-future instruments.

  16. Positron annihilation induced Auger electron spectroscopy

    NASA Technical Reports Server (NTRS)

    Weiss, Alex; Koymen, A. R.; Mehl, David; Jensen, K. O.; Lei, Chun; Lee, K. H.

    1990-01-01

    Recently, Weiss et al. have demonstrated that it is possible to excite Auger transitions by annihilating core electrons using a low energy (less than 30eV) beam of positrons. This mechanism makes possible a new electron spectroscopy, Positron annihilation induced Auger Electron Spectroscopy (PAES). The probability of exciting an Auger transition is proportional to the overlap of the positron wavefunction with atomic core levels. Since the Auger electron energy provides a signature of the atomic species making the transition, PAES makes it possible to determine the overlap of the positron wavefunction with a particular element. PAES may therefore provide a means of detecting positron-atom complexes. Measurements of PAES intensities from clean and adsorbate covered Cu surfaces are presented which indicate that approx. 5 percent of positrons injected into CU at 25eV produce core annihilations that result in Auger transitions.

  17. Position annihilation radiation from neutron stars

    NASA Technical Reports Server (NTRS)

    Ramaty, R.; Borner, G. A.; Cohen, J. M.

    1972-01-01

    Matter accreted on the surfaces of neutron stars consists of energetic particles of a few tens to a couple hundred MeV/nucleon, depending on the neutron star mass. In addition to heat, such particles produce nuclear reactions with the surface material. It is proposed that the recently observed 473 + or - 30 keV spectral feature from the galactic center is gravitationally red-shifted positron annihilation radiation produced at the surfaces of old neutron stars. The principal observational tests of the model would be the detection of nuclear gamma ray lines from the galactic center and red-shifted positron annihilation radiation from the galactic disk.

  18. Annihilation of Low Energy Antiprotons in Hydrogen

    SciTech Connect

    Ovchinnikov, S.Yu.; Macek, J.H.

    2003-08-26

    The cross sections for annihilation of antiprotons in hydrogen are very important for designing the High-Performance Antiproton Trap (HiPAT). When antiprotons are trapped they undergo atomic reactions with background gases which remove them from the trap. First, antiprotons are captured into highly excited bound states by ejecting the bound electrons, then they are radiationally deexcited and, finally, they annihilate by nuclear interaction. An understanding of these process require reliable cross sections for low-energy collisions of antiprotons with atoms. We have developed a theoretical technique for accurate calculations of these cross sections.

  19. Nondestructive examination using neutron activated positron annihilation

    DOEpatents

    Akers, Douglas W.; Denison, Arthur B.

    2001-01-01

    A method is provided for performing nondestructive examination of a metal specimen using neutron activated positron annihilation wherein the positron emitter source is formed within the metal specimen. The method permits in situ nondestructive examination and has the advantage of being capable of performing bulk analysis to determine embrittlement, fatigue and dislocation within a metal specimen.

  20. Neutrino-antineutrino annihilation around collapsing star

    NASA Technical Reports Server (NTRS)

    Berezinsky, V. S.; Prilutsky, O. F.

    1985-01-01

    Stellar collapse is accompanied by emission of E sub neutrino approximately 10 MeV neutrinos and antineutrinos with the energy output W sub neutrino approximately 10 to the 53rd power to 10 to the 54th power erg. Annihilation of these particles in the vicinity of collapsar is considered. The physical consequences are discussed.

  1. Gamma ray lines from dark matter annihilation

    SciTech Connect

    Giudice, G.F.

    1989-08-01

    If direct annihilation of dark matter particles into a pair of photons occurs in the galactic halo, a narrow {gamma}-ray line can be discovered at future {gamma}-ray detectors sensitive to the GeV region. The signals predicted by different dark matter candidates are analyzed. 16 refs., 3 figs.

  2. Hydrodynamic description for ballistic annihilation systems

    SciTech Connect

    Garcia de Soria, Maria Isabel; Trizac, Emmanuel; Maynar, Pablo; Schehr, Gregory; Barrat, Alain

    2009-01-21

    The problem of the validity of a hydrodynamic description for a system in which there are no collisional invariants is addressed. Hydrodynamic equations have been derived and successfully tested against simulation data for a system where particles annihilate with a probability p, or collide elastically otherwise. The response of the system to a linear perturbation is analyzed as well.

  3. Calculating the Annihilation Rate of Weakly Interacting Massive Particles

    NASA Astrophysics Data System (ADS)

    Baumgart, Matthew; Rothstein, Ira Z.; Vaidya, Varun

    2015-05-01

    We develop a formalism that allows one to systematically calculate the weakly interacting massive particle (WIMP) annihilation rate into gamma rays whose energy far exceeds the weak scale. A factorization theorem is presented which separates the radiative corrections stemming from initial-state potential interactions from loops involving the final state. This separation allows us to go beyond the fixed order calculation, which is polluted by large infrared logarithms. For the case of Majorana WIMPs transforming in the adjoint representation of SU(2), we present the result for the resummed rate at leading double-log accuracy in terms of two initial-state partial-wave matrix elements and one hard matching coefficient. For a given model, one may calculate the cross section by finding the tree level matching coefficient and determining the value of a local four-fermion operator. The effects of resummation can be as large as 100% for a 20 TeV WIMP. However, for lighter WIMP masses relevant for the thermal relic scenario, leading-log resummation modifies the Sudakov factors only at the 10% level. Furthermore, given comparably sized Sommerfeld factors, the total effect of radiative corrections on the semi-inclusive photon annihilation rate is found to be percent level. The generalization of the formalism to other types of WIMPs is discussed.

  4. Calculating the annihilation rate of weakly interacting massive particles.

    PubMed

    Baumgart, Matthew; Rothstein, Ira Z; Vaidya, Varun

    2015-05-29

    We develop a formalism that allows one to systematically calculate the weakly interacting massive particle (WIMP) annihilation rate into gamma rays whose energy far exceeds the weak scale. A factorization theorem is presented which separates the radiative corrections stemming from initial-state potential interactions from loops involving the final state. This separation allows us to go beyond the fixed order calculation, which is polluted by large infrared logarithms. For the case of Majorana WIMPs transforming in the adjoint representation of SU(2), we present the result for the resummed rate at leading double-log accuracy in terms of two initial-state partial-wave matrix elements and one hard matching coefficient. For a given model, one may calculate the cross section by finding the tree level matching coefficient and determining the value of a local four-fermion operator. The effects of resummation can be as large as 100% for a 20 TeV WIMP. However, for lighter WIMP masses relevant for the thermal relic scenario, leading-log resummation modifies the Sudakov factors only at the 10% level. Furthermore, given comparably sized Sommerfeld factors, the total effect of radiative corrections on the semi-inclusive photon annihilation rate is found to be percent level. The generalization of the formalism to other types of WIMPs is discussed. PMID:26066424

  5. Application of positron annihilation in materials science

    SciTech Connect

    Siegel, R.W.; Fluss, M.J.; Smedskjaer, L.C.

    1984-05-01

    Owing to the ability of the positron to annihilate from a variety of defect-trapped states, positron annihilation spectroscopy (PAS) has been applied increasingly to the characterization and study of defects in materials in recent years. In metals particularly, it has been demonstrated that PAS can yield defect-specific information which, by itself or in conjunction with more traditional experimental techniques, has already made a significant impact upon the determination of atomic-defect properties and the monitoring and characterization of vacancy-like microstructure development, as occurs during post-irradiation annealing. The applications of PAS are now actively expanding to the study of more complex defect-related phenomena in irradiated or deformed metals and alloys, phase transformations and structural disorder, surfaces and near-surface defect characterization. A number of these applications in materials science are reviewed and discussed with respect to profitable future directions.

  6. Defects in metals. [Positron annihilation spectroscopy

    SciTech Connect

    Siegel, R.W.

    1982-06-01

    The application of positron annihilation spectroscopy (PAS) to the study of defects in metals has led to increased knowledge on lattice-defect properties during the past decade in two areas: the determination of atomic defect properties, particularly those of monovacancies, and the monitoring and characterization of vacancy-like microstructure development during post-irradiation and post-quench annealing. The study of defects in metals by PAS is reviewed within the context of the other available techniques for defect studies. The strengths and weaknesses of PAS as a method for the characterization of defect microstructures are considered. The additional possibilities for using the positron as a localized probe of the atomic and electronic structures of atomic defects are discussed, based upon theoretical calculations of the annihilation characteristics of defect-trapped positrons and experimental observations. Finally, the present status and future potential of PAS as a tool for the study of defects in metals is considered. 71 references, 9 figures.

  7. Shocking signals of dark matter annihilation

    NASA Astrophysics Data System (ADS)

    Davis, Jonathan H.; Silk, Joseph; BÅ`hm, Céline; Kotera, Kumiko; Norman, Colin

    2016-05-01

    We examine whether charged particles injected by self-annihilating dark matter (DM) into regions undergoing diffuse shock acceleration can be accelerated to high energies. We consider three astrophysical sites where shock acceleration is supposed to occur, namely the Galactic center and galaxy cluster mergers. For the Milky Way, we find that the acceleration of cosmic rays injected by dark matter could lead to a bump in the cosmic ray spectrum provided that the product of the efficiency of the acceleration mechanism and the concentration of DM particles is high enough. Within the Galaxy, we find that the Fermi bubbles are a potentially more efficient accelerator than supernovae remnants. However, both could in principle accelerate electrons and protons injected by dark matter to very high energies. At the extragalactic level, the acceleration of dark matter annihilation products could be responsible for enhanced radio emission from colliding clusters.

  8. Method for photon activation positron annihilation analysis

    DOEpatents

    Akers, Douglas W.

    2006-06-06

    A non-destructive testing method comprises providing a specimen having at least one positron emitter therein; determining a threshold energy for activating the positron emitter; and determining whether a half-life of the positron emitter is less than a selected half-life. If the half-life of the positron emitter is greater than or equal to the selected half-life, then activating the positron emitter by bombarding the specimen with photons having energies greater than the threshold energy and detecting gamma rays produced by annihilation of positrons in the specimen. If the half-life of the positron emitter is less then the selected half-life, then alternately activating the positron emitter by bombarding the specimen with photons having energies greater then the threshold energy and detecting gamma rays produced by positron annihilation within the specimen.

  9. Positron annihilation radiation from solar flares

    NASA Technical Reports Server (NTRS)

    Share, G. H.; Chupp, E. L.; Forrest, D. J.; Rieger, E.

    1983-01-01

    Positron-annihilation radiation has been observed from the June 21, 1980 and June 3, 1982 flares by the gamma-ray spectrometer on the Solar Maximum Mission satellite. The observed 0.511-MeV line fluences from the flares were 14.6 + or - 3.3 gamma/sq cm and 103 + or - 8 gamma/sq cm, respectively. Measurement of the line width establishes an upper limit to the temperature in the annihilation region of 3 x 10 to the 6th K. The time dependence of the 0.511-MeV line during the 1980 flare is consistent with the calculations of Ramaty et al. (1983) for positrons created in the decay of radioactive nuclei. The time dependence of the 0.511-MeV line for the 1982 flare is more complex and requires more detailed study.

  10. Positron scattering and annihilation from hydrogenlike ions

    SciTech Connect

    Novikov, S.A.; Bromley, M.W.J.; Mitroy, J.

    2004-05-01

    The Kohn variational method is used with a configuration-interaction-type wave function to determine the J=0 and J=1 phase shifts and annihilation parameter Z{sub eff} for positron-hydrogenic ion scattering. The phase shifts are within 1-2% of the best previous calculations. The values of Z{sub eff} are small and do not exceed unity for any of the momenta considered. At thermal energies Z{sub eff} is minute with a value of order 10{sup -50} occurring for He{sup +} at k=0.05a{sub 0}{sup -1}. In addition to the variational calculations, analytic expressions for the phase shift and annihilation parameters within the Coulomb wave Born approximation are derived and used to help elucidate the dynamics of positron collisions with positive ions.

  11. Microemulsion systems studied by positron annihilation techniques

    SciTech Connect

    Boussaha, A.; Djermouni, B.; Fucugauchi, L.A.; Ache, H.J.

    1980-07-02

    The formation of thermalized positronium atoms is greatly reduced if increasing amounts of water become solubilized in reversed micelles formed by sodium bis(2-ethylhexyl) sulfosuccinate in apolar solvents. Similar observations have been made if the surfactant is Triton X-100. The application of the positron annihilation technique to the study of microemulsions consisting of potassium oleate-alcohol-oil-water mixtures indicates, consistent with previous results, that microemulsion formation requires a certain water/oil ratio if the oil is a long-chain aliphatic hydrocarbon such as hexadecane. This ratio is 0.4 in the case of a 1-pentanol- and 0.2 for a 1-hexanol-containing mixture. This minimum water content is strongly reduced if the oil is an aromatic hydrocarbon. The positron annihilation data also sensitively reflect structural rearrangements in these solutions occurring upon further addition of water, such as the transition of spherical aggregates to a disk-like lamellae structure.

  12. Ballistic annihilation and deterministic surface growth

    NASA Astrophysics Data System (ADS)

    Belitsky, Vladimir; Ferrari, Pablo A.

    1995-08-01

    A model of deterministic surface growth studied by Krug and Spohn, a model of the annihilating reaction A+B→inert studied by Elskens and Frisch, a one-dimensional three-color cyclic cellular automaton studied by Fisch, and a particular automaton that has the number 184 in the classification of Wolfram can be studied via a cellular automaton with stochastic initial data called ballistic annihilation. This automaton is defined by the following rules: At time t=0, one particle is put at each integer point of ℝ. To each particle, a velocity is assigned in such a way that it may be either +1 or -1 with probabilities 1/2, independent of the velocities of the other particles. As time goes on, each particle moves along ℝ at the velocity assigned to it and annihilates when it collides with another particle. In the present paper we compute the distribution of this automaton for each time t ∈ ℕ. We then use this result to obtain the hydrodynamic limit for the surface profile from the model of deterministic surface growth mentioned above. We also show the relation of this limit process to the process which we call moving local minimum of Brownian motion. The latter is the process B {/x min}, x ∈ ℝ, defined by B {/x min}≔min{ B y ; x-1≤ y≤ x+1} for every x ∈ ℝ, where B x , x ∈ ℝ, is the standard Brownian motion with B 0=0.

  13. Electroweak fragmentation functions for dark matter annihilation

    SciTech Connect

    Cavasonza, Leila Ali; Krämer, Michael; Pellen, Mathieu

    2015-02-18

    Electroweak corrections can play a crucial role in dark matter annihilation. The emission of gauge bosons, in particular, leads to a secondary flux consisting of all Standard Model particles, and may be described by electroweak fragmentation functions. To assess the quality of the fragmentation function approximation to electroweak radiation in dark matter annihilation, we have calculated the flux of secondary particles from gauge-boson emission in models with Majorana fermion and vector dark matter, respectively. For both models, we have compared cross sections and energy spectra of positrons and antiprotons after propagation through the galactic halo in the fragmentation function approximation and in the full calculation. Fragmentation functions fail to describe the particle fluxes in the case of Majorana fermion annihilation into light fermions: the helicity suppression of the lowest-order cross section in such models cannot be lifted by the leading logarithmic contributions included in the fragmentation function approach. However, for other classes of models like vector dark matter, where the lowest-order cross section is not suppressed, electroweak fragmentation functions provide a simple, model-independent and accurate description of secondary particle fluxes.

  14. Search for Dark Matter Annihilations in Draco with CACTUS

    SciTech Connect

    Chertok, M.; Afonso, P.; Lizarazo, J.; Marleau, P.; Maruyama, S.; Stilley, J.; Tripathi, S. M.

    2006-07-11

    CACTUS is a ground-based Air Cherenkov Telescope (ACT) at the Solar 2 facility located near Barstow, California, and operated by UC Davis. It uses an array of 160 large solar tracking mirrors (heliostats) and a camera with 80 photomultiplier tubes, which, in a multiplexed fashion provides an effective camera with about 300 channels. By incorporating novel techniques of time projection imaging and triggering, CACTUS improves upon the first generation sampling arrays of its kind. We have recently completed observations of Draco, a dwarf spheroidal galaxy that is known to be rich in dark matter content. Supersymmetry-inspired models for dark matter predict observable annihilation rates producing gamma rays. We present the first results from our Draco campaign.

  15. Dynamics of annihilation. I. Linearized Boltzmann equation and hydrodynamics.

    PubMed

    García de Soria, María Isabel; Maynar, Pablo; Schehr, Grégory; Barrat, Alain; Trizac, Emmanuel

    2008-05-01

    We study the nonequilibrium statistical mechanics of a system of freely moving particles, in which binary encounters lead either to an elastic collision or to the disappearance of the pair. Such a system of ballistic annihilation therefore constantly loses particles. The dynamics of perturbations around the free decay regime is investigated using the spectral properties of the linearized Boltzmann operator, which characterize linear excitations on all time scales. The linearized Boltzmann equation is solved in the hydrodynamic limit by a projection technique, which yields the evolution equations for the relevant coarse-grained fields and expressions for the transport coefficients. We finally present the results of molecular dynamics simulations that validate the theoretical predictions. PMID:18643046

  16. Positron-annihilation spectroscopy of vacancy defects in aluminum

    SciTech Connect

    Chakraborty, B.; Berko, S.; Fluss, M.J.; Hoffmann, K.; Lippel, P.; Siegel, R.W.

    1982-06-01

    Positron-annihilation characteristics in a monovacancy and a divacancy in aluminium have been calculated self-consistently using a local density functional formalism, into which the many-body enhancement effects have been incorporated. Results for the theoretical two-dimensional angular correlation of annihilation radiation spectra are compared to experimental results obtained from an aluminum single crystal at 20/sup 0/C, where positrons annihilate from a Bloch-state, and at higher temperatures, 500/sup 0/C and 630/sup 0/C, where they annihilate primarily from vacancy-trapped states.

  17. Energy-Resolved Positron Annihilation in Flight in Solid Targets

    NASA Astrophysics Data System (ADS)

    Weber, M. H.; Hunt, A. W.; Golovchenko, J. A.; Lynn, K. G.

    1999-11-01

    Energy-resolved two-quantum annihilation in flight of positrons with energies ranging from 10 to 71.6 keV was observed. An energy-dispersive two-detector coincidence system was used to observe the sum and difference energies of the γ rays from annihilating positron-electron pairs. For positrons penetrating carbon foils the c/v dependence of the annihilation cross section is confirmed. Spectra obtained from gold-coated carbon foils show evidence of in-flight annihilation with gold M-shell electrons.

  18. Concepts for the design of an antimatter annihilation rocket

    NASA Technical Reports Server (NTRS)

    Morgan, D. L., Jr.

    1982-01-01

    Matter-antimatter annihilation is considered for spacecraft propulsion. Annihilation produces considerably more energy per unit mass of propellant than any other known means of energy production. An antimatter annihilation rocket requires several systems and components that are unique to its nature. Among these are an antimatter storage system, a means to extract the antimatter from storage, a system to transport the antimatter to the rocket engine, and the engine wherein annihilation occurs and thrust is produced. Design concepts of these systems and components are presented and discussed.

  19. Branching-rate expansion around annihilating random walks.

    PubMed

    Benitez, Federico; Wschebor, Nicolás

    2012-07-01

    We present some exact results for branching and annihilating random walks. We compute the nonuniversal threshold value of the annihilation rate for having a phase transition in the simplest reaction-diffusion system belonging to the directed percolation universality class. Also, we show that the accepted scenario for the appearance of a phase transition in the parity conserving universality class must be improved. In order to obtain these results we perform an expansion in the branching rate around pure annihilation, a theory without branching. This expansion is possible because we manage to solve pure annihilation exactly in any dimension. PMID:23005353

  20. Exciton annihilation in dye-sensitized nanocrystalline semiconductor films

    NASA Astrophysics Data System (ADS)

    Namekawa, Akihiro; Katoh, Ryuzi

    2016-08-01

    Exciton annihilation in dye-sensitized nanocrystalline semiconductor (Al2O3) films has been studied through laser-induced fluorescence spectroscopy. The relative quantum yield of the fluorescence decreases with increasing excitation light intensity, the indication being that exciton annihilation occurred. The rate constants of the annihilation were estimated for three dyes, N719, D149, and MK2, that are known to be sensitizing dyes for efficient dye-sensitized solar cells. The hopping time between dye molecules and the diffusion length of excitons within their lifetime were also estimated to facilitate discussion of the relevance of exciton annihilation to primary processes in dye-sensitized solar cells.

  1. Dark matter annihilation at the galactic center

    NASA Astrophysics Data System (ADS)

    Linden, Tim

    Observations by the WMAP and PLANCK satellites have provided extraordinarily accurate observations on the densities of baryonic matter, dark matter, and dark energy in the universe. These observations indicate that our universe is composed of approximately five times as much dark matter as baryonic matter. However, efforts to detect a particle responsible for the energy density of dark matter have been unsuccessful. Theoretical models have indicated that a leading candidate for the dark matter is the lightest supersymmetric particle, which may be stable due to a conserved R-parity. This dark matter particle would still be capable of interacting with baryons via weak-force interactions in the early universe, a process which was found to naturally explain the observed relic abundance of dark matter today. These residual annihilations can persist, albeit at a much lower rate, in the present universe, providing a detectable signal from dark matter annihilation events which occur throughout the universe. Simulations calculating the distribution of dark matter in our galaxy almost universally predict the galactic center of the Milky Way Galaxy (GC) to provide the brightest signal from dark matter annihilation due to its relative proximity and large simulated dark matter density. Recent advances in telescope technology have allowed for the first multiwavelength analysis of the GC, with suitable effective exposure, angular resolution, and energy resolution in order to detect dark matter particles with properties similar to those predicted by the WIMP miracle. In this work, I describe ongoing efforts which have successfully detected an excess in gamma-ray emission from the region immediately surrounding the GC, which is difficult to describe in terms of standard diffuse emission predicted in the GC region. While the jury is still out on any dark matter interpretation of this excess, I describe several related observations which may indicate a dark matter origin. Finally, I

  2. Dark Matter Annihilation at the Galactic Center

    SciTech Connect

    Linden, Timothy Ryan

    2013-06-01

    Observations by the WMAP and PLANCK satellites have provided extraordinarily accurate observations on the densities of baryonic matter, dark matter, and dark energy in the universe. These observations indicate that our universe is composed of approximately ve times as much dark matter as baryonic matter. However, e orts to detect a particle responsible for the energy density of dark matter have been unsuccessful. Theoretical models have indicated that a leading candidate for the dark matter is the lightest supersymmetric particle, which may be stable due to a conserved R-parity. This dark matter particle would still be capable of interacting with baryons via weak-force interactions in the early universe, a process which was found to naturally explain the observed relic abundance of dark matter today. These residual annihilations can persist, albeit at a much lower rate, in the present universe, providing a detectable signal from dark matter annihilation events which occur throughout the universe. Simulations calculating the distribution of dark matter in our galaxy almost universally predict the galactic center of the Milky Way Galaxy (GC) to provide the brightest signal from dark matter annihilation due to its relative proximity and large simulated dark matter density. Recent advances in telescope technology have allowed for the rst multiwavelength analysis of the GC, with suitable e ective exposure, angular resolution, and energy resolution in order to detect dark matter particles with properties similar to those predicted by the WIMP miracle. In this work, I describe ongoing e orts which have successfully detected an excess in -ray emission from the region immediately surrounding the GC, which is di cult to describe in terms of standard di use emission predicted in the GC region. While the jury is still out on any dark matter interpretation of this excess, I describe several related observations which may indicate a dark matter origin. Finally, I discuss the

  3. Particle-antiparticle asymmetries from annihilations.

    PubMed

    Baldes, Iason; Bell, Nicole F; Petraki, Kalliopi; Volkas, Raymond R

    2014-10-31

    An extensively studied mechanism to create particle-antiparticle asymmetries is the out-of-equilibrium and CP violating decay of a heavy particle. We, instead, examine how asymmetries can arise purely from 2→2 annihilations rather than from the usual 1→2 decays and inverse decays. We review the general conditions on the reaction rates that arise from S-matrix unitarity and CPT invariance, and show how these are implemented in the context of a simple toy model. We formulate the Boltzmann equations for this model, and present an example solution. PMID:25396359

  4. On baryogenesis from dark matter annihilation

    SciTech Connect

    Bernal, Nicolás; Colucci, Stefano; Ubaldi, Lorenzo; Josse-Michaux, François-Xavier; Racker, J. E-mail: colucci@th.physik.uni-bonn.de E-mail: racker@ific.uv.es

    2013-10-01

    We study in detail the conditions to generate the baryon asymmetry of the universe from the annihilation of dark matter. This scenario requires a low energy mechanism for thermal baryogenesis, hence we first discuss some of these mechanisms together with the specific constraints due to the connection with the dark matter sector. Then we show that, contrary to what stated in previous studies, it is possible to generate the cosmological asymmetry without adding a light sterile dark sector, both in models with violation and with conservation of B−L. In addition, one of the models we propose yields some connection to neutrino masses.

  5. Minimal electroweak model for monopole annihilation

    SciTech Connect

    Farris, T.H. ); Kephart, T.W.; Weiler, T.J. ); Yuan, T.C. )

    1992-02-03

    We construct the minimal (most economical in fields) extension of the standard model implementing the Langacker-Pi mechanism for reducing the grand unified theory (GUT) monopole cosmic density to an allowed level. The model contains just a single charged scalar field in addition to the standard Higgs doublet, and is easily embeddable in any GUT. We identify the region of parameter space where monopoles annihilate in the higher temperature early Universe. A particularly alluring possibility is that the demise of monopoles at the electroweak scale is in fact the origin of the Universe's net baryon number.

  6. The Antiproton-Nucleon Annihilation Process (Antiproton Collaboration Experiment)

    DOE R&D Accomplishments Database

    Barkas, W. H.; Birge, R. W.; Chupp, W. W.; Ekspong, A. G.; Goldhaber, G.; Goldhaber, S.; Heckman, H. H.; Perkins, D. H.; Sandweiss, J.; Segre, E.; Smith, F. M.; Stork, D. H.; Rossum, L. Van; Amaldi, E.; Baroni, G.; Castagnoli, C.; Franzinetti, C.; Manfredini, A.

    1956-09-10

    In the exposure to a 700-MeV/c negative particle beam, 35 antiproton stars have been found. Of these antiprotons, 21 annihilate in flight and three give large-angle scatters ({Theta} > 15 , T{sub P-} > 50 Mev), while 14 annihilate at rest. From the interactions in flight we obtain the total cross section for antiproton interaction.

  7. CMB constraint on dark matter annihilation after Planck 2015

    NASA Astrophysics Data System (ADS)

    Kawasaki, Masahiro; Nakayama, Kazunori; Sekiguchi, Toyokazu

    2016-05-01

    We update the constraint on the dark matter annihilation cross section by using the recent measurements of the CMB anisotropy by the Planck satellite. We fully calculate the cascade of dark matter annihilation products and their effects on ionization, heating and excitation of the hydrogen, hence do not rely on any assumption on the energy fractions that cause these effects.

  8. Nucleon-antinucleon annihilation in chiral soliton model

    SciTech Connect

    Musakhanov, M.M. . Inst. for Nuclear Theory Tashkentskij Gosudarstvennyj Univ., Tashkent . Dept. of Theoretical Physics); Musatov, I.V. . Research Inst. of Applied Physics)

    1991-09-07

    We investigate annihilation process of nucleons in the chiral soliton model by the path integral method. A soliton-antisoliton pair is shown to decay into mesons at range of about 1fm, defined by the S{bar S} potential. Contribution of the annihilation channel to the elastic scattering is discussed.

  9. Photoinduced carrier annihilation in silicon pn junction

    NASA Astrophysics Data System (ADS)

    Sameshima, Toshiyuki; Motoki, Takayuki; Yasuda, Keisuke; Nakamura, Tomohiko; Hasumi, Masahiko; Mizuno, Toshihisa

    2015-08-01

    We report analysis of the photo-induced minority carrier effective lifetime (τeff) in a p+n junction formed on the top surfaces of a n-type silicon substrate by ion implantation of boron and phosphorus atoms at the top and bottom surfaces followed by activation by microwave heating. Bias voltages were applied to the p+ boron-doped surface with n+ phosphorus-doped surface kept at 0 V. The values of τeff were lower than 1 × 10-5 s under the reverse-bias condition. On the other hand, τeff markedly increased to 1.4 × 10-4 s as the forward-bias voltage increased to 0.7 V and then it leveled off when continuous-wave 635 nm light was illuminated at 0.74 mW/cm2 on the p+ surface. The carrier annihilation velocity S\\text{p + } at the p+ surface region was numerically estimated from the experimental τeff. S\\text{p + } ranged from 4000 to 7200 cm/s under the reverse-bias condition when the carrier annihilation velocity S\\text{n + } at the n+ surface region was assumed to be a constant value of 100 cm/s. S\\text{p + } markedly decreased to 265 cm/s as the forward-bias voltage increased to 0.7 V.

  10. Diffuse galactic annihilation radiation from supernova nucleosynthesis

    NASA Technical Reports Server (NTRS)

    Higdon, J. C.

    1985-01-01

    The propagation of MeV positrons in the outer ejecta of type I supernovae was investigated. It was found that the positrons created at times of approx 100 days propagated along magnetic field lines in the outer ejecta without any appreciable pitch-angle scattering or excitation of hydromagnetic waves. The lack of significant pitch-angle scattering is well consistent with models of wave excitation and scattering by resonant interactions. This occurs because time periods to scatter the particles or to excite waves are significantly longer than escape times. Thus it is expected that, when positrons are not coupled to the ejecta by Coulomb collisions, they escape from the relatively cold, dense ejecta and reside predominantly in the tenuous, hotter, shock-heated interstellar gas. In the tenuous shock-heated gas the positron lifetime against annihilation is much greater than lifetimes in the dense ejectra. Thus the production of steady-state diffuse annihilation radiation by some fraction of these escaped positrons seems probable.

  11. Resolvability of defect ensembles with positron annihilation studies

    SciTech Connect

    Fluss, M.J.; Howell, R.H.; Rosenberg, I.J.; Meyer, P.

    1984-11-12

    Recent advances in the use of positron annihilation to study defect ensembles in and on the surfaces of metals, are pointing the way towards studies where particular positron-electron annihilation modes may be identified and studied in the presence of one another. Although a great deal is understood about the annihilation of positrons in ostensibly defect-free metals, much less is understood when the positron annihilates in complex defect systems such as liquid metals, amorphous solids, or at or near the vacuum-solid interface. In this paper the results of three experiments, all of which demonstrate means by which we can resolve various poistron annihilation channels from one another, are discussed.

  12. Detecting Dark Matter annihilation lines with Fermi

    SciTech Connect

    Ylinen, Tomi; Edmonds, Yvonne; Bloom, Elliott D.; Conrad, Jan; /Royal Inst. Tech., Stockholm /Kalmar U. /KIPAC, Menlo Park /SLAC /Stockholm U.

    2009-05-15

    Dark matter constitutes one of the most intriguing but so far unresolved issues in physics today. In many extensions of the Standard Model the existence of a stable Weakly Interacting Massive Particle (WIMP) is predicted. The WIMP is an excellent dark matter particle candidate and one of the most interesting scenarios include an annihilation of two WIMPs into two gamma-rays. If the WIMPs are assumed to be non-relativistic, the resulting photons will both have an energy equal to the mass of the WIMP and manifest themselves as a monochromatic spectral line in the energy spectrum. This type of signal would represent a 'smoking gun' for dark matter, since no other known astrophysical process should be able to produce it. In these proceedings we give an overview of the different approaches to a search for dark matter lines that the Fermi-LAT collaboration is pursuing and the various challenges involved.

  13. Constraining weak annihilation using semileptonic D decays

    SciTech Connect

    Ligeti, Zoltan; Luke, Michael; Manohar, Aneesh V.

    2010-08-01

    The recently measured semileptonic D{sub s} decay rate can be used to constrain weak annihilation (WA) effects in semileptonic D and B decays. We revisit the theoretical predictions for inclusive semileptonic D{sub (s)} decays using a variety of quark mass schemes. The most reliable results are obtained if the fits to B decay distributions are used to eliminate the charm quark mass dependence, without using any specific charm mass scheme. Our fit to the available data shows that WA is smaller than commonly assumed. There is no indication that the WA octet contribution (which is better constrained than the singlet contribution) dominates. The results constrain an important source of uncertainty in the extraction of |V{sub ub}| from inclusive semileptonic B decays.

  14. Pair Production and Annihilation in Strong Magnetic Fields

    NASA Technical Reports Server (NTRS)

    Daugherty, J. K.; Harding, A. K.

    1983-01-01

    Electromagnetic phenomena occurring in the presence of strong magnetic fields are currently of great interest in high-energy astrophysics. In particular, the process of pair production by single photons in the presence of fields of order 10 to the 12th power Gauss is of importance in cascade models of pulsar gamma ray emission, and may also become significant in theories of other radiation phenomena whose sources may be neutron stars (e.g., gamma ray bursts). In addition to pair production, the inverse process of pair annihilation is greatly affected by the presence of superstrong magnetic fields. The most significant departures from annihilation processes in free space are a reduction in the total rate for annihilation into two photons, a broadening of the familiar 511-keV line for annihilation at rest, and the possibility for annihilation into a single photon (which dominates the two-photon annihilation for B ( 10 the 13th power Gauss). The physics of these pair conversion processes, which is reviewed briefly, can become quite complex in the teragauss regime, and can involve calculations which are technically difficult to incorporate into models of emission mechanisms in neutron star magnetospheres. However, theoretical work, especially the case of pair annihilation, also suggests potential techniques for more direct measurements of field strengths near the stellar surface.

  15. Position-resolved Positron Annihilation Lifetime Spectroscopy

    NASA Astrophysics Data System (ADS)

    Wagner, A.; Butterling, M.; Fiedler, F.; Fritz, F.; Kempe, M.; Cowan, T. E.

    2013-06-01

    A new method which allows for position-resolved positron lifetime spectroscopy studies in extended volume samples is presented. In addition to the existing technique of in-situ production of positrons inside large (cm3) bulk samples using high-energy photons up to 16 MeV from bremsstrahlung production, granular position-sensitive photon detectors have been employed. A beam of intense bremsstrahlung is provided by the superconducting electron linear accelerator ELBE (Electron Linear Accelerator with high Brilliance and low Emittance) which delivers electron bunches of less than 10 ps temporal width and an adjustable bunch separation of multiples of 38 ns, average beam currents of 1 mA, and energies up to 40 MeV. Since the generation of bremsstrahlung and the transport to the sample preserves the sharp timing of the electron beam, positrons generated inside the entire sample volume by pair production feature a sharp start time stamp for positron annihilation lifetime studies with high timing resolutions and high signal to background ratios due to the coincident detection of two annihilation photons. Two commercially available detectors from a high-resolution medial positron-emission tomography system are being employed with 169 individual Lu2SiO5:Ce scintillation crystals, each. In first experiments, a positron-lifetime gated image of a planar Si/SiO2 (pieces of 12.5 mm × 25 mm size) sample and a 3-D structured metal in Teflon target could be obtained proving the feasibility of a three dimensional lifetime-gated tomographic system.

  16. Operations

    ERIC Educational Resources Information Center

    Wilkins, Jesse L. M.; Norton, Anderson; Boyce, Steven J.

    2013-01-01

    Previous research has documented schemes and operations that undergird students' understanding of fractions. This prior research was based, in large part, on small-group teaching experiments. However, written assessments are needed in order for teachers and researchers to assess students' ways of operating on a whole-class scale. In this…

  17. Three-dimensional annihilation imaging of trapped antiprotons.

    PubMed

    Fujiwara, M C; Amoretti, M; Bonomi, G; Bouchta, A; Bowe, P D; Carraro, C; Cesar, C L; Charlton, M; Doser, M; Filippini, V; Fontana, A; Funakoshi, R; Genova, P; Hangst, J S; Hayano, R S; Jørgensen, L V; Lagomarsino, V; Landua, R; Lodi-Rizzini, E; Marchesotti, M; Macri, M; Madsen, N; Manuzio, G; Montagna, P; Riedler, P; Rotondi, A; Rouleau, G; Testera, G; Variola, A; van der Werf, D P; Yamazaki, Y

    2004-02-13

    We demonstrate three-dimensional imaging of antiprotons in a Penning trap, by reconstructing annihilation vertices from the trajectories of the charged annihilation products. The unique capability of antiparticle imaging has allowed, for the first time, the observation of the spatial distribution of the particle loss in a Penning trap. The radial loss of antiprotons on the trap wall is localized to small spots, strongly breaking the azimuthal symmetry expected for an ideal trap. Our observations have important implications for detection of antihydrogen annihilations. PMID:14995248

  18. Exchange explosions: Magnetization dynamics during vortex-antivortex annihilation.

    PubMed

    Hertel, Riccardo; Schneider, Claus M

    2006-10-27

    A magnetic vortex and an antivortex can annihilate, resulting in a homogeneous magnetization. A detailed description of the magnetization dynamics of such annihilation processes is obtained by micromagnetic simulations based on the Landau-Lifshitz-Gilbert equation. We show that, depending on the relative polarization of the vortex-antivortex pair, the annihilation process is either a continuous transformation of the magnetic structure or it involves the propagation of a micromagnetic singularity (Bloch point) causing a burstlike emission of spin waves. These results provide new insight into a fundamental micromagnetic process that has recently been proposed for a controlled generation of spin waves. PMID:17155502

  19. Matrix element analyses of dark matter scattering and annihilation

    NASA Astrophysics Data System (ADS)

    Kumar, Jason; Marfatia, Danny

    2013-07-01

    We provide a compendium of results at the level of matrix elements for a systematic study of dark matter scattering and annihilation. We identify interactions that yield spin-dependent and spin-independent scattering and specify whether the interactions are velocity and/or momentum suppressed. We identify the interactions that lead to s-wave or p-wave annihilation, and those that are chirality suppressed. We also list the interaction structures that can interfere in scattering and annihilation processes. Using these results, we point out situations in which deviations from the standard lore are obtained.

  20. Minimal semi-annihilating Bbb ZN scalar dark matter

    NASA Astrophysics Data System (ADS)

    Bélanger, Geneviève; Kannike, Kristjan; Pukhov, Alexander; Raidal, Martti

    2014-06-01

    We study the dark matter from an inert doublet and a complex scalar singlet stabilized by Bbb ZN symmetries. This field content is the minimal one that allows dimensionless semi-annihilation couplings for N > 2. We consider explicitly the Bbb Z3 and Bbb Z4 cases and take into account constraints from perturbativity, unitarity, vacuum stability, necessity for the electroweak Bbb ZN preserving vacuum to be the global minimum, electroweak precision tests, upper limits from direct detection and properties of the Higgs boson. Co-annihilation and semi-annihilation of dark sector particles as well as dark matter conversion significantly modify the cosmic abundance and direct detection phenomenology.

  1. Positron annihilation characteristics in mesostructural silica films with various porosities

    SciTech Connect

    Xiong, Bangyun; Mao, Wenfeng; Tang, Xiuqin; He, Chunqing

    2014-03-07

    Porous silica films with various porosities were prepared via a sol-gel method using a nonionic amphiphilic triblock copolymer F127 as the structure-directing agent. Doppler broadening of positron annihilation radiation (DBAR) spectra were collected for the prepared films using a variable energy slow positron beam. Different linear relationships between positron annihilation line shape parameters S and W are found for the as-deposited films and calcined ones, indicative of the decomposition of the copolymer porogen in the as-deposited films upon calcination. This also reveals the variation of positron annihilation sites as a function of F127 loading or porosity. Strong correlations between positronium 3γ annihilation fraction, S parameter and porosity of the mesoporous silica films with isolated pores are obtained, which may provide a complementary method to determine closed porosities of mesoporous silica films by DBAR.

  2. Coincidence Doppler Broadening of Positron Annihilation Radiation in Fe

    NASA Astrophysics Data System (ADS)

    do Nascimento, E.; Vanin, V. R.; Maidana, N. L.; Helene, O.

    2013-06-01

    We measured the Doppler broadening annihilation radiation spectrum in Fe, using 22NaCl as a positron source, and two Ge detectors in coincidence arrangement. The two-dimensional coincidence energy spectrum was fitted using a model function that included positron annihilation with the conduction band and 3d electrons, 3s and 3p electrons, and in-flight positron annihilation. Detectors response functions included backscattering and a combination of Compton and pulse pileup, ballistic deficit and shaping effects. The core electrons annihilation intensity was measured as 16.4(3) %, with almost all the remainder assigned to the less bound electrons. The obtained results are in agreement with published theoretical values.

  3. Black Hole Window into p -Wave Dark Matter Annihilation

    NASA Astrophysics Data System (ADS)

    Shelton, Jessie; Shapiro, Stuart L.; Fields, Brian D.

    2015-12-01

    We present a new method to measure or constrain p -wave-suppressed cross sections for dark matter (DM) annihilations inside the steep density spikes induced by supermassive black holes. We demonstrate that the high DM densities, together with the increased velocity dispersion, within such spikes combine to make thermal p -wave annihilation cross sections potentially visible in γ -ray observations of the Galactic center (GC). The resulting DM signal is a bright central point source with emission originating from DM annihilations in the absence of a detectable spatially extended signal from the halo. We define two simple reference theories of DM with a thermal p -wave annihilation cross section and establish new limits on the combined particle and astrophysical parameter space of these models, demonstrating that Fermi Large Area Telescope is currently sensitive to thermal p -wave DM over a wide range of possible scenarios for the DM distribution in the GC.

  4. Dark matter annihilation in the first galaxy haloes

    NASA Astrophysics Data System (ADS)

    Schön, S.; Mack, K. J.; Avram, C. A.; Wyithe, J. S. B.; Barberio, E.

    2015-08-01

    We investigate the impact of energy released from self-annihilating dark matter (DM) on heating of gas in the small, high-redshift DM haloes thought to host the first stars. A supersymmetric (SUSY)-neutralino-like particle is implemented as our DM candidate. The PYTHIA code is used to model the final, stable particle distributions produced during the annihilation process. We use an analytic treatment in conjunction with the code MEDEA2 to find the energy transfer and subsequent partition into heating, ionizing and Lyman α photon components. We consider a number of halo density models, DM particle masses and annihilation channels. We find that the injected energy from DM exceeds the binding energy of the gas within a 105-106 M⊙ halo at redshifts above 20, preventing star formation in early haloes in which primordial gas would otherwise cool. Thus we find that DM annihilation could delay the formation of the first galaxies.

  5. Black Hole Window into p-Wave Dark Matter Annihilation.

    PubMed

    Shelton, Jessie; Shapiro, Stuart L; Fields, Brian D

    2015-12-01

    We present a new method to measure or constrain p-wave-suppressed cross sections for dark matter (DM) annihilations inside the steep density spikes induced by supermassive black holes. We demonstrate that the high DM densities, together with the increased velocity dispersion, within such spikes combine to make thermal p-wave annihilation cross sections potentially visible in γ-ray observations of the Galactic center (GC). The resulting DM signal is a bright central point source with emission originating from DM annihilations in the absence of a detectable spatially extended signal from the halo. We define two simple reference theories of DM with a thermal p-wave annihilation cross section and establish new limits on the combined particle and astrophysical parameter space of these models, demonstrating that Fermi Large Area Telescope is currently sensitive to thermal p-wave DM over a wide range of possible scenarios for the DM distribution in the GC. PMID:26684108

  6. Search for dark matter annihilation in the Galactic Center with IceCube-79

    NASA Astrophysics Data System (ADS)

    Aartsen, M. G.; Abraham, K.; Ackermann, M.; Adams, J.; Aguilar, J. A.; Ahlers, M.; Ahrens, M.; Altmann, D.; Anderson, T.; Archinger, M.; Arguelles, C.; Arlen, T. C.; Auffenberg, J.; Bai, X.; Barwick, S. W.; Baum, V.; Bay, R.; Beatty, J. J.; Becker Tjus, J.; Becker, K.-H.; Beiser, E.; BenZvi, S.; Berghaus, P.; Berley, D.; Bernardini, E.; Bernhard, A.; Besson, D. Z.; Binder, G.; Bindig, D.; Bissok, M.; Blaufuss, E.; Blumenthal, J.; Boersma, D. J.; Bohm, C.; Börner, M.; Bos, F.; Bose, D.; Böser, S.; Botner, O.; Braun, J.; Brayeur, L.; Bretz, H.-P.; Brown, A. M.; Buzinsky, N.; Casey, J.; Casier, M.; Cheung, E.; Chirkin, D.; Christov, A.; Christy, B.; Clark, K.; Classen, L.; Coenders, S.; Cowen, D. F.; Cruz Silva, A. H.; Daughhetee, J.; Davis, J. C.; Day, M.; de André, J. P. A. M.; De Clercq, C.; Dembinski, H.; De Ridder, S.; Desiati, P.; de Vries, K. D.; de Wasseige, G.; de With, M.; DeYoung, T.; Díaz-Vélez, J. C.; Dumm, J. P.; Dunkman, M.; Eagan, R.; Eberhardt, B.; Ehrhardt, T.; Eichmann, B.; Euler, S.; Evenson, P. A.; Fadiran, O.; Fahey, S.; Fazely, A. R.; Fedynitch, A.; Feintzeig, J.; Felde, J.; Filimonov, K.; Finley, C.; Fischer-Wasels, T.; Flis, S.; Fuchs, T.; Glagla, M.; Gaisser, T. K.; Gaior, R.; Gallagher, J.; Gerhardt, L.; Ghorbani, K.; Gier, D.; Gladstone, L.; Glüsenkamp, T.; Goldschmidt, A.; Golup, G.; Gonzalez, J. G.; Góra, D.; Grant, D.; Gretskov, P.; Groh, J. C.; Groß, A.; Ha, C.; Haack, C.; Haj Ismail, A.; Hallgren, A.; Halzen, F.; Hansmann, B.; Hanson, K.; Hebecker, D.; Heereman, D.; Helbing, K.; Hellauer, R.; Hellwig, D.; Hickford, S.; Hignight, J.; Hill, G. C.; Hoffman, K. D.; Hoffmann, R.; Holzapfel, K.; Homeier, A.; Hoshina, K.; Huang, F.; Huber, M.; Huelsnitz, W.; Hulth, P. O.; Hultqvist, K.; In, S.; Ishihara, A.; Jacobi, E.; Japaridze, G. S.; Jero, K.; Jurkovic, M.; Kaminsky, B.; Kappes, A.; Karg, T.; Karle, A.; Kauer, M.; Keivani, A.; Kelley, J. L.; Kemp, J.; Kheirandish, A.; Kiryluk, J.; Kläs, J.; Klein, S. R.; Kohnen, G.; Kolanoski, H.; Konietz, R.; Koob, A.; Köpke, L.; Kopper, C.; Kopper, S.; Koskinen, D. J.; Kowalski, M.; Krings, K.; Kroll, G.; Kroll, M.; Kunnen, J.; Kurahashi, N.; Kuwabara, T.; Labare, M.; Lanfranchi, J. L.; Larson, M. J.; Lesiak-Bzdak, M.; Leuermann, M.; Leuner, J.; Lünemann, J.; Madsen, J.; Maggi, G.; Mahn, K. B. M.; Maruyama, R.; Mase, K.; Matis, H. S.; Maunu, R.; McNally, F.; Meagher, K.; Medici, M.; Meli, A.; Menne, T.; Merino, G.; Meures, T.; Miarecki, S.; Middell, E.; Middlemas, E.; Miller, J.; Mohrmann, L.; Montaruli, T.; Morse, R.; Nahnhauer, R.; Naumann, U.; Niederhausen, H.; Nowicki, S. C.; Nygren, D. R.; Obertacke, A.; Olivas, A.; Omairat, A.; O'Murchadha, A.; Palczewski, T.; Paul, L.; Pepper, J. A.; Pérez de los Heros, C.; Pfendner, C.; Pieloth, D.; Pinat, E.; Posselt, J.; Price, P. B.; Przybylski, G. T.; Pütz, J.; Quinnan, M.; Rädel, L.; Rameez, M.; Rawlins, K.; Redl, P.; Reimann, R.; Relich, M.; Resconi, E.; Rhode, W.; Richman, M.; Richter, S.; Riedel, B.; Robertson, S.; Rongen, M.; Rott, C.; Ruhe, T.; Ruzybayev, B.; Ryckbosch, D.; Saba, S. M.; Sabbatini, L.; Sander, H.-G.; Sandrock, A.; Sandroos, J.; Sarkar, S.; Schatto, K.; Scheriau, F.; Schimp, M.; Schmidt, T.; Schmitz, M.; Schoenen, S.; Schöneberg, S.; Schönwald, A.; Schukraft, A.; Schulte, L.; Seckel, D.; Seunarine, S.; Shanidze, R.; Smith, M. W. E.; Soldin, D.; Spiczak, G. M.; Spiering, C.; Stahlberg, M.; Stamatikos, M.; Stanev, T.; Stanisha, N. A.; Stasik, A.; Stezelberger, T.; Stokstad, R. G.; Stößl, A.; Strahler, E. A.; Ström, R.; Strotjohann, N. L.; Sullivan, G. W.; Sutherland, M.; Taavola, H.; Taboada, I.; Ter-Antonyan, S.; Terliuk, A.; Tešić, G.; Tilav, S.; Toale, P. A.; Tobin, M. N.; Tosi, D.; Tselengidou, M.; Unger, E.; Usner, M.; Vallecorsa, S.; van Eijndhoven, N.; Vandenbroucke, J.; van Santen, J.; Vanheule, S.; Veenkamp, J.; Vehring, M.; Voge, M.; Vraeghe, M.; Walck, C.; Wallraff, M.; Wandkowsky, N.; Weaver, Ch.; Wendt, C.; Westerhoff, S.; Whelan, B. J.; Whitehorn, N.; Wichary, C.; Wiebe, K.; Wiebusch, C. H.; Wille, L.; Williams, D. R.; Wissing, H.; Wolf, M.; Wood, T. R.; Woschnagg, K.; Xu, D. L.; Xu, X. W.; Xu, Y.; Yanez, J. P.; Yodh, G.; Yoshida, S.; Zarzhitsky, P.; Zoll, M.

    2015-10-01

    The Milky Way is expected to be embedded in a halo of dark matter particles, with the highest density in the central region, and decreasing density with the halo-centric radius. Dark matter might be indirectly detectable at Earth through a flux of stable particles generated in dark matter annihilations and peaked in the direction of the Galactic Center. We present a search for an excess flux of muon (anti-) neutrinos from dark matter annihilation in the Galactic Center using the cubic-kilometer-sized IceCube neutrino detector at the South Pole. There, the Galactic Center is always seen above the horizon. Thus, new and dedicated veto techniques against atmospheric muons are required to make the southern hemisphere accessible for IceCube. We used 319.7 live-days of data from IceCube operating in its 79-string configuration during 2010 and 2011. No neutrino excess was found and the final result is compatible with the background. We present upper limits on the self-annihilation cross-section, <σ _{A} v>, for WIMP masses ranging from 30 GeV up to 10 TeV, assuming cuspy (NFW) and flat-cored (Burkert) dark matter halo profiles, reaching down to ˜eq 4 \\cdot 10^{-24} cm^3 s^{-1}, and ˜eq 2.6 \\cdot 10^{-23} cm^3 s^{-1} for the ν overline{ν } channel, respectively.

  7. Gamma-ray constraints on dark-matter annihilation to electroweak gauge and Higgs bosons

    SciTech Connect

    Fedderke, Michael A.; Kolb, Edward W.; Lin, Tongyan; Wang, Lian-Tao E-mail: Rocky.Kolb@uchicago.edu E-mail: liantaow@uchicago.edu

    2014-01-01

    Dark-matter annihilation into electroweak gauge and Higgs bosons results in γ-ray emission. We use observational upper limits on the fluxes of both line and continuum γ-rays from the Milky Way Galactic Center and from Milky Way dwarf companion galaxies to set exclusion limits on allowed dark-matter masses. (Generally, Galactic Center γ-ray line search limits from the Fermi-LAT and the H.E.S.S. experiments are most restrictive.) Our limits apply under the following assumptions: a) the dark matter species is a cold thermal relic with present mass density equal to the measured dark-matter density of the universe; b) dark-matter annihilation to standard-model particles is described in the non-relativistic limit by a single effective operator O∝J{sub DM}⋅J{sub SM}, where J{sub DM} is a standard-model singlet current consisting of dark-matter fields (Dirac fermions or complex scalars), and J{sub SM} is a standard-model singlet current consisting of electroweak gauge and Higgs bosons; and c) the dark-matter mass is in the range 5 GeV to 20 TeV. We consider, in turn, the 34 possible operators with mass dimension 8 or lower with non-zero s-wave annihilation channels satisfying the above assumptions. Our limits are presented in a large number of figures, one for each of the 34 possible operators; these limits can be grouped into 13 classes determined by the field content and structure of the operators. We also identify three classes of operators (coupling to the Higgs and SU(2){sub L} gauge bosons) that can supply a 130 GeV line with the desired strength to fit the putative line signal in the Fermi-LAT data, while saturating the relic density and satisfying all other indirect constraints we consider.

  8. Nanostructured singlet fission photovoltaics subject to triplet-charge annihilation.

    PubMed

    Thompson, Nicholas J; Hontz, Eric; Congreve, Daniel N; Bahlke, Matthias E; Reineke, Sebastian; Van Voorhis, Troy; Baldo, Marc A

    2014-03-01

    Singlet exciton fission is an efficient multiple-exciton generation process that is vulnerable to a characteristic loss process: triplet-charge annihilation. This loss process is characterized in singlet-fission photovoltaics and losses as high as 40% are observed in poorly designed devices. Techniques are demonstrated to improve charge extraction and reduce triplet-charge annihilation to negligible levels at short-circuit conditions. PMID:24281738

  9. Cosmic microwave background constraint on residual annihilations of relic particles

    SciTech Connect

    McDonald, Patrick; Scherrer, Robert J.; Walker, Terry P.

    2001-01-15

    Energy injected into the cosmic microwave background at redshifts z{approx}<10{sup 6} will distort its spectrum permanently. In this paper we discuss the distortion caused by annihilations of relic particles. We use the observational bounds on deviations from a Planck spectrum to constrain a combination of annihilation cross section, mass, and abundance. For particles with an (s-wave) annihilation cross section <{sigma}|v|>(equivalent to){sigma}{sub 0}, the bound is f(m{sub X}/MeV){sup -1}[({sigma}{sub 0}/6x10{sup -27} cm{sup 3}s{sup -1})({Omega}{sub X{bar X}}h{sup 2}){sup 2}]<0.2, where m{sub X} is the particle mass, {Omega}{sub X{bar X}} is the fraction of the critical density the particle and its antiparticle contribute if they survive to the present time, h=H{sub 0}/100 kms{sup -1}Mpc{sup -1}, H{sub 0} is the Hubble constant, and f is the fraction of the annihilation energy that interacts electromagnetically. We also compute the less stringent limits for p-wave annihilation. We update other bounds on residual annihilations and compare them to our CMB bound.

  10. Energy-resolved positron annihilation rates for molecules

    SciTech Connect

    Barnes, L. D.; Young, J. A.; Surko, C. M.

    2006-07-15

    The development of high resolution positron beams has enabled measurements of annihilation rates for molecules as a function of incident positron energy. Vibrational Feshbach resonances in these spectra provide evidence for the existence of positron-molecule bound states. In this paper we present further studies of this phenomenon. Evidence is presented for positronically excited bound states (i.e., in addition to the ground state) in C{sub 12}H{sub 26} and C{sub 14}H{sub 30}. Measurements of the annihilation spectra of the halomethanes, CH{sub 3}F, CH{sub 3}Cl, and CH{sub 3}Br, exhibit strong resonances that vary significantly with the substituted halogen. Annihilation spectra for linear alkanes and ring molecules are compared. Annihilation spectra and infrared absorption spectra are compared for a number of molecules. Finally, annihilation rate measurements are presented for a variety of molecules at energies {>=}0.5 eV (i.e., above the vibrational resonances). These provide a measure of the annihilation rates in the absence of vibrational resonances.

  11. Structure formation constraints on Sommerfeld-enhanced dark matter annihilation

    SciTech Connect

    Armendariz-Picon, Cristian; Neelakanta, Jayanth T. E-mail: jtneelak@syr.edu

    2012-12-01

    We study the growth of cosmic structure in a ΛCDM universe under the assumption that dark matter self-annihilates with an averaged cross section times relative velocity that grows with the scale factor, an increase known as Sommerfeld-enhancement. Such an evolution is expected in models in which a light force carrier in the dark sector enhances the annihilation cross section of dark matter particles, and has been invoked, for instance, to explain anomalies in cosmic ray spectra reported in the past. In order to make our results as general as possible, we assume that dark matter annihilates into a relativistic species that only interacts gravitationally with the standard model. This assumption also allows us to test whether the additional relativistic species mildly favored by cosmic-microwave background data could originate from dark matter annihilation. We do not find evidence for Sommerfeld-enhanced dark matter annihilation and derive the corresponding upper limits on the annihilation cross-section.

  12. Positron Annihilation in Medical Substances of Insulin

    NASA Astrophysics Data System (ADS)

    Pietrzak, R.; Szatanik, R.

    2005-05-01

    Positrons lifetimes were measured in medical substances of insulin (human and animal), differing as far as the degree of purity and time of their activity in the organism are concerned. In all of the cases the spectrum of positron lifetime was distributed into three components, with the long-life component ranging from 1.8 to 2.08 ns and the intensity taking on values from 18 to 24%. Making use of Tao-Eldrup model, the average radius of the free volume, in which o-Ps annihilated, and the degree of filling in the volume were determined. It was found that the value of the long-life component for human insulin is higher than that of animal insulin. Moreover, the value of this component clearly depends on the manner of purification of the insulin. It was also noticed that there occurs a correlation between the value of this component and the time after which it begins to be active in the organism, as well as the total time of its activity.

  13. Positron annihilation studies of organic superconductivity

    SciTech Connect

    Yen, H.L.; Lou, Y.; Ali, E.H.

    1994-09-01

    The positron lifetimes of two organic superconductors, {kappa}-(ET){sub 2}Cu(NCS){sub 2} and {kappa}-(ET){sub 2}Cu[N(CN){sub 2}]Br, are measured as a function of temperature across {Tc}. A drop of positron lifetime below {Tc} is observed. Positron-electron momentum densities are measured by using 2D-ACAR to search for the Fermi surface in {kappa}-(ET){sub 2}Cu[N(CN){sub 2}]Br. Positron density distributions and positron-electron overlaps are calculated by using the orthogonalized linear combination atomic orbital (OLCAO) method to interprete the temperature dependence due to the local charge transfer which is inferred to relate to the superconducting transition. 2D-ACAR results in {kappa}-(ET){sub 2}Cu[N(CN){sub 2}]Br are compared with theoretical band calculations based on a first-principles local density approximation. Importance of performing accurate band calculations for the interpretation of positron annihilation data is emphasized.

  14. Monopole annihilation and highest energy cosmic rays

    SciTech Connect

    Bhattacharjee, P. Indian Institute of Astrophysics, Sarjapur Road, Koramangala, Bangalore 560 034 ); Sigl, G. NASA/Fermilab Astrophysics Center, Fermi National Accelerator Laboratory, Batavia, Illinois 60510-0500 )

    1995-04-15

    Cosmic rays with energies exceeding 10[sup 20] eV have been detected. The origin of these highest energy cosmic rays remains unknown. Established astrophysical acceleration mechanisms encounter severe difficulties in accelerating particles to these energies. Alternative scenarios where these particles are created by the decay of cosmic topological defects have been suggested in the literature. In this paper we study the possibility of producing the highest energy cosmic rays through a process that involves the formation of metastable magnetic monopole-antimonopole bound states and their subsequent collapse. The annihilation of the heavy monopole-antimonopole pairs constituting the monopolonia can produce energetic nucleons, [gamma] rays, and neutrinos whose expected flux we estimate and discuss in relation to experimental data so far available. The monopoles we consider are the ones that could be produced in the early Universe during a phase transition at the grand unification energy scale. We find that observable cosmic ray fluxes can be produced with monopole abundances compatible with present bounds.

  15. Effect of compressibility on the annihilation process

    NASA Astrophysics Data System (ADS)

    Hnatich, M.; Honkonen, J.; Lučivjanský, T.

    2013-07-01

    Using the renormalization group in the perturbation theory, we study the influence of a random velocity field on the kinetics of the single-species annihilation reaction at and below its critical dimension d c = 2. The advecting velocity field is modeled by a Gaussian variable self-similar in space with a finite-radius time correlation (the Antonov-Kraichnan model). We take the effect of the compressibility of the velocity field into account and analyze the model near its critical dimension using a three-parameter expansion in ∈, Δ, and η, where ∈ is the deviation from the Kolmogorov scaling, Δ is the deviation from the (critical) space dimension two, and η is the deviation from the parabolic dispersion law. Depending on the values of these exponents and the compressiblity parameter α, the studied model can exhibit various asymptotic (long-time) regimes corresponding to infrared fixed points of the renormalization group. We summarize the possible regimes and calculate the decay rates for the mean particle number in the leading order of the perturbation theory.

  16. Constraints on dark matter annihilation from CMB observations before Planck

    SciTech Connect

    Lopez-Honorez, Laura; Mena, Olga; Palomares-Ruiz, Sergio; Vincent, Aaron C. E-mail: omena@ific.uv.es E-mail: vincent@ific.uv.es

    2013-07-01

    We compute the bounds on the dark matter (DM) annihilation cross section using the most recent Cosmic Microwave Background measurements from WMAP9, SPT'11 and ACT'10. We consider DM with mass in the MeV–TeV range annihilating 100% into either an e{sup +}e{sup −} or a μ{sup +}μ{sup −} pair. We consider a realistic energy deposition model, which includes the dependence on the redshift, DM mass and annihilation channel. We exclude the canonical thermal relic abundance cross section ((σv) = 3 × 10{sup −26}cm{sup 3}s{sup −1}) for DM masses below 30 GeV and 15 GeV for the e{sup +}e{sup −} and μ{sup +}μ{sup −} channels, respectively. A priori, DM annihilating in halos could also modify the reionization history of the Universe at late times. We implement a realistic halo model taken from results of state-of-the-art N-body simulations and consider a mixed reionization mechanism, consisting on reionization from DM as well as from first stars. We find that the constraints on DM annihilation remain unchanged, even when large uncertainties on the halo model parameters are considered.

  17. The Isotropic Radio Background and Annihilating Dark Matter

    SciTech Connect

    Hooper, Dan; Belikov, Alexander V.; Jeltema, Tesla E.; Linden, Tim; Profumo, Stefano; Slatyer, Tracy R.

    2012-11-01

    Observations by ARCADE-2 and other telescopes sensitive to low frequency radiation have revealed the presence of an isotropic radio background with a hard spectral index. The intensity of this observed background is found to exceed the flux predicted from astrophysical sources by a factor of approximately 5-6. In this article, we consider the possibility that annihilating dark matter particles provide the primary contribution to the observed isotropic radio background through the emission of synchrotron radiation from electron and positron annihilation products. For reasonable estimates of the magnetic fields present in clusters and galaxies, we find that dark matter could potentially account for the observed radio excess, but only if it annihilates mostly to electrons and/or muons, and only if it possesses a mass in the range of approximately 5-50 GeV. For such models, the annihilation cross section required to normalize the synchrotron signal to the observed excess is sigma v ~ (0.4-30) x 10^-26 cm^3/s, similar to the value predicted for a simple thermal relic (sigma v ~ 3 x 10^-26 cm^3/s). We find that in any scenario in which dark matter annihilations are responsible for the observed excess radio emission, a significant fraction of the isotropic gamma ray background observed by Fermi must result from dark matter as well.

  18. Models of pair annihilation in 1E 1740.7-2942 and the HEAO 1 A-4 annihilation source

    NASA Technical Reports Server (NTRS)

    Maciolek-Niedzwiecki, Andrzej; Zdziarski, Andrzej

    1994-01-01

    We study possible models of two Galactic sources of transient pair annihilation radiation, 1E 1740.7-2942 and a source observed by High Energy Astronomy Observatory (HEAO) 1 A-4. We fit the observed spectral features by thermal annihilation spectra and find that the redshifts obtained by us are much larger than those obtained from fitting Caussian lines centered on 511 keV. This effect, which is due to the net blueshift (with respect to 511 keV) of the annihilation spectrum due to the thermal energies of pairs, puts strong constraints on models of sources. We consider those constraints first without considering the mechanism of positron production. From the shape of the observed spectra, we are able to rule out both spherical clouds and layers above cold matter as possible source geometries. The observed spectra are compatible with two source geometries: (1) a nearly face-on disk in the Kerr metric and (2) a jet close to a black hole. We consider, then, the origin of the pairs. Theories of both thermal and nonthermal pair equilibria predict that photon-pair production is unable to produce annihilation features that contain as much as half of the bolometric luminosity, which is observed. A possible solution to this problem is obscuration of a nonthermal source (in which pairs are produced by photon-photon collisions) and an outflow of pairs to an unobscured region. This makes annihilation in a jet the most likely model of the considered sources.

  19. [Positron annihilation lifetime spectrometry (PALS) and its pharmaceutical applications].

    PubMed

    Sebe, István; Szabó, Barnabás; Zelkó, Romána

    2012-01-01

    PALS is one of the most widely used "nuclear probe" techniques for the tracking of the structural characteristics of materials. The method is based on the matter-energy equivalence principle recognized by Einstein: the electrons and positrons as particle-antiparticle pairs disappear in mutual destruction of particles, they annihilate with high-energy gamma-radiation, thus "particle-energy transition" occurs. The properties of the resulting radiation exactly correspond to the relevant properties of the electron and positron preceding the annihilation. Since electrons occur in all types of materials, the phenomenon of positron annihilation can play in any environment; consequently the method can be used for the analysis of each type of materials (crystalline and amorphous, organic and inorganic, biotic and abiotic). The present paper provides an overview of the theoretical physical background, the practical realization and evaluation of methods, their limitations, and summarizes the pharmaceutical applications published in recent years. PMID:22570984

  20. Coincidence Efficiency of Sodium Iodide Detectors for Positron Annihilation

    NASA Astrophysics Data System (ADS)

    Eckert, Thomas; Vincett, Laurel; Yuly, Mark; Padalino, Stephen; Russ, Megan; Bienstock, Mollie; Simone, Angela; Ellison, Drew; Desmitt, Holly; Sangster, Craig; Regan, Sean

    2014-10-01

    One possible diagnostic technique for characterizing inertial confinement fusion reactions uses tertiary neutron activation of 12C via the 12C(n, 2n)11C reaction. A recent experiment to measure this cross section involved counting the positron annihilation gamma rays from the 11C decay by using sodium iodide detectors in coincidence. To determine the number of 11C decays requires an accurate value for the full-peak coincidence efficiency for the detector system. A new technique has been developed to measure this coincidence efficiency by detecting the positron prior to its annihilation, and vetoing events in which decay gamma rays other than the 511 keV annihilation gamma rays could enter the detectors. Measurements and simulation results for the absolute coincidence total and full-peak efficiencies are presented. Funded in part by a grant from the DOE through the Laboratory for Laser Energetics.

  1. Dark matter annihilation with s-channel internal Higgsstrahlung

    NASA Astrophysics Data System (ADS)

    Kumar, Jason; Liao, Jiajun; Marfatia, Danny

    2016-08-01

    We study the scenario of fermionic dark matter that annihilates to standard model fermions through an s-channel axial vector mediator. We point out that the well-known chirality suppression of the annihilation cross section can be alleviated by s-channel internal Higgsstrahlung. The shapes of the cosmic ray spectra are identical to that of t-channel internal Higgsstrahlung in the limit of a heavy mediating particle. Unlike the general case of t-channel bremsstrahlung, s-channel Higgsstrahlung can be the dominant annihilation process even for Dirac dark matter. Since the s-channel mediator can be a standard model singlet, collider searches for the mediator are easily circumvented.

  2. Phase behavior of microemulsion systems studied by positron annihilation techniques

    SciTech Connect

    Serrano, J.; Reynoso, R.; Lopez, R.; Olea, O.; Fucugauchi, L.A.

    1983-02-17

    The positron annihilation technique was applied to the study of phase behavior of sodium stearate (or oleate)-alcohol-oil-water microemulsion systems. The positron annihilation parameters revealed a dependence of the water/oil ratio at which microemulsion formation occurs on the hydrocarbon chain length of both alcohol cosurfactant and solvent as well as surfactant concentration. Dynamic laser light scattering has been utilized for substantiating the phase transitions determined in the different microemulsion systems by positron annihilation. The difference in the behavior between saturated and unsaturated surfactants is the most remarkable result of the investigation. Thus, replacing sodium stearate by sodium oleate in the surfactant-1-hexanol-isooctane systems obviated microemulsion formation. This behavior has been rationalized by considering packing and kink presence in microemulsion formation. 26 references.

  3. A Critical Reevaluation of Radio Constraints on Annihilating Dark Matter

    SciTech Connect

    Cholis, Ilias; Hooper, Dan; Linden, Tim

    2015-04-03

    A number of groups have employed radio observations of the Galactic center to derive stringent constraints on the annihilation cross section of weakly interacting dark matter. In this paper, we show that electron energy losses in this region are likely to be dominated by inverse Compton scattering on the interstellar radiation field, rather than by synchrotron, considerably relaxing the constraints on the dark matter annihilation cross section compared to previous works. Strong convective winds, which are well motivated by recent observations, may also significantly weaken synchrotron constraints. After taking these factors into account, we find that radio constraints on annihilating dark matter are orders of magnitude less stringent than previously reported, and are generally weaker than those derived from current gamma-ray observations.

  4. Non-positiveWigner Function and Non-Gaussianty Generated by Multiple Creation-then-annihilation Coherent State

    NASA Astrophysics Data System (ADS)

    Xiao, Jin; Xiong, Chao; Yuan, Hong-Chun; Chen, Lei; Zhu, Xi-Fang

    2016-03-01

    We investigate the nonclassicality of a kind of quantum state (MPCACS) generated by repeatedly operating creation-then-annihilation (CA) on the coherent state (CS). Its normalization factor is arduously derived in compact expression related to the Laguerre-polynomial. We explore two observable nonclassical properties of MPCACS, such as non-positive Wigner function and non-Guassianty, which exhibit their highly nonclassical behaviors depending on m. Here, we adopt the Hilbert-Schmidt distance to quantify its Non-Gaussian characters.

  5. Singlet-triplet annihilation in single LHCII complexes.

    PubMed

    Gruber, J Michael; Chmeliov, Jevgenij; Krüger, Tjaart P J; Valkunas, Leonas; van Grondelle, Rienk

    2015-08-14

    In light harvesting complex II (LHCII) of higher plants and green algae, carotenoids (Cars) have an important function to quench chlorophyll (Chl) triplet states and therefore avoid the production of harmful singlet oxygen. The resulting Car triplet states lead to a non-linear self-quenching mechanism called singlet-triplet (S-T) annihilation that strongly depends on the excitation density. In this work we investigated the fluorescence decay kinetics of single immobilized LHCIIs at room temperature and found a two-exponential decay with a slow (3.5 ns) and a fast (35 ps) component. The relative amplitude fraction of the fast component increases with increasing excitation intensity, and the resulting decrease in the fluorescence quantum yield suggests annihilation effects. Modulation of the excitation pattern by means of an acousto-optic modulator (AOM) furthermore allowed us to resolve the time-dependent accumulation and decay rate (∼7 μs) of the quenching species. Inspired by singlet-singlet (S-S) annihilation studies, we developed a stochastic model and then successfully applied it to describe and explain all the experimentally observed steady-state and time-dependent kinetics. That allowed us to distinctively identify the quenching mechanism as S-T annihilation. Quantitative fitting resulted in a conclusive set of parameters validating our interpretation of the experimental results. The obtained stochastic model can be generalized to describe S-T annihilation in small molecular aggregates where the equilibration time of excitations is much faster than the annihilation-free singlet excited state lifetime. PMID:26156159

  6. Annihilation physics of exotic galactic dark matter particles

    NASA Technical Reports Server (NTRS)

    Stecker, F. W.

    1990-01-01

    Various theoretical arguments make exotic heavy neutral weakly interacting fermions, particularly those predicted by supersymmetry theory, attractive candidates for making up the large amount of unseen gravitating mass in galactic halos. Such particles can annihilate with each other, producing secondary particles of cosmic-ray energies, among which are antiprotons, positrons, neutrinos, and gamma-rays. Spectra and fluxes of these annihilation products can be calculated, partly by making use of positron electron collider data and quantum chromodynamic models of particle production derived therefrom. These spectra may provide detectable signatures of exotic particle remnants of the big bang.

  7. Polarization of photons in matter–antimatter annihilation

    SciTech Connect

    Moskaliuk, S.S.

    2015-03-10

    In this work we demonstrate the possibility of generation of linear polarization of the electromagnetic field (EMF) due to the quantum effects in matter-antimatter annihilation process for anisotropic space of the I type according to Bianchi. We study the dynamics of this process to estimate the degree of polarisation of the EMF in the external gravitational field of the anisotropic Bianchi I model. It has been established that the quantum effects in matter-antimatter annihilation process in the external gravitational field of the anisotropic Bianchi I model provide contribution to the degree of polarisation of the EMF in quadrupole harmonics.

  8. Heavy dark matter annihilation from effective field theory.

    PubMed

    Ovanesyan, Grigory; Slatyer, Tracy R; Stewart, Iain W

    2015-05-29

    We formulate an effective field theory description for SU(2)_{L} triplet fermionic dark matter by combining nonrelativistic dark matter with gauge bosons in the soft-collinear effective theory. For a given dark matter mass, the annihilation cross section to line photons is obtained with 5% precision by simultaneously including Sommerfeld enhancement and the resummation of electroweak Sudakov logarithms at next-to-leading logarithmic order. Using these results, we present more accurate and precise predictions for the gamma-ray line signal from annihilation, updating both existing constraints and the reach of future experiments. PMID:26066425

  9. Study of Chemical Carcinogens by Positron Annihilation Lifetime Spectroscopy

    NASA Astrophysics Data System (ADS)

    Pivtsaev, A. A.; Razov, V. I.; Karasev, A. O.

    2013-11-01

    We have used positron annihilation lifetime spectroscopy to study the carcinogens C21H20BrN3, C4H7Cl2O4P, CCl4, CHCl3, AlF3, C8H12N4O, C6H4Cl2 and the non-carcinogens H2O, AlCl3, CH2Cl2, C2H6OS. We have established a correlation between the annihilation characteristics of the studied compounds and their degree of carcinogenicity.

  10. Positron annihilation studies in Li-implanted alumina

    NASA Astrophysics Data System (ADS)

    Gaikwad, Prashant V.; Sharma, S. K.; Mukherjee, S.; Sudarshan, K.; Maheshwari, P.; Pujari, P. K.; Kshirsagar, A.

    2015-06-01

    Depth dependent Doppler broadening of annihilation radiation (DBAR) measurements are carried out for a sample of Li ion implanted in alumina. The effect of Li ion implantation and the subsequent isochronal annealing at the temperatures up to 1100 °C on the Doppler broadening annihilation parameters (S-parameter) are studied. The S-parameter around the Li implantation depth (∼191 nm) increased with annealing temperature up to 700 °C and reduced beyond. The results suggest possible Li cluster formation in annealed sample.

  11. Atomistic processes of grain boundary motion and annihilation in graphene

    SciTech Connect

    Lee, Gun-Do; Yoon, Euijoon; Wang, Cai-Zhuang; Ho, Kai-Ming

    2013-03-19

    The motion and annihilation of a grain boundary (GB) in graphene are investigated by tight-binding molecular dynamics (TBMD) simulation and ab initio local density approximation total energy calculation. A meandering structure of the GB is found to be energetically more favorable than other structures, in good agreement with experiment. It is observed in the TBMD simulation that evaporation of carbon dimers and sequential Stone?Wales transformations of carbon bonds lead to rapid motion and annihilation of the GB. The dimer erection and evaporation are found to proceed by formation of an adatom due to bond breaking. These results shed interesting light on the fabrication of high-quality graphene.

  12. Measuring electron-positron annihilation radiation from laser plasma interactions

    SciTech Connect

    Chen, Hui; Tommasini, R.; Seely, J.; Szabo, C. I.; Feldman, U.; Pereira, N.; Gregori, G.; Falk, K.; Mithen, J.; Murphy, C. D.

    2012-10-15

    We investigated various diagnostic techniques to measure the 511 keV annihilation radiations. These include step-wedge filters, transmission crystal spectroscopy, single-hit CCD detectors, and streaked scintillating detection. While none of the diagnostics recorded conclusive results, the step-wedge filter that is sensitive to the energy range between 100 keV and 700 keV shows a signal around 500 keV that is clearly departing from a pure Bremsstrahlung spectrum and that we ascribe to annihilation radiation.

  13. Dark matter annihilation and the PAMELA, FERMI, and ATIC anomalies

    SciTech Connect

    El Zant, A. A.; Okada, H.; Khalil, S.

    2010-06-15

    If dark matter annihilation accounts for the tantalizing excess of cosmic ray electron/positrons, as reported by the PAMELA, ATIC, HESS, and FERMI observatories, then the implied annihilation cross section must be relatively large. This results, in the context of standard cosmological models, in very small relic dark matter abundances that are incompatible with astrophysical observations. We explore possible resolutions to this apparent conflict in terms of nonstandard cosmological scenarios; plausibly allowing for large cross sections, while maintaining relic abundances in accord with current observations.

  14. Intensity-Frontier Antiproton Physics with The Antiproton Annihilation Spectrometer (TAPAS) at Fermilab

    SciTech Connect

    Apollinari, Giorgio; Asner, David M.; Baldini, Wander; Bartoszek, Larry; Broemmelsiek, Daniel R.; Brown, Charles N.; Chakravorty, Alak; Colas, Paul; Derwent, Paul; Drutskoy, Alexey; Fortner, Michael; /Northern Illinois U. /Saclay /Indian Inst. Tech., Hyderabad

    2011-11-01

    The Fermilab Antiproton Source is the world's most intense source of antimatter. With the Tevatron program now behind us, this unique facility can help make the case for Fermilab's continued accelerator operations. The Antiproton Source can be used for unique, dedicated antimatter studies, including medium-energy {bar p}-annihilation experiments. We propose to assemble a powerful, yet cost-effective, solenoidal magnetic spectrometer for antiproton-annihilation events, and to use it at the Fermilab Antiproton Accumulator to measure the charm production cross section, study rare hyperon decays, search for hyperon CP asymmetry, precisely measure the properties of several charmonium and nearby states, and make the first measurements of the Drell-Yan continuum in medium-energy antiproton annihilation. Should the charm production cross section be as large as some have proposed, we will also be able to measure D{sup 0}-{bar D}{sup 0} mixing with high precision and discover (or sensitively limit) charm CP violation. The observation of charm or hyperon CP violation would be evidence for physics beyond the Standard Model, with possible implications for the origin of the baryon asymmetry of the universe - the question of what happened to all the antimatter that must have been produced in the Big Bang. The experiment will be carried out by an international collaboration and will require some four years of running time. As possibly the sole hadron experiment in progress at Fermilab during that time, it will play an important role in maintaining a broad particle physics program at Fermilab and in the U.S. It will thus help us to continue attracting creative and capable young people into science and technology, and introducing them to the important technologies of accelerators, detectors, and data acquisition and analysis - key roles in society that accelerator-based particle physics has historically played.

  15. Monoenergetic neutrinos from dark matter annihilation: Issues of exposure

    NASA Astrophysics Data System (ADS)

    Kumar, Jason

    2016-06-01

    We consider searches for dark matter annihilation in the Sun resulting in monoenergetic neutrinos, produced either directly or through the decay of stopped pions and kaons. We find that this strategy is very successful at increasing the signal-to-background ratio, but that current experiments may be signal limited. We discuss the exposures need to fully exploit this search strategy.

  16. The HAWC Sensitivity to Dark Matter Annihilation and Decay

    NASA Astrophysics Data System (ADS)

    Yapici, Tolga; HAWC Collaboration

    2016-03-01

    The High Altitude Water Cherenkov (HAWC) Observatory is an extensive air shower array in the state of Puebla, Mexico at an altitude of 4100m. The HAWC observatory will perform an indirect search for dark matter via GeV-TeV photons resulting from dark matter annihilation and decay, including annihilation from extended dark matter sources. We consider the HAWC sensitivity to a subset of the sources, including the M31 galaxy, the Virgo cluster, and the Galactic center. We simulate the HAWC response to gamma rays from the sources in well-motivated dark matter annihilation channels. We show the limits HAWC can place on the dark matter cross-section or lifetime from these sources if gamma-ray excess is not observed. In particular, for dark matter annihilating into gauge bosons, HAWC will be able to measure a narrow range of dark matter masses to cross-sections below that expected for a thermal relic. HAWC should also be sensitive to cross-sections higher than thermal for masses up to nearly 1000 TeV. HAWC will be sensitive to decaying dark matter for these masses as well. HAWC can explore higher dark matter masses than are currently constrained.

  17. New Limits on Thermally Annihilating Dark Matter from Neutrino Telescopes

    NASA Astrophysics Data System (ADS)

    Lopes, J.; Lopes, I.

    2016-08-01

    We used a consistent and robust solar model to obtain upper limits placed by neutrino telescopes, such as IceCube and Super-Kamiokande, on the dark matter-nucleon scattering cross-section, for a general model of dark matter with a velocity dependent (p-wave) thermally averaged cross-section. In this picture, the Boltzmann equation for the dark matter abundance is numerically solved, satisfying the dark matter density measured from the cosmic microwave background. We show that for lower cross-sections and higher masses, the dark matter annihilation rate drops sharply, resulting in upper bounds on the scattering cross-section that are one order of magnitude above those derived from a velocity independent (s-wave) annihilation cross-section. Our results show that upper limits on the scattering cross-section obtained from dark matter annihilating in the Sun are sensible to the uncertainty in current standard solar models, fluctuating by a maximum of 20% depending on the annihilation channel.

  18. Annihilations of superheavy dark matter in superdense clumps

    SciTech Connect

    Berezinsky, V.; Dokuchaev, V.; Eroshenko, Yu.; Kachelriess, M.; Solberg, M. A.

    2010-05-15

    Superheavy dark matter (SHDM) exchanges energy with its environment much slower than particles with masses close to the electroweak scale and has therefore different small-scale clustering properties. Using the neutralino as candidate for the SHDM, we find that free-streaming allows the formation of DM clumps of all masses down to {approx}260m{sub {chi}}in the case of bino. If small-scale clumps evolve from a nonstandard, spiky spectrum of perturbations, DM clumps may form during the radiation-dominated era. These clumps are not destroyed by tidal interactions and can be extremely dense. In the case of a bino, a 'gravithermal catastrophe' can develop in the central part of the most dense clumps, increasing further the central density and thus the annihilation signal. In the case of a Higgsino, the annihilation signal is enhanced by the Sommerfeld effect. As a result annihilations of superheavy neutralinos in dense clumps may lead to observable fluxes of annihilation products in the form of ultrahigh energy particles, for both cases, Higgsinos and binos, as lightest supersymmetric particles.

  19. Applications of positron annihilation spectroscopy in materials research

    NASA Technical Reports Server (NTRS)

    Singh, Jag J.

    1988-01-01

    Positron Annihilation Spectroscopy (PAS) has emerged as a powerful technique for research in condensed matter. It has been used extensively in the study of metals, ionic crystals, glasses and polymers. The present review concentrates on applications of positron lifetime measurements for elucidation of the physicochemical structure of polymers.

  20. C. Y. Chao, Pair Creation and Pair Annihilation

    NASA Astrophysics Data System (ADS)

    Li, Bing An; Yang, C. N.

    C. Y. Chao's contribution to physicists' acceptance of QED in 1933-1934 through his experiments of 1930 is analyzed. It is pointed out that Blackett and Occhialini's key suggestion of 1933 about hole theory was based on identifying Chao's "additional scattered rays" (1930) as due to pair annihilation.

  1. C. Y. Chao, Pair Creation and Pair Annihilation

    NASA Astrophysics Data System (ADS)

    Li, Bing An; Yang, C. N.

    2013-05-01

    C. Y. Chao's contribution to physicists' acceptance of QED in 1933-1934 through his experiments of 1930 is analyzed. It is pointed out that Blackett and Occhialini's key suggestion of 1933 about hole theory was based on identifying Chao's "additional scattered rays" (1930) as due to pair annihilation.

  2. Effects of bound states on dark matter annihilation

    NASA Astrophysics Data System (ADS)

    An, Haipeng; Wise, Mark B.; Zhang, Yue

    2016-06-01

    We study the impact of bound state formation on dark matter annihilation rates in models where dark matter interacts via a light mediator, the dark photon. We derive the general cross section for radiative capture into all possible bound states, and point out its nontrivial dependence on the dark matter velocity and the dark photon mass. For indirect detection, our result shows that dark matter annihilation inside bound states can play an important role in enhancing signal rates over the rate for direct dark matter annihilation with Sommerfeld enhancement. The effects are strongest for large dark gauge coupling and when the dark photon mass is smaller than the typical momentum of dark matter in the Galaxy. As an example, we show that for thermal dark matter the Fermi gamma ray constraint is substantially increased once bound state effects are taken into account. We also find that bound state effects are not important for dark matter annihilation during the freeze-out and recombination epochs.

  3. The many faces of brane-flux annihilation

    NASA Astrophysics Data System (ADS)

    Gautason, Fridrik Freyr; Truijen, Brecht; Van Riet, Thomas

    2015-10-01

    Fluxes can decay via the nucleation of Brown-Teitelboim bubbles, but when the decaying fluxes induce D-brane charges this process must be accompanied with an annihilation of D-branes. This occurs via dynamics inside the bubble wall as was well described for overline{D3} branes annihilating against 3-form fluxes. In this paper we extend this to the other overline{Dp} branes with p smaller than seven. Generically there are two decay channels: one for the RR flux and one for the NSNS flux. The RR channel is accompanied by brane annihilation that can be understood from the overline{Dp} branes polarising into D( p + 2) branes, whereas the NSNS channel corresponds to overline{Dp} branes polarising into NS5 branes or KK5 branes. We illustrate this with the decay of antibranes probing local toroidal throat geometries obtained from T-duality of the D6 solution in massive type IIA. We show that overline{Dp} branes are metastable against annihilation in these backgrounds, at least at the probe level.

  4. Exciton bimolecular annihilation dynamics in supramolecular nanostructures of conjugated oligomers

    NASA Astrophysics Data System (ADS)

    Daniel, Clément; Herz, Laura M.; Silva, Carlos; Hoeben, Freek J.; Jonkheijm, Pascal; Schenning, Albertus P.; Meijer, E. W.

    2003-12-01

    We present femtosecond transient absorption measurements on π-conjugated supramolecular assemblies in a high-pump-fluence regime. Oligo(p-phenylenevinylene) monofunctionalized with ureido-s-triazine (MOPV) self-assembles into chiral stacks in dodecane solution below 75 °C at a concentration of 4×10-4 M. We observe exciton bimolecular annihilation in MOPV stacks at high excitation fluence, indicated by the fluence-dependent decay of 11Bu-exciton spectral signatures and by the sublinear fluence dependence of time- and wavelength-integrated photoluminescence (PL) intensity. These two characteristics are much less pronounced in MOPV solution where the phase equilibrium is shifted significantly away from supramolecular assembly, slightly below the transition temperature. A mesoscopic rate-equation model is applied to extract the bimolecular annihilation rate constant from the excitation fluence dependence of transient absorption and PL signals. The results demonstrate that the bimolecular annihilation rate is very high with a square-root dependence in time. The exciton annihilation results from a combination of fast exciton diffusion and resonance energy transfer. The supramolecular nanostructures studied here have electronic properties that are intermediate between molecular aggregates and polymeric semiconductors.

  5. Antiproton annihilation dynamics in the Gasdynamic Fusion Rocket

    SciTech Connect

    Kammash, T.; Lee, M.

    1996-03-01

    The use of antiprotons to initiate the fusion reactions in the Gasdynamic Fusion Rocket (GDFR) is examined as potential replacement of the neutral beam injection system often cited in connection with fusion power reactors. The effectiveness of this approach depends critically, however, on the ability of the antiprotons to penetrate the plasma and reach the center of the engine without undergoing many annihilation reactions along the way. Using expressions for the annihilation rate per unit distance and the stopping power of antiprotons in a fully ionized hydrogenous plasma we calculate the annihilation distribution and the fraction of antiprotons that reach the central region in a relatively cold deuterium-tritium plasma. We apply these results to a rocket engine 16 m in length and containing plasma with 10{sup 16} cm{sup {minus}3} density, and we find that well over 90{percent} of the annihilations take place within a few centimeters from the midplane of the engine when the initial plasma temperature is 20 eV. Under these conditions we find that about 10{sup {minus}5} grams per second of antiprotons injected at an energy of about 4 MeV are required to ignite the plasma in this rocket engine. {copyright} {ital 1996 American Institute of Physics.}

  6. A study on symmetrization of 2D ACAR positron annihilation data

    NASA Astrophysics Data System (ADS)

    Smedskjaer, L. C.; Legnini, D. G.

    1990-07-01

    The important problem of symmetrization of two-dimensional angular correlation positron annihilation data is discussed in detail. Interest in this problem is motivated by the potential for a substantial improvement of the data quality. The artefacts present in our Anger cameras have been studied experimentally, and form the basis for a quantitative discussion of the symmetrization operation. The main conclusion is that symmetrization of the two-dimensional angular correlation spectra is allowed, if the symmetry center can be defined. It is argued that the center can be defined if the instrumental artefacts are small. Finally, it is shown that it is unlikely that the instrumental artefacts interfere constructively during the symmetrization operation.

  7. Crater annihilation on silver by cluster ion impacts

    NASA Astrophysics Data System (ADS)

    Henriksson, K. O. E.; Nordlund, K.; Keinonen, J.

    2007-02-01

    Using the MD/MC-CEM potential we have investigated the impacts of 20 keV Ag 13 cluster ions on (0 0 1) silver surfaces having one initial crater. This one was made in the zeroth ion impact. The degree of annihilation of the initial crater was investigated as a function of the lateral distance ri between the crater and the ion. The impact points were selected randomly inside a circular area with a radius of 75 Å centered on the crater. To reduce the total number of simulations, the circular area was divided into annuli. The initial and final atomic positions in the impact simulations were analyzed and the degree of annihilation of the initial crater was determined. The results indicate that for r ≲ 60 Å there is a net growth of the initial crater, and for distances r ∈ (60, 80) Å there is a small net filling of the crater.

  8. Positron annihilation lifetime spectroscopy source correction determination: A simulation study

    NASA Astrophysics Data System (ADS)

    Kanda, Gurmeet S.; Keeble, David J.

    2016-02-01

    Positron annihilation lifetime spectroscopy (PALS) can provide sensitive detection and identification of vacancy-related point defects in materials. These measurements are normally performed using a positron source supported, and enclosed by, a thin foil. Annihilation events from this source arrangement must be quantified and are normally subtracted from the spectrum before analysis of the material lifetime components proceeds. Here simulated PALS spectra reproducing source correction evaluation experiments have been systematically fitted and analysed using the packages PALSfit and MELT. Simulations were performed assuming a single lifetime material, and for a material with two lifetime components. Source correction terms representing a directly deposited source and various foil supported sources were added. It is shown that in principle these source terms can be extracted from suitably designed experiments, but that fitting a number of independent, nominally identical, spectra is recommended.

  9. Self-sustained annihilation of magnetic islands in helical plasmas

    SciTech Connect

    Itoh, Kimitaka; Itoh, Sanae-I.; Yagi, Masatoshi

    2005-07-15

    The evolution of the magnetic island which is induced by the resonant deformation by external currents in helical systems (such as the large helical device (LHD) [A. Iiyoshi, Phys. Plasmas 2, 2349 (1995)]) is analyzed. The defect of the bootstrap current, caused by the magnetic island, has a parity which reduces the size of the magnetic island, if the bootstrap current enhances the vacuum rotational transform. The width of magnetic island can be suppressed to the level of ion banana width if the pressure gradient exceeds a threshold value. This island annihilation is self-sustained. That is, the annihilation continues, for fixed beta value, until the external drive for island generation exceeds a threshold. The effects of the reversal of the direction of the bootstrap current and of the sign of radial electric field are also investigated. The possibility of the neoclassical tearing mode in the LHD-like plasma is discussed.

  10. Dark matter distribution and annihilation at the Galactic center

    NASA Astrophysics Data System (ADS)

    Dokuchaev, V. I.; Eroshenko, Yu N.

    2016-02-01

    We describe a promising method for measuring the total dark matter mass near a supermassive black hole at the Galactic center based on observations of nonrelativistic precession of the orbits of fast S0 stars. An analytical expression for the precession angle has been obtained under the assumption of a power-law profile of the dark matter density. The awaited weighing of the dark matter at the Galactic center provides the strong constraints on the annihilation signal from the neuralino dark matter particle candidate. The mass of the dark matter necessary for the explanation of the observed excess of gamma-radiation owing to the annihilation of the dark matter particles has been calculated with allowance for the Sommerfeld effect.

  11. Fields annihilation and particles creation in DBI inflation

    SciTech Connect

    Firouzjahi, Hassan; Khoeini-Moghaddam, Salomeh E-mail: khoeini@ipm.ir

    2011-02-01

    We consider a model of DBI inflation where two stacks of mobile branes are moving ultra relativistically in a warped throat. The stack closer to the tip of the throat is annihilated with the background anti-branes while inflation proceeds by the second stack. The effects of branes annihilation and particles creation during DBI inflation on the curvature perturbations power spectrum and the scalar spectral index are studied. We show that for super-horizon scales, modes which are outside the sound horizon at the time of branes collision, the spectral index has a shift to blue spectrum compared to the standard DBI inflation. For small scales the power spectrum approaches to its background DBI inflation value with the decaying superimposed oscillatory modulations.

  12. High nuclear temperatures by antimatter-matter annihilation

    SciTech Connect

    Gibbs, W.R.; Strottman, D.

    1985-01-01

    It is suggested that the quark-gluon phase be created through the use of antiproton or antideuteron beams. The first advantage to this method, using higher energy antiprotons than 1.5 GeV/c, is that the higher momenta antiprotons penetrate more deeply so that mesons produced are more nearly contained within the nucleus. Another advantage is that the annihilation products are very forward-peaked and tend to form a beam of mesons so that the energy density does not disperse very rapidly. Calculations were performed using the intranuclear cascade to try to follow the process of annihilation in some detail. The intranuclear cascade type calculation method is compared to the hydrodynamic approach. 8 refs., 8 figs. (LEW)

  13. Unified treatment of hadronic annihilation and protonium formation in slow collisions of antiprotons with hydrogen atoms

    NASA Astrophysics Data System (ADS)

    Sakimoto, Kazuhiro

    2013-07-01

    Antiproton (p¯) collisions with hydrogen atoms, resulting in the hadronic process of particle-antiparticle annihilation and the atomic process of protonium (p¯p) formation (or p¯ capture), are investigated theoretically. As the collision energy decreases, the collision time required for the p¯ capture becomes necessarily longer. Then, there is the possibility that the p¯-p annihilation occurs significantly before the p¯ capture process completes. In such a case, one can no longer consider the annihilation decay separately from the p¯ capture process. The present study develops a rigorous unified quantum-mechanical treatment of the annihilation and p¯ capture processes. For this purpose, an R-matrix approach for atomic collisions is extended to have complex-valued R-matrix elements allowing for the hadronic annihilation. Detailed calculations are carried out at low collision energies ranging from 10-8 to 10-1 eV, and the annihilation and the p¯ capture (total and product-state selected) cross sections are reported. Consideration is given to the difference between the direct annihilation occurring during the collision and the annihilation of p¯p occurring after the p¯ capture. The present annihilation process is also compared with the annihilation in two-body p¯+p collisions.

  14. Direct Detection of Dark Matter with Resonant Annihilation

    NASA Astrophysics Data System (ADS)

    Li, Bo; Zhou, Yu-Feng

    2015-07-01

    In the scenario where the dark matter (DM) particles χbar chi pair annihilate through a resonance particle R, the constraint from DM relic density makes the corresponding cross section for DM-nuclei elastic scattering extremely small, and can be below the neutrino background induced by the coherent neutrino-nuclei scattering, which makes the DM particle beyond the reach of the conventional DM direct detection experiments. We present an improved analytical calculation of the DM relic density in the case of resonant DM annihilation for s- and p-wave cases and invesitgate the condition for the DM-nuclei scattering cross section to be above the neutrino background. We show that in Higgs-portal type models, for DM particles with s-wave annihilation, the spin-independent DM-nucleus scattering cross section is proportional to ΓR/mR, the ratio of the decay width and the mass of R. For a typical DM particle mass ˜ 50 GeV, the condition leads to ΓR/mR gtrsim Script O(10-4). In p-wave annihilation case, the spin-independent scattering cross section is insensitive to ΓR/mR, and is always above the neutrino background, as long as the DM particle is lighter than the top quark. The real singlet DM model is discussed as a concrete example. Supported by the National Basic Research Program of China (973 Program) under Grant No. 2010CB833000; the National Nature Science Foundation of China (NSFC) under Grant Nos. 10975170, 10821504, 10905084, and 11335012; and the Project of Knowledge Innovation Program (PKIP) of the Chinese Academy of Science

  15. Complete light annihilation in an ultrathin layer of gold nanoparticles.

    PubMed

    Svedendahl, Mikael; Johansson, Peter; Käll, Mikael

    2013-07-10

    We experimentally demonstrate that an incident light beam can be completely annihilated in a single layer of randomly distributed, widely spaced gold nanoparticle antennas. Under certain conditions, each antenna dissipates more than 10 times the number of photons that enter its geometric cross-sectional area. The underlying physics can be understood in terms of a critical coupling to localized plasmons in the nanoparticles or, equivalently, in terms of destructive optical Fano interference and so-called coherent absorption. PMID:23806090

  16. Rapid Coarsening of Ion Beam Ripple Patterns by Defect Annihilation

    SciTech Connect

    Hansen, Henri; Messlinger, Sebastian; Stoian, Georgiana; Redinger, Alex; Krug, Joachim; Michely, Thomas

    2009-04-10

    Ripple patterns formed on Pt(111) through grazing incidence ion beam erosion coarsen rapidly. At and below 450 K coarsening of the patterns is athermal and kinetic, unrelated to diffusion and surface free energy. Similar to the situation for sand dunes, coarsening takes place through annihilation reactions of mobile defects in the pattern. The defect velocity derived on the basis of a simple model agrees quantitatively with the velocity of monatomic steps illuminated by the ion beam.

  17. Zero-Annihilation Periodic Control For Damping Vibrations

    NASA Technical Reports Server (NTRS)

    Bayard, David S.; Boussalis, Dhemetrios

    1995-01-01

    Report presents study on use of recently developed zero-annihilation periodic (ZAP) controller for active suppression of vibrations in flexible structures characterized by non-minimum-phase transfer functions. Non-minimum-phase situation occurs if certain kinds of vibration-sensor/vibration-actuator pairs (e.g., piezoelectric) used, and/or if vibration sensor(s) not colocated with vibration actuator(s).

  18. High sensitivity of positron annihilation to thermal oxidation of polyethylene

    NASA Astrophysics Data System (ADS)

    Ito, Kenji; Kobayashi, Yoshinori; Nanasawa, Atsushi

    2003-01-01

    We demonstrate the high sensitivity of positron annihilation to compositional changes related to the thermal degradation of polyethylene (PE). Positron annihilation γ-ray and lifetime measurements were conducted for PE films with and without antioxidant (1000-ppm Ciba® IRGANOX® 1076), subjected to heat treatment at 100 °C for different periods, to a maximum of 30 days. For the film without antioxidant, the positron Doppler parameter (S) and ortho-positronium formation probability (Io-Ps) appreciably decreased with increased heat treatment times, whereas they barely changed for the film with antioxidant. This, together with the Fourier transform infrared measurements, demonstrated that the variations of S and Io-Ps are caused by the thermal oxidation of PE. The S parameter was found to be sensitive to the early stage of degradation, where the carbonyl concentration is inferred to be lower than 100 ppm. The high sensitivity results from the large positron mobility in PE and from the high positron affinity of oxygen-containing polar groups. This work provides the basis for an application of positron annihilation to sensitive detection of the initial degradation of PE and other nonpolar polymers.

  19. Defect motion and annihilation in block copolymer thin films

    NASA Astrophysics Data System (ADS)

    Mueller, Marcus; Li, Weihua

    2015-03-01

    Using self-consistent field theory and computer simulation of a soft, coarse-grained particle model we study defect motion and annihilation in thin films of lamella-forming block copolymers on neutral and chemically patterned substrates. By virtue of the strain-field mediated interactions, dislocation defects with opposite orientation move towards each other. This motion depends both on the thermodynamic, strain-field mediated driving force and the single-chain dynamics that is required to alter the morphology and reduce the distance between the defect cores. This interplay results in a qualitative dependence of the time evolution on the topology of the defect morphology. Upon collision of the defects, they either spontaneously annihilate or form a metastable, tight defect pair. In the latter case, a free-energy barrier has to be overcome to finally produce a defect-free structure. Computing the minimum free-energy path within self-consistent field theory we investigate the dependence of the free-energy barriers of defect motion and annihilation on incompatibility, strength of the chemical surface pattern, and defect morphology. European Union FP7 / GA No. 619793 CoLiSA.MMP.

  20. Compton-backscattered annihilation radiation from the Galactic Center region

    NASA Technical Reports Server (NTRS)

    Smith, D. M.; Lin, R. P.; Feffer, P.; Slassi, S.; Hurley, K.; Matteson, J.; Bowman, H. B.; Pelling, R. M.; Briggs, M.; Gruber, D.

    1993-01-01

    On 1989 May 22, the High Energy X-ray and Gamma-ray Observatory for Nuclear Emissions, a balloon-borne high-resolution germanium spectrometer with an 18-deg FOV, observed the Galactic Center (GC) from 25 to 2500 keV. The GC photon spectrum is obtained from the count spectrum by a model-independent method which accounts for the effects of passive material in the instrument and scattering in the atmosphere. Besides a positron annihilation line with a flux of (10.0 +/- 2.4) x 10 exp -4 photons/sq cm s and a full width at half-maximum (FWHM) of (2.9 + 1.0, -1.1) keV, the spectrum shows a peak centered at (163.7 +/- 3.4) keV with a flux of (1.55 +/- 0.47) x 10 exp -3 photons/sq cm s and a FWHM of (24.4 +/- 9.2) keV. The energy range 450-507 keV shows no positronium continuum associated with the annihilation line, with a 2-sigma upper limit of 0.90 on the positronium fraction. The 164 keV feature is interpreted as Compton backscatter of broadened and redshifted annihilation radiation, possibly from the source 1E 1740.7-2942.

  1. Dark matter annihilation via Higgs and gamma-ray channels

    NASA Astrophysics Data System (ADS)

    Chan, Man Ho

    2016-09-01

    Recent studies show that the GeV gamma-ray excess signal from the Milky Way center can be best explained by ˜ 40 GeV dark matter annihilating via bbar{b} channel. However, the recent observations of the nearby Milky Way dwarf spheroidal satellite galaxies by Fermi-LAT and the radio observations of the Milky Way center and the M31 galaxy tend to rule out this proposal. In this article, we discuss the possibility of the dark matter interpretation of the GeV gamma-ray excess by proposing 130 GeV dark matter annihilating via both Higgs and gamma-ray channels. Recent analyses show that dark matter annihilating via Higgs channel can satisfactorily explain the Milky Way GeV gamma-ray excess observed. We show that this model can satisfy the upper limits of the gamma-ray constraint of the Milky Way dwarf spheroidal satellite galaxies and the constraint from the radio observations of the M31 galaxy.

  2. CALET's sensitivity to Dark Matter annihilation in the galactic halo

    NASA Astrophysics Data System (ADS)

    Motz, H.; Asaoka, Y.; Torii, S.; Bhattacharyya, S.

    2015-12-01

    CALET (Calorimetric Electron Telescope), installed on the ISS in August 2015, directly measures the electron+positron cosmic rays flux up to 20 TeV. With its proton rejection capability of 1 : 105 and an aperture of 1200 cm2· sr, it will provide good statistics even well above one TeV, while also featuring an energy resolution of 2%, which allows it to detect fine structures in the spectrum. Such structures may originate from Dark Matter annihilation or decay, making indirect Dark Matter search one of CALET's main science objectives among others such as identification of signatures from nearby supernova remnants, study of the heavy nuclei spectra and gamma astronomy. The latest results from AMS-02 on positron fraction and total electron+positron flux can be fitted with a parametrization including a single pulsar as an extra power law source with exponential cut-off, which emits an equal amount of electrons and positrons. This single pulsar scenario for the positron excess is extrapolated into the TeV region and the expected CALET data for this case are simulated. Based on this prediction for CALET data, the sensitivity of CALET to Dark Matter annihilation in the galactic halo has been calculated. It is shown that CALET could significantly improve the limits compared to current data, especially for those Dark Matter candidates that feature a large fraction of annihilation directly into e+ + e-, such as the LKP (Lightest Kaluza-Klein particle).

  3. Soft collinear effective theory for heavy WIMP annihilation

    NASA Astrophysics Data System (ADS)

    Bauer, Martin; Cohen, Timothy; Hill, Richard J.; Solon, Mikhail P.

    2015-01-01

    In a large class of models for Weakly Interacting Massive Particles (WIMPs), the WIMP mass M lies far above the weak scale m W . This work identifies universal Sudakov-type logarithms ˜ α log2(2 M/m W ) that spoil the naive convergence of perturbation theory for annihilation processes. An effective field theory (EFT) framework is presented, allowing the systematic resummation of these logarithms. Another impact of the large separation of scales is that a long-distance wavefunction distortion from electroweak boson exchange leads to observable modifications of the cross section. Careful accounting of momentum regions in the EFT allows the rigorous disentanglement of this so-called Sommerfeld enhancement from the short-distance hard annihilation process. The WIMP is described as a heavy-particle field, while the electroweak gauge bosons are treated as soft and collinear fields. Hard matching coefficients are computed at renormalization scale μ ˜ 2 M , then evolved down to μ ˜ m W , where electroweak symmetry breaking is incorporated and the matching onto the relevant quantum mechanical Hamiltonian is performed. The example of an SU(2) W triplet scalar dark matter candidate annihilating to line photons is used for concreteness, allowing the numerical exploration of the impact of next-to-leading order corrections and log resummation. For M ≃ 3 TeV, the resummed Sommerfeld enhanced cross section is reduced by a factor of ˜ 3 with respect to the treelevel fixed order result.

  4. Positron annihilation in neutron irradiated iron-based materials

    NASA Astrophysics Data System (ADS)

    Lambrecht, M.; Almazouzi, A.

    2011-01-01

    The hardening and embrittlement of reactor pressure vessel steels is of great concern in the actual nuclear power plant life assessment. This embrittlement is caused by irradiation-induced damage, like vacancies, interstitials, solutes and their clusters. But the reason for the embrittlement of the material is not yet totally known. The real nature of the irradiation damage should thus be examined as well as its evolution in time. Positron annihilation spectroscopy has been shown to be a powerful method for analyzing some of these defects. In fact, both vacancy type clusters and precipitates can be visualized by positrons. Recently, at SCK·CEN, a new setup has been constructed, calibrated and optimized to measure the coincidence Doppler broadening and lifetime of neutron irradiated materials. To be able to compare the results obtained by the positron studies, with those of other techniques (such as transmission electron microscopy, atom probe tomography and small angle neutron scattering), quantitative estimations of the size and density of the annihilation sites are needed. Using the approach proposed by Vehanen et al., an attempt is made to calculate the needed quantities in Fe and Fe-Cu binary alloys that were neutron irradiated to different doses. The results obtained are discussed highlighting the difficulties in defining the annihilation centres even in these simple model alloys, in spite of using both lifetime and Doppler broadening measurements in the same samples.

  5. Testing the neutrino annihilation model for launching GRB jets

    NASA Astrophysics Data System (ADS)

    Leng, Mingbin; Giannios, Dimitrios

    2014-11-01

    The mechanism behind the launching of gamma-ray burst (GRB) jets remains debated resulting in large uncertainty over the jet composition. Both magnetohydrodynamical and neutrino annihilation models have been proposed for the energy extraction in a black hole/accretion-disc central engine. In particular, for the extreme accretion rates dot{M}˜ 0.1-1 M⊙ s-1 expected for bursts of duration T ≲ 100 s, the disc can be an efficient neutrino emitter. Neutrino-antineutrino annihilation results in an energy deposition rate at the jet that can, in principle, account for the burst's energetics. Recent discoveries of X-ray flares hours after the burst and of ultra-long GRBs suggest that GRB activity can last for ˜104 s or longer. These long-lived events have fluence similar to that of classical GRBs. In view of these findings, we re-evaluate the neutrino annihilation model. We derive the maximum possible energy of a neutrino-powered jet as a function of the burst duration and show that the available energy drops fast for longer bursts. For a standard choice of the parameters, the model falls short by three to four orders of magnitude in explaining the observed energetics of events that last longer than ˜103 s.

  6. A Scintillation Counter System Design To Detect Antiproton Annihilation using the High Performance Antiproton Trap(HiPAT)

    NASA Technical Reports Server (NTRS)

    Martin, James J.; Lewis, Raymond A.; Stanojev, Boris

    2003-01-01

    The High Performance Antiproton Trap (HiPAT), a system designed to hold up to l0(exp 12) charge particles with a storage half-life of approximately 18 days, is a tool to support basic antimatter research. NASA's interest stems from the energy density represented by the annihilation of matter with antimatter, 10(exp 2)MJ/g. The HiPAT is configured with a Penning-Malmberg style electromagnetic confinement region with field strengths up to 4 Tesla, and 20kV. To date a series of normal matter experiments, using positive and negative ions, have been performed evaluating the designs performance prior to operations with antiprotons. The primary methods of detecting and monitoring stored normal matter ions and antiprotons within the trap includes a destructive extraction technique that makes use of a micro channel plate (MCP) device and a non-destractive radio frequency scheme tuned to key particle frequencies. However, an independent means of detecting stored antiprotons is possible by making use of the actual annihilation products as a unique indicator. The immediate yield of the annihilation event includes photons and pie mesons, emanating spherically from the point of annihilation. To "count" these events, a hardware system of scintillators, discriminators, coincident meters and multi channel scalars (MCS) have been configured to surround much of the HiPAT. Signal coincidence with voting logic is an essential part of this system, necessary to weed out the single cosmic ray events from the multi-particle annihilation shower. This system can be operated in a variety of modes accommodating various conditions. The first is a low-speed sampling interval that monitors the background loss or "evaporation" rate of antiprotons held in the trap during long storage periods; provides an independent method of validating particle lifetimes. The second is a high-speed sample rate accumulating information on a microseconds time-scale; useful when trapped antiparticles are extracted

  7. Multiphase monitoring by annihilation radiation coincidence mode

    NASA Astrophysics Data System (ADS)

    Vidal, A.; Viesti, G.; Osorio, C.; Pino, F.; Horvath, A.; Barros, H.; Caldogno, M.; Greaves, E. D.; Sajo-Bohus, L.

    2012-02-01

    A multiphase monitoring system employing nuclear techniques is reported, which is aimed to provide a rapid - decision tool in oilfield applications. Liquid phase time variation is monitored employing two large volume BaF2 detectors. The radioisotope source of 22Na is a positron emitter, therefore two antiparallel gammas are produced per decay, and phase flow in pipes is related to the count rate of gamma pulses in coincidence providing information on transient liquid phase during transport. Oil, gas, water fraction measurements were performed at a specialized test station assembled in our laboratory to model a wide range of field operating conditions. The time dependence of the mixed substances is monitored with the two most relevant hydrodynamic parameters, the density (type of the fluid) and the flow rate, in a LabView® environment. Performance of the monitoring system; its limitations and the possibility for further improvements are also provided.

  8. Positron annihilation study of Fe-ion irradiated reactor pressure vessel model alloys

    NASA Astrophysics Data System (ADS)

    Chen, L.; Li, Z. C.; Schut, H.; Sekimura, N.

    2016-01-01

    The degradation of reactor pressure vessel steels under irradiation, which results from the hardening and embrittlement caused by a high number density of nanometer scale damage, is of increasingly crucial concern for safe nuclear power plant operation and possible reactor lifetime prolongation. In this paper, the radiation damage in model alloys with increasing chemical complexity (Fe, Fe-Cu, Fe-Cu-Si, Fe-Cu-Ni and Fe-Cu-Ni-Mn) has been studied by Positron Annihilation Doppler Broadening spectroscopy after 1.5 MeV Fe-ion implantation at room temperature or high temperature (290 oC). It is found that the room temperature irradiation generally leads to the formation of vacancy-type defects in the Fe matrix. The high temperature irradiation exhibits an additional annealing effect for the radiation damage. Besides the Cu-rich clusters observed by the positron probe, the results show formation of vacancy-Mn complexes for implantation at low temperatures.

  9. Potential energy curves using unrestricted Møller-Plesset perturbation theory with spin annihilation

    NASA Astrophysics Data System (ADS)

    Schlegel, H. Bernhard

    1986-04-01

    Unrestricted Hartree-Fock and unrestricted Møller-Plesset perturbation theory are convenient methods to compute potential energy curves for bond dissociation, since these methods approach the correct dissociation limit. Unfortunately, a spin unrestricted wave function can contain large contributions from unwanted spin states that can distort the potential energy surface significantly. The spin contamination can be removed by projection or annihilation operators. As is well known, the spin project unrestricted Hartree-Fock bond dissociation curves have a large kink at the onset of the UHF/RHF instability, and a spurious minimum just beyond. However, the spurious minimum disappears and the kink is very much less pronounced at the unrestricted Møller-Plesset level with spin projection. Bond dissociation potentials for LiH and CH4 were computed at the fourth order Møller-Plesset level plus spin projection,4 and good agreement was found with full CI and MR-CISD calculations.

  10. Positron and gamma-ray signatures of dark matter annihilation and big-bang nucleosynthesis

    SciTech Connect

    Hisano, Junji; Kawasaki, Masahiro; Kohri, Kazunori; Nakayama, Kazunori

    2009-03-15

    The positron excess observed by the PAMELA experiment may come from dark matter annihilation, if the annihilation cross section is large enough. We show that the dark matter annihilation scenarios to explain the positron excess may also be compatible with the discrepancy of the cosmic lithium abundances between theory and observations. The winolike neutralino in the supersymmetric standard model is a good example for it. This scenario may be confirmed by Fermi satellite experiments.

  11. Positron-annihilation study of the equilibrium vacancy ensemble in aluminum

    SciTech Connect

    Fluss, M.J.; Berko, S.; Chakraborty, B.; Hoffmann, K.; Lippel, P.; Siegel, R.W.

    1982-06-01

    A preliminary report is presented of a positron-annihilation study of the equilibrium vacancy ensemble in aluminum using one- and two-dimensional angular correlation of annihilation radiation (ACAR) measurements versus temperature. The annihilation characteristics of a positron from the Bloch state, and the monovancy- and divacancy-trapped states have been calculated self-consistently within a supercell, including many-body enhancement effects, and are compared with experiment. 4 figures.

  12. Determination and applications of enhancement factors for positron and ortho-positronium annihilations

    NASA Astrophysics Data System (ADS)

    Mitroy, J.

    2005-12-01

    Electron-positron annihilation rates calculated directly from the electron and positron densities are known to underestimate the true annihilation rate. A correction factor, known as the enhancement factor, allows for the local increase of the electron density around the positron caused by the attractive electron-positron interaction. Enhancement factors are given for positrons annihilating with the 1s electron in H, He+ , He, Li2+ , and Li+ . The enhancement factor for a free positron annihilating with He+ and He is found to be close to that of ortho-positronium (i.e., Ps in its triplet state) annihilating with these atoms. The enhancement factor for Ps-He scattering is used in conjunction with the known annihilation rate for pickoff annihilation to derive a scattering length of 1.47a0 for Ps-He scattering. Further, enhancement factors for e+ -Ne and e+ -Ar annihilation are used in conjunction with the pickoff annihilation rate to estimate scattering lengths of 1.46a0 for Ps-Ne scattering and 1.75a0 for Ps-Ar scattering.

  13. Determination and applications of enhancement factors for positron and ortho-positronium annihilations

    SciTech Connect

    Mitroy, J.

    2005-12-15

    Electron-positron annihilation rates calculated directly from the electron and positron densities are known to underestimate the true annihilation rate. A correction factor, known as the enhancement factor, allows for the local increase of the electron density around the positron caused by the attractive electron-positron interaction. Enhancement factors are given for positrons annihilating with the 1s electron in H, He{sup +}, He, Li{sup 2+}, and Li{sup +}. The enhancement factor for a free positron annihilating with He{sup +} and He is found to be close to that of ortho-positronium (i.e., Ps in its triplet state) annihilating with these atoms. The enhancement factor for Ps-He scattering is used in conjunction with the known annihilation rate for pickoff annihilation to derive a scattering length of 1.47a{sub 0} for Ps-He scattering. Further, enhancement factors for e{sup +}-Ne and e{sup +}-Ar annihilation are used in conjunction with the pickoff annihilation rate to estimate scattering lengths of 1.46a{sub 0} for Ps-Ne scattering and 1.75a{sub 0} for Ps-Ar scattering.

  14. Early annihilation and diffuse backgrounds in models of weakly interacting massive particles in which the cross section for pair annihilation is enhanced by 1/upsilon.

    PubMed

    Kamionkowski, Marc; Profumo, Stefano

    2008-12-31

    Recent studies have considered modifications to the standard weakly interacting massive particle scenario in which the pair annihilation cross section (times relative velocity v) is enhanced by a factor 1/upsilon to approximately 10(-3) in the Galaxy, enough to explain several puzzling Galactic radiation signals. We show that in these scenarios a burst of weakly interacting massive particle annihilation occurs in the first collapsed dark-matter halos. We show that severe constraints to the annihilation cross section derive from measurements of the diffuse extragalactic radiation and from ionization and heating of the intergalactic medium. PMID:19437633

  15. Dark matter annihilation effects on the first stars

    NASA Astrophysics Data System (ADS)

    Iocco, F.; Bressan, A.; Ripamonti, E.; Schneider, R.; Ferrara, A.; Marigo, P.

    2008-11-01

    We study the effects of weakly interacting massive particles (WIMPs) dark matter (DM) on the collapse and evolution of the first stars in the Universe. Using a stellar evolution code, we follow the pre-main-sequence (pre-MS) phase of a grid of metal-free stars with masses in the range 5 <= M* <= 600Msolar forming in the centre of a 106Msolar halo at z = 20. DM particles of the parent halo are accreted in the protostellar interior by adiabatic contraction and scattering/capture processes, reaching central densities of O(1012 GeVcm-3) at radii of the order of 10au. Energy release from annihilation reactions can effectively counteract the gravitational collapse, in agreement with results from other groups. We find this stalling phase (known as a dark star) is transient and lasts from 2.1 × 103yr (M* = 600Msolar) to 1.8 × 104yr (M* = 9Msolar). Later in the evolution, DM scattering/capture rate becomes high enough that energy deposition from annihilations significantly alters the pre-MS evolution of the star in a way that depends on DM (i) velocity dispersion, , (ii) density, ρ, (iii) elastic scattering cross-section with baryons, σ0. For our fiducial set of parameters we find that the evolution of stars of mass M* < 40Msolar `freezes' on the HR diagram before reaching the zero-age main sequence (ZAMS). Stars with M* >= 40Msolar manage to ignite nuclear reactions; however, DM `burning' prolongs their lifetimes by a factor of 2 (5) for a 600Msolar (40Msolar) star. For ρ >~ 1012GeVcm-3, and same values of the other parameters, we find that all our models are entirely supported by DM annihilation and `freeze' on the HR diagram before igniting nuclear reactions.

  16. Comprehensive search for dark matter annihilation in dwarf galaxies

    NASA Astrophysics Data System (ADS)

    Geringer-Sameth, Alex; Koushiappas, Savvas M.; Walker, Matthew G.

    2015-04-01

    We present a new formalism designed to discover dark matter annihilation occurring in the Milky Way's dwarf galaxies. The statistical framework extracts all available information in the data by simultaneously combining observations of all the dwarf galaxies and incorporating the impact of particle physics properties, the distribution of dark matter in the dwarfs, and the detector response. The method performs maximally powerful frequentist searches and produces confidence limits on particle physics parameters. Probability distributions of test statistics under various hypotheses are constructed exactly, without relying on large sample approximations. The derived limits have proper coverage by construction and claims of detection are not biased by imperfect background modeling. We implement this formalism using data from the Fermi Gamma-ray Space Telescope to search for an annihilation signal in the complete sample of Milky Way dwarfs whose dark matter distributions can be reliably determined. We find that the observed data are consistent with background for each of the dwarf galaxies individually as well as in a joint analysis. The strongest constraints are at small dark matter particle masses. Taking the median of the systematic uncertainty in dwarf density profiles, the cross section upper limits are below the pure s -wave weak scale relic abundance value (2.2 ×1 0-26 cm3 s-1 ) for dark matter masses below 26 GeV (for annihilation into b b ¯), 29 GeV (τ+τ-), 35 GeV (u u ¯,d d ¯,s s ¯,c c ¯, and g g ), 6 GeV (e+e-), and 114 GeV (γ γ ). For dark matter particle masses less than 1 TeV, these represent the strongest limits obtained to date using dwarf galaxies.

  17. {phi} meson production in pp annihilation at rest

    SciTech Connect

    Srisuphaphon, S.; Yan, Y.; Gutsche, Thomas; Lyubovitskij, Valery E.

    2011-10-01

    Apparent channel-dependent violations of the Okubo-Zwieg-Iizuka (OZI) rule in nucleon-antinucleon annihilation reactions in the presence of an intrinsic strangeness component in the nucleon are discussed. Admixture of ss quark pairs in the nucleon wave function enables the direct coupling to the {phi}-meson in the annihilation channel without violating the OZI rule. Three forms are considered in this work for the strangeness content of the proton wave function, namely, the uud cluster with a ss sea-quark component, kaon-hyperon clusters based on a simple chiral quark model, and the pentaquark picture uudss. Nonrelativistic quark model calculations reveal that the strangeness magnetic moment {mu}{sub s} and the strangeness contribution to the proton spin {sigma}{sub s} from the first two models are consistent with recent experimental data, where {mu}{sub s} and {sigma}{sub s} are negative. For the third model, the uuds subsystem with the configurations [31]{sub FS}[211]{sub F}[22]{sub S} and [31]{sub FS}[31]{sub F}[22]{sub S} leads to negative values of {mu}{sub s} and {sigma}{sub s}. With effective quark line diagrams incorporating the {sup 3}P{sub 0} model, we give estimates for the branching ratios of the annihilation reactions at rest pp{yields}{phi}X (X={pi}{sup 0}, {eta}, {rho}{sup 0}, {omega}). Results for the branching ratios of {phi}X production from atomic pp s-wave states are for the first and third model found to be strongly channel dependent, in good agreement with measured rates.

  18. Models for the positive latitude e{-}e{+} annihilation feature

    NASA Astrophysics Data System (ADS)

    von Ballmoos, P.; Guessoum, N.; Jean, P.; Knödlseder, J.

    2003-01-01

    Galactic maps of e-e+ annihilation radiation based on CGRO-OSSE, SMM and TGRS data have indicated the existence of an extended component at positive Galactic latitudes (l~ -2 deg, b~ 7 deg), in addition to the emission from the galactic bulge and disk (Purcell et al. \\cite{Purcell97}; Cheng et al. \\cite{Cheng97}; Milne et al. \\cite{Milne00}; Milne et al. \\cite{Milne01}). This Positive Latitude Enhancement (PLE) was first attributed to an ``annihilation fountain" in the Galactic center (Dermer & Skibo \\cite{Dermer97}) but has since been the object of several models. After discussing the observational evidence for the PLE, we investigate various models for the PLE: besides the scenarios proposed in the literature, we have introduced a number of models requiring relatively modest positron rates due to a local origin of the e-e+ emission (local galactic-, solar system-, earth- and spacecraft-environment origins). The various scenarios for the PLE are constrained in the light of the latest OSSE-SMM-TGRS data analysis results: we have looked at the possible positron production mechanisms as well as the annihilation conditions in the different physical environments (temperature and dust grain content) proposed for the positive-latitude region. By constraining those parameters, based on the recent limits for the line width and the positronium fraction, we found that some of the models can essentially be discarded. A number of other scenarios will have to await further measurements and maps, such as will be possible with INTEGRAL's SPI and IBIS instruments. We present a table/checklist of model-falsification criteria.

  19. Neutrino Fluxes from NUHM LSP Annihilations in the Sun

    SciTech Connect

    Ellis, John; Olive, Keith A.; Savage, Christopher; Spanos, Vassilis C.; /Democritos Nucl. Res. Ctr.

    2011-08-12

    We extend our previous studies of the neutrino fluxes expected from neutralino LSP annihilations inside the Sun to include variants of the minimal supersymmetric extension of the Standard Model (MSSM) with squark, slepton and gaugino masses constrained to be universal at the GUT scale, but allowing one or two non-universal supersymmetry-breaking parameters contributing to the Higgs masses (NUHM1,2). As in the constrained MSSM (CMSSM) with universal Higgs masses, there are large regions of the NUHM parameter space where the LSP density inside the Sun is not in equilibrium, so that the annihilation rate may be far below the capture rate, and there are also large regions where the capture rate is not dominated by spin-dependent LSP-proton scattering. The spectra possible in the NUHM are qualitatively similar to those in the CMSSM. We calculate neutrino-induced muon fluxes above a threshold energy of 10 GeV, appropriate for the IceCube/DeepCore detector, for points where the NUHM yields the correct cosmological relic density for representative choices of the NUHM parameters. We find that the IceCube/DeepCore detector can probe regions of the NUHM parameter space in addition to analogues of the focus-point strip and the tip of the coannihilation strip familiar from the CMSSM. These include regions with enhanced Higgsino-gaugino mixing in the LSP composition, that occurs where neutralino mass eigenstates cross over. On the other hand, rapid-annihilation funnel regions in general yield neutrino fluxes that are unobservably small.

  20. Soft collinear effective theory for heavy WIMP annihilation

    DOE PAGESBeta

    Bauer, Martin; Cohen, Timothy; Hill, Richard J.; Solon, Mikhail P.

    2015-01-19

    In a large class of models for Weakly Interacting Massive Particles (WIMPs), the WIMP mass M lies far above the weak scale mW . This work identifies universal Sudakov-type logarithms ~ α log2(2 M/mW) that spoil the naive convergence of perturbation theory for annihilation processes. An effective field theory (EFT) framework is presented, allowing the systematic resummation of these logarithms. Another impact of the large separation of scales is that a long-distance wavefunction distortion from electroweak boson exchange leads to observable modifications of the cross section. Careful accounting of momentum regions in the EFT allows the rigorous disentanglement of thismore » so-called Sommerfeld enhancement from the short-distance hard annihilation process. In addition, the WIMP is described as a heavy-particle field, while the electroweak gauge bosons are treated as soft and collinear fields. Hard matching coefficients are computed at renormalization scale μ ~ 2 M , then evolved down to μ ~ mW , where electroweak symmetry breaking is incorporated and the matching onto the relevant quantum mechanical Hamiltonian is performed. The example of an SU(2)W triplet scalar dark matter candidate annihilating to line photons is used for concreteness, allowing the numerical exploration of the impact of next-to-leading order corrections and log resummation. As a result, for M ≃ 3 TeV, the resummed Sommerfeld enhanced cross section is reduced by a factor of ~ 3 with respect to the treelevel fixed order result.« less

  1. Soft collinear effective theory for heavy WIMP annihilation

    SciTech Connect

    Bauer, Martin; Cohen, Timothy; Hill, Richard J.; Solon, Mikhail P.

    2015-01-19

    In a large class of models for Weakly Interacting Massive Particles (WIMPs), the WIMP mass M lies far above the weak scale mW . This work identifies universal Sudakov-type logarithms ~ α log2(2 M/mW) that spoil the naive convergence of perturbation theory for annihilation processes. An effective field theory (EFT) framework is presented, allowing the systematic resummation of these logarithms. Another impact of the large separation of scales is that a long-distance wavefunction distortion from electroweak boson exchange leads to observable modifications of the cross section. Careful accounting of momentum regions in the EFT allows the rigorous disentanglement of this so-called Sommerfeld enhancement from the short-distance hard annihilation process. In addition, the WIMP is described as a heavy-particle field, while the electroweak gauge bosons are treated as soft and collinear fields. Hard matching coefficients are computed at renormalization scale μ ~ 2 M , then evolved down to μ ~ mW , where electroweak symmetry breaking is incorporated and the matching onto the relevant quantum mechanical Hamiltonian is performed. The example of an SU(2)W triplet scalar dark matter candidate annihilating to line photons is used for concreteness, allowing the numerical exploration of the impact of next-to-leading order corrections and log resummation. As a result, for M ≃ 3 TeV, the resummed Sommerfeld enhanced cross section is reduced by a factor of ~ 3 with respect to the treelevel fixed order result.

  2. The nuclear dynamo; Can a nuclear tornado annihilate nations

    SciTech Connect

    McNally, J.R. Jr.

    1991-01-01

    This paper reports on the development of the hypothesis of a nuclear dynamo for a controlled nuclear fusion reactor. This dynamo hypothesis suggests properties for a nuclear tornado that could annihilate nations if accidentally triggered by a single high yield to weight nuclear weapon detonation. The formerly classified reports on ignition of the atmosphere, the properties of a nuclear dynamo, methods to achieve a nuclear dynamo in the laboratory, and the analogy of a nuclear dynamo to a nuclear tornado are discussed. An unclassified international study of this question is urged.

  3. Rate for annihilation of galactic dark matter into two photons

    NASA Technical Reports Server (NTRS)

    Giudice, Gian F.; Griest, Kim

    1989-01-01

    A calculation of the cross section for neutralino-neutralino annihilation into two photons is performed and applied to dark matter in the galactic halo to find the counting rate in a large gamma ray detector such as EGRET (Energetic Gamma Ray Experiment Telescope) or ASTROGAM. Combining constraints from particle accelerators with the requirement that the neutralinos make up the dark matter, it is found that rates of over a few dozen events per year are unlikely. The assumptions that go into these conclusions are listed. Other particle dark matter candidates which could give larger and perhaps observable signals are suggested.

  4. Pair annihilation into neutrinos in strong magnetic fields.

    NASA Technical Reports Server (NTRS)

    Canuto, V.; Fassio-Canuto, L.

    1973-01-01

    Among the processes that are of primary importance for the thermal history of a neutron star is electron-positron annihilation into neutrinos and photoneutrinos. These processes are computed in the presence of a strong magnetic field typical of neutron stars, and the results are compared with the zero-field case. It is shown that the neutrino luminosity Q(H) is greater than Q(O) for temperatures up to T about equal to 3 x 10 to the 8th power K and densities up to 1,000,000 g/cu cm.

  5. Exotic mesons in /bar N/N annihilation

    SciTech Connect

    Dover, C.B.

    1988-01-01

    We investigate the utility of the antinucleon-nucleon (/bar N/N) annihilation process as a means of producing exotic (non /bar Q/Q) mesons. Several examples are considered of J/sup ..pi..//sup C/ exotic formation in the /bar p/p ..-->.. ..pi..X reaction. We emphasize the usefulness of quantum number filtration, achieved by preparing the initial /bar p/p atom in tagged L = 0,1 states and focusing on selected exclusive final states. 36 refs., 4 tabs.

  6. PIMC Simulation of Ps Annihilation: From Micro to Mesopores

    SciTech Connect

    Bug, A R; Sterne, P A

    2005-08-23

    Path Integral Monte Carlo (PIMC) can reproduce the results of simple analytical calculations in which a single quantum particle is used to represent positronium within an idealized, spherical pore. Our calculations improve on this approach by explicitly treating the positronium as a two-particle e{sup -}, e{sup +} system interacting via the Coulomb interaction. We study the lifetime and the internal contact density, {kappa}, which controls the self-annihilation behavior, for positronium in model spherical pores, as a function of temperature and pore size. We compare the results with both PIMC and analytical calculations for a single-particle model.

  7. Positron annihilation spectroscopy of biological tissue in 11C irradiation

    NASA Astrophysics Data System (ADS)

    Sakurai, Hiroshi; Itoh, Fumitake; Hirano, Yoshiyuki; Nitta, Munetaka; Suzuki, Kosuke; Kato, Daisuke; Yoshida, Eiji; Nishikido, Fumihiko; Wakizaka, Hidekatsu; Kanai, Tatsuaki; Yamaya, Taiga

    2014-11-01

    Positron annihilation spectroscopy (PAS) spectra of biological tissue in 11C irradiation are reported and spatial resolution coefficient of positron emission tomography (PET) obtained from the PAS spectrum is discussed for 11C irradiation. A PAS spectrum of the biological tissue with water is the same as that of the water pool phantom in 11C irradiation. However, a PAS spectrum of the biological tissue with less water differs from that of the water pool phantom. The PET spatial resolution coefficient depends on the kind of biological tissue. However, the PET spatial resolution coefficient, 0.00243  ±  0.00014, can be used as a common value of maximum limit.

  8. First Study of Rapidity Gaps in e+e- Annihilation

    NASA Astrophysics Data System (ADS)

    Abe, K.; Abe, K.; Abt, I.; Akagi, T.; Allen, N. J.; Ash, W. W.; Aston, D.; Baird, K. G.; Baltay, C.; Band, H. R.; Barakat, M. B.; Baranko, G.; Bardon, O.; Barklow, T.; Bashindzhagyan, G. L.; Bazarko, A. O.; Ben-David, R.; Benvenuti, A. C.; Bilei, G. M.; Bisello, D.; Blaylock, G.; Bogart, J. R.; Bolton, T.; Bower, G. R.; Brau, J. E.; Breidenbach, M.; Bugg, W. M.; Burke, D.; Burnett, T. H.; Burrows, P. N.; Busza, W.; Calcaterra, A.; Caldwell, D. O.; Calloway, D.; Camanzi, B.; Carpinelli, M.; Cassell, R.; Castaldi, R.; Castro, A.; Cavalli-Sforza, M.; Chou, A.; Church, E.; Cohn, H. O.; Coller, J. A.; Cook, V.; Cotton, R.; Cowan, R. F.; Coyne, D. G.; Crawford, G.; D'Oliveira, A.; Damerell, C. J.; Daoudi, M.; de Sangro, R.; de Simone, P.; dell'Orso, R.; Dervan, P. J.; Dima, M.; Dong, D. N.; Du, P. Y.; Dubois, R.; Eisenstein, B. I.; Elia, R.; Etzion, E.; Falciai, D.; Fan, C.; Fero, M. J.; Frey, R.; Furuno, K.; Gillman, T.; Gladding, G.; Gonzalez, S.; Hallewell, G. D.; Hart, E. L.; Hasan, A.; Hasegawa, Y.; Hasuko, K.; Hedges, S.; Hertzbach, S. S.; Hildreth, M. D.; Huber, J.; Huffer, M. E.; Hughes, E. W.; Hwang, H.; Iwasaki, Y.; Jackson, D. J.; Jacques, P.; Jaros, J.; Johnson, A. S.; Johnson, J. R.; Johnson, R. A.; Junk, T.; Kajikawa, R.; Kalelkar, M.; Kang, H. J.; Karliner, I.; Kawahara, H.; Kendall, H. W.; Kim, Y.; King, M. E.; King, R.; Kofler, R. R.; Krishna, N. M.; Kroeger, R. S.; Labs, J. F.; Langston, M.; Lath, A.; Lauber, J. A.; Leith, D. W.; Lia, V.; Liu, M. X.; Liu, X.; Loreti, M.; Lu, A.; Lynch, H. L.; Ma, J.; Mancinelli, G.; Manly, S.; Mantovani, G.; Markiewicz, T. W.; Maruyama, T.; Massetti, R.; Masuda, H.; Mazzucato, E.; McKemey, A. K.; Meadows, B. T.; Messner, R.; Mockett, P. M.; Moffeit, K. C.; Mours, B.; Muller, D.; Nagamine, T.; Narita, S.; Nauenberg, U.; Neal, H.; Nussbaum, M.; Ohnishi, Y.; Osborne, L. S.; Panvini, R. S.; Park, H.; Pavel, T. J.; Peruzzi, I.; Piccolo, M.; Piemontese, L.; Pieroni, E.; Pitts, K. T.; Plano, R. J.; Prepost, R.; Prescott, C. Y.; Punkar, G. D.; Quigley, J.; Ratcliff, B. N.; Reeves, T. W.; Reidy, J.; Rensing, P. E.; Rochester, L. S.; Rowson, P. C.; Russell, J. J.; Saxton, O. H.; Schalk, T.; Schindler, R. H.; Schumm, B. A.; Sen, S.; Serbo, V. V.; Shaevitz, M. H.; Shank, J. T.; Shapiro, G.; Sherden, D. J.; Shmakov, K. D.; Simopoulos, C.; Sinev, N. B.; Smith, S. R.; Snyder, J. A.; Stamer, P.; Steiner, H.; Steiner, R.; Strauss, M. G.; Su, D.; Suekane, F.; Sugiyama, A.; Suzuki, S.; Swartz, M.; Szumilo, A.; Takahashi, T.; Taylor, F. E.; Torrence, E.; Trandafir, A. I.; Turk, J. D.; Usher, T.; Va'Vra, J.; Vannini, C.; Vella, E.; Venuti, J. P.; Verdier, R.; Verdini, P. G.; Wagner, S. R.; Waite, A. P.; Watts, S. J.; Weidemann, A. W.; Weiss, E. R.; Whitaker, J. S.; White, S. L.; Wickens, F. J.; Williams, D. A.; Williams, D. C.; Williams, S. H.; Willocq, S.; Wilson, R. J.; Wisniewski, W. J.; Woods, M.; Word, G. B.; Wyss, J.; Yamamoto, R. K.; Yamartino, J. M.; Yang, X.; Yellin, S. J.; Young, C. C.; Yuta, H.; Zapalac, G.; Zdarko, R. W.; Zeitlin, C.; Zhou, J.

    1996-06-01

    We present the first study of rapidity gaps in e+e- annihilations, using Z0 decays collected by the SLAC Linear Collider Large Detector experiment. Our measured rapidity gap spectra fall exponentially with increasing gap size over five decades, and we observe no anomalous class of events containing large gaps. This supports the interpretation of the large-gap events measured in pp¯ and ep collisions in terms of exchange of color-singlet objects. The presence of heavy flavors or additional jets does not affect these conclusions.

  9. Inclusive Production Λ c in the e + e - - Annihilation

    NASA Astrophysics Data System (ADS)

    Osati, T.; Movlanaei, M.

    2016-09-01

    In the framework of the quark-diquark model of baryons, Λ c can be considered as constituent c quark and ud diquark. In hadronizasion process baryon Λ c can be produced from ud scalar diquark and c quark fragmentation. So in this work, in the lowest order of perturbative QCD, fragmentation functions c → Λ c and ud → Λ c are calculated and finally in the electron-positron annihilation in LEP, the inclusive cross section production of Λ c is calculated about pole of z 0.

  10. Particle tracking at cryogenic temperatures: the Fast Annihilation Cryogenic Tracking (FACT) detector for the AEgIS antimatter gravity experiment

    NASA Astrophysics Data System (ADS)

    Storey, J.; Aghion, S.; Amsler, C.; Ariga, A.; Ariga, T.; Belov, A.; Bonomi, G.; Braunig, P.; Bremer, J.; Brusa, R.; Cabaret, L.; Caccia, M.; Caravita, R.; Castelli, F.; Cerchiari, G.; Chlouba, K.; Cialdi, S.; Comparat, D.; Consolati, G.; Derking, H.; Di Noto, L.; Doser, M.; Dudarev, A.; Ereditato, A.; Ferragut, R.; Fontana, A.; Gerber, S.; Giammarchi, M.; Gligorova, A.; Gninenko, S.; Haider, S.; Hogan, S.; Holmestad, H.; Huse, T.; Jordan, E. J.; Kawada, J.; Kellerbauer, A.; Kimura, M.; Krasnicky, D.; Lagomarsino, V.; Lehner, S.; Magnani, A.; Malbrunot, C.; Mariazzi, S.; Matveev, V.; Mazzotta, Z.; Nebbia, G.; Nedelec, P.; Oberthaler, M.; Pacifico, N.; Penasa, L.; Petracek, V.; Pistillo, C.; Prelz, F.; Prevedelli, M.; Ravelli, L.; Riccardi, C.; Røhne, O. M.; Rosenberger, S.; Rotondi, A.; Sandaker, H.; Santoro, R.; Scampoli, P.; Simon, M.; Spacek, M.; Strojek, I. M.; Subieta, M.; Testera, G.; Vaccarone, R.; Widmann, E.; Yzombard, P.; Zavatarelli, S.; Zmeskal, J.

    2015-02-01

    The AEgIS experiment is an interdisciplinary collaboration between atomic, plasma and particle physicists, with the scientific goal of performing the first precision measurement of the Earth's gravitational acceleration on antimatter. The principle of the experiment is as follows: cold antihydrogen atoms are synthesized in a Penning-Malmberg trap and are Stark accelerated towards a moiré deflectometer, the classical counterpart of an atom interferometer, and annihilate on a position sensitive detector. Crucial to the success of the experiment is an antihydrogen detector that will be used to demonstrate the production of antihydrogen and also to measure the temperature of the anti-atoms and the creation of a beam. The operating requirements for the detector are very challenging: it must operate at close to 4 K inside a 1 T solenoid magnetic field and identify the annihilation of the antihydrogen atoms that are produced during the 1 μs period of antihydrogen production. Our solution—called the FACT detector—is based on a novel multi-layer scintillating fiber tracker with SiPM readout and off the shelf FPGA based readout system. This talk will present the design of the FACT detector and detail the operation of the detector in the context of the AEgIS experiment.

  11. Positron annihilation studies in solid 2-aminopyridine, 3-aminopyridine, 4-aminopyridine and 2-aminopyrimidine

    NASA Astrophysics Data System (ADS)

    Netto, A. Marques; Bicalho, S. M. C. M.; Filgueiras, Ca. L.; Machado, J. C.

    1985-09-01

    Positron annihilation lifetimes and Doppler-broadened annihilation lines have been measured in solid 2-aminopyridine (2-APY), 3-aminopyridine (3-APY), 4-aminopyridine (4-APY) and 2-aminopyrimidine (2-APYM). The results point to the formation of positronium in the solid pyridines and the yields are discussed in terms of the structures and the electron donation character of the compounds.

  12. The 3P0-VERSUS 3S1-MODELS for Quark-Antiquark Annihilation

    NASA Astrophysics Data System (ADS)

    Green, A. M.; Niskanen, J. A.

    A comparison is made between the 3S1- and 3P0-models for quark-antiquark annihilation or creation. Even though the former appears, at first sight, to be superior for Nbar {N} annihilation into two mesons, it is argued from their effects in meson decays that this conclusion is premature.

  13. Atomic Ionization at the Positron-Electron Annihilation in Process of β+-DECAY

    NASA Astrophysics Data System (ADS)

    Fedotkin, S. N.; Zheltonozhskii, V. A.

    2013-03-01

    The process of atomic shell ionization during the annihilation of a positron, emitted at β+- decay with K-electron of daughter's atom, is considered. The ratio of probabilities of these processes to the probability of ordinary β+-decay is found. It excitation of atomic shell at the positron annihilation at β+-decay of was studied the 4522Ti.

  14. An Experiment to Demonstrate the Energy Broadening of Annihilation Gamma Rays

    ERIC Educational Resources Information Center

    Ouseph, P. J.; DuBard, James L.

    1978-01-01

    Shows that when positions annihilate in solid materials the energy distribution of the annihilation gamma rays is much broader than that of a 0.511-Mev gamma peak. This broadening is caused by the momentum distribution of the electrons in the material. (Author/GA)

  15. Optical-vortex pair creation and annihilation and helical astigmatism of a nonplanar ring resonator

    SciTech Connect

    Heckenberg, N.R.; Vaupel, M.; Malos, J.T.; Weiss, C.O.

    1996-09-01

    The creation and annihilation of pairs of optical vortices have been studied in transitions between patterns produced in a photorefractive oscillator. Smooth metamorphosis between stable patterns occurs through pair creation or annihilation but can be modeled using superposition of modes taking into account lifting of degeneracy of helical modes by helical astigmatism of the resonator. {copyright} {ital 1996 The American Physical Society.}

  16. The dark matter annihilation boost from low-temperature reheating

    NASA Astrophysics Data System (ADS)

    Erickcek, Adrienne L.

    2015-11-01

    The evolution of the Universe between inflation and the onset of big bang nucleosynthesis is difficult to probe and largely unconstrained. This ignorance profoundly limits our understanding of dark matter: we cannot calculate its thermal relic abundance without knowing when the Universe became radiation dominated. Fortunately, small-scale density perturbations provide a probe of the early Universe that could break this degeneracy. If dark matter is a thermal relic, density perturbations that enter the horizon during an early matter-dominated era grow linearly with the scale factor prior to reheating. The resulting abundance of substructure boosts the annihilation rate by several orders of magnitude, which can compensate for the smaller annihilation cross sections that are required to generate the observed dark matter density in these scenarios. In particular, thermal relics with masses less than a TeV that thermally and kinetically decouple prior to reheating may already be ruled out by Fermi-LAT observations of dwarf spheroidal galaxies. Although these constraints are subject to uncertainties regarding the internal structure of the microhalos that form from the enhanced perturbations, they open up the possibility of using gamma-ray observations to learn about the reheating of the Universe.

  17. Annihilation Lines from Dark Matter with the Fermi-LAT

    NASA Astrophysics Data System (ADS)

    Ylinen, Tomi

    2010-06-01

    Dark matter is today one of the most intriguing but so far unresolved issues in physics. Many extensions of the Standard Model of particle physics predict a stable Weakly Interacting Massive Particle (WIMP) that may annihilate directly into two gamma-rays. If the WIMPs are non-relativistic, the gamma-rays from this channel will have an energy equal to the mass of the WIMP. The signature caused by this annihilation is a spectral line, smeared out only by the energy resolution of the detector. The signal would be a ``smoking gun'' for dark matter, since no other astrophysical source should be able to produce it. We present here the preliminary results from the search for a dark matter line on a limited data set from the Fermi Large Area Telescope (LAT), the main instrument onboard the Fermi Gamma-ray Space Telescope, which was successfully launched on June 11, 2008. The Fermi-LAT is a pair-conversion detector for gamma-rays with an energy range from 20 MeV to 300 GeV and has an unprecedented resolution and sensitivity.

  18. Detecting electron neutrinos from solar dark matter annihilation by JUNO

    NASA Astrophysics Data System (ADS)

    Guo, Wan-Lei

    2016-01-01

    We explore the electron neutrino signals from light dark matter (DM) annihilation in the Sun for the large liquid scintillator detector JUNO. In terms of the spectrum features of three typical DM annihilation channels χχ → νbar nu, τ+τ-, bbar b, we take two sets of selection conditions to calculate the expected signals and atmospheric neutrino backgrounds based on the Monte Carlo simulation data. Then the JUNO sensitivities to the spin independent DM-nucleon and spin dependent DM-proton cross sections are presented. It is found that the JUNO projected sensitivities are much better than the current spin dependent direct detection experimental limits for the νbar nu and τ+τ- channels. In the spin independent case, the JUNO will give the better sensitivity to the DM-nucleon cross section than the LUX and CDMSlite limits for the νbar nu channel with the DM mass lighter than 6.5 GeV . If the νbar nu or τ+τ- channel is dominant, the future JUNO results are very helpful for us to understand the tension between the DAMA annual modulation signal and other direct detection exclusions.

  19. DENSE, PARSEC-SCALE CLUMPS NEAR THE GREAT ANNIHILATOR

    SciTech Connect

    Hodges-Kluck, Edmund; Pound, Marc W.; Harris, Andrew I.; Lamb, James W.; Hodges, Mark

    2009-05-10

    We report on Combined Array for Research in Millimeter-Wave Astronomy and James Clerk Maxwell Telescope observations toward the Einstein source 1E 1740.7-2942, a low-mass X-ray binary commonly known as the 'Great Annihilator'. The Great Annihilator is known to be near a small, bright molecular cloud in a region largely devoid of emission in {sup 12}CO surveys of the Galactic center. This region is of interest because it is interior to the dust lanes which may be the shock zones where atomic gas from the HI nuclear disk is converted into molecular gas. We find that the region is populated with a large number of dense (n {approx} 10{sup 5} cm{sup -3}) regions of excited gas with small filling factors. The gas appears to have turbulent support and may be the result of sprays of material from collisions in the shock zone. We estimate that {approx}(1-3) x 10{sup 5} M {sub sun} of shocked gas resides in our r {approx} 3', {delta}v {sub LSR} = 100 km s{sup -1} field. If this gas has recently shocked and is interior to the inner Lindblad resonance of the dominant bar, it is in transit to the x {sub 2} disk, suggesting that a significant amount of mass may be transported to the disk by a low filling factor population of molecular clouds with low surface brightness in larger surveys.

  20. Annihilation Lines from Dark Matter with the Fermi-LAT

    SciTech Connect

    Ylinen, Tomi

    2010-06-23

    Dark matter is today one of the most intriguing but so far unresolved issues in physics. Many extensions of the Standard Model of particle physics predict a stable Weakly Interacting Massive Particle (WIMP) that may annihilate directly into two gamma-rays. If the WIMPs are non-relativistic, the gamma-rays from this channel will have an energy equal to the mass of the WIMP. The signature caused by this annihilation is a spectral line, smeared out only by the energy resolution of the detector. The signal would be a ''smoking gun'' for dark matter, since no other astrophysical source should be able to produce it. We present here the preliminary results from the search for a dark matter line on a limited data set from the Fermi Large Area Telescope (LAT), the main instrument onboard the Fermi Gamma-ray Space Telescope, which was successfully launched on June 11, 2008. The Fermi-LAT is a pair-conversion detector for gamma-rays with an energy range from 20 MeV to 300 GeV and has an unprecedented resolution and sensitivity.

  1. Upper limits to the annihilation radiation luminosity of Centaurus A

    NASA Technical Reports Server (NTRS)

    Gehrels, N.; Cline, T. L.; Paciesas, W. S.; Teegarden, B. J.; Tueller, J.; Dirouchoux, P.; Hameury, J. M.

    1983-01-01

    A high resolution observation of the active nucleus galaxy Centaurus A (NGC 5128) was made by the GSFC low energy gamma-ray spectrometer (LEGS) during a balloon flight on 1981 November 19. The measured spectrum between 70 and 500 keV is well represented by a power law of the form 1.05 x 10 (-4) (E/100 keV) (-1.59) ph/sq cm/s with no breaks or line features observed. The 98 percent confidence (2 sigma) flux upper limit for a narrow (3 keV) 511-keV positron annihilation line is 9.9 x 10 (-4) ph/sq cm/s. Using this upper limit, the ratio of the narrow-line annihilation radiation luminosity to the integral or = 511 keV luminosity is estimated to be 0.09 (2 sigma upper limit). This is compared with the measured value for our Galactic center in the Fall of 1979 of 0.10 to 0.13, indicating a difference in the emission regions in the nuclei of the two galaxies.

  2. Positron Annihilation Spectroscopy Study of Barnett Shale Core

    NASA Astrophysics Data System (ADS)

    Ameena, Fnu; Alsleben, Helge; Quarles, Carroll A.

    Measurements are reported of positron annihilation lifetime and Doppler broadening parameters on 14 samples of Barnett shale core selected from 196 samples ranging from depths of 6107 to 6402 feet. The Barnett shale core was taken from EOG well Two-O-Five 2H located in Johnson county TX. The selected samples are dark clay-rich mudstone consisting of fine-grained clay minerals. The samples are varied in shape, typically a few inches long and about 1/2 inch in width and thickness, and are representative of the predominant facies in the core. X-ray fluorescence (XRF), X-ray diffraction (XRD), petrographic analysis and geochemical analysis of total organic carbon (TOC) were already available for each of the selected samples. The lifetime data are analyzed in terms of three lifetime components with the shortest lifetime fixed at 125 ps. The second lifetime is attributed to positron annihilation in the bulk and positron trapping; and the third lifetime is due to positronium. Correlations of the lifetimes, intensities, the average lifetime and S and W parameters with TOC, XRF and XRD parameters are discussed. The observed correlations suggest that positron spectroscopy may be a useful tool in characterizing shale.

  3. Positron Annihilation 3-D Momentum Spectrometry by Synchronous 2D-ACAR and DBAR

    NASA Astrophysics Data System (ADS)

    Burggraf, Larry W.; Bonavita, Angelo M.; Williams, Christopher S.; Fagan-Kelly, Stefan B.; Jimenez, Stephen M.

    2015-05-01

    A positron annihilation spectroscopy system capable of determining 3D electron-positron (e--e+) momentum densities has been constructed and tested. In this technique two opposed HPGe strip detectors measure angular coincidence of annihilation radiation (ACAR) and Doppler broadening of annihilation radiation (DBAR) in coincidence to produce 3D momentum datasets in which the parallel momentum component obtained from the DBAR measurement can be selected for annihilation events that possess a particular perpendicular momentum component observed in the 2D ACAR spectrum. A true 3D momentum distribution can also be produced. Measurement of 3-D momentum spectra in oxide materials has been demonstrated including O-atom defects in 6H SiC and silver atom substitution in lithium tetraborate crystals. Integration of the 3-D momentum spectrometer with a slow positron beam for future surface resonant annihilation spectrometry measurements will be described. Sponsorship from Air Force Office of Scientific Research

  4. Applications of slow positrons to cancer research: Search for selectivity of positron annihilation to skin cancer

    NASA Astrophysics Data System (ADS)

    Jean, Y. C.; Li, Ying; Liu, Gaung; Chen, Hongmin; Zhang, Junjie; Gadzia, Joseph E.

    2006-02-01

    Slow positrons and positron annihilation spectroscopy (PAS) have been applied to medical research in searching for positron annihilation selectivity to cancer cells. We report the results of positron lifetime and Doppler broadening energy spectroscopies in human skin samples with and without cancer as a function of positron incident energy (up to 8 μm depth) and found that the positronium annihilates at a significantly lower rate and forms at a lower probability in the samples having either basal cell carcinoma (BCC) or squamous cell carcinoma (SCC) than in the normal skin. The significant selectivity of positron annihilation to skin cancer may open a new research area of developing positron annihilation spectroscopy as a novel medical tool to detect cancer formation externally and non-invasively at the early stages.

  5. Positron line radiation from halo WIMP annihilations as a dark matter signature

    NASA Technical Reports Server (NTRS)

    Turner, Michael S.; Wilczek, Frank

    1989-01-01

    We suggest a new signature for dark matter annihilation in the halo: high energy positron line radiation. Because the cosmic ray positron spectrum falls rapidly with energy, e+'s from halo WIMP annihilations can be a significant, clean signal for very massive WIMP's (approx. greater than 30 GeV). In the case that the e+e- annihilation channel has an appreciable branch, the e+ signal should be above background in a future detector, such as have been proposed for ASTROMAG, and of potential importance as a dark matter signature. A significant e+e- branching ratio can occur for neutralinos or Dirac neutrinos. High-energy, continuum positron radiation may also be an important signature for massive neutralino annihilations, especially near or above the threshold of the W+W- and ZoZo annihilation channels.

  6. Characterization of the melting process of PTFE using positron annihilation spectroscopy

    NASA Astrophysics Data System (ADS)

    Honda, Y.; Nishijima, S.

    2015-06-01

    Poly(tetrafluoroethylene) (PTFE) is a semi-crystalline polymer and the lifetime of ortho-positronium(o-Ps) is known to be able to be separated into two components due to annihilation in the crystal region and in the amorphous region. The melting process of PTFE was investigated using positron annihilation spectroscopy and X-ray diffraction. The results indicated that volume expansion with an increase of temperature is dominantly due to the expansion of the amorphous region and a Ps bubble is formed at melting in both regions. The o-Ps relating to the crystal region definitely remains on the surface of crystal at the time of annihilation. The production of lower energy electrons at melting was deduced by the analysis of the Doppler broadened annihilation photopeak, and the increase in the number of such electrons was found to have great influence on the formation of the o-Ps and annihilation processes of positron and o-Ps.

  7. Positron and Positronium Annihilation Lifetime, and Free Volume in Polymers.

    NASA Astrophysics Data System (ADS)

    Yu, Zhibin

    1995-01-01

    Positron annihilation lifetime measurements were carried out for six polycarbonates of different structures and four polystyrenes of different molecular weight over a wide temperature range covering the glass transition region. The o-Ps mean lifetime is very sensitive to the changes of free volume in those polymers which occur due to change of molecular structure, chain length, and temperature. The influence of the unavoidable e^{+} irradiation and physical aging on the mean lifetime and the intensity of o-Ps annihilation were studied by conducting time dependent measurements on both very aged and rejuvenated samples. Both irradiation and physical aging reduce the formation of positronium, but have no effect on the mean lifetime of Ps atoms. The free volume fraction h obtained from the positron lifetime measurements was compared with the prediction of the statistical mechanical theory of Simha and Somcynsky; good agreement was found in the melt state though clear deviations were observed in the glassy state. A free volume quantity, computed from the bulk volume, which is in a good numerical agreement with the Simha-Somcynsky h-function in the melt, gives improved agreement with the h value calculated from the positron lifetime measurements. To investigate certain anomalies observed in the computer analysis of the positron annihilation lifetime spectra on polymers, we developed a computer simulation of the experimental data, which then was used to test the accuracy of the fitting results in the different circumstances. The influence caused by a possible distribution of the o-Ps mean lifetimes and the width of the spectrometer time resolution function were studied. The theoretical connection between the o-Ps mean lifetime and the free volume hole size was reviewed based on a finite spherical potential well model, and the status of the localized Ps atom in polymers was evaluated by calculation of the barrier transmission probability and the escaping probability of the

  8. Semi-inclusive wino and higgsino annihilation to LL'

    NASA Astrophysics Data System (ADS)

    Baumgart, Matthew; Vaidya, Varun

    2016-03-01

    We systematically compute the annihilation rate for winos and higgsinos into the final state relevant for indirect detection experiments, γ + X. The radiative corrections to this process receive enhancement from the large Bloch-Nordsieck-Violating Sudakov logarithm, log(2 M χ /M W ). We resum the double logs and include single logs to fixed order using a formalism that combines nonrelativistic and soft-collinear effective field theories. For the wino case, we update an earlier exclusion adapting results of the HESS experiment. At the thermal relic mass of 3 TeV, LL' corrections result in a ˜30% reduction in rate relative to LL. Nonetheless, single logs do not save the wino, and it is still excluded by an order of magnitude. Experimental cuts produce an endpoint region which, our results show, significantly effects the higgsino rate at its thermal-relic mass near 1 TeV and is deserving of further study.

  9. Neutrinos from dark matter annihilations at the galactic center

    SciTech Connect

    Bertone, Gianfranco; Orloff, Jean; Silk, Joseph

    2004-09-15

    We discuss the prospects for detection of high energy neutrinos from dark matter (DM) annihilation at the galactic center (GC). Despite the large uncertainties associated with our poor knowledge of the distribution of dark matter in the innermost regions of the Galaxy, we determine an upper limit on the neutrino flux by requiring that the associated gamma-ray emission does not exceed the observed flux. We conclude that a neutrino flux from the GC will not be observable by Antares if dark matter is made of neutralinos with mass smaller than 650 GeV, while for heavier neutralinos, corresponding to models that will soon be probed by HESS (high energy stereoscopic system), the upper limit on the neutrino flux is barely above the Antares sensitivity. The detection of a larger flux would either require an alternative explanation, in terms of astrophysical processes, or the adoption of other dark matter candidates, disfavouring the case for neutralinos.

  10. Time correlation of two γ rays resulting from positronium annihilation

    NASA Astrophysics Data System (ADS)

    Saito, Haruo; Shibuya, Kengo

    2012-04-01

    We have obtained the wave function and time correlation of two γ rays resulting from the annihilation of a spin-singlet positronium. We have modified the calculations made by Gauthier and Hawton [Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.81.062121 81, 062121 (2010)] in consideration of the real experimental conditions. It has been found that the time correlation is determined by the center-of-mass motion of the positronium, and that the exponential decay component shown by Gauthier and Hawton does not appear in the time-correlation function. We have also conducted an experiment focused on the exponential component in the time-correlation function. The experimental results are consistent with our calculation.

  11. Positron-annihilation spectroscopy of defects in metals: an assessment

    SciTech Connect

    Siegel, R.W.

    1982-06-01

    Positron annihilation spectroscopy (PAS) has made significant contributions to our knowledge regarding lattice defects in metals in two areas: (i) the determination of atomic defect properties, particularly those of monovacancies, and (ii) the monitoring and characterization of vacancy-like microstructure development during post-irradiation of post-quench annealing. The application of PAS to the study of defects in metals is selectively reviewed and critically assessed within the context of other available techniques for such investigations. Possibilities for using the positron as a localized probe of the structure of atomic defects are discussed. Finally, the present status and future potential of PAS as a tool for the study of defects in metals are considered relative to other available techniques. 92 references, 20 figures.

  12. Positron annihilation lifetime spectroscopy study of Kapton thin foils

    NASA Astrophysics Data System (ADS)

    Kanda, G. S.; Ravelli, L.; Löwe, B.; Egger, W.; Keeble, D. J.

    2016-01-01

    Variable energy positron annihilation lifetime spectroscopy (VE-PALS) experiments on polyimide material Kapton are reported. Thin Kapton foils are widely used in a variety of mechanical, electronic applications. PALS provides a sensitive probe of vacancy-related defects in a wide range of materials, including open volume in polymers. Varying the positron implantation energy enables direct measurement of thin foils. Thin Kapton foils are also commonly used to enclose the positron source material in conventional PALS measurements performed with unmoderated radionuclide sources. The results of depth-profiled positron lifetime measurements on 7.6 μm and 25 μm Kapton foils are reported and determine a dominant 385(1) ps lifetime component. The absence of significant nanosecond lifetime component due to positronium formation is confirmed.

  13. Induced absorption and annihilation in hadronic hydrogen atoms

    NASA Astrophysics Data System (ADS)

    Pomerantsev, Vladimir N.; Popov, Vladimir P.

    The induced absorption or annihilation in the collisions of the hydrogen hadronic atoms in the excited states with ordinary hydrogen have been described in a unified manner with the elastic scattering, Stark transitions, and Coulomb de-excitation in the framework of a close-coupling approach including both the open and closed channels corresponding to both the stationary and non-stationary states of hadronic atom. The general features of the induced absorption cross sections have been studied in a wide range of the complex energy-shift values. The total and differential cross sections of all processes have been calculated for π - p, K - p, and bar p p atoms with the principal quantum numbers n = 2 - 8 and kinetic energy from 0.001 eV up to 100 eV.

  14. Induced absorption and annihilation in hadronic hydrogen atoms

    NASA Astrophysics Data System (ADS)

    Pomerantsev, Vladimir N.; Popov, Vladimir P.

    2012-05-01

    The induced absorption or annihilation in the collisions of the hydrogen hadronic atoms in the excited states with ordinary hydrogen have been described in a unified manner with the elastic scattering, Stark transitions, and Coulomb de-excitation in the framework of a close-coupling approach including both the open and closed channels corresponding to both the stationary and non-stationary states of hadronic atom. The general features of the induced absorption cross sections have been studied in a wide range of the complex energy-shift values. The total and differential cross sections of all processes have been calculated for π - p, K - p, and bar p p atoms with the principal quantum numbers n = 2 - 8 and kinetic energy from 0.001 eV up to 100 eV.

  15. Defect annihilation at grain boundaries in alpha-Fe

    PubMed Central

    Di Chen; Wang, Jing; Chen, Tianyi; Shao, Lin

    2013-01-01

    Understanding radiation responses of Fe-based metals is essential to develop radiation tolerant steels for longer and safer life cycles in harsh reactor environments. Nanograined metals have been explored as self-healing materials due to point-defect recombination at grain boundaries. The fundamental defect-boundary interactions, however, are not yet well understood. We discover that the interactions are always mediated by formation and annealing of chain-like defects, which consist of alternately positioned interstitials and vacancies. These chain-like defects are closely correlated to the patterns of defect formation energy minima on the grain boundary, which depend on specific boundary configurations. Through chain-like defects, a point defect effectively translates large distances, to annihilate with its opposite, thus grain boundaries act as highly efficient defect sinks that cannot saturate under extreme radiation conditions. PMID:23519086

  16. Defect annihilation at grain boundaries in alpha-Fe.

    PubMed

    Chen, Di; Wang, Jing; Chen, Tianyi; Shao, Lin

    2013-01-01

    Understanding radiation responses of Fe-based metals is essential to develop radiation tolerant steels for longer and safer life cycles in harsh reactor environments. Nanograined metals have been explored as self-healing materials due to point-defect recombination at grain boundaries. The fundamental defect-boundary interactions, however, are not yet well understood. We discover that the interactions are always mediated by formation and annealing of chain-like defects, which consist of alternately positioned interstitials and vacancies. These chain-like defects are closely correlated to the patterns of defect formation energy minima on the grain boundary, which depend on specific boundary configurations. Through chain-like defects, a point defect effectively translates large distances, to annihilate with its opposite, thus grain boundaries act as highly efficient defect sinks that cannot saturate under extreme radiation conditions. PMID:23519086

  17. Single-shot positron annihilation lifetime spectroscopy with LYSO scintillators

    NASA Astrophysics Data System (ADS)

    Alonso, A. M.; Cooper, B. S.; Deller, A.; Cassidy, D. B.

    2016-08-01

    We have evaluated the application of a lutetium yttrium oxyorthosilicate (LYSO) based detector to single-shot positron annihilation lifetime spectroscopy. We compare this detector directly with a similarly configured PbWO4 scintillator, which is the usual choice for such measurements. We find that the signal to noise ratio obtained using LYSO is around three times higher than that obtained using PbWO4 for measurements of Ps excited to longer-lived (Rydberg) levels, or when they are ionized soon after production. This is due to the much higher light output for LYSO (75% and 1% of NaI for LYSO and PbWO4 respectively). We conclude that LYSO is an ideal scintillator for single-shot measurements of positronium production and excitation performed using a low-intensity pulsed positron beam.

  18. Fragmentation production of charmed hadrons in electron-positron annihilation

    SciTech Connect

    Novoselov, A. A.

    2010-10-15

    Processes involving the production of D* mesons and {Lambda}{sub c} baryons in electron-positron annihilation at the energies of 10.58 and 91.18 GeV are considered. At the energy of 10.58 GeV, the production of pairs of B mesons that is followed by their decay to charmed particles is analyzed along with direct charm production. The violation of scaling in the respective fragmentation functions is taken into account in the next-to-leading-logarithmic approximation of perturbative QCD. The required nonperturbative fragmentation functions are extracted numerically from experimental data obtained at B factories and are approximated by simple analytic expressions. It is shown that the difference in the nonperturbative fragmentation functions for transitions to mesons and baryons can readily be explained on the basis of the quark-counting rules.

  19. Electron momentum distribution in amorphous metals investigated by positron annihilation

    NASA Astrophysics Data System (ADS)

    Kristiakova, K.; Kristiak, J.; Galan, P.

    Electron momentum distribution in amorphous metals and the crystalline form of Ni xFe 80- xB 20 ( x = 10, 20, 30, 40) were investigated by positron annihilation. The samples were 30 mn thick ribbons, produced by rapid quenching of liquid metal on a rotating Cu wheel. The positron source was 22Na on mylar or blotting paper between two samples in sandwich arrangement. The γ-radiation was detected by a Ge(Li) detector which has a resolution at 511.9 keV ( 106Ru) of 1.6 keV. An unfolding method based on Bayes principle was applied to calculate the Doppler-broadening; S-parameter values were also determined. The calculated momentum distribution revealed a difference for the Ni 30Fe 50B 20 sample.

  20. Development of positron annihilation spectroscopy for characterizing neutron irradiated tungsten

    SciTech Connect

    C.N. Taylor; M. Shimada; D.W. Akers; M.W. Drigert; B.J. Merrill; Y. Hatano

    2013-05-01

    Tungsten samples (6 mm diameter, 0.2 mm thick) were irradiated to 0.025 and 0.3 dpa with neutrons in the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory. Samples were then exposed to deuterium plasma in the tritium plasma experiment (TPE) at 100, 200 and 500ºC to a total fluence of 1 x 1026 m-2. Nuclear reaction analysis (NRA) and Doppler broadening positron annihilation spectroscopy (DB-PAS) were performed at various stages to characterize damage and retention. We present the first known results of neutron damaged tungsten characterized by DB-PAS in order to study defect concentration. Two positron sources, 22Na and 68Ge, probe ~58 µm and through the entire 200 µm thick samples, respectively. DB-PAS results reveal clear differences between the various irradiated samples. These results, and the calibration of DB-PAS to NRA data are presented.

  1. Primary cosmic ray positrons and galactic annihilation radiation

    NASA Technical Reports Server (NTRS)

    Lingenfelter, R. E.; Ramaty, R.

    1980-01-01

    The observation (Leventhal et al, 1978) of positron annihilation radiation at 0.511 MeV from the direction of the Galactic Center is reexamined, suggesting the possibility of a primary positron component of the cosmic rays. The observed 0.511 MeV emission requires a positron production rate nearly two orders of magnitude greater than the production rate of secondary cosmic ray positrons from pion decay produced in cosmic ray interactions. Possible sources of positrons are reviewed with both supernovae and pulsars appearing to be the more likely candidates. If only about 1% of these positrons were accelerated along with the cosmic ray nucleons and electrons to energies not less than 100 MeV, it is believed that these primary positrons would be comparable in intensity to those secondary positrons resulting from pion decay. Some observational evidence for the existence of primary positrons in the cosmic rays is also discussed.

  2. Moisture dependence of positron annihilation spectra in nylon-6

    NASA Technical Reports Server (NTRS)

    Singh, J. J.; St. Clair, T. L.; Holt, W. H.; Mock, W., Jr.

    1984-01-01

    Positron annihilation time spectra have been measured in nylon-6 samples as a function of their moisture content. The measured average long life component lifetime values are: 1722 + or - 47 ps (dry), 1676 + or - 40 ps (14.6 percent saturation value), 1719 + or - 26 ps (29.3 percent saturation value), 1720 + or - 35 ps (50 percent of saturation value), 1857 + or - 35 ps (78.1 percent saturation value), and 1936 + or - 57 ps (saturated). It appears that nylon-6 has a special affinity for water at low concentration levels where H2O molecules enter between the (C = O - H-N) chemical bonds between nylon molecular chains. As the water concentration increases beyond a critical level, nylon-6 specimens start trapping H2O molecules in other bond sites or potential wells. The trapped water increases the free volume in the test specimens and reduces Ps atom formation as well as its subsequent decay rate.

  3. Pair production and annihilation in strong magnetic fields. [of neutron stars and pulsars

    NASA Technical Reports Server (NTRS)

    Daugherty, J. K.; Harding, A. K.

    1983-01-01

    Electromagnetic phenomena occurring in the presence of strong magnetic fields are currently of great interest in high-energy astrophysics. In particular, the process of pair production by single photons in the presence of fields of order 10 to the 12th power Gauss is of importance in cascade models of pulsar gamma ray emission, and may also become significant in theories of other radiation phenomena whose sources may be neutron stars (e.g., gamma ray bursts). In addition to pair production, the inverse process of pair annihilation is greatly affected by the presence of superstrong magnetic fields. The most significant departures from annihilation processes in free space are a reduction in the total rate for annihilation into two photons, a broadening of the familiar 511-keV line for annihilation at rest, and the possibility for annihilation into a single photon which dominates the two-photon annihilation for B (10 to 13th power Gauss) The physics of these pair conversion processes, which is reviewed briefly, can become quite complex in the teragauss regime, and can involve calculations which are technically difficult to incorporate into models of emission mechanisms in neutron star magnetospheres. However, theoretical work, especially the case of pair annihilation, also suggests potential techniques for more direct measurements of field strengths near the stellar surface.

  4. Positron annihilation in AlN and GaN

    NASA Astrophysics Data System (ADS)

    Arutyunov, N. Yu.; Emtsev, V. V.; Mikhailin, A. V.; Davidov, V. Yu.

    2001-12-01

    The measurements of one-dimensional angular correlation of the annihilation radiation (1D-ACAR) have been carried out for AlN and GaN as well as for some related materials (Al, Ga, GaP, GaAs, GaSb) which have been used as samples of references the analysis of results. The numeral values of characteristic length of radius of spherical volume to be occupied by annihilating electron ( rs‧) have differed significantly from the corresponding values ( rs) calculated by the conventional independent-particle-model (IPM) for ideal Fermi-gas: rs‧ (AlN)≃1.28 rs, where rs (AlN)≃1.61 a.u., and rs‧ (GaN)≃1.66 rs, where rs (GaN)≃1.64 a.u. The electron-positron “ion radii” reconstructed by the high-momentum components (HMC) of 1D-ACAR for Al 3+, Ga 3+ cores as well as numeral rs‧ values provide some reasons to believe that Ga- and Al-vacancies and their impurity complexes are effective centers of the positron localization in AlN and GaN; it is assumed that these complexes include V Ga, V Al, and N atom (V Ga-N Ga in GaN and V Al-N Al in AlN) where the nitrogen atom is likely to be in the configuration of substitution (anti-site), N +Ga and N +Al, respectively.

  5. Defect identification in semiconductors with positron annihilation: experiment and theory

    NASA Astrophysics Data System (ADS)

    Tuomisto, Filip

    2015-03-01

    Positron annihilation spectroscopy is a very powerful technique for the detection, identification and quantification of vacancy-type defects in semiconductors. In the past decades, it has been used to reveal the relationship between opto-electronic properties and specific defects in a wide variety of materials - examples include parasitic yellow luminescence in GaN, dominant acceptor defects in ZnO and broad-band absorption causing brown coloration in natural diamond. In typical binary compound semiconductors, the selective sensitivity of the technique is rather strongly limited to cation vacancies that possess significant open volume and suitable charge (negative of neutral). On the other hand, oxygen vacancies in oxide semiconductors are a widely debated topic. The properties attributed to oxygen vacancies include the inherent n-type conduction, poor p-type dopability, coloration (absorption), deep level luminescence and non-radiative recombination, while the only direct experimental evidence of their existence has been obtained on the crystal surface. We will present recent advances in combining state-of-the-art positron annihilation experiments and ab initio computational approaches. The latter can be used to model both the positron lifetime and the electron-positron momentum distribution - quantities that can be directly compared with experimental results. We have applied these methods to study vacancy-type defects in III-nitride semiconductors (GaN, AlN, InN) and oxides such as ZnO, SnO2, In2O3andGa2O3. We will show that cation-vacancy-related defects are important compensating centers in all these materials when they are n-type. In addition, we will show that anion (N, O) vacancies can be detected when they appear as complexes with cation vacancies.

  6. Constraint on the velocity dependent dark matter annihilation cross section from Fermi-LAT observations of dwarf galaxies

    NASA Astrophysics Data System (ADS)

    Zhao, Yi; Bi, Xiao-Jun; Jia, Huan-Yu; Yin, Peng-Fei; Zhu, Feng-Rong

    2016-04-01

    The γ -ray observation of dwarf spheroidal satellites (dSph's) is an ideal approach for probing the dark matter (DM) annihilation signature. The latest Fermi-LAT dSph searches have set stringent constraints on the velocity independent annihilation cross section in the small DM mass range, which gives very strong constraints on the scenario to explain the AMS-02 positron excess by DM annihilation. However, the dSph constraints would change in the velocity dependent annihilation scenarios, because the velocity dispersion in the dSph's varies from that in the Milky Way. In this work, we use a likelihood map method to set constraints on the velocity dependent annihilation cross section from the Fermi-LAT observation of six dSph's. We consider three typical forms of the annihilation cross section, i.e. p-wave annihilation, Sommerfeld enhancement, and Breit-Wigner resonance. For the p-wave annihilation and Sommerfeld enhancement, the dSph limits would become much weaker and stronger compared with those for the velocity independent annihilation, respectively. For the Breit-Wigner annihilation, the dSph limits would vary depending on the model parameters. We show that the scenario to explain the AMS-02 positron excess by DM annihilation is still viable in the velocity dependent cases.

  7. Revisiting big-bang nucleosynthesis constraints on dark-matter annihilation

    NASA Astrophysics Data System (ADS)

    Kawasaki, Masahiro; Kohri, Kazunori; Moroi, Takeo; Takaesu, Yoshitaro

    2015-12-01

    We study the effects of dark-matter annihilation during the epoch of big-bang nucleosynthesis on the primordial abundances of light elements. We improve the calculation of the light-element abundances by taking into account the effects of anti-nucleons emitted by the annihilation of dark matter and the interconversion reactions of neutron and proton at inelastic scatterings of energetic nucleons. Comparing the theoretical prediction of the primordial light-element abundances with the latest observational constraints, we derive upper bounds on the dark-matter pair-annihilation cross section. Implication to some of particle-physics models are also discussed.

  8. Dark matter annihilation into right-handed neutrinos and the galactic center gamma-ray excess

    NASA Astrophysics Data System (ADS)

    Tang, Yi-Lei; Zhu, Shou-hua

    2016-03-01

    In this paper, we will discuss a specific case that the dark matter particles annihilate into right-handed neutrinos. We calculate the predicted gamma-ray excess from the galactic center and compare our results with the data from the Fermi-LAT. An approximately 10-60 GeV right-handed neutrino with heavier dark matter particle can perfectly explain the observed spectrum. The annihilation cross section <σ v> falls within the range 0 .5-4 × 10-26 cm3 /s, which is roughly compatible with the WIMP annihilation cross section.

  9. Sommerfeld enhancement of invisible dark matter annihilation in galaxies and galaxy clusters

    NASA Astrophysics Data System (ADS)

    Chan, Man Ho

    2016-07-01

    Recent observations indicate that core-like dark matter structures exist in many galaxies, while numerical simulations reveal a singular dark matter density profile at the center. In this article, I show that if the annihilation of dark matter particles gives invisible sterile neutrinos, the Sommerfeld enhancement of the annihilation cross-section can give a sufficiently large annihilation rate to solve the core-cusp problem. The resultant core density, core radius, and their scaling relation generally agree with recent empirical fits from observations. Also, this model predicts that the resultant core-like structures in dwarf galaxies can be easily observed, but not for large normal galaxies and galaxy clusters.

  10. Fast magnetic field annihilation driven by two laser pulses in underdense plasma

    SciTech Connect

    Gu, Y. J.; Kumar, D.; Weber, S.; Korn, G.; Klimo, O.; Bulanov, S. V.; Esirkepov, T. Zh.

    2015-10-15

    Fast magnetic annihilation is investigated by using 2.5-dimensional particle-in-cell simulations of two parallel ultra-short petawatt laser pulses co-propagating in underdense plasma. The magnetic field generated by the laser pulses annihilates in a current sheet formed between the pulses. Magnetic field energy is converted to an inductive longitudinal electric field, which efficiently accelerates the electrons of the current sheet. This new regime of collisionless relativistic magnetic field annihilation with a timescale of tens of femtoseconds can be extended to near-critical and overdense plasma with the ultra-high intensity femtosecond laser pulses.

  11. Eternal annihilations: New constraints on long-lived particles from big-bang nucleosynthesis

    NASA Astrophysics Data System (ADS)

    Frieman, Joshua A.; Kolb, Edward W.; Turner, Michael S.

    1990-05-01

    In the early Universe, the relative abundance of a massive weakly interacting particle species ``freezes out'' when the annihilation rate becomes less than the expansion rate. Although ineffective in reducing the total number of the species, occasional annihilations still occur after freeze-out. The residual annihilations of massive particles (10 MeV<~mX<~1 GeV) after primordial nucleosynthesis can strongly alter the light-element abundances through photodissociation. For particles with typical weak-interaction cross sections and lifetimes τX>~5×106 sec, we find that the mass range mX<~1 GeV is ruled out, independent of how they subsequently decay.

  12. CMB constraints on dark matter models with large annihilation cross section

    SciTech Connect

    Galli, Silvia; Iocco, Fabio; Bertone, Gianfranco; Melchiorri, Alessandro

    2009-07-15

    The injection of secondary particles produced by dark matter (DM) annihilation around redshift {approx}1000 would inevitably affect the process of recombination, leaving an imprint on cosmic microwave background (CMB) anisotropies and polarization. We show that the most recent CMB measurements provided by the WMAP satellite mission place interesting constraints on DM self-annihilation rates, especially for models that exhibit a large Sommerfeld enhancement of the annihilation cross section, as recently proposed to fit the PAMELA and ATIC results. Furthermore, we argue that upcoming CMB experiments such as Planck, will improve the constraints by at least 1 order of magnitude, thus providing a sensitive probe of the properties of DM particles.

  13. Neutrino emissivity from electron-positron annihilation in hot matter in a strong magnetic field

    SciTech Connect

    Amsterdamski, P.; Haensel, P. )

    1990-10-15

    The neutrino emissivity due to electron-positron annihilation in a strong magnetic field is computed. A strong magnetic field can significantly increase the neutrino emissivity at {ital T}{similar to}10{sup 9} K.

  14. Leptonic widths of heavy quarkonia: S-wave QCD/NRQCD matching coefficients for the electromagnetic vector annihilation current at O(αsv2)

    NASA Astrophysics Data System (ADS)

    Hart, A.; von Hippel, G. M.; Horgan, R. R.

    2007-01-01

    We construct the S-wave part of the electromagnetic vector annihilation current to O(αsv2) on the lattice for heavy quarks whose dynamics are described by the NRQCD action, and v is the nonrelativistic quark velocity inside the meson. The lattice vector current for QQ¯ annihilation is expressed as a linear combination of lattice operators with quantum numbers L=0, JP=1-, and the coefficients are determined by matching this lattice current to the corresponding continuum current in QCD to O(v2) at one-loop. The annihilation channel gives a complex amplitude and a proper choice for the contours of integration is needed; a simple Wick rotation is not possible. In this way, and with a careful choice of subtraction functions in the numerical integration, the Coulomb-exchange and infrared singularities appearing in the amplitudes are successfully treated. The matching coefficients are given as a function of the heavy quark mass Ma in lattice units. An automated vertex generation program written in Python is employed, allowing us to use a realistic NRQCD action and an improved gluon lattice action. A change in the definition of either action is easily accommodated in this procedure. The final result, when combined with lattice simulation results, describes the electromagnetic decays of heavy quarkonia, notably the Υ meson.

  15. p -wave annihilating dark matter from a decaying predecessor and the Galactic Center excess

    NASA Astrophysics Data System (ADS)

    Choquette, Jeremie; Cline, James M.; Cornell, Jonathan M.

    2016-07-01

    Dark matter (DM) annihilations have been widely studied as a possible explanation of excess gamma rays from the Galactic Center seen by Fermi/LAT. However most such models are in conflict with constraints from dwarf spheroidals. Motivated by this tension, we show that p -wave annihilating dark matter can easily accommodate both sets of observations due to the lower DM velocity dispersion in dwarf galaxies. Explaining the DM relic abundance is then challenging. We outline a scenario in which the usual thermal abundance is obtained through s -wave annihilations of a metastable particle, that eventually decays into the p -wave annihilating DM of the present epoch. The couplings and lifetime of the decaying particle are constrained by big bang nucleosynthesis, the cosmic microwave background and direct detection, but significant regions of parameter space are viable. A sufficiently large p -wave cross section can be found by annihilation into light mediators, that also give rise to Sommerfeld enhancement. A prediction of the scenario is enhanced annihilations in galaxy clusters.

  16. Cogenerating and pre-annihilating dark matter by a new gauge interaction in a unified model

    NASA Astrophysics Data System (ADS)

    Barr, S. M.; Scherrer, Robert J.

    2016-05-01

    Grand unified theories based on large groups (with rank >= 6) are a natural context for dark matter models. They contain Standard-Model-singlet fermions that could be dark matter candidates, and can contain new non-abelian interactions whose sphalerons convert baryons, leptons, and dark matter into each other, ``cogenerating" a dark matter asymmetry comparable to the baryon asymmetry. In this paper it is shown that the same non-abelian interactions can ``pre-annihilate" the symmetric component of heavy dark matter particles χ, which then decay late into light stable dark matter particles ζ that inherit their asymmetry. We derive cosmological constraints on the parameters of such models. The mass of χ must be < 3000 TeV and their decays must happen when 2 × 10‑7 < Tdec/mχ < 10‑4. It is shown that such decays can come from d=5 operators with coefficients of order 1/MGUT or 1/MPl. We present a simple realization of our model based on the group SU(7).

  17. Positron annihilation lifetime spectroscopy of ZnO bulk samples

    SciTech Connect

    Zubiaga, A.; Plazaola, F.; Garcia, J. A.; Tuomisto, F.; Munoz-Sanjose, V.; Tena-Zaera, R.

    2007-08-15

    In order to gain a further insight into the knowledge of point defects of ZnO, positron annihilation lifetime spectroscopy was performed on bulk samples annealed under different atmospheres. The samples were characterized at temperatures ranging from 10 to 500 K. Due to difficulties in the conventional fitting of the lifetime spectra caused by the low intensity of the defect signals, we have used an alternative method as a solution to overcome these difficulties and resolve all the lifetime components present in the spectra. Two different vacancy-type defects are identified in the samples: Zn vacancy complexes (V{sub Zn}-X) and vacancy clusters consisting of up to five missing Zn-O pairs. In addition to the vacancies, we observe negative-ion-type defects, which are tentatively attributed to intrinsic defects in the Zn sublattice. The effect of the annealing on the observed defects is discussed. The concentrations of the V{sub Zn}-X complexes and negative-ion-type defects are in the 0.2-2 ppm range, while the cluster concentrations are 1-2 orders of magnitude lower.

  18. Multiwavelength signals of dark matter annihilations at the Galactic center

    SciTech Connect

    Regis, Marco; Ullio, Piero

    2008-08-15

    We perform a systematic study of the multiwavelength signal induced by weakly interacting massive particle (WIMP) annihilations at the Galactic Center (GC). Referring to a generic WIMP dark matter (DM) scenario and depending on astrophysical inputs, we discuss spectral and angular features and sketch correlations among signals in the different energy bands. None of the components which have been associated to the GC source Sgr A*, nor the diffuse emission components from the GC region, have spectral or angular features typical of a DM source. Still, data sets at all energy bands, namely, the radio, near-infrared, x-ray and gamma-ray bands, contribute to place significant constraints on the WIMP parameter space. In general, the gamma-ray energy range is not the one with the largest signal to background ratio. In the case of large magnetic fields close to the GC, x-ray data give the tightest bounds. The emission in the radio band, which is less model dependent, is very constraining as well. The recent detection by HESS of a GC gamma-ray source, and of a diffuse gamma-ray component, limits the possibility of a DM discovery with the next generation of gamma-ray telescopes, like GLAST and CTA. We find that most of the region in the parameter space accessible to these instruments is actually already excluded at other wavelengths. On the other hand, there may be still an open window to improve constraints with wide-field radio observations.

  19. Positron annihilation in cardo-based polymer membranes.

    PubMed

    Kobayashi, Y; Kazama, Shingo; Inoue, K; Toyama, T; Nagai, Y; Haraya, K; Mohamed, Hamdy F M; O'Rouke, B E; Oshima, N; Kinomura, A; Suzuki, R

    2014-06-01

    Positron annihilation lifetime spectroscopy (PALS) is applied to a series of bis(aniline)fluorene and bis(xylidine)fluorene-based cardo polyimide and bis(phenol)fluorene-based polysulfone membranes. It was found that favorable amounts of positronium (Ps, the positron-electron bound state) form in cardo polyimides with the 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) moiety and bis(phenol)fluorene-based cardo polysulfone, but no Ps forms in most of the polyimides with pyromellitic dianhydride (PMDA) and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BTDA) moieties. A bis(xylidine)fluorene-based polyimide membrane containing PMDA and BTDA moieties exhibits a little Ps formation but the ortho-positronium (o-Ps, the triplet state of Ps) lifetime of this membrane anomalously shortens with increasing temperature, which we attribute to chemical reaction of o-Ps. Correlation between the hole size (V(h)) deduced from the o-Ps lifetime and diffusion coefficients of O2 and N2 for polyimides with the 6FDA moiety and cardo polysulfone showing favorable Ps formation is discussed based on free volume theory of gas diffusion. It is suggested that o-Ps has a strong tendency to probe larger holes in rigid chain polymers with wide hole size distributions such as those containing cardo moieties, resulting in deviations from the previously reported correlations for common polymers such as polystyrene, polycarbonate, polysulfone, and so forth. PMID:24815092

  20. Molecular pathways for defect annihilation in directed self-assembly.

    PubMed

    Hur, Su-Mi; Thapar, Vikram; Ramírez-Hernández, Abelardo; Khaira, Gurdaman; Segal-Peretz, Tamar; Rincon-Delgadillo, Paulina A; Li, Weihua; Müller, Marcus; Nealey, Paul F; de Pablo, Juan J

    2015-11-17

    Over the last few years, the directed self-assembly of block copolymers by surface patterns has transitioned from academic curiosity to viable contender for commercial fabrication of next-generation nanocircuits by lithography. Recently, it has become apparent that kinetics, and not only thermodynamics, plays a key role for the ability of a polymeric material to self-assemble into a perfect, defect-free ordered state. Perfection, in this context, implies not more than one defect, with characteristic dimensions on the order of 5 nm, over a sample area as large as 100 cm(2). In this work, we identify the key pathways and the corresponding free energy barriers for eliminating defects, and we demonstrate that an extraordinarily large thermodynamic driving force is not necessarily sufficient for their removal. By adopting a concerted computational and experimental approach, we explain the molecular origins of these barriers and how they depend on material characteristics, and we propose strategies designed to overcome them. The validity of our conclusions for industrially relevant patterning processes is established by relying on instruments and assembly lines that are only available at state-of-the-art fabrication facilities, and, through this confluence of fundamental and applied research, we are able to discern the evolution of morphology at the smallest relevant length scales-a handful of nanometers-and present a view of defect annihilation in directed self-assembly at an unprecedented level of detail. PMID:26515095

  1. Hunting for glueballs in electron-positron annihilation

    SciTech Connect

    Stanley Brodsky; Alfred Scharff Goldhaber; Jungil Lee

    2003-05-01

    We calculate the cross section for the exclusive production of J{sup PC} = 0{sup ++} glueballs G{sub 0} in association with the J/{psi} in e{sup +}e{sup -} annihilation using the pQCD factorization formalism. The required long-distance matrix element for the glueball is bounded by CUSB data from a search for resonances in radiative {Upsilon} decay. The cross section for e{sup +}e{sup -} {yields} J/{psi} + G{sub 0} at {radical}s = 10.6 GeV is similar to exclusive charmonium-pair production e{sup +}e{sup -} {yields} J/{psi} + h for h = {eta}{sub c} and {chi}{sub c0}, and is larger by a factor 2 than that for h = {eta}{sub c}(2S). As the subprocesses {gamma}* {yields} (c {bar c}) (c {bar c}) and {gamma}* {yields} (c {bar c}) (g g) are of the same nominal order in perturbative QCD, it is possible that some portion of the anomalously large signal observed by Belle in e{sup +}e{sup -} {yields} J/{psi} X may actually be due to the production of charmonium-glueball J/{psi} G{sub J} pairs.

  2. Positron states and annihilation in nanometric semiconducting superlattices

    NASA Astrophysics Data System (ADS)

    Sekkal, Nadir; Arutyunov, N. Yu.

    2009-12-01

    The electron and positron states in the band structure of GaAs-AlAs, (GaAs) m((AlAs) 1-x(vacancy/pore) x) n and (GaAs) m((AlAs) 1-xGe x) n superlattices have been analyzed on the basis of empirical pseudopotential method of calculations. When possible, the validity of results has been checked by comparing them with the data obtained for relevant constituents of the superlattices with the help of the angular correlation of annihilation radiation (ACAR) spectroscopy. The most important finding is that positron is capable of being selectively confined in the superlattices even when they are defect-free. In the presence of defects of a vacancy-type, the regime of confinement may be changed to the one of trapping of positron. Being “fingerprints” of certain types of defects, the ACAR spectra may be used for non-destructive characterization of superlattices. The question of sensitivity of the positron particle microprobe for studying electron structure of superlattices is discussed.

  3. Positron annihilation study for cadmium (electronic structure and enhancement effect)

    NASA Astrophysics Data System (ADS)

    Hamid, A.

    2003-12-01

    The three dimensional electron density in momentum space ρ(p) and in wave vector space n(k) was reconstructed for cadmium (Cd). The measurements were performed using the two dimensional angular correlation of annihilation radiation (2D-ACAR) technique. Enhanced contributions in the spectra were observed around 5.5 mrad, discussed in terms of a Kahana-like enhancement effect. From another viewpoint, Fermi radii were analyzed in the (λM K), (ALM) and (AHK) planes, and they showed a maximum deviation of about 4% from the free electron Fermi radius. Moreover, comparisons to a radio-frequency size effect (RFSE) experiment and theoretical band structure calculations (using augmented plane wave (APW), linear combination of atomic orbital (LCAO) and linear muffin tin orbital (LMTO) methods) were examined. The results showed a qualitative agreement with both APW and LCAO calculations. However, a favorable agreement with the APW method was determined via Fermi surface dimensions. The differences of bands' occupation of n(k) between the current work and the APW method were argued in view of positron wave function in Cd.

  4. Timelike Virtual Compton Scattering from Electron-Positron Radiative Annihilation

    SciTech Connect

    Afanasev, Andrei; Brodsky, Stanley J.; Carlson, Carl E.; Mukherjee, Asmita; /Indian Inst. Tech., Mumbai

    2009-03-31

    We propose measurements of the deeply virtual Compton amplitude (DVCS) {gamma}* {yields} H{bar H}{gamma} in the timelike t = (p{sub H} + p{sub {bar H}}){sup 2} > 0 kinematic domain which is accessible at electron-positron colliders via the radiative annihilation process e{sup +}e{sup -} {yields} H{bar H}{gamma}. These processes allow the measurement of timelike deeply virtual Compton scattering for a variety of H{bar H} hadron pairs such as {pi}{sup +}{pi}{sup -}, K{sup +}K{sup -}, and D{bar D} as well as p{bar p}. As in the conventional spacelike DVCS, there are interfering coherent amplitudes contributing to the timelike processes involving C = - form factors. The interference between the amplitudes measures the phase of the C = + timelike DVCS amplitude relative to the phase of the timelike form factors and can be isolated by considering the forward-backward e{sup +} {leftrightarrow} e{sup -} asymmetry. The J = 0 fixed pole contribution which arises from the local coupling of the two photons to the quark current plays a special role. As an example we present a simple model.

  5. Timelike Virtual Compton Scattering from Electron-Positron Radiative Annihilation

    SciTech Connect

    Andrei Afanaciev,Andrei Afanasev, Stanley J. Brodsky, Carl E. Carlson, Asmita Mukherjee

    2010-02-01

    We propose measurements of the deeply virtual Compton amplitude (DVCS), gamma* to H H-bar gamma, in the timelike t = (p_{H} + p_{H-bar})^2 > 0 kinematic domain which is accessible at electron-positron colliders via the radiative annihilation process e+ e- to H H-bar gamma. These processes allow the measurement of timelike deeply virtual Compton scattering for a variety of H H-bar hadron pairs such as pi+ pi-, K+ K-, and D D-bar as well as p p-bar. As in the conventional spacelike DVCS, there are interfering coherent amplitudes contributing to the timelike processes involving C= - form factors. The interference between the amplitudes measures the phase of the C=+ timelike DVCS amplitude relative to the phase of the timelike form factors and can be isolated by considering the forward-backward e+ \\leftrightarrow e- asymmetry. The J=0 fixed pole contribution which arises from the local coupling of the two photons to the quark current plays a special role. As an example we present a simple model.

  6. Attraction, merger, reflection, and annihilation in magnetic droplet soliton scattering

    NASA Astrophysics Data System (ADS)

    Maiden, M. D.; Bookman, L. D.; Hoefer, M. A.

    2014-05-01

    The interaction behaviors of solitons are defining characteristics of these nonlinear, coherent structures. Due to recent experimental observations, thin ferromagnetic films offer a promising medium in which to study the scattering properties of two-dimensional magnetic droplet solitons, particle-like, precessing dipoles. Here, a rich set of two-droplet interaction behaviors are classified through micromagnetic simulations. Repulsive and attractive interaction dynamics are generically determined by the relative phase and speeds of the two droplets and can be classified into four types: (1) merger into a breather bound state, (2) counterpropagation trapped along the axis of symmetry, (3) reflection, and (4) violent droplet annihilation into spin wave radiation and a breather. Utilizing a nonlinear method of images, it is demonstrated that these dynamics describe repulsive/attractive scattering of a single droplet off of a magnetic boundary with pinned/free spin boundary conditions, respectively. These results explain the mechanism by which propagating and stationary droplets can be stabilized in a confined ferromagnet.

  7. Molecular pathways for defect annihilation in directed self-assembly

    PubMed Central

    Hur, Su-Mi; Thapar, Vikram; Ramírez-Hernández, Abelardo; Khaira, Gurdaman; Segal-Peretz, Tamar; Rincon-Delgadillo, Paulina A.; Li, Weihua; Müller, Marcus; Nealey, Paul F.; de Pablo, Juan J.

    2015-01-01

    Over the last few years, the directed self-assembly of block copolymers by surface patterns has transitioned from academic curiosity to viable contender for commercial fabrication of next-generation nanocircuits by lithography. Recently, it has become apparent that kinetics, and not only thermodynamics, plays a key role for the ability of a polymeric material to self-assemble into a perfect, defect-free ordered state. Perfection, in this context, implies not more than one defect, with characteristic dimensions on the order of 5 nm, over a sample area as large as 100 cm2. In this work, we identify the key pathways and the corresponding free energy barriers for eliminating defects, and we demonstrate that an extraordinarily large thermodynamic driving force is not necessarily sufficient for their removal. By adopting a concerted computational and experimental approach, we explain the molecular origins of these barriers and how they depend on material characteristics, and we propose strategies designed to overcome them. The validity of our conclusions for industrially relevant patterning processes is established by relying on instruments and assembly lines that are only available at state-of-the-art fabrication facilities, and, through this confluence of fundamental and applied research, we are able to discern the evolution of morphology at the smallest relevant length scales—a handful of nanometers—and present a view of defect annihilation in directed self-assembly at an unprecedented level of detail. PMID:26515095

  8. Hunting for Glueballs in Electron-Positron Annihilation

    NASA Astrophysics Data System (ADS)

    Brodsky, Stanley J.; Goldhaber, Alfred Scharff; Lee, Jungil

    2003-09-01

    We calculate the cross section for the exclusive production of JPC=0++ glueballs G0 in association with the J/ψ in e+e- annihilation using the perturbative QCD factorization formalism. The required long-distance matrix element for the glueball is bounded by CUSB data from a search for resonances in radiative ϒ decay. The cross section for e+e-→J/ψ+G0 at (s)=10.6 GeV is similar to exclusive charmonium-pair production e+e-→J/ψ+h for h=ηc and χc0, and is larger by a factor of 2 than that for h=ηc(2S). As the subprocesses γ*→(cc¯)(cc¯) and γ*→(cc¯)(gg) are of the same nominal order in perturbative QCD, it is possible that some portion of the anomalously large signal observed by Belle in e+e-→J/ψX may actually be due to the production of charmonium-glueball J/ψGJ pairs.

  9. Molecular pathways for defect annihilation in directed self-assembly.

    DOE PAGESBeta

    Hur, Su-Mi; Thapar, Vikram; Ramirez-Hernandez, Abelardo; Khaira, Gurdaman S.; Segal-Peretz, Tamar; Rincon-Delgadillo, Paulina A.; Li, Weihua; Muller, Marcus; Nealey, Paul F.; de Pablo, Juan J.

    2015-11-17

    Over the last few years, the directed self-assembly of block copolymers by surface patterns has transitioned from academic curiosity to viable contender for commercial fabrication of next-generation nanocircuits by lithography. Recently, it has become apparent that kinetics, and not only thermodynamics, plays a key role for the ability of a polymeric material to self-assemble into a perfect, defect-free ordered state. Perfection, in this context, implies not more than one defect, with characteristic dimensions on the order of 5 nm, over a sample area as large as 100 cm2. In this work, we identify the key pathways and the corresponding free-energymore » barriers for eliminating defects, and we demonstrate that an extraordinarily large thermodynamic driving force is not necessarily sufficient for their removal. By adopting a concerted computational and experimental approach, we explain the molecular origins of these barriers, how they depend on material characteristics, and we propose strategies designed to over-come them. The validity of our conclusions for industrially-relevant patterning processes is established by relying on instruments and assembly lines that are only available at state-of-the-art fabrication facilities and, through this confluence of fundamental and applied research, we are able to discern the evolution of morphology at the smallest relevant length scales - a handful of nanometers -, and present a view of defect annihilation in directed self-assembly at an unprecedented level of detail.« less

  10. Gamma rays from top-mediated dark matter annihilations

    SciTech Connect

    Jackson, C.B.; Servant, Géraldine; Shaughnessy, Gabe; Tait, Tim M.P.; Taoso, Marco E-mail: chris@uta.edu E-mail: ttait@uci.edu

    2013-07-01

    Lines in the energy spectrum of gamma rays are a fascinating experimental signal, which are often considered ''smoking gun'' evidence of dark matter annihilation. The current generation of gamma ray observatories are currently closing in on parameter space of great interest in the context of dark matter which is a thermal relic. We consider theories in which the dark matter's primary connection to the Standard Model is via the top quark, realizing strong gamma ray lines consistent with a thermal relic through the forbidden channel mechanism proposed in the Higgs in Space Model. We consider realistic UV-completions of the Higgs in Space and related theories, and show that a rich structure of observable gamma ray lines is consistent with a thermal relic as well as constraints from dark matter searches and the LHC. Particular attention is paid to the one loop contributions to the continuum gamma rays, which can easily swamp the line signals in some cases, and have been largely overlooked in previous literature.

  11. Development of positron annihilation spectroscopy for characterizing neutron irradiated tungsten

    NASA Astrophysics Data System (ADS)

    Taylor, C. N.; Shimada, M.; Merrill, B. J.; Drigert, M. W.; Akers, D. W.; Hatano, Y.

    2014-04-01

    Tungsten samples (6 mm diameter and 0.2 mm thick) were irradiated to 0.025 and 0.3 dpa with neutrons in the High Flux Isotope Reactor at Oak Ridge National Laboratory as part of the US/Japan Tritium, Irradiation and Thermofluids for America and Nippon (TITAN) collaboration. Samples were then exposed to deuterium plasma in Idaho National Laboratory's Tritium Plasma Experiment at 100, 200 and 500 °C to a total fluence of 1 × 1026 m-2. Nuclear reaction analysis (NRA) and Doppler broadening positron annihilation spectroscopy (DB-PAS) were performed at various stages to characterize radiation damage and retention. We present the first results of neutron irradiated tungsten characterized by DB-PAS in order to study defect concentration. Two positron sources, 22Na and 68Ge, probe ˜58 μm and through the entire 200 μm thick samples, respectively. DB-PAS results reveal clear differences between the various irradiated samples. These results, and a correlation between DB-PAS and NRA data, are presented.

  12. Molecular pathways for defect annihilation in directed self-assembly.

    SciTech Connect

    Hur, Su-Mi; Thapar, Vikram; Ramirez-Hernandez, Abelardo; Khaira, Gurdaman S.; Segal-Peretz, Tamar; Rincon-Delgadillo, Paulina A.; Li, Weihua; Muller, Marcus; Nealey, Paul F.; de Pablo, Juan J.

    2015-11-17

    Over the last few years, the directed self-assembly of block copolymers by surface patterns has transitioned from academic curiosity to viable contender for commercial fabrication of next-generation nanocircuits by lithography. Recently, it has become apparent that kinetics, and not only thermodynamics, plays a key role for the ability of a polymeric material to self-assemble into a perfect, defect-free ordered state. Perfection, in this context, implies not more than one defect, with characteristic dimensions on the order of 5 nm, over a sample area as large as 100 cm2. In this work, we identify the key pathways and the corresponding free-energy barriers for eliminating defects, and we demonstrate that an extraordinarily large thermodynamic driving force is not necessarily sufficient for their removal. By adopting a concerted computational and experimental approach, we explain the molecular origins of these barriers, how they depend on material characteristics, and we propose strategies designed to over-come them. The validity of our conclusions for industrially-relevant patterning processes is established by relying on instruments and assembly lines that are only available at state-of-the-art fabrication facilities and, through this confluence of fundamental and applied research, we are able to discern the evolution of morphology at the smallest relevant length scales - a handful of nanometers -, and present a view of defect annihilation in directed self-assembly at an unprecedented level of detail.

  13. Annihilation of edge dislocations in smectic- A liquid crystals

    NASA Astrophysics Data System (ADS)

    Ambrožič, M.; Kralj, S.; Sluckin, T. J.; Žumer, S.; Svenšek, D.

    2004-11-01

    This paper presents a theoretical study of the annihilation of edge dislocations in the same smectic plane in a bulk smectic- A phase. We use a time-dependent Landau-Ginzburg approach where the smectic ordering is described by the complex order parameter ψ(r⃗,t)=ηeiϕ . This quantity allows both the degree of layering and the position of the layers to be monitored. We are able to follow both precollision and postcollision regimes, and distinguish different early and late behaviors within these regimes. The early precollision regime is driven by changes in the ϕ(r⃗) configuration. The relative velocity of the defects is approximately inversely proportional to the interdefect separation distance. In the late precollision regime the symmetry changes within the cores of defects also become influential. Following the defect collision, in the early postcollision stage, bulk layer order is approached exponentially in time. At very late times, however, there seems to be a long-time power-law tail in the order parameter fluctuation relaxation.

  14. The 21 cm signal and the interplay between dark matter annihilations and astrophysical processes

    NASA Astrophysics Data System (ADS)

    Lopez-Honorez, Laura; Mena, Olga; Moliné, Ángeles; Palomares-Ruiz, Sergio; Vincent, Aaron C.

    2016-08-01

    Future dedicated radio interferometers, including HERA and SKA, are very promising tools that aim to study the epoch of reionization and beyond via measurements of the 21 cm signal from neutral hydrogen. Dark matter (DM) annihilations into charged particles change the thermal history of the Universe and, as a consequence, affect the 21 cm signal. Accurately predicting the effect of DM strongly relies on the modeling of annihilations inside halos. In this work, we use up-to-date computations of the energy deposition rates by the products from DM annihilations, a proper treatment of the contribution from DM annihilations in halos, as well as values of the annihilation cross section allowed by the most recent cosmological measurements from the Planck satellite. Given current uncertainties on the description of the astrophysical processes driving the epochs of reionization, X-ray heating and Lyman-α pumping, we find that disentangling DM signatures from purely astrophysical effects, related to early-time star formation processes or late-time galaxy X-ray emissions, will be a challenging task. We conclude that only annihilations of DM particles with masses of ~100 MeV, could leave an unambiguous imprint on the 21 cm signal and, in particular, on the 21 cm power spectrum. This is in contrast to previous, more optimistic results in the literature, which have claimed that strong signatures might also be present even for much higher DM masses. Additional measurements of the 21 cm signal at different cosmic epochs will be crucial in order to break the strong parameter degeneracies between DM annihilations and astrophysical effects and undoubtedly single out a DM imprint for masses different from ~100 MeV.

  15. SUSY implications from WIMP annihilation into scalars at the Galactic Center

    NASA Astrophysics Data System (ADS)

    Gherghetta, Tony; von Harling, Benedict; Medina, Anibal D.; Schmidt, Michael A.; Trott, Timothy

    2015-05-01

    An excess in γ rays emanating from the Galactic Center has recently been observed in the Fermi-LAT data. This signal can be interpreted as resulting from weakly interacting massive particle annihilation, with the spectrum well fit by dark matter annihilating dominantly into either bottom-quark or Higgs pairs. Supersymmetric models provide a well-motivated framework to study the implications of this signal in these channels. With a neutralino dark matter candidate, the γ -ray excess cannot be easily accommodated in the minimal supersymmetric model, which in any case requires tuning below the percent level to explain the observed Higgs mass. Instead we are naturally led to consider the next-to-minimal model with a singlet superfield. This not only allows for the annihilation channel into bottom-quark pairs to be implemented but also provides new possibilities for annihilation into Higgs-pseudoscalar pairs. We show that the fit to the γ -ray excess for the Higgs-pseudoscalar channel can be just as good as for annihilation into bottom-quark pairs. Moreover, in the parameter range of interest, the next-to-minimal supersymmetric model solves the μ problem and can explain the 125 GeV Higgs mass with improved naturalness. We also consider an extension by adding a right-handed neutrino superfield with the right-handed sneutrino acting as a dark matter candidate. Interestingly, this allows for the annihilation into pseudoscalar pairs which also provide a good fit to the γ -ray excess. Furthermore, in the case of a neutralino lightest supersymmetric particle, the late decay of a sneutrino next-to-lightest supersymmetric particle can nonthermally produce the observed relic abundance. Finally, the weakly interacting massive particle annihilation into scalar pairs allows for the possibility of detecting the Higgs or pseudoscalar decay into two photons, providing a smoking-gun signal of the model.

  16. Positron annihilation lifetime study of radiation-damaged natural zircons

    NASA Astrophysics Data System (ADS)

    Roberts, J.; Gaugliardo, P.; Farnan, I.; Zhang, M.; Vance, E. R.; Davis, J.; Karatchevtseva, I.; Knott, R. B.; Mudie, S.; Buckman, S. J.; Sullivan, J. P.

    2016-04-01

    Zircons are a well-known candidate waste form for actinides and their radiation damage behaviour has been widely studied by a range of techniques. In this study, well-characterised natural single crystal zircons have been studied using Positron Annihilation Lifetime Spectroscopy (PALS). In some, but not all, of the crystals that had incurred at least half of the alpha-event damage of ∼1019 α/g required to render them structurally amorphous, PALS spectra displayed long lifetimes corresponding to voids of ∼0.5 nm in diameter. The long lifetimes corresponded to expectations from published Small-Angle X-ray Scattering data on similar samples. However, the non-observation by PALS of such voids in some of the heavily damaged samples may reflect large size variations among the voids such that no singular size can be distinguished or. Characterisation of a range of samples was also performed using scanning electron microscopy, optical absorption spectroscopy, Raman scattering and X-ray scattering/diffraction, with the degree of alpha damage being inferred mainly from the Raman technique and X-ray diffraction. The observed void diameters and intensities of the long lifetime components were changed somewhat by annealing at 700 °C; annealing at 1200 °C removed the voids entirely. The voids themselves may derive from He gas bubbles or voids created by the inclusion of small quantities of organic and hydrous matter, notwithstanding the observation that no voidage was evidenced by PALS in two samples containing hydrous and organic matter.

  17. Asymmetric dark matter annihilation as a test of non-standard cosmologies

    SciTech Connect

    Gelmini, Graciela B.; Huh, Ji-Haeng; Rehagen, Thomas E-mail: jhhuh@physics.ucla.edu

    2013-08-01

    We show that the relic abundance of the minority component of asymmetric dark matter can be very sensitive to the expansion rate of the Universe and the temperature of transition between a non-standard pre-Big Bang Nucleosynthesis cosmological phase and the standard radiation dominated phase, if chemical decoupling happens before this transition. In particular, because the annihilation cross section of asymmetric dark matter is typically larger than that of symmetric dark matter in the standard cosmology, the decrease in relic density of the minority component in non-standard cosmologies with respect to the majority component may be compensated by the increase in annihilation cross section, so that the annihilation rate at present of asymmetric dark matter, contrary to general belief, could be larger than that of symmetric dark matter in the standard cosmology. Thus, if the annihilation cross section of the asymmetric dark matter candidate is known, the annihilation rate at present, if detectable, could be used to test the Universe before Big Bang Nucleosynthesis, an epoch from which we do not yet have any data.

  18. Positron annihilation investigation of BaSrFBr:Eu by X-ray irradiation

    NASA Astrophysics Data System (ADS)

    Lee, C. Y.

    2014-12-01

    The mechanical property of the BaSrFBr:Eu phosphor layer of X-ray image plates was investigated by using resolution (LP/mm) and coincidence Doppler broadening (CDB) positron annihilation as well as positron annihilation lifetime (PAL). The image plate samples of BaSrFBr:Eu phosphors in this experiment were irradiated by using hospital X-rays. The LP/mm values of the irradiated BaSrFBr:Eu image plates varied from 3.35 to 1.25 for up to 20,000 exposures. CDB positron annihilation and lifetime spectroscopy were used to analyze defect structures in the phosphor layer. Even when the LP/mm values were greatly decreased due to exposures, the S parameter and the lifetime ( τ 1, τ 2) values were almost constant with increasing number of exposures. A positive relationship existed between the SEM images and positron annihilation spectroscopy (PAS). According to the SEM images and the positron annihilation spectroscopy (PAS) results, measurements of the defects with PAS indicate that the image-plate phosphor can be safely used for hospital X-rays in the course of diagnostic radiography at an average rate of 20,000 times for one year.

  19. Higher order dark matter annihilations in the Sun and implications for IceCube

    SciTech Connect

    Ibarra, Alejandro; Totzauer, Maximilian; Wild, Sebastian E-mail: maximilian.totzauer@mytum.de

    2014-04-01

    Dark matter particles captured in the Sun would annihilate producing a neutrino flux that could be detected at the Earth. In some channels, however, the neutrino flux lies in the MeV range and is thus undetectable at IceCube, namely when the dark matter particles annihilate into e{sup +}e{sup −}, μ{sup +}μ{sup −} or light quarks. On the other hand, the same interaction that mediates the annihilations into light fermions also leads, via higher order effects, to the production of weak gauge bosons (and in the case of quarks also gluons) that generate a high energy neutrino flux potentially observable at IceCube. We consider in this paper tree level annihilations into a fermion-antifermion pair with the associated emission of one gauge boson and one loop annihilations into two gauge bosons, and we calculate the limits on the scattering cross section of dark matter particles with protons in scenarios where the dark matter particle couples to electrons, muons or light quarks from the non-observation of an excess of neutrino events in the direction of the Sun. We find that the limits on the spin-dependent scattering cross section are, for some scenarios, stronger than the limits from direct detection experiments.

  20. Weak annihilation cusp inside the dark matter spike about a black hole

    NASA Astrophysics Data System (ADS)

    Shapiro, Stuart L.; Shelton, Jessie

    2016-06-01

    We reinvestigate the effect of annihilations on the distribution of collisionless dark matter (DM) in a spherical density spike around a massive black hole. We first construct a very simple, pedagogic, analytic model for an isotropic phase space distribution function that accounts for annihilation and reproduces the "weak cusp" found by Vasiliev for DM deep within the spike and away from its boundaries. The DM density in the cusp varies as r-1 /2 for s -wave annihilation, where r is the distance from the central black hole, and is not a flat "plateau" profile. We then extend this model by incorporating a loss cone that accounts for the capture of DM particles by the hole. The loss cone is implemented by a boundary condition that removes capture orbits, resulting in an anisotropic distribution function. Finally, we evolve an initial spike distribution function by integrating the Boltzmann equation to show how the weak cusp grows and its density decreases with time. We treat two cases, one for s -wave and the other for p -wave DM annihilation, adopting parameters characteristic of the Milky Way nuclear core and typical WIMP models for DM. The cusp density profile for p -wave annihilation is weaker, varying like ˜r-0.34, but is still not a flat plateau.

  1. Bremsstrahlung and gamma ray lines in 3 scenarios of dark matter annihilation

    SciTech Connect

    Giacchino, Federica; Tytgat, Michel H.G.; Lopez-Honorez, Laura E-mail: llopezho@vub.ac.be

    2014-08-01

    Gamma ray spectral features are of interest for indirect searches of dark matter (DM). Following Barger et al. we consider 3 simple scenarios of DM that annihilates into Standard Model (SM) fermion pairs. Scenario 1 is a Majorana DM candidate coupled to a charged scalar, scenario 2 is a Majorana DM coupled to a charged gauge boson and scenario 3 is a real scalar DM coupled a charged vector-like fermion. As shown by Barger et al., these 3 scenarios share precisely the same internal Bremsstrahlung spectral signature into gamma rays. Their phenomenology is however distinct. In particular for annihilation into light SM fermions, in the chiral limit, the 2-body annihilation cross section is p-wave suppressed for the Majorana candidates while it is d-wave suppressed for the real scalar. In the present work we study the annihilation into 2 gammas, showing that these three scenarios have distinct, and so potentially distinguishable, spectral signatures into gamma rays. In the case of the real scalar candidate we provide a new calculation of the amplitude for annihilation into 2 gammas.

  2. Future sensitivity of neutrino telescopes to dark matter annihilations from the cosmic diffuse neutrino signal

    NASA Astrophysics Data System (ADS)

    Moliné, Ángeles; Ibarra, Alejandro; Palomares-Ruiz, Sergio

    2015-06-01

    Cosmological observations and cold dark matter N-body simulations indicate that our Universe is populated by numerous halos, where dark matter particles annihilate, potentially producing Standard Model particles. In this paper we calculate the contribution to the diffuse neutrino background from dark matter annihilations in halos at all redshifts and we estimate the future sensitivity to the annihilation cross section of neutrino telescopes such as IceCube or ANTARES. We consider various parametrizations to describe the internal halo properties and for the halo mass function in order to bracket the theoretical uncertainty in the limits from the modeling of the cosmological annihilation flux. We find that observations of the cosmic diffuse neutrino flux at large angular distances from the galactic center lead to constraints on the dark matter annihilation cross section which are complementary to (and for some extrapolations of the astrophysical parameters, better than) those stemming from observations of the Milky Way halo, especially for neutrino telescopes not pointing directly to the Milky Way center, as is the case of IceCube.

  3. The annihilation of positrons in the cold phase of the interstellar medium revisited

    NASA Astrophysics Data System (ADS)

    Wallyn, P.; Durouchoux, Ph.; Chapuis, C.; Leventhal, M.

    1994-02-01

    The positron cross sections in H and H2 media are reevaluated, taking into account new experimental results. Using a Monte Carlo simulation, we find a positronium fraction before thermalization of 0.90 for H2, in good agreement with the previous experimental result given by Brown et al. (1986). For H we obtain an upper limit of 0.98. We study the behavior of the charge exchange annihilation in a cold phase (molecular cloud). We calculate a formula for the slowing-down time t, before annihilation lasting Delta t, via charge exchange, of a positron beam with a given energy for different medium densities and initial energies. An upper limit of 0.7 MeV for the initial energy of the positrons, annihilating in the molecular cloud G0.86 - 0.08 near the gamma ray source positronium and gives new time constraints on their possible observation.

  4. INTEGRAL/SPI Limits on Electron-Positron Annihilation Radiation from the Galactic Plane

    NASA Technical Reports Server (NTRS)

    Teegarden, B. J.; Watanabe, K.; Jean, P.; Knoedlseder, J.; Lonjou, V.; Roques, J. P.; Skinner, G. K.; vonBallmoos, P.; Weidenspointner, G.; Bazzano, A.

    2005-01-01

    The center of our Galaxy is a known strong source of electron-positron 511- keV annihilation radiation. Thus far, however, there have been no reliable detections of annihilation radiation outside of the central radian of our Galaxy. One of the primary objectives of the INTEGRAL (INTErnational Gamma-RAy Astrophysics Laboratory) mission, launched in Oct. 2002, is the detailed study of this radiation. The Spectrometer on INTEGRAL (SPI) is a high resolution coded-aperture gamma-ray telescope with an unprecedented combination of sensitivity, angular resolution and energy resolution. We report results from the first 10 months of observation. During this period a significant fraction of the observing time was spent in or near the Galactic Plane. No positive annihilation flux was detected outside of the central region (|l| greater than 40 degrees) of our Galaxy. In this paper we describe the observations and data analysis methods and give limits on the 511-keV flux.

  5. Minimal semi-annihilating ℤ{sub N} scalar dark matter

    SciTech Connect

    Bélanger, Geneviève; Kannike, Kristjan; Pukhov, Alexander; Raidal, Martti

    2014-06-10

    We study the dark matter from an inert doublet and a complex scalar singlet stabilized by ℤ{sub N} symmetries. This field content is the minimal one that allows dimensionless semi-annihilation couplings for N>2. We consider explicitly the ℤ{sub 3} and ℤ{sub 4} cases and take into account constraints from perturbativity, unitarity, vacuum stability, necessity for the electroweak ℤ{sub N} preserving vacuum to be the global minimum, electroweak precision tests, upper limits from direct detection and properties of the Higgs boson. Co-annihilation and semi-annihilation of dark sector particles as well as dark matter conversion significantly modify the cosmic abundance and direct detection phenomenology.

  6. Dimeric character of annihilation of fluorescence of higher electron states of metalloporphyrins

    SciTech Connect

    Ksenofontova, N.M.; Stel-makh, G.F.; Tsvirko, M.P.

    1987-01-01

    The reaction of two triplet-excited molecules can result in triplet-triplet annihilation (TTA) and the appearance of slowed annihilation fluorescence (SAF). The fluorescence of the S/sub 2/ state of a series of metalloporphyrins was studied in this article: Zn-tetraphenylporphyrin (ZnTPP), Zn-tetrabenzoporphyrin (ZnTBP), and CdTBP, in one-quantum direct excitation and two-quantum annihilation excitation. The spectral-luminescence measurements were made on a Ramalog-4 Raman scattering spectrometer and a Spex Fluorolog spectrofluorometer. The SAF was measured in oxygen-free solutions with excitation by steady-state radiation from an argon, krypton, or helium-neon laser falling in the S/sub 0/ ..-->.. S/sub 1/ absorption bands of the metalloporphyrins. The use of steady-state anti-Stokes excitation permits recording the SAF from the S/sub 2/ state.

  7. INTEGRAL/SPI Observations of Electron-Positron Annihilation Radiation from our Galaxy

    NASA Technical Reports Server (NTRS)

    Teegarden, B. J.; Watanabe, K.; Knoedlseder, J.; Jean, P.; Lonjou, V.; Weidenspointer, G.; Skinner, G.; Vedrenne, G.; Roques, J.-P.; Schanne, S.; Schoenfelder, V.

    2005-01-01

    The spectrometer on INTEGRAL (SPI) is a coded-aperture gamma-ray telescope with moderate angular resolution (3 deg) and superior energy resolution (2 keV at 511 kev). One of it's principal science goals is the detailed study of 511 keV electron-positron annihilation from our Galaxy. The origin of this radiation remains a mystery, however current morphological studies suggest an older stellar population. There has also been recent speculation on the possibility of the existence of light (< 100 MeV) dark matter particles whose annihilation or decay could produce the observed 511 keV emission. In this paper we summarize the current results from SPI, compare them with previous results and discuss their implication on possible models for the production of the annihilation radiation.

  8. Confronting Galactic center and dwarf spheroidal gamma-ray observations with cascade annihilation models

    NASA Astrophysics Data System (ADS)

    Dutta, Bhaskar; Gao, Yu; Ghosh, Tathagata; Strigari, Louis E.

    2015-10-01

    Many particle dark matter models predict that the dark matter undergoes cascade annihilations, i.e. the annihilation products are 4-body final states. In the context of model-independent cascade annihilation processes, we study the compatibility of the dark matter interpretation of the Fermi-LAT Galactic center gamma-ray emission with null detections from dwarf spheroidal galaxies. For canonical values of the Milky Way density profile and the local dark matter density, we find that the dark matter interpretation to the Galactic center emission is strongly constrained. However, uncertainties in the dark matter distribution weaken the constraints and leave open dark matter interpretations over a wide range of mass scales.

  9. Minimal semi-annihilating Z{sub N} scalar dark matter

    SciTech Connect

    Bélanger, Geneviève; Kannike, Kristjan; Raidal, Martti; Pukhov, Alexander E-mail: kristjan.kannike@cern.ch E-mail: martti.raidal@cern.ch

    2014-06-01

    We study the dark matter from an inert doublet and a complex scalar singlet stabilized by Z{sub N} symmetries. This field content is the minimal one that allows dimensionless semi-annihilation couplings for N > 2. We consider explicitly the Z{sub 3} and Z{sub 4} cases and take into account constraints from perturbativity, unitarity, vacuum stability, necessity for the electroweak Z{sub N} preserving vacuum to be the global minimum, electroweak precision tests, upper limits from direct detection and properties of the Higgs boson. Co-annihilation and semi-annihilation of dark sector particles as well as dark matter conversion significantly modify the cosmic abundance and direct detection phenomenology.

  10. The annihilation of positrons in the cold phase of the interstellar medium revisited

    NASA Technical Reports Server (NTRS)

    Wallyn, P.; Durouchoux, PH.; Chapuis, C.; Leventhal, M.

    1994-01-01

    The positron cross sections in H and H2 media are reevaluated, taking into account new experimental results. Using a Monte Carlo simulation, we find a positronium fraction before thermalization of 0.90 for H2, in good agreement with the previous experimental result given by Brown et al. (1986). For H we obtain an upper limit of 0.98. We study the behavior of the charge exchange annihilation in a cold phase (molecular cloud). We calculate a formula for the slowing-down time t, before annihilation lasting Delta t, via charge exchange, of a positron beam with a given energy for different medium densities and initial energies. An upper limit of 0.7 MeV for the initial energy of the positrons, annihilating in the molecular cloud G0.86 - 0.08 near the gamma ray source positronium and gives new time constraints on their possible observation.

  11. Positron-Electron Annihilation Process in (2,2)-Difluoropropane Molecule

    NASA Astrophysics Data System (ADS)

    Yang, Liu; Xiao-Guang, Ma; Ying-Hao, Zhu

    2016-04-01

    The positron-electron annihilation process in (2,2)-difluoropropane molecule and the corresponding gamma-ray spectra are studied by quantum chemistry method. The positrophilic electrons in (2,2)-difluoropropane molecule are found for the first time. The theoretical predictions show that the outermost 2s electrons of fluoride atoms play an important role in positron-electron annihilation process of (2,2)-difiuoropropane. In the present scheme, the correlation coefficient between the theoretical gamma-ray spectra and the experiments can be 99%. The present study gives an alternative annihilation model for positron-electron pair in larger molecules. Supported by the National Natural Science Foundation of China under Grant No. 11347011 and the Natural Science Foundation Project of Shandong Province under Grant No. ZR2011AM010 and 2014 Technology Innovation Fund of Ludong University under Grant Nos. 1d151007 and ld15l016

  12. Theory of triplet-triplet annihilation in optically detected magnetic resonance

    NASA Astrophysics Data System (ADS)

    Keevers, T. L.; McCamey, D. R.

    2016-01-01

    Triplet-triplet annihilation allows two low-energy photons to be upconverted into a single high-energy photon. By essentially engineering the solar spectrum, this allows solar cells to be made more efficient and even exceed the Shockley-Quiesser limit. Unfortunately, optimizing the reaction pathway is difficult, especially with limited access to the microscopic time scales and states involved in the process. Optical measurements can provide detailed information: triplet-triplet annihilation is intrinsically spin dependent and exhibits substantial magnetoluminescence in the presence of a static magnetic field. Pulsed optically detected magnetic resonance is especially suitable, since it combines high spin sensitivity with coherent manipulation. In this paper, we develop a time-domain theory of triplet-triplet annihilation for complexes with arbitrary spin-spin coupling. We identify unique "Rabi fingerprints" for each coupling regime and show that this can be used to characterize the microscopic Hamiltonian.

  13. Positron annihilation studies of Eu and Dy doped α'-Sr2SiO4

    NASA Astrophysics Data System (ADS)

    Gupta, S. K.; Sudarshan, K.; Sharma, S. K.; Pujari, P. K.; Natarajan, V.

    2015-06-01

    Sr2SiO4 is an important inorganic host for lanthanide doped white light emitting diodes (LEDs). Strontium silicate (Sr2SiO4) samples doped with 1.0 mol% of Eu3+ and Dy3+ content were prepared via sol-gel route and characterized by X-ray diffraction (XRD), Raman spectroscopy and positron annihilation spectroscopy (PAS). The concentration of the dopant ion and the temperature of annealing were optimized for maximum luminescence intensity. The positron annihilation lifetime and coincidence Doppler broadening (CDB) measurements indicated that the local environment around the positron annihilation site is different in Eu+3 doped and Dy+3 doped samples. The results could be explained based on the different local site occupancy of Eu+3 and Dy+3 in the matrix.

  14. Natural resonance extraction and annihilation filtering methods for radar target identification

    NASA Astrophysics Data System (ADS)

    Murphy, Timothy J.

    1990-09-01

    This thesis represents an initial attempt to demonstrate aspect independent target identification of complex radar targets using annihilation filters based on the natural resonances of the targets. The Cadzow-Solomon signal processing algorithm is tested to determine its suitability for the task of extracting the poles from complex targets to a degree of accuracy required for successful implementation of an annihilation filtering target identification system. This testing was conducted through the use of noise polluted synthetic data as well as measured transient scattering data from thin-wire and silver coated scale model aircraft targets. The testing revealed that the Cadzow-Solomon algorithm can return pole clusters at false pole locations when processing the scattered returns from complex targets. Properties of annihilation filters which may affect their ability to discriminate complex targets are examined.

  15. Revisiting the constraints on annihilating dark matter by the radio observational data of M31

    NASA Astrophysics Data System (ADS)

    Chan, Man Ho

    2016-07-01

    Recent gamma-ray observations and radio observations put strong constraints on the parameters of dark matter annihilation. In this article, we derive new constraints for six standard model annihilation channels by using the recent radio data of the M31 galaxy. The new constraints are generally tighter than the constraints obtained from 6 years of Fermi Large Area Telescope gamma-ray observations of the Milky Way dwarf spheroidal satellite galaxies. The conservative lower limits of dark matter mass annihilating via b b ¯, μ+μ- and τ+τ- channels are 90, 90 and 80 GeV respectively with the canonical thermal relic cross section and the Burkert profile being the dark matter density profile. Hence, our results do not favor the most popular models of the dark matter interpretation of the Milky Way GeV gamma-ray excess.

  16. Novel System for Potential Nondestructive Material Inspection Using Positron Annihilation Lifetime Spectroscopy

    NASA Astrophysics Data System (ADS)

    Yamawaki, Masato; Kobayashi, Yoshinori; Hattori, Kanehisa; Watanabe, Yoshihiro

    2011-08-01

    A new positron annihilation lifetime spectrometer consisting of a start γ-ray detector, a stop γ-ray detector, a digital oscilloscope, and a positron detector, which is a plastic scintillator coupled to a photomultiplier tube, is described. A 22Na source is placed between the positron detector and a sample to be studied. γ-ray signals related to positrons annihilating in the positron detector are rejected by anti-coincidence processing. Comparison of the positron lifetime spectrum of a steel strip collected with the new system with that collected with a conventional system using two specimens sandwiching the 22Na source shows that accurate positron lifetime measurements are possible with the new system. The new system does not require cutting of the samples and is potentially applicable to truly nondestructive onsite inspection of various materials such as those used in nuclear power plants, aircraft and cars, etc., by positron annihilation lifetime spectroscopy (PALS).

  17. Neutrino flavor ratios as diagnostic of solar WIMP annihilation

    NASA Astrophysics Data System (ADS)

    Lehnert, Ralf; Weiler, Thomas J.

    2008-06-01

    We consider the neutrino (and antineutrino) flavors arriving at the Earth for neutrinos produced in the annihilation of weakly interacting massive particles (WIMPs) in the sun’s core. Solar-matter effects on the flavor propagation of the resulting ≳GeV neutrinos are studied analytically within a density-matrix formalism. Matter effects, including mass-state level crossings, influence the flavor fluxes considerably. The exposition herein is somewhat pedagogical, in that it starts with adiabatic evolution of single flavors from the sun’s center, with θ13 set to zero, and progresses to fully realistic processing of the flavor ratios expected in WIMP decay, from the sun’s core to the Earth. In the fully realistic calculation, nonadiabatic level crossing is included, as are possible nonzero values for θ13 and the CP-violating phase δ. Because of resonance enhancement in matter, nonzero values of θ13 even smaller than a degree can noticeably affect flavor propagation. Both normal and inverted neutrino-mass hierarchies are considered. Our main conclusion is that measuring flavor ratios (in addition to energy spectra) of ≳GeV solar neutrinos can provide discrimination between WIMP models. In particular, we demonstrate the flavor differences at the Earth for neutrinos from the two main classes of WIMP final states, namely W+W- and 95%bb¯+5%τ+τ-. Conversely, if WIMP properties were to be learned from production in future accelerators, then the flavor ratios of ≳GeV solar neutrinos might be useful for inferring θ13 and the mass hierarchy. From the full calculations, we find (and prove) some general features: a flavor-democratic flux produced at the sun’s core arrives at the Earth still flavor democratic; for maximal θ32 but arbitrary θ21 and θ13, the replacement δ→π-δ leaves the νe flavor spectra unaltered but interchanges νμ and ντ spectra at the Earth; and, only for neutrinos in the inverted hierarchy and antineutrinos in the normal

  18. Fermi-LAT constraints on dark matter annihilation cross section from observations of the Fornax cluster

    SciTech Connect

    Ando, Shin'ichiro; Nagai, Daisuke E-mail: daisuke.nagai@yale.edu

    2012-07-01

    We analyze 2.8-yr data of 1–100 GeV photons for clusters of galaxies, collected with the Large Area Telescope onboard the Fermi satellite. By analyzing 49 nearby massive clusters located at high Galactic latitudes, we find no excess gamma-ray emission towards directions of the galaxy clusters. Using flux upper limits, we show that the Fornax cluster provides the most stringent constraints on the dark matter annihilation cross section. Stacking a large sample of nearby clusters does not help improve the limit for most dark matter models. This suggests that a detailed modeling of the Fornax cluster is important for setting robust limits on the dark matter annihilation cross section based on clusters. We therefore perform the detailed mass modeling and predict the expected dark matter annihilation signals from the Fornax cluster, by taking into account effects of dark matter contraction and substructures. By modeling the mass distribution of baryons (stars and gas) around a central bright elliptical galaxy, NGC 1399, and using a modified contraction model motivated by numerical simulations, we show that the dark matter contraction boosts the annihilation signatures by a factor of 4. For dark matter masses around 10 GeV, the upper limit obtained on the annihilation cross section times relative velocity is (σν)∼<(2–3) × 10{sup −25} cm{sup 3} s{sup −1}, which is within a factor of 10 from the value required to explain the dark matter relic density. This effect is more robust than the annihilation boost due to substructure, and it is more important unless the mass of the smallest subhalos is much smaller than that of the Sun.

  19. CONSTRAINTS ON DARK MATTER ANNIHILATION IN CLUSTERS OF GALAXIES FROM DIFFUSE RADIO EMISSION

    SciTech Connect

    Storm, Emma; Jeltema, Tesla E.; Profumo, Stefano; Rudnick, Lawrence

    2013-05-10

    Annihilation of dark matter can result in the production of stable Standard Model particles including electrons and positrons that, in the presence of magnetic fields, lose energy via synchrotron radiation, observable as radio emission. Galaxy clusters are excellent targets to search for or to constrain the rate of dark matter annihilation, as they are both massive and dark matter dominated. In this study, we place limits on dark matter annihilation in a sample of nearby clusters using upper limits on the diffuse radio emission, low levels of observed diffuse emission, or detections of radio mini-halos. We find that the strongest limits on the annihilation cross section are better than limits derived from the non-detection of clusters in the gamma-ray band by a factor of {approx}3 or more when the same annihilation channel and substructure model, but different best-case clusters, are compared. The limits on the cross section depend on the assumed amount of substructure, varying by as much as two orders of magnitude for increasingly optimistic substructure models as compared to a smooth Navarro-Frenk-White profile. In our most optimistic case, using the results of the Phoenix Project, we find that the derived limits reach below the thermal relic cross section of 3 Multiplication-Sign 10{sup -26} cm{sup 3} s{sup -1} for dark matter masses as large as 400 GeV, for the b b-bar annihilation channel. We discuss uncertainties due to the limited available data on the magnetic field structure of individual clusters. We also report the discovery of diffuse radio emission from the central 30-40 kpc regions of the groups M49 and NGC 4636.

  20. Gamma-Ray background spectrum and annihilation rate in the baryon-symmetric big-bang cosmology

    NASA Technical Reports Server (NTRS)

    Puget, J. L.

    1973-01-01

    An attempt was made to extract experimental data on baryon symmetry by observing annihilation products. Specifically, gamma rays and neutrons with long mean free paths were analyzed. Data cover absorption cross sections and radiation background of the 0.511 MeV gamma rays from positron annihilations and the 70 MeV gamma rays from neutral pion decay.

  1. Positron annihilation lifetime characterization of oxygen ion irradiated rutile TiO2

    NASA Astrophysics Data System (ADS)

    Luitel, Homnath; Sarkar, A.; Chakrabarti, Mahuya; Chattopadhyay, S.; Asokan, K.; Sanyal, D.

    2016-07-01

    Ferromagnetic ordering at room temperature has been induced in rutile phase of TiO2 polycrystalline sample by O ion irradiation. 96 MeV O ion induced defects in rutile TiO2 sample has been characterized by positron annihilation spectroscopic techniques. Positron annihilation results indicate the formation of cation vacancy (VTi, Ti vacancy) in these irradiated TiO2 samples. Ab initio density functional theoretical calculations indicate that in TiO2 magnetic moment can be induced either by creating Ti or O vacancies.

  2. Positron-annihilation 2D-ACAR studies of disordered and defected alloys

    SciTech Connect

    Bansil, A.; Prasad, R.; Smedskjaer, L.C.; Benedek, R.; Mijnarends, P.E.

    1987-09-01

    Theoretical and experimental progess in connection with 2D-ACAR positron annihilation studies of ordered, disordered, and defected alloys is discussed. We present, in particular, some of the recent developments concerning the electronic structure of disordered alloys, and the work in the area of annihilation from positrons trapped at vacancy-type defects in metals and alloys. The electronic structure and properties of a number of compounds are also discussed briefly; we comment specifically on high T/sub c/ ceramic superconductors, Heusler alloys, and transition-metal aluminides. 58 refs., 116 figs.

  3. Gamma-rays from Dark Matter Annihilation in the Central Region of the Galaxy

    SciTech Connect

    Serpico, Pasquale Dario; Hooper, Dan; /Fermilab /Chicago U., Astron. Astrophys. Ctr.

    2009-02-01

    In this article, we review the prospects for the FERMI satellite (formerly known as GLAST) to detect gamma-rays from dark matter annihilations in the Central Region of the Milky Way, in light of the recent observations and discoveries of Imaging Atmospheric Cherenkov Telescopes. While the existence of significant astrophysical backgrounds in this part of the sky limits FERMI's discovery potential to some degree, this can be mitigated by exploiting the peculiar energy spectrum and angular distribution of the dark matter annihilation signal relative to those of astrophysical backgrounds.

  4. Spectra, fluxes, and observability of gamma rays from dark matter annihilation in the Galaxy

    NASA Technical Reports Server (NTRS)

    Stecker, F. W.; Tylka, A. J.

    1989-01-01

    Details of the physics of gamma-ray production by the annihilation of dark matter particles in the Galaxy are presented. Improved gamma-ray spectra and fluxes are calculated and compared with present observational data on cosmic gamma-ray fluxes at high Galactic latitudes. A comparison with the gamma-ray flux from cosmic-ray interactions is made. It is found that gamma-rays from dark matter annihilation are most potentially observable from patches of the sky at high Galactic latitudes in directions having an unusually low total column density of gas and from a dark matter core at the Galactic center.

  5. Jahn-Teller distortion of neutral divacancy in Si studied by positron annihilation spectroscopy

    NASA Astrophysics Data System (ADS)

    Nagai, Y.; Inoue, K.; Tang, Z.; Yonenaga, I.; Chiba, T.; Saito, M.; Hasegawa, M.

    2003-12-01

    Jahn-Teller (JT) distortion of the diamagnetic neutral divacancy (V20) in Si is studied by positron annihilation spectroscopy. Based on the anisotropy of electron momentum distribution around the divacancies obtained by two-dimensional angular correlation of positron annihilation radiation (2D-ACAR) technique, the preferred alignment of the divacancy in a specimen by compressing uniaxial stress along the [0 1 1] axis is detected. The direction of the alignment evidences the pairing JT distortion rather than the resonant bonding distortion, which is similar to the distortion in the singly negative divacancy (V2-).

  6. Temperature Dependence of Positron Annihilation in beta-Cyclodextrin and beta-Cyclodextrin Complexes

    NASA Astrophysics Data System (ADS)

    Hu, Y.; Hsu Hadley, F. H., Jr.; Trinh, T.

    1996-11-01

    The effects of temperature on positron annihilation in beta-cyclodextrin and beta-cyclodextrin complexed with benzyl salicylate, benzyl acetate, ethyl salicylate, geraniol, linalool and nerol were studied. Samples were prepared by slurry, air-dried and freeze-dried methods. Lifetime spectra were measured as a function of temperature for each sample. Comparison of the annihilation rate and intensity of the longer-lived component showed that positronium formation was affected by guest molecules, preparation methods and temperature variations. Results can be used to explain beta-cyclodextrin complex formation with different guest molecules.

  7. Asymmetries involving dihadron fragmentation functions: from DIS to e+ e- annihilation

    SciTech Connect

    Bacchetta, Alessandro; Radici, M.; Mukherjee, Asmita; Ceccopieri, Federico

    2009-01-01

    Using a model calculation of dihadron fragmentation functions, we fit the spin asymmetry recently extracted by HERMES for the semi-inclusive pion pair production in deep-inelastic scattering on a transversely polarized proton target. By evolving the obtained dihadron fragmentation functions, we make predictions for the correlation of the angular distributions of two pion pairs produced in electron-positron annihilations at BELLE kinematics. Our study shows that the combination of two-hadron inclusive deep-inelastic scattering and electron-positron annihilation measurements can provide a valid alternative to Collins effect for the extraction of the quark transversity distribution in the nucleon.

  8. Jet algorithms in electron-positron annihilation: perturbative higher order predictions

    NASA Astrophysics Data System (ADS)

    Weinzierl, Stefan

    2011-02-01

    This article gives results on several jet algorithms in electron-positron annihilation: Considered are the exclusive sequential recombination algorithms Durham, Geneva, Jade-E0 and Cambridge, which are typically used in electron-positron annihilation. In addition also inclusive jet algorithms are studied. Results are provided for the inclusive sequential recombination algorithms Durham, Aachen and anti- k t , as well as the infrared-safe cone algorithm SISCone. The results are obtained in perturbative QCD and are N3LO for the two-jet rates, NNLO for the three-jet rates, NLO for the four-jet rates and LO for the five-jet rates.

  9. Distinguishing neutrino mass hierarchies using dark matter annihilation signals at IceCube

    SciTech Connect

    Allahverdi, Rouzbeh; Dutta, Bhaskar; Ghosh, Dilip Kumar; Knockel, Bradley; Saha, Ipsita

    2015-12-01

    We explore the possibility of distinguishing neutrino mass hierarchies through the neutrino signal from dark matter annihilation at neutrino telescopes. We consider a simple extension of the standard model where the neutrino masses and mixing angles are obtained via the type-II seesaw mechanism as an explicit example. We show that future extensions of IceCube neutrino telescope may detect the neutrino signal from DM annihilation at the Galactic Center and inside the Sun, and differentiate between the normal and inverted mass hierarchies, in this model.

  10. Asymmetric 511 keV Positron Annihilation Line Emission from the Inner Galactic Disk

    NASA Technical Reports Server (NTRS)

    Skinner, Gerry; Weidenspointner, Georg; Jean, Pierre; Knodlseder, Jurgen; Ballmoos, Perer von; Bignami, Giovanni; Diehl, Roland; Strong, Andrew; Cordier, Bertrand; Schanne, Stephane; Winkler, Christoph

    2008-01-01

    A recently reported asymmetry in the 511 keV gamma-ray line emission from the inner galactic disk is unexpected and mimics an equally unexpected one in the distribution of LMXBs seen at hard X-ray energies. A possible conclusion is that LMXBs are an important source of the positrons whose annihilation gives rise to the line. We will discuss these results, their statistical significance and that of any link between the two. The implication of any association between LMXBs and positrons for the strong annihilation radiation from the galactic bulge will be reviewed.

  11. Probing dark matter annihilation to primary neutrinos with IceCube

    SciTech Connect

    Allahverdi, Rouzbeh

    2014-06-24

    We investigate the prospects for discovery and discrimination of dark matter annihilation into primary neutrinos from other final states at IceCube/DeepCore. By taking detector considerations into account, we perform a fit to obtain sensitivity limits for the primary neutrino final states from annihilation of dark matter particles gravitationally captured inside the Sun. We show that for dark matter in the 50 GeV–1 TeV mass range, primary neutrinos can be distinguished from other final states at a statistically significant level with multi-year data from IceCube/DeepCore.

  12. Is there a dark matter signal in the galactic positron annihilation radiation?

    PubMed

    Lingenfelter, R E; Higdon, J C; Rothschild, R E

    2009-07-17

    Assuming Galactic positrons do not go far before annihilating, a difference between the observed 511 keV annihilation flux distribution and that of positron production, expected from beta+ decay in Galactic iron nucleosynthesis, was evoked as evidence of a new source and signal of dark matter. We show, however, that the dark matter sources cannot account for the observed positronium fraction without extensive propagation. Yet with such propagation, standard nucleosynthetic sources can fully account for the spatial differences and positronium fraction, leaving no new signal for dark matter to explain. PMID:19659265

  13. Decaying vs. annihilating dark matter in light of a tentative gamma-ray line

    SciTech Connect

    Buchmüller, Wilfried; Garny, Mathias E-mail: mathias.garny@desy.de

    2012-08-01

    Recently reported tentative evidence for a gamma-ray line in the Fermi-LAT data is of great potential interest for identifying the nature of dark matter. We compare the implications for decaying and annihilating dark matter taking the constraints from continuum gamma-rays, antiproton flux and morphology of the excess into account. We find that higgsino and wino dark matter are excluded, also for nonthermal production. Generically, the continuum gamma-ray flux severely constrains annihilating dark matter. Consistency of decaying dark matter with the spatial distribution of the Fermi-LAT excess would require an enhancement of the dark matter density near the Galactic center.

  14. The cosmic-ray antiproton spectrum from dark matter annihilation and its astrophysical implications - A new look

    NASA Technical Reports Server (NTRS)

    Stecker, F. W.; Tylka, A. J.

    1989-01-01

    The spectrum of antiprotons from dark matter annihilation are calculated using the Lund Monte Carlo program, and simple analytic expressions for the spectrum and low-energy antiproton/proton ratio are derived. Comparing the results with recent upper limits on low energy antiprotons, it is concluded that the reported 4-13 GeV antiproton flux cannot be accounted for by dark matter annihilation. The new upper limits do not provide useful constraints on dark matter particles. They restrict the annihilation rate and imply that annihilation gamma ray and e(+) fluxes would be far below the fluxes produced by cosmic-ray collisions. It may be possible to look for a dark matter halo annihilation signal at antiprotons energies below 0.5 GeV, where the flux from cosmic-ray collisions is expected to be negligible.

  15. Review of Heavy Lepton Production in e{sup +}e{sup -} Annihilation

    DOE R&D Accomplishments Database

    Perl, M. L.

    1977-10-01

    The existing data on e{sup +-}..mu..{sup -+}, e{sup +-}x{sup -+}, ..mu..{sup +-}x{sup -+}, and related events produced in e{sup +}e{sup -} annihilation are reviewed. All data are consistent with the existence of a new charged lepton, tau{sup +-}, of mass 1.9 +- .1 GeV/c{sup 2}.

  16. A novel way of constraining WIMPs annihilations in the Sun: MeV neutrinos

    SciTech Connect

    Bernal, Nicolás; Martín-Albo, Justo; Palomares-Ruiz, Sergio E-mail: justo.martin-albo@ific.uv.es

    2013-08-01

    Annihilation of dark matter particles accumulated in the Sun would produce a flux of high-energy neutrinos whose prospects of detection in neutrino telescopes and detectors have been extensively discussed in the literature. However, for annihilations into Standard Model particles, there would also be a flux of neutrinos in the MeV range from the decays at rest of muons and positively charged pions. These low-energy neutrinos have never been considered before and they open the possibility to also constrain dark matter annihilation in the Sun into e{sup +}e{sup −}, μ{sup +}μ{sup −} or light quarks. Here we perform a detailed analysis using the recent Super-Kamiokande data in the few tens of MeV range to set limits on the WIMP-nucleon scattering cross section for different annihilation channels and computing the evaporation rate of WIMPs from the Sun for all values of the scattering cross section in a consistent way.

  17. Optimized perturbation theory applied to jet cross sections in e + e - annihilation

    NASA Astrophysics Data System (ADS)

    Kramer, G.; Lampe, B.

    1988-03-01

    The optimized perturbation theory proposed by Stevenson to deal with coupling constant scheme dependence is applied to the calculation of π tot and jet multiplicities in e + e - annihilation. The results are compared with those of simple perturbation theory and with recent experimental cluster multiplicities.

  18. Experimental results on QCD (Quantum Chromodynamics) from e/sup +/e/sup -/ annihilation

    SciTech Connect

    de Boer, W.

    1987-09-01

    A review is given on QCD results from studying e/sup +/e/sup -/ annihilation with the PEP and PETRA storage rings with special emphasis on jet physics and the determination of the strong coupling constant ..cap alpha../sub s/. 92 refs., 28 figs., 3 tabs.

  19. Positron annihilation process in Ni/sub c/Cu/sub 1-c/ alloys

    SciTech Connect

    Szotek, Z.; Gyorffy, B.L.; Stocks, G.M.; Temmerman, W.M.

    1982-01-01

    New, accurate, calculations of the electron momentum distribution function for the Cu/sub 60/Ni/sub 40/ random solid solution are presented and the role played by the positron wavefunction in determining the Angular Correlation of the Annihilation Radiation (ACAR) is discussed in quantitative terms.

  20. Gamma-ray lines and one-loop continuum from s-channel dark matter annihilations

    NASA Astrophysics Data System (ADS)

    Jackson, C. B.; Servant, Géraldine; Shaughnessy, Gabe; Tait, Tim M. P.; Taoso, Marco

    2013-07-01

    The era of indirect detection searches for dark matter has begun, with the sensitivities of gamma-ray detectors now approaching the parameter space relevant for weakly interacting massive particles. In particular, gamma ray lines would be smoking gun signatures of dark matter annihilation, although they are typically suppressed compared to the continuum. In this paper, we pay particular attention to the 1-loop continuum generated together with the gamma-ray lines and investigate under which conditions a dark matter model can naturally lead to a line signal that is relatively enhanced. We study generic classes of models in which DM is a fermion that annihilates through an s-channel mediator which is either a vector or scalar and identify the coupling and mass conditions under which large line signals occur. We focus on the ``forbidden channel mechanism" advocated a few years ago in the ``Higgs in space" scenario for which tree level annihilation is kinematically forbidden today. Detailed calculations of all 1-loop annihilation channels are provided. We single out very simple models with a large line over continuum ratio and present general predictions for a large range of WIMP masses that are relevant not only for Fermi and Hess II but also for the next generation of telescopes such as CTA and Gamma-400. Constraints from the relic abundance, direct detection and collider bounds are also discussed.

  1. Relic density and CMB constraints on dark matter annihilation with Sommerfeld enhancement

    SciTech Connect

    Zavala, Jesus; White, Simon D. M.; Vogelsberger, Mark

    2010-04-15

    We calculate how the relic density of dark matter particles is altered when their annihilation is enhanced by the Sommerfeld mechanism due to a Yukawa interaction between the annihilating particles. Maintaining a dark matter abundance consistent with current observational bounds requires the normalization of the s-wave annihilation cross section to be decreased compared to a model without enhancement. The level of suppression depends on the specific parameters of the particle model, with the kinetic decoupling temperature having the most effect. We find that the cross section can be reduced by as much as an order of magnitude for extreme cases. We also compute the {mu}-type distortion of the CMB energy spectrum caused by energy injection from such Sommerfeld-enhanced annihilation. Our results indicate that in the vicinity of resonances, associated with bound states, distortions can be large enough to be excluded by the upper limit |{mu}|{<=}9.0x10{sup -5} found by the FIRAS (Far Infrared Absolute Spectrophotometer) instrument on the COBE (Cosmic Background Explorer) satellite.

  2. The study of synthetic food dyes by positron annihilation lifetime spectroscopy.

    NASA Astrophysics Data System (ADS)

    Pivtsaev, A. A.; Razov, V. I.

    2015-06-01

    By method of positron annihilation lifetime spectroscopy (PALS), substances are food dyes were studied: E-102 (Tartrazine), E-124 (Ponso 4R), E 132 (Indigo carmine), E-133 (Brilliant Blue), E-151 (Black Shiny). They are examined for the presence of carcinogenic properties. The difference between dyes having explicit carcinogenic properties and mutagenic properties (non-explicit carcinogens) is established.

  3. 'Void existence' as against 'annihilation existence': Differentiating two qualities in primitive mental states.

    PubMed

    Valdarsky, Irit Hameiri

    2015-10-01

    This paper attempts to distil out a particular quality of psychic (non)existence, which I call here 'void existence', from the quality predominantly explored in the psychoanalytic discourse on primitive mental states, which I call 'annihilation existence'. Achieving this phenomenological differentiation may make it easier to identify and work through extreme states in the analytic situation, when the patient is under the dominance of 'void existence'. I suggest that it is, as it were, a one-dimensional existence, in an infinite contour-less void, lacking any substantial internal object, lacking any substantial sense of psychic and/or somatic occurrences, and lacking any live representation of this very state of being. Hence, it lacks distress and anxiety, as well as calmness and peace. One might say that it is the inorganic within the organic; a quality of non-alive-ness within life. 'Annihilation existence' is existence in a two- or three-dimensional hollowed world, with flat and/or partial representations of self and object, which attracts acute distress and annihilation anxiety. It is a sort of existence on the brink of non-life, on the brink of the void; where a sense of catastrophic danger is brought on by the never-ending potentiality of the annihilation's realization. Both these psychic qualities can be encapsulated within neurotic and personality disorders, and the dominance of each can serve as defence against the dominance of the other. The theoretical discussion is supported by excerpts from an analysis. PMID:26298559

  4. Quantum efficiency harmonic analysis of exciton annihilation in organic light emitting diodes

    SciTech Connect

    Price, J. S.; Giebink, N. C.

    2015-06-29

    Various exciton annihilation processes are known to impact the efficiency roll-off of organic light emitting diodes (OLEDs); however, isolating and quantifying their contribution in the presence of other factors such as changing charge balance continue to be a challenge for routine device characterization. Here, we analyze OLED electroluminescence resulting from a sinusoidal dither superimposed on the device bias and show that nonlinearity between recombination current and light output arising from annihilation mixes the quantum efficiency measured at different dither harmonics in a manner that depends uniquely on the type and magnitude of the annihilation process. We derive a series of analytical relations involving the DC and first harmonic external quantum efficiency that enable annihilation rates to be quantified through linear regression independent of changing charge balance and evaluate them for prototypical fluorescent and phosphorescent OLEDs based on the emitters 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran and platinum octaethylporphyrin, respectively. We go on to show that, in most cases, it is sufficient to calculate the needed quantum efficiency harmonics directly from derivatives of the DC light versus current curve, thus enabling this analysis to be conducted solely from standard light-current-voltage measurement data.

  5. Particle creation and annihilation at interior boundaries: one-dimensional models

    NASA Astrophysics Data System (ADS)

    Keppeler, Stefan; Sieber, Martin

    2016-03-01

    We describe creation and annihilation of particles at external sources in one spatial dimension in terms of interior-boundary conditions (IBCs). We derive explicit solutions for spectra, (generalised) eigenfunctions, as well as Green functions, spectral determinants, and integrated spectral densities. Moreover, we introduce a quantum graph version of IBC-Hamiltonians.

  6. Prospects of antideuteron detection from dark matter annihilations or decays at AMS-02 and GAPS

    SciTech Connect

    Ibarra, Alejandro; Wild, Sebastian E-mail: sebastian.wild@ph.tum.de

    2013-02-01

    The search for cosmic antideuterons has been proposed as a promising method to indirectly detect dark matter, due to the very small background flux from spallations expected at the energies relevant to experiments. The antideuteron flux from dark matter annihilations or decays is, however, severely constrained by the non-observation of an excess in the antiproton-to-proton fraction measured by PAMELA. In this paper we calculate, for representative dark matter annihilation and decay channels, upper limits on the number of antideuteron events at AMS-02 and GAPS from requiring that the associated antiproton flux is in agreement with the PAMELA data. To this end, we first analyze in detail the formation of antideuterons in the coalescence model using an event-by-event Monte Carlo simulation and using data from various high energy experiments. We find that the resulting coalescence momentum shows a dependence on the underlying process and on the center of mass energy involved. Then, we calculate, using a diffusion model, the flux of antideuterons at the Earth from dark matter annihilations or decays. Our results indicate that, despite the various sources of uncertainty, the observation of an antideuteron flux at AMS-02 or GAPS from dark matter annihilations or decays will be challenging.

  7. Dark matter annihilations into two light fermions and one gauge boson: general analysis and antiproton constraints

    SciTech Connect

    Garny, Mathias; Ibarra, Alejandro; Vogl, Stefan E-mail: alejandro.ibarra@ph.tum.de

    2012-04-01

    We study in this paper the scenario where the dark matter is constituted by Majorana particles which couple to a light Standard Model fermion and an extra scalar via a Yukawa coupling. In this scenario, the annihilation rate into the light fermions with the mediation of the scalar particle is strongly suppressed by the mass of the fermion. Nevertheless, the helicity suppression is lifted by the associated emission of a gauge boson, yielding annihilation rates which could be large enough to allow the indirect detection of the dark matter particles. We perform a general analysis of this scenario, calculating the annihilation cross section of the processes χχ→f f-bar V when the dark matter particle is a SU(2){sub L} singlet or doublet, f is a lepton or a quark, and V is a photon, a weak gauge boson or a gluon. We point out that the annihilation rate is particularly enhanced when the dark matter particle is degenerate in mass to the intermediate scalar particle, which is a scenario barely constrained by collider searches of exotic charged or colored particles. Lastly, we derive upper limits on the relevant cross sections from the non-observation of an excess in the cosmic antiproton-to-proton ratio measured by PAMELA.

  8. Power spectrum tomography of dark matter annihilation with local galaxy distribution

    SciTech Connect

    Ando, Shin'ichiro

    2014-10-01

    Cross-correlating the gamma-ray background with local galaxy catalogs potentially gives stringent constraints on dark matter annihilation. We provide updated theoretical estimates of sensitivities to the annihilation cross section from gamma-ray data with Fermi telescope and 2MASS galaxy catalogs, by elaborating the galaxy power spectrum and astrophysical backgrounds, and adopting the Markov-Chain Monte Carlo simulations. In particular, we show that taking tomographic approach by dividing the galaxy catalogs into more than one redshift slice will improve the sensitivity by a factor of a few to several. If dark matter halos contain lots of bright substructures, yielding a large annihilation boost (e.g., a factor of ∼100 for galaxy-size halos), then one may be able to probe the canonical annihilation cross section for thermal production mechanism up to masses of ∼700 GeV. Even with modest substructure boost (e.g., a factor of ∼10 for galaxy-size halos), on the other hand, the sensitivities could still reach a factor of three larger than the canonical cross section for dark matter masses of tens to a few hundreds of GeV.

  9. Complete particle-pair annihilation as a dynamical signature of the spectral singularity

    SciTech Connect

    Li, G.R.; Zhang, X.Z.; Song, Z.

    2014-10-15

    Motivated by the physical relevance of a spectral singularity of interacting many-particle system, we explore the dynamics of two bosons as well as fermions in one-dimensional system with imaginary delta interaction strength. Based on the exact solution, it shows that the two-particle collision leads to amplitude-reduction of the wave function. For fermion pair, the amplitude-reduction depends on the spin configuration of two particles. In both cases, the residual amplitude can vanish when the relative group velocity of two single-particle Gaussian wave packets with equal width reaches the magnitude of the interaction strength, exhibiting complete particle-pair annihilation at the spectral singularity. - Highlights: • We investigate the physical relevance of a spectral singularity. • The two-particle collision leads to amplitude-reduction of the wave function. • There is a singularity spectrum which leads to complete particle-pair annihilation. • Complete particle-pair annihilation can only occur for two distinguishable bosons and singlet fermions. • Pair annihilation provides a detection method of the spectral singularity in the experiment.

  10. Searching for Dark Matter Annihilation in the Smith High-Velocity Cloud

    NASA Technical Reports Server (NTRS)

    Drlica-Wagner, Alex; Gomez-Vargas, German A.; Hewitt, John W.; Linden, Tim; Tibaldo, Luigi

    2014-01-01

    Recent observations suggest that some high-velocity clouds may be confined by massive dark matter halos. In particular, the proximity and proposed dark matter content of the Smith Cloud make it a tempting target for the indirect detection of dark matter annihilation. We argue that the Smith Cloud may be a better target than some Milky Way dwarf spheroidal satellite galaxies and use gamma-ray observations from the Fermi Large Area Telescope to search for a dark matter annihilation signal. No significant gamma-ray excess is found coincident with the Smith Cloud, and we set strong limits on the dark matter annihilation cross section assuming a spatially extended dark matter profile consistent with dynamical modeling of the Smith Cloud. Notably, these limits exclude the canonical thermal relic cross section (approximately 3 x 10 (sup -26) cubic centimeters per second) for dark matter masses less than or approximately 30 gigaelectronvolts annihilating via the B/B- bar oscillation or tau/antitau channels for certain assumptions of the dark matter density profile; however, uncertainties in the dark matter content of the Smith Cloud may significantly weaken these constraints.

  11. Annihilation and Reanimation of a Tornado in the Improved Tornado Tube

    NASA Astrophysics Data System (ADS)

    Bednarek, Stanisław

    2016-02-01

    Some new experiments using an improved version of the "tornado tube" are described here. The improved tornado tube consists of two plastic transparent bottles whose openings are connected with a ball valve, available at most hardware stores. After being filled with fluid and inverting, this tube allows demonstration of the generation, annihilation, and reanimation of vortices, or tornados.

  12. Evaporated particles in the annihilation of K{sup −} mesons in a nuclear photoemulsion

    SciTech Connect

    Dubinina, V. V.; Egorenkova, N. P.; Pozharova, E. A.; Smirnitsky, V. A.

    2015-01-15

    The emission of light nuclei (p, d, t) in the annihilation of K{sup −} mesons stopped in a nuclear photoemulsion is measured. The deuteron-to-proton yield ratio is found to be d/p = 0.32 ± 0.05. The observed excess of evaporated protons is due to intranuclear-nucleon correlations.

  13. Measurement of {phi}- and {omega}-meson production in antiproton annihilation at rest on deuterium

    SciTech Connect

    Ableev, V.G.; Denisov, O.Yu.; Gorchakov, O.E.

    1994-10-01

    The branching ratios of {phi}{pi}{sup {minus}} and {omega}{pi}{sup {minus}} final states were measured for the antiproton annihilation at rest on gaseous deuterium. Significant deviation from the OZI-rule prediction was found from the value of the {phi}/{omega} ratio. 25 refs., 4 figs., 1 tab.

  14. PROSPECTS FOR PENTAQUARK SEARCHES IN E+D- ANNIHILATIONS AND VV COLLISIONS.

    SciTech Connect

    ARMSTRONG,S.; MELLADO,B.; WU,S.L.

    2004-06-28

    Recent strong experimental evidence of a narrow exotic S = +1 baryon resonance, {Theta}{sup +}, suggests the existence of other exotic baryons. We discuss the prospects of confirming earlier experimental evidence of {Theta}{sup +} and the observation of additional hypothetical exotic baryons in e{sup +}e{sup -} annihilations and {gamma}{gamma} collisions at LEP and B Factories.

  15. Dense DM clumps seeded by cosmic string loops and DM annihilation

    SciTech Connect

    Berezinsky, V.S.; Dokuchaev, V.I.; Eroshenko, Yu.N. E-mail: dokuchaev@inr.ac.ru

    2011-12-01

    We develop a model of production of the very dense clumps of DM in RD epoch due to the accretion of DM on the loops of cosmic strings as the seeds. At some time the loops disappear, for example due to the gravitational radiation, and the remaining dense clumps produce the enhancement of the annihilation signal. We take into account the velocity distribution of the strings, and consider the two extreme regimes of DM annihilation: fast decay and continuous evaporation. The produced annihilation flux of gamma radiation is detectable, and for some parameters of DM particles and the strings can exceed the extragalactic flux of the gamma-radiation observed by Fermi. For the fixed parameters of DM particles (e.g. neutralino with fixed masses and cross-section of annihilation) one can obtain the limits on the basic string parameter, tension μ, which is stronger than (more general) limits obtained from WMAP observations, cosmological nucleosynthesis and gravitational lensing. In particular for the neutralino with 100 GeV mass we exclude the interval 5 × 10{sup −10} < Gμ/c{sup 2} < 5.1 × 10{sup −9}.

  16. Gamma-ray lines and one-loop continuum from s-channel dark matter annihilations

    SciTech Connect

    Jackson, C.B.; Servant, Géraldine; Shaughnessy, Gabe; Tait, Tim M.P.; Taoso, Marco E-mail: chris@uta.edu E-mail: ttait@uci.edu

    2013-07-01

    The era of indirect detection searches for dark matter has begun, with the sensitivities of gamma-ray detectors now approaching the parameter space relevant for weakly interacting massive particles. In particular, gamma ray lines would be smoking gun signatures of dark matter annihilation, although they are typically suppressed compared to the continuum. In this paper, we pay particular attention to the 1-loop continuum generated together with the gamma-ray lines and investigate under which conditions a dark matter model can naturally lead to a line signal that is relatively enhanced. We study generic classes of models in which DM is a fermion that annihilates through an s-channel mediator which is either a vector or scalar and identify the coupling and mass conditions under which large line signals occur. We focus on the ''forbidden channel mechanism'' advocated a few years ago in the ''Higgs in space'' scenario for which tree level annihilation is kinematically forbidden today. Detailed calculations of all 1-loop annihilation channels are provided. We single out very simple models with a large line over continuum ratio and present general predictions for a large range of WIMP masses that are relevant not only for Fermi and Hess II but also for the next generation of telescopes such as CTA and Gamma-400. Constraints from the relic abundance, direct detection and collider bounds are also discussed.

  17. Searching for dark matter annihilation in the Smith high-velocity cloud

    SciTech Connect

    Drlica-Wagner, Alex; Gómez-Vargas, Germán A.; Hewitt, John W.; Linden, Tim; Tibaldo, Luigi

    2014-07-20

    Recent observations suggest that some high-velocity clouds may be confined by massive dark matter halos. In particular, the proximity and proposed dark matter content of the Smith Cloud make it a tempting target for the indirect detection of dark matter annihilation. We argue that the Smith Cloud may be a better target than some Milky Way dwarf spheroidal satellite galaxies and use γ-ray observations from the Fermi Large Area Telescope to search for a dark matter annihilation signal. No significant γ-ray excess is found coincident with the Smith Cloud, and we set strong limits on the dark matter annihilation cross section assuming a spatially extended dark matter profile consistent with dynamical modeling of the Smith Cloud. Notably, these limits exclude the canonical thermal relic cross section (∼ 3 × 10{sup –26} cm{sup 3} s{sup –1}) for dark matter masses ≲ 30 GeV annihilating via the b b-bar or τ{sup +}τ{sup –} channels for certain assumptions of the dark matter density profile; however, uncertainties in the dark matter content of the Smith Cloud may significantly weaken these constraints.

  18. A general strategy for biocompatible, high-effective upconversion nanocapsules based on triplet-triplet annihilation.

    PubMed

    Liu, Qian; Yin, Baoru; Yang, Tianshe; Yang, Yongchao; Shen, Zhen; Yao, Ping; Li, Fuyou

    2013-04-01

    A general strategy for constructing high-effective upconversion nanocapsules based on triplet-triplet annihilation (TTA) was developed by loading both sensitizer and annihilator into BSA-dextran stabilized oil droplets. This strategy can maintain high translational mobility of the chromophores, avoid luminescence quenching of chromophore by aggregation, and decrease the O2-induced quenching of TTA-based upconversion emission. Pt(II)-tetraphenyl-tetrabenzoporphyrin (PtTPBP) and BODIPY dyes (BDP-G and BDP-Y with the maximal fluorescence emission at 528 and 546 nm, respectively) were chosen as sensitizer/annihilator couples to fabricate green and yellow upconversion luminescent emissive nanocapsules, named UCNC-G and UCNC-Y, respectively. In water under the atmospheric environment, interestingly, UCNC-G and UCNC-Y exhibit intense upconversion luminescence (UCL) emission (λex = 635 nm) with the quantum efficiencies (ΦUCL) of 1.7% and 4.8%, respectively, whereas very weak UCL emission (ΦUCL < 0.1%) was observed for the corresponding previous reported SiO2-coating nanosystems because of aggregation-induced fluorescence quenching of annihilators. Furthermore, application of theses upconversion nanocapsules for high-contrast UCL bioimaging in vivo of living mice without removing the skin was demonstrated under 635-nm excitation with low power density of 12.5 mW cm(-2). PMID:23464990

  19. Doing the "Second Shift": Gendered Labour and the Symbolic Annihilation of Teacher Educators' Work

    ERIC Educational Resources Information Center

    Spencer, Ingrid

    2013-01-01

    Reflecting on the experience of being a participant in the Work of Teacher Education (WoTE) research, and drawing on conceptualisations of teacher education as "domestic labour," I argue that teacher educators' closeness to classroom practice acts as a determining factor in their symbolic annihilation, a concept usually applied to…

  20. Dense DM clumps seeded by cosmic string loops and DM annihilation

    NASA Astrophysics Data System (ADS)

    Berezinsky, V. S.; Dokuchaev, V. I.; Eroshenko, Yu. N.

    2011-12-01

    We develop a model of production of the very dense clumps of DM in RD epoch due to the accretion of DM on the loops of cosmic strings as the seeds. At some time the loops disappear, for example due to the gravitational radiation, and the remaining dense clumps produce the enhancement of the annihilation signal. We take into account the velocity distribution of the strings, and consider the two extreme regimes of DM annihilation: fast decay and continuous evaporation. The produced annihilation flux of gamma radiation is detectable, and for some parameters of DM particles and the strings can exceed the extragalactic flux of the gamma-radiation observed by Fermi. For the fixed parameters of DM particles (e.g. neutralino with fixed masses and cross-section of annihilation) one can obtain the limits on the basic string parameter, tension μ, which is stronger than (more general) limits obtained from WMAP observations, cosmological nucleosynthesis and gravitational lensing. In particular for the neutralino with 100 GeV mass we exclude the interval 5 × 10-10 < Gμ/c2 < 5.1 × 10-9.

  1. Surface states and annihilation characteristics of positrons trapped at the (100) and (111) surfaces of silicon

    NASA Astrophysics Data System (ADS)

    Fazleev, N. G.; Fry, J. L.; Weiss, A. H.

    2004-10-01

    Recent studies of Si(100) and Si(111) using positron annihilation induced Auger-electron spectroscopy (PAES) reveal that experimental annihilation probabilities of surface trapped positrons with relevant Si core-level electrons differ significantly for two faces of clean Si, an elemental semiconductor. These experimental results are investigated theoretically by performing calculations of the “image-potential” positron surface states and annihilation characteristics of the surface trapped positrons with relevant Si core-level electrons for the ideally terminated, nonreconstructed and reconstructed Si(100)-(2×1) and Si(111)-(7×7) surfaces. Computed positron surface binding energies demonstrate their sensitivity to the specific atomic structure of the topmost layers of surfaces, and, when compared to positron work functions, the stability of positron surface states on all studied Si(100) and Si(111) surfaces. The positron surface state wave function was found to be localized in a potential well on the vacuum side at both nonreconstructed semiconductor surfaces. The (2×1) reconstruction of the Si(100) surface causes the positron surface state wave function to extend into the lattice in the regions where atoms are displaced away from their ideal terminated positions. A comparison of theoretical and experimental positron surface binding energies for Si(100) shows that the best agreement is achieved when the reconstructed Si(100)-(2×1) surface is described within the asymmetric dimer model. Calculations indicate that the positron surface state wave function is localized in all three dimensions in the corner hole regions of the reconstructed Si(111)-(7×7) surface. This localization provides an explanation for previous experiments that failed to show the anisotropy in the electron-positron pair momentum density distribution expected for a positron surface state delocalized in the plane of the surface. Positron annihilation characteristics are calculated for each

  2. Monte Carlo modelling of the propagation and annihilation of nucleosynthesis positrons in the Galaxy

    NASA Astrophysics Data System (ADS)

    Alexis, A.; Jean, P.; Martin, P.; Ferrière, K.

    2014-04-01

    Aims: We want to estimate whether the positrons produced by the β+-decay of 26Al, 44Ti, and 56Ni synthesised in massive stars and supernovae are sufficient to explain the 511 keV annihilation emission observed in our Galaxy. Such a possibility has often been put forward in the past. In a previous study, we showed that nucleosynthesis positrons cannot explain the full annihilation emission. Here, we extend this work using an improved propagation model. Methods: We developed a Monte Carlo Galactic propagation code for ~MeV positrons in which the Galactic interstellar medium, the Galactic magnetic field, and the propagation are finely described. This code allows us to simulate the spatial distribution of the 511 keV annihilation emission. We tested several Galactic magnetic fields models and several positron escape fractions from type-Ia supernova for 56Ni positrons to account for the large uncertainties in these two parameters. We considered the collisional/ballistic transport mode and then compared the simulated 511 keV intensity spatial distributions to the INTEGRAL/SPI data. Results: Regardless of the Galactic magnetic field configuration and the escape fraction chosen for 56Ni positrons, the 511 keV intensity distributions are very similar. The main reason is that ~MeV positrons do not propagate very far away from their birth sites in our model. The direct comparison to the data does not allow us to constrain the Galactic magnetic field configuration and the escape fraction for 56Ni positrons. In any case, nucleosynthesis positrons produced in steady state cannot explain the full annihilation emission. The comparison to the data shows that (a) the annihilation emission from the Galactic disk can be accounted for; (b) the strongly peaked annihilation emission from the inner Galactic bulge can be explained by positrons annihilating in the central molecular zone, but this seems to require more positron sources than the population of massive stars and type Ia

  3. Implications of the first AMS-02 measurement for dark matter annihilation and decay

    SciTech Connect

    Jin, Hong-Bo; Wu, Yue-Liang; Zhou, Yu-Feng E-mail: ylwu@itp.ac.cn

    2013-11-01

    In light of the first measurement of the positron fraction by the AMS-02 experiment, we perform a detailed global analysis on the interpretation of the latest data of PAMELA, Fermi-LAT, and AMS-02 in terms of dark matter (DM) annihilation and decay in various propagation models. The allowed regions for the DM particle mass and annihilation cross section or decay life-time are obtained for channels with leptonic final states: 2e, 2μ, 2τ, 4e, 4μ and 4τ. We show that for the conventional astrophysical background the AMS-02 positron fraction data alone favour a DM particle mass ∼ 500(800) GeV if DM particles annihilate dominantly into 2μ(4μ) final states, which is significantly lower than that favoured by the Fermi-LAT data of the total flux of electrons and positrons. The allowed regions by the two experiments do not overlap at a high confidence level (99.99999%C.L.). We consider a number of propagation models with different halo height Z{sub h}, diffusion parameters D{sub 0} and δ{sub 1/2}, and power indices of primary nucleon sources γ{sub p1/p2}. The normalization and the slope of the electron background are also allowed to vary. We find that the tension between the two experiments can be only slightly reduced in the propagation model with large Z{sub h} and D{sub 0}. The consistency of fit is improved for annihilation channels with 2τ and 4τ final states which favour TeV scale DM particle with large cross sections above ∼ 10{sup −23} cm{sup 3}s{sup −1}. In all the considered leptonic channels, the current data favour the scenario of DM annihilation over DM decay. In the decay scenario, the charge asymmetric DM decay is slightly favoured.

  4. Dark Matter annihilations in halos and high-redshift sources of reionization of the universe

    NASA Astrophysics Data System (ADS)

    Poulin, Vivian; Serpico, Pasquale D.; Lesgourgues, Julien

    2015-12-01

    It is well known that annihilations in the homogeneous fluid of dark matter (DM) can leave imprints in the cosmic microwave background (CMB) anisotropy power spectrum. However, the relevance of DM annihilations in halos for cosmological observables is still subject to debate, with previous works reaching different conclusions on this point. Also, all previous studies used a single type of parameterization for the astrophysical reionization, and included no astrophysical source for the heating of the intergalactic medium. In this work, we revisit these problems. When standard approaches are adopted, we find that the ionization fraction does exhibit a very particular (and potentially constraining) pattern, but the currently measurable τreio is left almost unchanged: in agreement with most of the previous literature, for plausible halo models we find that the modification of the signal with respect to the one coming from annihilations in the smooth background is tiny, below cosmic variance within currently allowed parameter space. However, if different and probably more realistic treatments of the astrophysical sources of reionization and heating are adopted, a more pronounced effect of the DM annihilation in halos is possible. We thus conclude that within currently adopted baseline models the impact of the virialised DM structures cannot be uncovered by CMB power spectra measurements, but a larger impact is possible if peculiar models are invoked for the redshift evolution of the DM annihilation signal or different assumptions are made for the astrophysical contributions. A better understanding (both theoretical and observational) of the reionization and temperature history of the universe, notably via the 21 cm signal, seems the most promising way for using halo formation as a tool in DM searches, improving over the sensitivity of current cosmological probes.

  5. Limits on a muon flux from neutralino annihilations in the Sun with the IceCube 22-string detector

    SciTech Connect

    IceCube Collaboration; Klein, Spencer

    2009-04-28

    A search for muon neutrinos from neutralino annihilations in the Sun has been performed with the IceCube 22-string neutrino detector using data collected in 104.3 days of live-time in 2007. No excess over the expected atmospheric background has been observed. Upper limits have been obtained on the annihilation rate of captured neutralinos in the Sun and converted to limits on the WIMP-proton cross-sections for WIMP masses in the range 250-5000 GeV. These results are the most stringent limits to date on neutralino annihilation in the Sun.

  6. Reverse Micelle Formation of Triton X-100 in Butanol and n-Heptane Mixed Solvents Studied by the Positron Annihilation Technique

    PubMed

    Das; Ganguly

    1997-08-01

    The positron annihilation technique (PAT) has been applied to study the molecular association phenomenon of Triton X-100 (TX-100) and formation of reversed micelles in the mixed solvent of butanol and n-heptane. The results indicate the sensitivity of positronium (Ps) parameters to the phase transition region due to the self-aggregation phenomenon of TX-100 within the system. The intensity of the long-lived ortho-Ps component, I3, and its lifetime, tau3, show a remarkable change at a critical concentration of the surfactant at approximately 1.5 mM coined as the operational CMC of TX-100 in both (1:1) and (1:2) butanol-n-heptane (BuHp) systems. The narrow component/para-Ps intensity as computed from Doppler broadening of annihilation radiation indicates discernable changes at the same concentration region ( approximately 1.5 mM) of TX-100 in the system. Further, microphase changes due to the association of water molecules within the nonaqueous phase has been studied by Ps parameters, which reveals a clear demarcation of the polar and nonpolar zones. PMID:9268557

  7. Cosmic X-ray and gamma-ray background from dark matter annihilation

    NASA Astrophysics Data System (ADS)

    Zavala, Jesús; Vogelsberger, Mark; Slatyer, Tracy R.; Loeb, Abraham; Springel, Volker

    2011-06-01

    The extragalactic background light (EBL) observed at multiple wavelengths is a promising tool to probe the nature of dark matter. This radiation might contain a significant contribution from gamma-rays produced promptly by dark matter particle annihilation in the many halos and subhalos within our past-light cone. Additionally, the electrons and positrons produced in the annihilation give energy to the cosmic microwave photons to populate the EBL with X-rays and gamma-rays. To study these signals, we create full-sky maps of the expected radiation from both of these contributions using the high-resolution Millennium-II simulation of cosmic structure formation. Our method also accounts for a possible enhancement of the annihilation rate by a Sommerfeld mechanism due to a Yukawa interaction between the dark matter particles prior to annihilation. We use upper limits on the contributions of unknown sources to the EBL to constrain the intrinsic properties of dark matter using a model-independent approach that can be employed as a template to test different particle physics models. These upper limits are based on observational measurements spanning 8 orders of magnitude in energy (from soft X-rays measured by the CHANDRA satellite to gamma-rays measured by the Fermi satellite), and on expectations for the contributions from nonblazar active galactic nuclei, blazars and star-forming galaxies. To exemplify this approach, we analyze a set of benchmark Sommerfeld-enhanced models that give the correct abundance of dark matter, satisfy constraints from the cosmic microwave background, and fit the cosmic ray spectra measured by PAMELA and Fermi without any contribution from local substructure. We find that these models are in conflict with the EBL constraints unless the contribution of unresolved substructure is small and the dark matter annihilation signal dominates the EBL. We conclude that provided the collisionless cold dark matter paradigm is accurate, even for

  8. A search for neutrino signal from dark matter annihilation in the center of the Milky Way with Baikal NT200

    NASA Astrophysics Data System (ADS)

    Avrorin, A. D.; Avrorin, A. V.; Aynutdinov, V. M.; Bannasch, R.; Belolaptikov, I. A.; Bogorodsky, D. Yu.; Brudanin, V. B.; Budnev, N. M.; Danilchenko, I. A.; Demidov, S. V.; Domogatsky, G. V.; Doroshenko, A. A.; Dyachok, A. N.; Dzhilkibaev, Zh.-A. M.; Fialkovsky, S. V.; Gafarov, A. R.; Gaponenko, O. N.; Golubkov, K. V.; Gress, T. I.; Honz, Z.; Kebkal, K. G.; Kebkal, O. G.; Konischev, K. V.; Korobchenko, A. V.; Koshechkin, A. P.; Koshel, F. K.; Kozhin, A. V.; Kulepov, V. F.; Kuleshov, D. A.; Ljashuk, V. I.; Milenin, M. B.; Mirgazov, R. A.; Osipova, E. R.; Panfilov, A. I.; Pan'kov, L. V.; Pliskovsky, E. N.; Rozanov, M. I.; Rjabov, E. V.; Shaybonov, B. A.; Sheifler, A. A.; Shelepov, M. D.; Skurihin, A. V.; Smagina, A. A.; Suvorova, O. V.; Tabolenko, V. A.; Tarashansky, B. A.; Yakovlev, S. A.; Zagorodnikov, A. V.; Zhukov, V. A.; Zurbanov, V. L.

    2016-08-01

    We reanalyze the dataset collected during the years 1998-2003 by the deep underwater neutrino telescope NT200 in the lake Baikal with the low energy threshold (10 GeV) in searches for neutrino signal from dark matter annihilations near the center of the Milky Way. Two different approaches are used in the present analysis: counting events in the cones around the direction towards the Galactic Center and the maximum likelihood method. We assume that the dark matter particles annihilate dominantly over one of the annihilation channels bbbar , W+W- , τ+τ- , μ+μ- or ννbar . No significant excess of events towards the Galactic Center over expected neutrino background of atmospheric origin is found and we derive 90% CL upper limits on the annihilation cross section of dark matter.

  9. Improvements to the calculation of indirect signals of diffuse gamma-rays and neutrinos from dark matter annihilation

    NASA Astrophysics Data System (ADS)

    Campbell, Sheldon Scott

    A new formalism is presented for calculating the mean intensity spectrum and angular power spectrum of gamma-rays or neutrinos from extragalactic annihilating dark matter, taking into account the dependence of the relative motions of the annihilating particles on the annihilation cross section. To model the large scale dark matter distribution of mass and relative velocities, the halo distribution model is comprehensively summarized, and extended to include a universal radial profile of the particles’ velocity variance, based on results from N-body computer simulations of dark matter halos. A velocity variance profile, associated with the NFW density profile, is proposed by enforcing a power-law profile of the pseudo phase-space density. This allows the large-scale velocity distribution to be described by virialized, gravitationally bound dark matter halos, as opposed to thermal motions used to describe the velocity distribution in the early Universe. The recent particle motion history of the Universe is presented for the described model. Sample extragalactic gamma-ray intensities from dark matter annihilation are shown for dark matter annihilating with p-wave, according to a relative-velocity-weighted annihilation cross section σv = a + bv2, for constants a and b, with examples taken from supersymmetric models. For thermally produced dark matter, the p-wave suppresses the signal intensity. If b/a ≳ 106, the p-wave hardens the intensity spectrum by an estimated factor of 1 + (6b/a)ΔI( Eγ), and increases the angular power spectrum by a factor also depending on new coefficients D1 Cl (Eγ) and D2 Cl (Eγ). The energy-dependence of the new p-wave coefficients ΔI, D1 Cl , and D2 Cl are shown for various annihilation spectra. Sample intensity spectra are also presented for Sommerfeld-enhanced annihilation. The intensity of neutrinos from dark matter annihilation is also considered. The variations between the dark matter annihilation signals for different

  10. Time Warp Operating System, Version 2.5.1

    NASA Technical Reports Server (NTRS)

    Bellenot, Steven F.; Gieselman, John S.; Hawley, Lawrence R.; Peterson, Judy; Presley, Matthew T.; Reiher, Peter L.; Springer, Paul L.; Tupman, John R.; Wedel, John J., Jr.; Wieland, Frederick P.; Younger, Herbert C.

    1993-01-01

    Time Warp Operating System, TWOS, is special purpose computer program designed to support parallel simulation of discrete events. Complete implementation of Time Warp software mechanism, which implements distributed protocol for virtual synchronization based on rollback of processes and annihilation of messages. Supports simulations and other computations in which both virtual time and dynamic load balancing used. Program utilizes underlying resources of operating system. Written in C programming language.

  11. Gamma-ray Background Spectrum and Annihilation Rate in the Baryon-symmetric Big-bang Cosmology

    NASA Technical Reports Server (NTRS)

    Puget, J. L.

    1973-01-01

    An attempt was made to acquire experimental information on the problem of baryon symmetry on a large cosmological scale by observing the annihilation products. Data cover absorption cross sections and background radiation due to other sources for the two main products of annihilation, gamma rays and neutrinos. Test results show that the best direct experimental test for the presence of large scale antimatter lies in the gamma ray background spectrum between 1 and 70 MeV.

  12. Macromolecular conformation in solution. Study of carbonic anhydrase by the positron annihilation technique.

    PubMed Central

    Handel, E D; Graf, G; Glass, J C

    1980-01-01

    The structural features of carbonic anhydrase (carbonate hydro-lyase; EC 4.2.1.1) in aqueous solution were probed by the positron annihilation technique. The data obtained under varying conditions of temperature, pH, and enzyme concentration were interpreted in terms of the free volume model. The change of enzymic activity with temperature is accompanied by a change in free volume of the protein. Upon thermal denaturation an irreversible change in free volume of the molecule occurred. At low temperatures the protein-water interactions were investigated. These results are discussed in terms of current concepts of structure-function relationships in proteins. This study shows the sensitivity of the positron annihilation method toward the structure of proteins related to their overall conformation and to the nature of bound water. PMID:6789901

  13. High Energy Electron Signals from Dark Matter Annihilation in the Sun

    SciTech Connect

    Schuster, Philip; Toro, Natalia; Weiner, Neal; Yavin, Itay; /New York U., CCPP

    2012-04-09

    In this paper we discuss two mechanisms by which high energy electrons resulting from dark matter annihilations in or near the Sun can arrive at the Earth. Specifically, electrons can escape the sun if DM annihilates into long-lived states, or if dark matter scatters inelastically, which would leave a halo of dark matter outside of the sun. Such a localized source of electrons may affect the spectra observed by experiments with narrower fields of view oriented towards the sun, such as ATIC, differently from those with larger fields of view such as Fermi. We suggest a simple test of these possibilities with existing Fermi data that is more sensitive than limits from final state radiation. If observed, such a signal will constitute an unequivocal signature of dark matter.

  14. Search for dark matter annihilations in the sun with the 79-string IceCube detector.

    PubMed

    Aartsen, M G; Abbasi, R; Abdou, Y; Ackermann, M; Adams, J; Aguilar, J A; Ahlers, M; Altmann, D; Auffenberg, J; Bai, X; Baker, M; Barwick, S W; Baum, V; Bay, R; Beattie, K; Beatty, J J; Bechet, S; Becker Tjus, J; Becker, K-H; Bell, M; Benabderrahmane, M L; BenZvi, S; Berdermann, J; Berghaus, P; Berley, D; Bernardini, E; Bernhard, A; Bertrand, D; Besson, D Z; Bindig, D; Bissok, M; Blaufuss, E; Blumenthal, J; Boersma, D J; Bohaichuk, S; Bohm, C; Bose, D; Böser, S; Botner, O; Brayeur, L; Brown, A M; Bruijn, R; Brunner, J; Buitink, S; Carson, M; Casey, J; Casier, M; Chirkin, D; Christy, B; Clark, K; Clevermann, F; Cohen, S; Cowen, D F; Cruz Silva, A H; Danninger, M; Daughhetee, J; Davis, J C; De Clercq, C; De Ridder, S; Desiati, P; de Vries-Uiterweerd, G; de With, M; DeYoung, T; Díaz-Vélez, J C; Dreyer, J; Dunkman, M; Eagan, R; Eberhardt, B; Eisch, J; Ellsworth, R W; Engdegård, O; Euler, S; Evenson, P A; Fadiran, O; Fazely, A R; Fedynitch, A; Feintzeig, J; Feusels, T; Filimonov, K; Finley, C; Fischer-Wasels, T; Flis, S; Franckowiak, A; Franke, R; Frantzen, K; Fuchs, T; Gaisser, T K; Gallagher, J; Gerhardt, L; Gladstone, L; Glüsenkamp, T; Goldschmidt, A; Golup, G; Goodman, J A; Góra, D; Grant, D; Groß, A; Gurtner, M; Ha, C; Haj Ismail, A; Hallgren, A; Halzen, F; Hanson, K; Heereman, D; Heimann, P; Heinen, D; Helbing, K; Hellauer, R; Hickford, S; Hill, G C; Hoffman, K D; Hoffmann, R; Homeier, A; Hoshina, K; Huelsnitz, W; Hulth, P O; Hultqvist, K; Hussain, S; Ishihara, A; Jacobi, E; Jacobsen, J; Japaridze, G S; Jero, K; Jlelati, O; Kaminsky, B; Kappes, A; Karg, T; Karle, A; Kelley, J L; Kiryluk, J; Kislat, F; Kläs, J; Klein, S R; Köhne, J-H; Kohnen, G; Kolanoski, H; Köpke, L; Kopper, C; Kopper, S; Koskinen, D J; Kowalski, M; Krasberg, M; Kroll, G; Kunnen, J; Kurahashi, N; Kuwabara, T; Labare, M; Landsman, H; Larson, M J; Lesiak-Bzdak, M; Leute, J; Lünemann, J; Madsen, J; Maruyama, R; Mase, K; Matis, H S; McNally, F; Meagher, K; Merck, M; Mészáros, P; Meures, T; Miarecki, S; Middell, E; Milke, N; Miller, J; Mohrmann, L; Montaruli, T; Morse, R; Nahnhauer, R; Naumann, U; Niederhausen, H; Nowicki, S C; Nygren, D R; Obertacke, A; Odrowski, S; Olivas, A; Olivo, M; O'Murchadha, A; Paul, L; Pepper, J A; Pérez de los Heros, C; Pfendner, C; Pieloth, D; Pirk, N; Posselt, J; Price, P B; Przybylski, G T; Rädel, L; Rawlins, K; Redl, P; Resconi, E; Rhode, W; Ribordy, M; Richman, M; Riedel, B; Rodrigues, J P; Rott, C; Ruhe, T; Ruzybayev, B; Ryckbosch, D; Saba, S M; Salameh, T; Sander, H-G; Santander, M; Sarkar, S; Schatto, K; Scheel, M; Scheriau, F; Schmidt, T; Schmitz, M; Schoenen, S; Schöneberg, S; Schönherr, L; Schönwald, A; Schukraft, A; Schulte, L; Schulz, O; Seckel, D; Seo, S H; Sestayo, Y; Seunarine, S; Sheremata, C; Smith, M W E; Soiron, M; Soldin, D; Spiczak, G M; Spiering, C; Stamatikos, M; Stanev, T; Stasik, A; Stezelberger, T; Stokstad, R G; Stößl, A; Strahler, E A; Ström, R; Sullivan, G W; Taavola, H; Taboada, I; Tamburro, A; Ter-Antonyan, S; Tilav, S; Toale, P A; Toscano, S; Usner, M; van der Drift, D; van Eijndhoven, N; Van Overloop, A; van Santen, J; Vehring, M; Voge, M; Vraeghe, M; Walck, C; Waldenmaier, T; Wallraff, M; Wasserman, R; Weaver, Ch; Wellons, M; Wendt, C; Westerhoff, S; Whitehorn, N; Wiebe, K; Wiebusch, C H; Williams, D R; Wissing, H; Wolf, M; Wood, T R; Woschnagg, K; Xu, C; Xu, D L; Xu, X W; Yanez, J P; Yodh, G; Yoshida, S; Zarzhitsky, P; Ziemann, J; Zierke, S; Zilles, A; Zoll, M

    2013-03-29

    We have performed a search for muon neutrinos from dark matter annihilation in the center of the Sun with the 79-string configuration of the IceCube neutrino telescope. For the first time, the DeepCore subarray is included in the analysis, lowering the energy threshold and extending the search to the austral summer. The 317 days of data collected between June 2010 and May 2011 are consistent with the expected background from atmospheric muons and neutrinos. Upper limits are set on the dark matter annihilation rate, with conversions to limits on spin-dependent and spin-independent scattering cross sections of weakly interacting massive particles (WIMPs) on protons, for WIMP masses in the range 20-5000  GeV/c2. These are the most stringent spin-dependent WIMP-proton cross section limits to date above 35  GeV/c2 for most WIMP models. PMID:23581307

  15. Surfaces of colloidal PbSe nanocrystals probed by thin-film positron annihilation spectroscopy

    SciTech Connect

    Chai, L.; Schut, H.; Schaarenburg, L. C. van; Eijt, S. W. H.; Al-Sawai, W.; Barbiellini, B.; Bansil, A.; Gao, Y.; Houtepen, A. J.; Mijnarends, P. E.; Huis, M. A. van; Ravelli, L.; Egger, W.; Kaprzyk, S.

    2013-08-01

    Positron annihilation lifetime spectroscopy and positron-electron momentum density (PEMD) studies on multilayers of PbSe nanocrystals (NCs), supported by transmission electron microscopy, show that positrons are strongly trapped at NC surfaces, where they provide insight into the surface composition and electronic structure of PbSe NCs. Our analysis indicates abundant annihilation of positrons with Se electrons at the NC surfaces and with O electrons of the oleic ligands bound to Pb ad-atoms at the NC surfaces, which demonstrates that positrons can be used as a sensitive probe to investigate the surface physics and chemistry of nanocrystals inside multilayers. Ab initio electronic structure calculations provide detailed insight in the valence and semi-core electron contributions to the positron-electron momentum density of PbSe. Both lifetime and PEMD are found to correlate with changes in the particle morphology characteristic of partial ligand removal.

  16. Structure of a Magnetic Flux Annihilation Layer Formed by the Collision of Supersonic, Magnetized Plasma Flows.

    PubMed

    Suttle, L G; Hare, J D; Lebedev, S V; Swadling, G F; Burdiak, G C; Ciardi, A; Chittenden, J P; Loureiro, N F; Niasse, N; Suzuki-Vidal, F; Wu, J; Yang, Q; Clayson, T; Frank, A; Robinson, T S; Smith, R A; Stuart, N

    2016-06-01

    We present experiments characterizing the detailed structure of a current layer, generated by the collision of two counterstreaming, supersonic and magnetized aluminum plasma flows. The antiparallel magnetic fields advected by the flows are found to be mutually annihilated inside the layer, giving rise to a bifurcated current structure-two narrow current sheets running along the outside surfaces of the layer. Measurements with Thomson scattering show a fast outflow of plasma along the layer and a high ion temperature (T_{i}∼Z[over ¯]T_{e}, with average ionization Z[over ¯]=7). Analysis of the spatially resolved plasma parameters indicates that the advection and subsequent annihilation of the inflowing magnetic flux determines the structure of the layer, while the ion heating could be due to the development of kinetic, current-driven instabilities. PMID:27314720

  17. Limits on dark matter annihilation in the sun using the ANTARES neutrino telescope

    NASA Astrophysics Data System (ADS)

    Adrián-Martínez, S.; Albert, A.; André, M.; Anton, G.; Ardid, M.; Aubert, J.-J.; Avgitas, T.; Baret, B.; Barrios-Martí, J.; Basa, S.; Bertin, V.; Biagi, S.; Bormuth, R.; Bouwhuis, M. C.; Bruijn, R.; Brunner, J.; Busto, J.; Capone, A.; Caramete, L.; Carr, J.; Celli, S.; Chiarusi, T.; Circella, M.; Coleiro, A.; Coniglione, R.; Costantini, H.; Coyle, P.; Creusot, A.; Deschamps, A.; De Bonis, G.; Distefano, C.; Donzaud, C.; Dornic, D.; Drouhin, D.; Eberl, T.; El Bojaddaini, I.; Elsässer, D.; Enzenhöfer, A.; Fehn, K.; Felis, I.; Fusco, L. A.; Galatà, S.; Gay, P.; Geißelsöder, S.; Geyer, K.; Giordano, V.; Gleixner, A.; Glotin, H.; Gracia-Ruiz, R.; Graf, K.; Hallmann, S.; van Haren, H.; Heijboer, A. J.; Hello, Y.; Hernández-Rey, J. J.; Hößl, J.; Hofestädt, J.; Hugon, C.; Illuminati, G.; James, C. W.; de Jong, M.; Jongen, M.; Kadler, M.; Kalekin, O.; Katz, U.; Kießling, D.; Kouchner, A.; Kreter, M.; Kreykenbohm, I.; Kulikovskiy, V.; Lachaud, C.; Lahmann, R.; Lefèvre, D.; Leonora, E.; Loucatos, S.; Marcelin, M.; Margiotta, A.; Marinelli, A.; Martínez-Mora, J. A.; Mathieu, A.; Melis, K.; Michael, T.; Migliozzi, P.; Moussa, A.; Mueller, C.; Nezri, E.; Păvălaş, G. E.; Pellegrino, C.; Perrina, C.; Piattelli, P.; Popa, V.; Pradier, T.; Racca, C.; Riccobene, G.; Roensch, K.; Saldaña, M.; Samtleben, D. F. E.; Sánchez-Losa, A.; Sanguineti, M.; Sapienza, P.; Schnabel, J.; Schüssler, F.; Seitz, T.; Sieger, C.; Spurio, M.; Stolarczyk, Th.; Taiuti, M.; Tönnis, C.; Trovato, A.; Tselengidou, M.; Turpin, D.; Vallage, B.; Vallée, C.; Van Elewyck, V.; Vivolo, D.; Wagner, S.; Wilms, J.; Zornoza, J. D.; Zúñiga, J.

    2016-08-01

    A search for muon neutrinos originating from dark matter annihilations in the Sun is performed using the data recorded by the ANTARES neutrino telescope from 2007 to 2012. In order to obtain the best possible sensitivities to dark matter signals, an optimisation of the event selection criteria is performed taking into account the background of atmospheric muons, atmospheric neutrinos and the energy spectra of the expected neutrino signals. No significant excess over the background is observed and 90% C.L. upper limits on the neutrino flux, the spin-dependent and spin-independent WIMP-nucleon cross-sections are derived for WIMP masses ranging from 50 GeV to 5 TeV for the annihilation channels WIMP + WIMP → b b bar ,W+W- and τ+τ-.

  18. Extended Glauber Model of Antiproton-Nucleus Annihilation for All Energies and Mass Numbers

    SciTech Connect

    Lee, Teck-Ghee; Wong, Cheuk-Yin

    2014-01-01

    Previous analytical formulas in the Glauber model for high-energy nucleus-nucleus collisions developed by Wong are utilized and extended to study Antiproton-nucleus annihilations for both high and low energies, after taking into account the effects of Coulomb and nuclear interactions, and the change of the antiproton momentum inside a nucleus. The extended analytical formulas capture the main features of the experimental antiproton-nucleus annihilation cross sections for all energies and mass numbers. At high antiproton energies, they exhibit the granular property for the lightest nuclei and the black-disk limit for the heavy nuclei. At low antiproton energies, they display the effect of the antiproton momentum increase due to the nuclear interaction for the light nuclei, and the effect of the magnification due to the attractive Coulomb interaction for the heavy nuclei.

  19. GRO: Red-shifted electron-positron annihilation gamma-rays from radiopulsars

    NASA Technical Reports Server (NTRS)

    Ruderman, Malvin

    1993-01-01

    Reported red-shifted e(+) + e(-) yields gamma + gamma 511 keV gamma-rays from the Crab pulsar would, if ultimately confirmed, provide crucial clues about the structure of the powerful magnetospheric accelerator in that rapidly spinning gamma-ray pulsar. In an attempt to understand the origin of this component of the Crab pulsar's emission, we try to account for the following: (1) a flow of approximately 10 exp 40 e(+/-)/s into near the surface of the neutron star; (2) a relatively narrow annihilation line implying that the annihilating e(+/-) pairs probably had a velocity (along vector B) less than or approximately = 10(exp -1)c; and (3) a tentative light curve suggesting a doubly peaked structure different from that of the rest of the Crab pulsar's nonthermal radiation.

  20. Order-disorder transition in clathrate Ba6Ge25 studied by positron annihilation

    NASA Astrophysics Data System (ADS)

    Li, X. F.; Zhao, B.; Zhang, T.; He, H. F.; Zhang, Q.; Yang, D. W.; Chen, Z. Q.; Tang, X. F.

    2015-07-01

    Clathrate Ba6Ge25 is prepared by melt method and spark plasma sintering. Structural transition below room temperature is studied by positron annihilation and X-ray diffraction measurements. There is a pronounced transition in the temperature range of 200-250 K which might be involved with the movement of Ba atoms in Ge cages and result in disordered structure. This transition is further confirmed by the theoretical calculation of positron annihilation states. Thus our results confirm the structural models proposed by Carrillo-Cabrera et al. (2005). The measured specific heat capacity, electric resistivity and magnetic susceptibility all show anomalous transition in the same temperature range, indicating that the movement of Ba atoms in the cage has influence on the thermal, electric as well as magnetic properties of Ba6Ge25.

  1. Atomic scale study of the life cycle of a dislocation in graphene from birth to annihilation

    NASA Astrophysics Data System (ADS)

    Lehtinen, O.; Kurasch, S.; Krasheninnikov, A. V.; Kaiser, U.

    2013-06-01

    Dislocations, one of the key entities in materials science, govern the properties of any crystalline material. Thus, understanding their life cycle, from creation to annihilation via motion and interaction with other dislocations, point defects and surfaces, is of fundamental importance. Unfortunately, atomic-scale investigations of dislocation evolution in a bulk object are well beyond the spatial and temporal resolution limits of current characterization techniques. Here we overcome the experimental limits by investigating the two-dimensional graphene in an aberration-corrected transmission electron microscope, exploiting the impinging energetic electrons both to image and stimulate atomic-scale morphological changes in the material. The resulting transformations are followed in situ, atom-by-atom, showing the full life cycle of a dislocation from birth to annihilation. Our experiments, combined with atomistic simulations, reveal the evolution of dislocations in two-dimensional systems to be governed by markedly long-ranging out-of-plane buckling.

  2. Spin dependent momentum density and Fermi surface of ferromagnetic Ni obtained by positron annihilation experiments

    NASA Astrophysics Data System (ADS)

    Hamid, A. S.; Uedono, A.

    2004-11-01

    The spin-dependent momentum density and Fermi surface of ferromagnetic Ni have been obtained through positron annihilation experiments. The measurements were carried out through 2D angular correlation of annihilation radiation (ACAR) using longitudinally polarized positrons. The magnetic field direction was reversed in order to study the effect of the spin-dependent positron-electron momentum space density on the Fermi surface of Ni. The results showed that ferromagnetic Ni had different Fermi surfaces for the majority-spin and minority-spin states. The differences due to the spin-states were studied in the momentum space and in the wave vector space. In general, the experimental results showed good agreement with previous theoretical calculations.

  3. Local electron-electron interaction strength in ferromagnetic nickel determined by spin-polarized positron annihilation

    NASA Astrophysics Data System (ADS)

    Ceeh, Hubert; Weber, Josef Andreass; Böni, Peter; Leitner, Michael; Benea, Diana; Chioncel, Liviu; Ebert, Hubert; Minár, Jan; Vollhardt, Dieter; Hugenschmidt, Christoph

    2016-02-01

    We employ a positron annihilation technique, the spin-polarized two-dimensional angular correlation of annihilation radiation (2D-ACAR), to measure the spin-difference spectra of ferromagnetic nickel. The experimental data are compared with the theoretical results obtained within a combination of the local spin density approximation (LSDA) and the many-body dynamical mean-field theory (DMFT). We find that the self-energy defining the electronic correlations in Ni leads to anisotropic contributions to the momentum distribution. By direct comparison of the theoretical and experimental results we determine the strength of the local electronic interaction U in ferromagnetic Ni as 2.0 ± 0.1 eV.

  4. Local electron-electron interaction strength in ferromagnetic nickel determined by spin-polarized positron annihilation

    PubMed Central

    Ceeh, Hubert; Weber, Josef Andreass; Böni, Peter; Leitner, Michael; Benea, Diana; Chioncel, Liviu; Ebert, Hubert; Minár, Jan; Vollhardt, Dieter; Hugenschmidt, Christoph

    2016-01-01

    We employ a positron annihilation technique, the spin-polarized two-dimensional angular correlation of annihilation radiation (2D-ACAR), to measure the spin-difference spectra of ferromagnetic nickel. The experimental data are compared with the theoretical results obtained within a combination of the local spin density approximation (LSDA) and the many-body dynamical mean-field theory (DMFT). We find that the self-energy defining the electronic correlations in Ni leads to anisotropic contributions to the momentum distribution. By direct comparison of the theoretical and experimental results we determine the strength of the local electronic interaction U in ferromagnetic Ni as 2.0 ± 0.1 eV. PMID:26879249

  5. Structure of a Magnetic Flux Annihilation Layer Formed by the Collision of Supersonic, Magnetized Plasma Flows

    NASA Astrophysics Data System (ADS)

    Suttle, L. G.; Hare, J. D.; Lebedev, S. V.; Swadling, G. F.; Burdiak, G. C.; Ciardi, A.; Chittenden, J. P.; Loureiro, N. F.; Niasse, N.; Suzuki-Vidal, F.; Wu, J.; Yang, Q.; Clayson, T.; Frank, A.; Robinson, T. S.; Smith, R. A.; Stuart, N.

    2016-06-01

    We present experiments characterizing the detailed structure of a current layer, generated by the collision of two counterstreaming, supersonic and magnetized aluminum plasma flows. The antiparallel magnetic fields advected by the flows are found to be mutually annihilated inside the layer, giving rise to a bifurcated current structure—two narrow current sheets running along the outside surfaces of the layer. Measurements with Thomson scattering show a fast outflow of plasma along the layer and a high ion temperature (Ti˜Z ¯ Te , with average ionization Z ¯=7 ). Analysis of the spatially resolved plasma parameters indicates that the advection and subsequent annihilation of the inflowing magnetic flux determines the structure of the layer, while the ion heating could be due to the development of kinetic, current-driven instabilities.

  6. Local electron-electron interaction strength in ferromagnetic nickel determined by spin-polarized positron annihilation.

    PubMed

    Ceeh, Hubert; Weber, Josef Andreass; Böni, Peter; Leitner, Michael; Benea, Diana; Chioncel, Liviu; Ebert, Hubert; Minár, Jan; Vollhardt, Dieter; Hugenschmidt, Christoph

    2016-01-01

    We employ a positron annihilation technique, the spin-polarized two-dimensional angular correlation of annihilation radiation (2D-ACAR), to measure the spin-difference spectra of ferromagnetic nickel. The experimental data are compared with the theoretical results obtained within a combination of the local spin density approximation (LSDA) and the many-body dynamical mean-field theory (DMFT). We find that the self-energy defining the electronic correlations in Ni leads to anisotropic contributions to the momentum distribution. By direct comparison of the theoretical and experimental results we determine the strength of the local electronic interaction U in ferromagnetic Ni as 2.0 ± 0.1 eV. PMID:26879249

  7. Positron annihilation lifetime spectroscopy of poly(ethylene terephthalate): Contributions from rigid and mobile amorphous fractions

    NASA Astrophysics Data System (ADS)

    Olson, Brian; Lin, Jun; Nazarenko, Sergei; Jamieson, Alexander

    2004-03-01

    Systematic divergences in the orthopositronium (o-Ps) annihilation lifetimes, τ_3, and intensities, I_3, are observed, when comparing melt-crystallized and cold-crystallized poly(ethylene terephthalate) (PET) as a function of crystallinity. Following a previous analysis of corresponding deviations in oxygen permeability, the divergences in I3 and τ3 are traced to distinct characteristic values for the probability of o-Ps formation and o-Ps lifetime in the rigid amorphous phase (RAF) associated with the crystalline lamellae and the mobile amorphous regions (MAF) which are unperturbed by the presence of the crystal phase. Utilizing independent information on the volume fractions of RAF and MAF, a quantitative analysis of the o-Ps annihilation parameters is possible.

  8. Synthesis of triplet-triplet annihilation upconversion nanocapsules under protective conditions.

    PubMed

    Katta, Kartheek; Busko, Dmitry; Avlasevich, Yuri; Muñoz-Espí, Rafael; Baluschev, Stanislav; Landfester, Katharina

    2015-06-01

    Triplet-triplet annihilation upconversion (TTA-UC) nanocapsules are synthesized under oxygen-protective conditions (i.e., complete darkness and argon atmosphere) by free-radical miniemulsion polymerization. These conditions help to exclude the oxidation of the emitter molecules caused by singlet oxygen, generated during the synthesis at daylight conditions and oxygen-rich environment. Subsequently, keeping all the other experimental conditions the same, samples synthesized at protective conditions demonstrate substantially increased UC efficiency. These experimental facts strongly support the hypothesis that posterior removing of oxygen from TTA-UC nanocapsules is not sufficient to obtain reproducible and sustainable UC results. The schematic representation shows the influence of sunlight on the formation of singlet oxygen and its effect on the triplet-triplet annihilation upconversion process. PMID:25630569

  9. Can Astrophysical Gamma Ray Sources Mimic Dark Matter Annihilation in Galactic Satellites?

    SciTech Connect

    Baltz, Edward A.; Taylor, James E.; Wai, Lawrence L.; /KIPAC, Menlo Park

    2006-11-01

    The nature of the cosmic dark matter is unknown. The most compelling hypothesis is that dark matter consists of weakly interacting massive particles (WIMPs) in the 100 GeV mass range. Such particles would annihilate in the galactic halo, producing high-energy gamma rays which might be detectable in gamma ray telescopes such as the GLAST satellite. We investigate the ability of GLAST to distinguish between the WIMP annihilation spectrum and the spectrum of known astrophysical source classes. Focusing on the emission from the galactic satellite halos predicted by the cold dark matter model, we find that the WIMP gamma-ray spectrum is unique; the separation from known source classes can be done in a convincing way. We discuss the follow-up of possible WIMP sources with Imaging Atmospheric Cerenkov Telescopes. Finally we discuss the impact that Large Hadron Collider data might have on the study of galactic dark matter.

  10. When some elementary free volumes in polymers are not seen by positron annihilation experiments

    NASA Astrophysics Data System (ADS)

    Shantarovich, V. P.; Bekeshev, V. G.; Pastukhov, A. V.; Davankov, V. A.; Krasil'nikova, O. K.; Belousova, E. V.; Kevdina, I. B.; Filimonov, M. K.; Gustov, V. W.

    2015-06-01

    Size distributions of elementary free volumes have been studied in mesoporous micro-heterogeneous polymer sorbents. Positron annihilation lifetime spectroscopy (PALS), low temperature gas adsorption (BET) and thermo-stimulated luminescence (TSL) measurements are employed as complementary instruments for the study. It is shown that small admixtures of rubbers are very effective for variations of the pore size distribution. While BET technique was very informative for measurements of mesopores(2-50 nm), positron annihilation was sensitive to micropores(<2 nm), but not for mesopores. The last specificity is explained by the limited positronium diffusion length in a polymer and also by inhomogeneous distribution of mesoporesin heterogeneous systems. TSL measurements gave information on sizes of rubber inclusions in compositions.

  11. Branching and annihilating random walks: exact results at low branching rate.

    PubMed

    Benitez, Federico; Wschebor, Nicolás

    2013-05-01

    We present some exact results on the behavior of branching and annihilating random walks, both in the directed percolation and parity conserving universality classes. Contrary to usual perturbation theory, we perform an expansion in the branching rate around the nontrivial pure annihilation (PA) model, whose correlation and response function we compute exactly. With this, the nonuniversal threshold value for having a phase transition in the simplest system belonging to the directed percolation universality class is found to coincide with previous nonperturbative renormalization group (RG) approximate results. We also show that the parity conserving universality class has an unexpected RG fixed point structure, with a PA fixed point which is unstable in all dimensions of physical interest. PMID:23767512

  12. Exciton-exciton annihilation and relaxation pathways in semiconducting carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Chmeliov, Jevgenij; Narkeliunas, Jonas; Graham, Matt W.; Fleming, Graham R.; Valkunas, Leonas

    2016-01-01

    We present a thorough analysis of one- and two-color transient absorption measurements performed on single- and double-walled semiconducting carbon nanotubes. By combining the currently existing models describing exciton-exciton annihilation--the coherent and the diffusion-limited ones--we are able to simultaneously reproduce excitation kinetics following both E11 and E22 pump conditions. Our simulations revealed the fundamental photophysical behavior of one-dimensional coherent excitons and non-trivial excitation relaxation pathways. In particular, we found that after non-linear annihilation a doubly-excited exciton relaxes directly to its E11 state bypassing the intermediate E22 manifold, so that after excitation resonant with the E11 transition, the E22 state remains unpopulated. A quantitative explanation for the observed much faster excitation kinetics probed at E22 manifold, comparing to those probed at the E11 band, is also provided.

  13. Resonant Compton cooling and annihilation line production in gamma-ray bursts

    NASA Technical Reports Server (NTRS)

    Preece, R. D.; Harding, A. K.

    1992-01-01

    Attention is given to a synchrotron self-Compton emission model for gamma-ray bursts which produces narrow annihilation features for a variety of field strengths, primary electron injection energies, and injection rates. In this model, primary electrons are injected and cooled by synchrotron emission in a strong, homogeneous magnetic field, resulting in a pair cascade. Multiple resonant scattering with cyclotron photons efficiently traps and cools pairs in the ground state to an average energy where the Compton energy loss rate is zero, which is in agreement with previous estimates of a Compton temperature. The particle distributions in the ground state are determined by numerically solving the Fokker-Planck equation in the steady state. In the case of isotropic injection of primary electrons, a significant narrow-line feature appears in the overall emission. In the case of beamed injection, the annihilation line is broadened to the extent that it would not be observable.

  14. Reducing exciton-polaron annihilation in organic planar heterojunction solar cells

    NASA Astrophysics Data System (ADS)

    Verreet, Bregt; Bhoolokam, Ajay; Brigeman, Alyssa; Dhanker, Rijul; Cheyns, David; Heremans, Paul; Stesmans, Andre; Giebink, Noel C.; Rand, Barry P.

    2014-09-01

    We investigate the relationship between charge concentration, exciton concentration, and photocurrent generation in fullerene-containing heterojunction diodes. Impedance measurements on C60 diodes reveal a charge buildup at the C60/bathocuproine (BCP) interface that can be swept out under reverse bias. In solar cell structures, a similar charge buildup is observed in dark conditions, and increases as a function of incident light intensity. Photoluminescence measurements reveal that the C60 exciton concentration is voltage dependent, explained via the process of exciton-polaron annihilation. This process has a negative impact on the generated photocurrent of the solar cells and thereby decreases the fill factor. A combination of electroabsorption, photoluminescence, and impedance measurements reveal a decrease in charge buildup and the associated exciton-polaron annihilation through the use of a BCP/3,4,9,10-perylenetetracarboxylic bis-benzimidazole/Ag cathode.

  15. Free volume structure of realgar α-As4S4 by positron annihilation lifetime spectroscopy

    NASA Astrophysics Data System (ADS)

    Shpotyuk, O.; Ingram, A.; Demchenko, P.

    2015-04-01

    Atomic-deficient free volume structure of realgar α-As4S4, the low-temperature modification, of tetraarsenic tetrasulfide polymorphs, is studied using positron annihilation lifetime spectroscopy. Eventual channels of positron annihilation in this molecular crystal are shown to be connected with low electron density entities around cage As4S4 molecules composing realgar-type structure of monoclinic P21/n space group. The overlapped spaces of bond-free solid angles around S atoms forming self-closed As4S4 molecules contribute preferentially to positron trapping modes, while a competitive influence of bound positron-electron states (positronium) stabilized in intermolecular spaces occurs also to be essential in the decomposed lifetime spectra too.

  16. Cosmic-ray antiprotons, positrons, and gamma rays from halo dark matter annihilation

    NASA Technical Reports Server (NTRS)

    Rudaz, S.; Stecker, F. W.

    1988-01-01

    The subject of cosmic ray antiproton production is reexamined by considering other choices for the nature of the Majorana fermion chi other than the photino considered in a previous article. The calculations are extended to include cosmic-ray positrons and cosmic gamma rays as annihilation products. Taking chi to be a generic higgsino or simply a heavy Majorana neutrino with standard couplings to the Z-zero boson allows the previous interpretation of the cosmic antiproton data to be maintained. In this case also, the annihilation cross section can be calculated independently of unknown particle physics parameters. Whereas the relic density of photinos with the choice of parameters in the previous paper turned out to be only a few percent of the closure density, the corresponding value for Omega in the generic higgsino or Majorana case is about 0.2, in excellent agreement with the value associated with galaxies and one which is sufficient to give the halo mass.

  17. Role of pentaquark components in ϕ meson production proton-antiproton annihilation reactions

    NASA Astrophysics Data System (ADS)

    Srisuphaphon, S.; Kaewsnod, A.; Limphirat, A.; Khosonthongkee, K.; Yan, Y.

    2016-02-01

    The pentaquark component uuds s ¯ is included in the proton wave functions to study ϕ meson production proton-antiproton annihilation reactions. With all possible configurations of the uuds subsystem proposed for describing the strangeness spin and magnetic moment of the proton, we estimate the branching ratios of the annihilation reactions at rest p p ¯→ϕ X (X =π0,η ,ρ0,ω ) from atomic p p ¯ S - and P -wave states by using effective quark line diagrams incorporating the 3P0 model. The best agreement of theoretical prediction with the experimental data is found when the pentaquark configuration of the proton wave function takes the flavor-spin symmetry [4] FS[22] F[22] S .

  18. Theory of exciton annihilation in complexes of a finite number of molecular sites.

    PubMed

    Gülen, D

    1990-11-01

    A theory of the kinematics of singlet exciton annihilation in complexes of a finite number of molecular sites is developed. The theory is based on a specific scheme suggested earlier by Gülen, Wittmershaus, and Knox [Biophys J. 49:469-477 (1986)]. It is adequate to address the excitation kinetics and dynamics in such systems, especially under high excitation intensities. A Pauli master equation is formulated and is solved to give explicit expressions for observables such as quantum yield and fluorescence intensity. The excitation intensity dependence of the observables is taken into account by introducing Poisson statistics. Details relevant to its application to the annihilation of excitons in photosynthetic systems and its connection to earlier theories are presented. PMID:2134489

  19. Theoretical studies of positron states and annihilation characteristics at the oxidized Cu(100) surface

    SciTech Connect

    Fazleev, N. G.; Weiss, A. H.

    2013-04-19

    In this work we present the results of theoretical studies of positron surface and bulk states and annihilation probabilities of surface-trapped positrons with relevant core electrons at the oxidized Cu(100) surface under conditions of high oxygen coverage. An ab-initio study of the electronic properties of the Cu(100) missing row reconstructed surface at various on surface and sub-surface oxygen coverages has been performed on the basis of the density functional theory (DFT) using the Dmol3 code and the generalized gradient approximation (GGA). Surface structures in calculations have been constructed by adding oxygen atoms to various surface hollow and sub-surface octahedral sites of the 0.5 monolayer (ML) missing row reconstructed phase of the Cu(100) surface with oxygen coverages ranging from 0.5 to 1.5 ML. The charge redistribution at the surface and variations in atomic structure and chemical composition of the topmost layers associated with oxidation and surface reconstruction have been found to affect the spatial extent and localization of the positron surface state wave function and annihilation probabilities of surface trapped positrons with relevant core electrons. Theoretical results are compared with experimental data obtained from studies of oxidation of the Cu(100) surface using positron annihilation induced Auger electron spectroscopy (PAES). It has been shown that positron annihilation probabilities with Cu 3s and 3p core electrons decrease when total (on-surface and sub-surface) oxygen coverage of the Cu(100) surface increases up to 1 ML. The calculations show that for high oxygen coverage when total oxygen coverage is 1. 5 ML the positron is not bound to the surface.

  20. Could the cosmological recombination spectrum help us understand annihilating dark matter?

    NASA Astrophysics Data System (ADS)

    Chluba, J.

    2010-02-01

    In this paper, we explore the potential effects of dark matter (DM) annihilations on the cosmological recombination spectrum. With this example, we want to demonstrate that the cosmological recombination spectrum in principle is sensitive to details related to possible extra energy release during recombination. We restrict ourselves to DM models which produce a negligible primordial distortion of the cosmic microwave background (CMB) energy spectrum (usually characterized as μ- and y-type distortions). However, since during the epoch of cosmological recombination (z ~ 1000) a large fraction of the deposited energy can directly go into ionizations and excitations of neutral atoms, both the cosmological recombination spectrum and ionization history can still be affected significantly. We compute the modifications to the cosmological recombination spectrum using our multilevel HI and HeI recombination code, showing that additional photons are created due to uncompensated loops of transitions which are induced by DM annihilations. As we illustrate here, the results depend on the detailed branching of the deposited energy into heating, ionizations and excitations. This dependence in principle should allow us to shed light on the nature of the underlying annihilating DM model (or more generally speaking, the mechanism leading to energy injection) when measuring the cosmological recombination spectrum. However, for current upper limits on the potential DM annihilation rate during recombination the cosmological recombination spectrum is only affected at the level of a few per cent. Nevertheless, we argue here that the cosmological recombination spectrum would provide another independent and very direct way of checking for the presence of sources of extra ionizing or exciting photons at high redshifts. This would open a new window to possible (non-standard) processes occurring before, during and between the three epochs of recombination.

  1. Forty-five Years of e{sup +}e{sup -} Annihilation Physics: 1956 to 2001

    DOE R&D Accomplishments Database

    Richter, B.

    1984-08-01

    The history of e{sup +}e{sup -} physics in the 1950's and 1960's is reviewed, followed by some highlights of the spectacular discoveries in e{sup +}e{sup -} annihilation made during the 1970's. The consolidation of knowledge during the last few years is summarized. Some predictions are made for the field of e{sup +}e{sup -} physics for the next decade and beyond. (LEW)

  2. Constraints on dark matter annihilations from diffuse gamma-ray emission in the Galaxy

    SciTech Connect

    Tavakoli, Maryam; Evoli, Carmelo; Cholis, Ilias; Ullio, Piero E-mail: cholis@fnal.gov E-mail: ullio@sissa.it

    2014-01-01

    Recent advances in γ-ray cosmic ray, infrared and radio astronomy have allowed us to develop a significantly better understanding of the galactic medium properties in the last few years. In this work using the DRAGON code, that numerically solves the CR propagation equation and calculating γ-ray emissivities in a 2-dimensional grid enclosing the Galaxy, we study in a self consistent manner models for the galactic diffuse γ-ray emission. Our models are cross-checked to both the available CR and γ-ray data. We address the extend to which dark matter annihilations in the Galaxy can contribute to the diffuse γ-ray flux towards different directions on the sky. Moreover we discuss the impact that astrophysical uncertainties of non DM nature, have on the derived γ-ray limits. Such uncertainties are related to the diffusion properties on the Galaxy, the interstellar gas and the interstellar radiation field energy densities. Light ∼ 10 GeV dark matter annihilating dominantly to hadrons is more strongly constrained by γ-ray observations towards the inner parts of the Galaxy and influenced the most by assumptions of the gas distribution; while TeV scale DM annihilating dominantly to leptons has its tightest constraints from observations towards the galactic center avoiding the galactic disk plane, with the main astrophysical uncertainty being the radiation field energy density. In addition, we present a method of deriving constraints on the dark matter distribution profile from the diffuse γ-ray spectra. These results critically depend on the assumed mass of the dark matter particles and the type of its end annihilation products.

  3. Different ways of dealing with Compton scattering and positron annihilation experimental data

    NASA Astrophysics Data System (ADS)

    Kontrym-Sznajd, G.; Samsel-Czekała, M.

    2005-05-01

    Different ways of dealing with one-dimensional (1D) spectra, measured e.g., in the Compton scattering or angular correlation of positron annihilation radiation (ACAR) experiments, are presented. Using the example of divalent hexagonal close packed metals, we show what kind of information on the electronic structure one can get from 1D profiles interpreted in terms of either 2D or 3D momentum densities.

  4. Fluxes and spectra of quasimonochromatic annihilation photons for studying E1 giant resonances in nuclei

    SciTech Connect

    Dzhilavyan, L. Z.

    2014-12-15

    The fluxes and spectra of quasimonochromatic photons originating from the in-flight annihilation of positrons interacting with electrons of targets are analyzed in the energy region characteristic of the excitation of E1 giant resonances in nuclei. Targets of small thickness and low atomic number are used. The dependences of the spectra on the energy and angle (and their scatter) for positrons incident to the target, on the collimation angle for photons, and on the target thickness are studied.

  5. Inverse Compton Gamma Rays from Dark Matter Annihilation in the Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Medhi, Jayashri; Duorah, H. L.; Barua, A. G.; Duorah, K.

    2016-09-01

    Dwarf spheroidal (dSph) galaxies are thought to be good candidates for dark matter search due to their high mass-to-light (M/L) ratio. One of the most favored dark matter candidates is the lightest neutralino (neutral χ particle) as predicted in the Minimal Supersymmetric Standard Model (MSSM). In this study, we model the gamma ray emission from dark matter annihilation coming from the nearby dSph galaxies Draco, Segue 1, Ursa Minor and Willman 1, taking into account the contribution from prompt photons and photons produced from inverse Compton scattering off starlight and Cosmic Microwave Background (CMB) photons by the energetic electrons and positrons from dark matter annihilation. We also compute the energy spectra of electrons and positrons from the decay of dark matter annihilation products. Gamma ray spectra and fluxes for both prompt and inverse Compton emission have been calculated for neutralino annihilation over a range of masses and found to be in agreement with the observed data. It has been found that the ultra faint dSph galaxy Segue 1 gives the largest gamma ray flux limits while the lowest gamma ray flux limits has been obtained from Ursa Minor. It is seen that for larger M/L ratio of dwarf galaxies the intensity pattern originating from e + e - pairs scattering off CMB photons is separated by larger amount from that off the starlight photons for the same neutralino mass. As the e + e - energy spectra have an exponential cut off at high energies, this may allow to discriminate some dark matter scenarios from other astrophysical sources. Finally, some more detailed study about the effect of inverse Compton scattering may help constrain the dark matter signature in the dSph galaxies.

  6. Measurements of the Collins asymmetries for kaons and pions in e+e- annihilations at BABAR

    NASA Astrophysics Data System (ADS)

    Filippi, A.

    2016-07-01

    New measurements of the Collins asymmetries were performed by BABAR exploiting inclusive e+e- → h1h2 X annihilations (with h1,2 = π and/or K) mainly at the energy of the ϒ(4S), which corresponds to a squared transferred momentum Q2 ~ 110 GeV2c4. For the first time asymmetries following strange quarks fragmentation could be derived as a function of the fractional energy carried out by inclusively emitted hadron pairs.

  7. Precise tests of QCD in e{sup +}e{sup {minus}} annihilation

    SciTech Connect

    Burrows, P.N.

    1997-03-01

    A pedagogical review is given of precise tests of QCD in electron-positron annihilation. Emphasis is placed on measurements that have served to establish QCD as the correct theory of strong interactions, as well as measurements of the coupling parameter {alpha}{sub s}. An outlook is given for future important tests at a high-energy e{sup +}e{sup {minus}} collider.

  8. Forty-five years of e/sup +/e/sup -/ annihilation physics: 1956 to 2001

    SciTech Connect

    Richter, B.

    1985-04-01

    The history of e/sup +/e/sup -/ physics in the 1950's and 1960's is reviewed, followed by some highlights of the spectacular discoveries in e/sup +/e/sup -/ annihilation made during the 1970's. The consolidation of knowledge during the last few years is summarized. Some predictions are made for the field of e/sup +/e/sup -/ physics for the next decade and beyond. (LEW)

  9. Dynamics of defects in x-ray irradiated alkali chloride crystals studied by positron annihilation

    SciTech Connect

    Stern, S.H.

    1982-01-01

    Data on the time dependence of positron-electron annihilation characteristics in single crystals of the homologous series NaCl, KCl, RbCl, and CsCl after large doses of x irradiation are reported. A new instrument, the ..pi..-radian coincidence apparatus (PICA), recorded the coincidence count rate P of the two 0.5-MeV annihilation ..gamma.. rays emerging 180/sup 0/ apart from the crystal during isothermal and isochronal heating conditions. In most crystals an initial rapid increase of P to a maximum followed by a slow decline toward the coincidence count rate corresponding to the pre-irradiation state of the crystal was observed. Positron-annihilation data were completed by independent measurements of the optical absorption in KCl and NaCl crystals after various durations of isothermal heating. Absorption spectrophotometry revealed enhancement of the M band in KCl, of the R and N bands in NaCl, at the expense of the F band during the interpretation that positrons are trapped by radiation-induced color centers in which they annihilate with a higher P than in the bulk of the crystal. The dynamics associated with the incipient rise of P during the initial heating period is attributable to the agglomeration of F centers into aggregate centers. The rise times of P give access to the diffusion rates for agglomeration. At equal temperatures, a strong dependence of the rate of defect diffusion on the size of the cation was observed. The data must be corrected for the effects of decoloration of the crystals by the positrons during the measurements. Activation energies for defect diffusion annealing are extracted.

  10. Charge distribution and charge correlation in the annihilation of antiprotons on nuclei

    NASA Astrophysics Data System (ADS)

    Cugnon, J.; Deneye, P.; Vandermeulen, J.

    1988-08-01

    A schematic model is devised to account for the charged track pattern in antiproton nucleus annihilation at low momenta. The ejection mechanism is assumed to correspond to a clan picture, where the ancestors are pions. Good agreement is obtained for multiplicity distributions, in neon and in emulsion, and in particular for the very strong correlation observed in neon between negative pions and the total number of charged tracks.

  11. Systematic uncertainties in constraining dark matter annihilation from the cosmic microwave background

    NASA Astrophysics Data System (ADS)

    Galli, Silvia; Slatyer, Tracy R.; Valdes, Marcos; Iocco, Fabio

    2013-09-01

    Anisotropies of the cosmic microwave background (CMB) have proven to be a very powerful tool to constrain dark matter annihilation at the epoch of recombination. However, CMB constraints are currently derived using a number of reasonable but yet untested assumptions that could potentially lead to a misestimation of the true bounds (or any reconstructed signal). In this paper we examine the potential impact of these systematic effects. In particular, we separately study the propagation of the secondary particles produced by annihilation in two energy regimes: first following the shower from the initial particle energy to the keV scale, and then tracking the resulting secondary particles from this scale to the absorption of their energy as heat, ionization, or excitation of the medium. We improve both the high- and low-energy parts of the calculation, in particular finding that our more accurate treatment of losses to sub-10.2 eV photons produced by scattering of high-energy electrons weakens the constraints on particular dark matter annihilation models by up to a factor of 2. On the other hand, we find that the uncertainties we examine for the low-energy propagation do not significantly affect the results for current and upcoming CMB data. We include the evaluation of the precise amount of excitation energy, in the form of Lyman-α photons, produced by the propagation of the shower, and examine the effects of varying the helium fraction and helium ionization fraction. In the recent literature, simple approximations for the fraction of energy absorbed in different channels have often been used to derive CMB constraints: we assess the impact of using accurate vs approximate energy fractions. Finally we check that the choice of recombination code (between RECFAST v1.5 and COSMOREC), to calculate the evolution of the free electron fraction in the presence of dark matter annihilation, introduces negligible differences.

  12. Analytical singlet α{/s 4} QCD contributions into the e + e --annihilation Adler function and the generalized Crewther relations

    NASA Astrophysics Data System (ADS)

    Kataev, A. L.

    2012-02-01

    The generalized Crewther relations in the channels of the non-singlet and vector quark currents are considered. These relations follow from the double application of the operator product expansion approach to the same axial vector-vector-vector triangle amplitude in two regions, adjoining to the angle sides ( x, y) (or p 2, q 2). We assume that the generalized Crewther relations in these two kinematic regimes result in the existence of the same perturbation expression for two products of the coefficient functions of annihilation and deepinelastic scattering processes in the non-singlet and vector channels. This feature explains the conformal symmetry motivated cancellations between the singlet α{/s 3} corrections to the Gross-Llewellyn Smith sum rule S GLS of ν N deep inelastic scattering and the singlet α{/s 3} correction to the e + e --annihilation Adler function D {/A V } in the product of the corresponding perturbative series. Taking into account the Baikov-Chetyrkin-Kuhn fourth order result for S GLS and the perturbative effects of the violation of the conformal symmetry in the generalized Crewther relation, we obtain the analytical contribution to the singlet α{/s 4} correction to the D {/A V } function. Its a-posteriori comparison with the recent result of direct diagram-by-diagram evaluation of the singlet fourth order corrections to D {/A V } function demonstrates the coincidence of the predicted and obtained ζ{3/2}-contributions to the singlet term. They can be obtained in the conformal invariant limit from the original Crewther relation. Therefore, on the contrary to previous belief, the appearance of ζ3-terms in the perturbative series in quantum field theory gauge models does not contradict to the property of the conformal symmetry and can be considered as regular feature. The Banks-Zaks motivated relation between our predicted and the obtained directly fourth order corrections is mentioned. It confirms the expectation, previously made by Baikov

  13. Neutrino emissivity from e sup minus e+ annihilation in a strong magnetic field: Hot, nondegenerate plasma

    SciTech Connect

    Kaminker, A.D.; Gnedin, O.Y.; Yakovlev, D.G. ); Amsterdamski, P.; Haensel, P. )

    1992-11-15

    The neutrino emissivity from {ital e}{sup {minus}}{ital e+} pair annihilation is calculated for a hot, nondegenerate plasma, {ital T}{much gt}{ital T}{sub {ital F}} ({ital T}{sub {ital F}} is the electron degeneracy temperature), in a magnetic field {bold B} of arbitrary strength. The results are fitted by an analytic expression. A not-very-strong magnetic field, {ital b}={ital B}/{ital B}{sub {ital c}}{much lt}1 ({ital B}{sub {ital c}}=4.41{times}10{sup 13} G), enhances the emissivity of a nonrelativistic plasma, {ital t}={ital T}/{ital T}{sub {ital c}}{approx lt}{ital b} ({ital T}{sub {ital c}}=6{times}10{sup 9} K), and does not affect the emissivity at higher {ital T}. Stronger fields, {ital b}{much gt}1, influence the pair annihilation if {ital t}{approx lt} {radical}{ital b} . At {ital t}{approx gt}{ital b}{sup 1/4} they suppress the process, and at {ital t}{much lt}{ital b}{sup 1/4} they enhance it. As a rule the pair annihilation dominates over other neutrino production mechanisms in a hot plasma of neutron-star envelopes.

  14. Cross sections for inelastic meson-meson scattering via quark-antiquark annihilation

    NASA Astrophysics Data System (ADS)

    Shen, Zhen-Yu; Xu, Xiao-Ming; Weber, H. J.

    2016-08-01

    We study inelastic meson-meson scattering that is governed by quark-antiquark annihilation and creation involving a quark and an antiquark annihilating into a gluon, and subsequently the gluon creating another quark-antiquark pair. The resultant hadronic reactions include for I =1 : π π →ρ ρ , K K ¯→K*K¯*, K K¯*→K*K¯*, K*K ¯→K*K¯*, as well as π π →K K ¯, π ρ →K K¯*, π ρ →K*K ¯, and K K ¯→ρ ρ . In each reaction, one or two Feynman diagrams are involved in the Born approximation. We derive formulas for the unpolarized cross section, the transition amplitude, and the transition potential for quark-antiquark annihilation and creation. The unpolarized cross sections for the reactions are calculated at six temperatures, and prominent temperature dependence is found. It is due to differences among mesonic temperature dependence in hadronic matter.

  15. Annihilation momentum density of positrons trapped at vacancy-type defects in metals and alloys

    SciTech Connect

    Bansil, A.; Prasad, R.; Benedek, R.

    1988-01-01

    Positron annihilation, especially the angular correlation of annihilation radiation, is a powerful tool for investigating the electronic spectra of ordered as well as defected materials. The tendency of positrons to trap at vacancy-type defects should enable this technique to study the local environment of such defects. However, we need to develop a theoretical basis for calculating the two-photon annihilation momentum density rho/sub 2gamma/(p-vector). We have recently formulated and implemented a theory of rho/sub 2gamma/(p-vector) from vacancy-type defects in metals and alloys. This article gives an outline of our approach together with a few of our results. Section 2 summarizes the basic equations for evaluating rho/sub 2gamma/(p-vector). Our Green's function-based approach is nonperturbative and employs a realistic (one-particle) muffin-tin Hamiltonian for treating electrons and positrons. Section 3 presents and discusses rho/sub 2gamma/(p-vector) results for a mono-vacancy in Cu. We have neglected the effects of electron-positron correlations and of lattice distortion around the vacancy. Section 4 comments briefly on the question of treating defects such as divacancies and metal-impurity complexes in metals and alloys. Finally, in Section 5, we remark on the form of rho/sub 2gamma/(p-vector) for a mono-vacancy in jellium. 2 figs.

  16. The spatial distribution of dark matter annihilation originating from a gamma-ray line signal

    NASA Astrophysics Data System (ADS)

    Lu, Tong-Suo; Dong, Tie-Kuang; Wu, Jian

    2014-05-01

    The GeV-TeV γ-ray line signal is the smoking gun signature of dark matter annihilation or decay. The detection of such a signal is one of the main targets of some space-based telescopes, including Fermi-LAT and the upcoming missions CALET, DAMPE and Gamma-400. An important feature of γ-ray line photons that originate from dark-matter-annihilation is that they are concentrated at the center of the Galaxy. So far, no reliable γ-ray line has been detected by Fermi-LAT, and the upper limits on the cross section of annihilation into γ-rays have been reported. We use these upper limits to estimate the “maximal” number of γ-ray line photons detectable for Fermi-LAT, DAMPE and Gamma-400, and then investigate the spatial distribution of these photons. We show that the center of the distribution will usually be offset from the Galactic center (Sgr A*) due to the limited statistics. Such a result is almost independent of models of the dark matter distribution, and will render the reconstruction of the dark matter distribution with the γ-ray line signal very challenging for foreseeable space-based detectors.

  17. Energetic neutrinos from heavy-neutralino annihilation in the Sun. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Kamionkowski, Marc

    1991-01-01

    Neutralinos may be captured in the sun and annihilated therein producing high-energy neutrinos. Present limits on the flux of such neutrinos from underground detectors such as IMB and Kamiokande 2 may be used to rule out certain supersymmetric dark matter candidates, while in many other supersymmetric models the rates are large enough that if neutralinos do reside in the galactic halo, observation of a neutrino signal may be possible in the near future. Neutralinos that are either nearly pure Higgsino or a Higgsino/gaugino combination are generally captured in the sun by coherent scattering off nuclei via exchange of the lightest Higgs boson. If the squark mass is not much greater than the neutralino mass, then capture of neutralinos that are primarily gaugino occurs predominantly by spin-dependent scattering off hydrogen in the sun. The neutrino signal from annihilation of WIMPs with masses in the range of 80 to 1000 GeV in the sun should generally be stronger than that from weakly interacting massive particle (WIMP) annihilation in the earth, and detection rates for mixed-state neutralinos are generally higher than those for Higgsinos or gauginos.

  18. Annihilation dynamics of stringlike topological defects in a nematic lyotropic liquid crystal.

    PubMed

    Guimarães, R R; Mendes, R S; Fernandes, P R G; Mukai, H

    2013-10-01

    Topological defects can appear whenever there is some type of ordering. Its ubiquity in nature has been the subject of several studies, from early Universe to condensed matter. In this work, we investigated the annihilation dynamics of defects and antidefects in a lyotropic nematic liquid crystal (ternary mixture of potassium laurate, decanol and deionized-destillated water) using the polarized optical light microscopy technique. We analyzed Schlieren textures with topological defects produced due to a symmetry breaking in the transition of the isotropic to nematic calamitic phase after a temperature quench. As result, we obtained for the distance D between two annihilating defects (defect-antidefect pair), as a function of time t remaining for the annihilation, the scaling law D ∝ t(α), with α = 0.390 and standard deviation σ = 0.085. Our findings go in the direction to extend experimental results related to dynamics of defects in liquid crystals since only thermotropic and polymerics ones had been investigated. In addition, our results are in good quantitative agreement with previous investigations on the subject. PMID:24025970

  19. Study of PRIMAVERA steel samples by a positron annihilation spectroscopy technique

    NASA Astrophysics Data System (ADS)

    Grafutin, V.; Ilyukhina, O.; Krsjak, V.; Burcl, R.; Hähner, P.; Erak, D.; Zeman, A.

    2010-11-01

    In the present article, a positron annihilation spectroscopy investigation of VVER-440/230 weld materials is discussed. Important characteristics of metals such as Fermi energy, concentration of electrons in the conduction band, size and concentration of defects were experimentally determined for three model materials with higher level of copper (0.16 wt.%) and phosphorus (0.027-0.038 wt.%). The impact of neutron irradiation and subsequent annealing on crystal lattice parameters was investigated. The experiments with the angular correlation of positron annihilation radiation (ACAR) complement the published positron annihilation spectroscopy (PAS) studies of the radiation treated VVER materials as well as previous experiments on PRIMAVERA materials. The availability of the experimental reactor to prepare strong 64Cu positron sources provided for unique experimental conditions, such as good resolution of spectra (0.4 mrad) and reasonable short time of measurement (36 h). The present paper aims to contribute to further understanding of RPV (reactor pressure vessel) steels behaviour under irradiation conditions as well as annealing recovery procedures, which have already been applied at several VVER NPP units in Europe.

  20. Isotropic extragalactic flux from dark matter annihilations: lessons from interacting dark matter scenarios

    NASA Astrophysics Data System (ADS)

    Moliné, Ángeles; Schewtschenko, Jascha A.; Palomares-Ruiz, Sergio; Bœhm, Céline; Baugh, Carlton M.

    2016-08-01

    The extragalactic γ-ray and neutrino emission may have a contribution from dark matter (DM) annihilations. In the case of discrepancies between observations and standard predictions, one could infer the DM pair annihilation cross section into cosmic rays by studying the shape of the energy spectrum. So far all analyses of the extragalactic DM signal have assumed the standard cosmological model (ΛCDM) as the underlying theory. However, there are alternative DM scenarios where the number of low-mass objects is significantly suppressed. Therefore the characteristics of the γ-ray and neutrino emission in these models may differ from ΛCDM as a result. Here we show that the extragalactic isotropic signal in these alternative models has a similar energy dependence to that in ΛCDM, but the overall normalisation is reduced. The similarities between the energy spectra combined with the flux suppression could lead one to misinterpret possible evidence for models beyond ΛCDM as being due to CDM particles annihilating with a much weaker cross section than expected.

  1. Helium reionization in the presence of self-annihilating clumpy dark matter

    NASA Astrophysics Data System (ADS)

    Bandyopadhyay, Bidisha; Schleicher, Dominik R. G.

    2015-07-01

    The reionization of helium describes the transition from its singly ionized state to a doubly ionized state in the intergalactic medium. This process is important for the thermal evolution of the intergalactic medium and influences the mean free path of photons with energies above 54.4 eV. While it is well known that helium reionization is mostly driven by the contribution of energetic quasars at z <6 , we study here how helium reionization proceeds if there is an additional contribution due to the annihilation of dark matter. We explore the effects of different dark matter profiles for the dark matter clumping factor, which can significantly enhance the annihilation rate at late times. We find that the presence of dark matter annihilation enhances the He++ abundance at early stages where it would be zero within the standard model, and it can further increase during structure formation, reflecting the increase of the dark matter clumping factor. The latter is, however, degenerate with the buildup of the quasar contribution, and we therefore expect no significant changes at late times. We expect that future studies of the He+ Lyman α forest may help to assess whether the evolution is consistent with the contribution from quasars alone, or if an additional component may be required.

  2. Thermal Stability of MgyTi1-y Thin Films Investigated by Positron Annihilation Spectroscopy

    NASA Astrophysics Data System (ADS)

    Anastasopol, A.; Eijt, S. W. H.; Schut, H.; Mulder, F. M.; Plazaola, F.; Dam, B.

    Mg-Ti compounds are attractive candidates as hydrogen storage materials for their fast sorption kinetics and high storage capacity. In this context, an investigation of their thermal stability is of great importance. The thermal stability of MgyTi1-y thin films was investigated using positron annihilation spectroscopy. Despite the positive enthalpy of mixing of Mg and Ti, positron Doppler Broadening of Annihilation Radiation (DBAR) depth profiling showed that Mg0.9Ti0.1 films are stable up to 300°C. However, for Mg0.7Ti0.3 films, segregation of Mg and Ti was observed at 300oC by the appearance of a clear Ti signature in the S-W diagrams and in the Doppler broadening depth profiles analyzed using VEPFIT. The thickness of the 250-300 nm thin films remained unchanged during the heating treatments. We further present ab-initio calculations of positron lifetimes of the corresponding metal and metal hydride phases for comparison to our previous positron annihilation lifetime spectroscopy (PALS) study.

  3. Positron annihilation lifetime study of polyvinylpyrrolidone for nanoparticle-stabilizing pharmaceuticals.

    PubMed

    Shpotyuk, O; Bujňáková, Z; Baláž, P; Ingram, A; Shpotyuk, Y

    2016-01-01

    Positron annihilation lifetime spectroscopy was applied to characterize free-volume structure of polyvinylpyrrolidone used as nonionic stabilizer in the production of many nanocomposite pharmaceuticals. The polymer samples with an average molecular weight of 40,000 g mol(-1) were pelletized in a single-punch tableting machine under an applied pressure of 0.7 GPa. Strong mixing in channels of positron and positronium trapping were revealed in the polyvinylpyrrolidone pellets. The positron lifetime spectra accumulated under normal measuring statistics were analysed in terms of unconstrained three- and four-term decomposition, the latter being also realized under fixed 0.125 ns lifetime proper to para-positronium self-annihilation in a vacuum. It was shown that average positron lifetime extracted from each decomposition was primary defined by long-lived ortho-positronium component. The positron lifetime spectra treated within unconstrained three-term fitting were in obvious preference, giving third positron lifetime dominated by ortho-positronium pick-off annihilation in a polymer matrix. This fitting procedure was most meaningful, when analysing expected positron trapping sites in polyvinylpyrrolidone-stabilized nanocomposite pharmaceuticals. PMID:26444751

  4. Identification of effective exciton-exciton annihilation in squaraine-squaraine copolymers.

    PubMed

    Hader, Kilian; May, Volkhard; Lambert, Christoph; Engel, Volker

    2016-05-11

    Ultrafast time-resolved transient absorption spectroscopy is able to monitor the fate of the excited state population in molecular aggregates or polymers. Due to many competing decay processes, the identification of exciton-exciton annihilation (EEA) is difficult. Here, we use a microscopic model to describe exciton annihilation processes in squaraine-squaraine copolymers. Transient absorption time traces measured at different laser powers exhibit an unusual time-dependence. The analysis points towards dynamics taking place on three time-scales. Immediately after laser-excitation a localization of excitons takes place within the femtosecond time-regime. This is followed by exciton-exciton annihilation which is responsible for a fast decay of the exciton population. At later times, excitations being localized on units which are not directly connected remain so that diffusion dominates the dynamics and leads to a slower decay. We thus provide evidence for EEA tracked by time-resolved spectroscopy which has not been reported that clearly before. PMID:27120976

  5. Search of dark matter annihilation in the galactic centre using the ANTARES neutrino telescope

    NASA Astrophysics Data System (ADS)

    The ANTARES Collaboration

    2015-10-01

    A search for high-energy neutrinos coming from the direction of the Galactic Centre is performed using the data recorded by the ANTARES neutrino telescope from 2007 to 2012. The event selection criteria are chosen to maximise the sensitivity to possible signals produced by the self-annihilation of weakly interacting massive particles accumulated around the centre of the Milky Way with respect to the atmospheric background. After data unblinding, the number of neutrinos observed in the line of sight of the Galactic Centre is found to be compatible with background expectations. The 90% C.L. upper limits in terms of the neutrino+anti-neutrino flux, Φνμ+bar nuμ, and the velocity averaged annihilation cross-section, langleσAvrangle, are derived for the WIMP self-annihilation channels into bbar b, W+W-, τ+τ-, μ+μ-, νbar nu. The ANTARES limits for langleσAvrangle are shown to be the most stringent for a neutrino telescope over the WIMP masses 25 GeV < MWIMP < 10 TeV.

  6. Extracting the Gamma Ray Signal from Dark Matter Annihilation in the Galactic Center Region

    SciTech Connect

    Dodelson, Scott; Hooper, Dan; Serpico, Pasquale D.

    2007-11-01

    The GLAST satellite mission will study the gamma ray sky with considerably greater exposure than its predecessor EGRET. In addition, it will be capable of measuring the arrival directions of gamma rays with much greater precision. These features each significantly enhance GLAST's potential for identifying gamma rays produced in the annihilations of dark matter particles. The combined use of spectral and angular information, however, is essential if the full sensitivity of GLAST to dark matter is to be exploited. In this paper, we discuss techniques for separating dark matter annihilation products from astrophysical backgrounds, focusing on the Galactic Center region, and perform a forecast for such an analysis. We consider both point-like and diffuse astrophysical backgrounds and model them using a realistic point-spread-function for GLAST. While the results of our study depend on the specific characteristics of the dark matter signal and astrophysical backgrounds, we find that in many scenarios it is possible to successfully identify dark matter annihilation radiation, even in the presence of significant astrophysical backgrounds.

  7. Positron annihilation study of neutron irradiated model alloys and of a reactor pressure vessel steel

    NASA Astrophysics Data System (ADS)

    Lambrecht, M.; Almazouzi, A.

    2009-03-01

    The hardening and embrittlement of reactor pressure vessel steels are of great concern in the actual nuclear power plant life assessment. This embrittlement is caused by irradiation-induced damage, and positron annihilation spectroscopy has been shown to be a suitable method for analysing most of these defects. In this paper, this technique (both positron annihilation lifetime spectroscopy and coincidence Doppler broadening) has been used to investigate neutron irradiated model alloys, with increasing chemical complexity and a reactor pressure vessel steel. It is found that the clustering of copper takes place at the very early stages of irradiation using coincidence Doppler broadening, when this element is present in the alloy. On the other hand, considerations based on positron annihilation spectroscopy analyses suggest that the main objects causing hardening are most probably self-interstitial clusters decorated with manganese in Cu-free alloys. In low-Cu reactor pressure vessel steels and in (Fe, Mn, Ni, Cu) alloys, the main effect is still due to Cu-rich precipitates at low doses, but the role of manganese-related features becomes pre-dominant at high doses.

  8. Positron Annihilation Spectroscopy of High Performance Polymer Films under CO2 Pressure

    SciTech Connect

    C.A. Quarles; John R. Klaehn; Eric S. Peterson; Jagoda M. Urban-Klaehn

    2010-08-01

    Positron annihilation Lifetime and Doppler broadening measurements are reported for six polymer films as a function of carbon dioxide absolute pressure ranging from 0 to 45 psi. Since the polymer films were thin and did not absorb all positrons, corrections were made in the lifetime analysis for the absorption of positrons in the positron source and sample holder using the Monte Carlo transport code MCNP. Different polymers are found to behave differently. Some polymers studied form positronium and some, such as the polyimide structures, do not. For those samples that form positronium an interpretation in terms of free volume is possible; for those that don’t form positronium, further work is needed to determine how best to describe the behavior in terms of the bulk positron annihilation parameters. Some polymers exhibit changes in positron lifetime and intensity under CO2 pressure which may be described by the Henry or Langmuir sorption models, while the positron response of other polymers is rather insensitive to the CO2 pressure. The results demonstrate the usefulness of positron annihilation spectroscopy in investigating the sorption of CO2 into various polymers at pressures up to about 3 atm.

  9. Extragalactic Inverse Compton Light from Dark Matter annihilation and the Pamela positron excess

    SciTech Connect

    Profumo, Stefano; Jeltema, Tesla E. E-mail: tesla@ucolick.org

    2009-07-01

    We calculate the extragalactic diffuse emission originating from the up-scattering of cosmic microwave photons by energetic electrons and positrons produced in particle dark matter annihilation events at all redshifts and in all halos. We outline the observational constraints on this emission and we study its dependence on both the particle dark matter model (including the particle mass and its dominant annihilation final state) and on assumptions on structure formation and on the density profile of halos. We find that for low-mass dark matter models, data in the X-ray band provide the most stringent constraints, while the gamma-ray energy range probes models featuring large masses and pair-annihilation rates, and a hard spectrum for the injected electrons and positrons. Specifically, we point out that the all-redshift, all-halo inverse Compton emission from many dark matter models that might provide an explanation to the anomalous positron fraction measured by the Pamela payload severely overproduces the observed extragalactic gamma-ray background.

  10. Positron annihilation and magnetic properties studies of copper substituted nickel ferrite nanoparticles

    NASA Astrophysics Data System (ADS)

    Kargar, Z.; Asgarian, S. M.; Mozaffari, M.

    2016-05-01

    Single phase copper substituted nickel ferrite Ni1-xCuxFe2O4 (x = 0.0, 0.1, 0.3 and 0.5) nanoparticles were synthesized by the sol-gel method. TEM images of the samples confirm formation of nano-sized particles. The Rietveld refinement of the X-ray diffraction patterns showed that lattice constant increase with increase in copper content from 8.331 for x = 0.0 to 8.355 Å in x = 0.5. Cation distribution of samples has been determined by the occupancy factor, using Rietveld refinement. The positron lifetime spectra of the samples were convoluted into three lifetime components. The shortest lifetime is due to the positrons that do not get trapped by the vacancy defects. The second lifetime is ascribed to annihilation of positrons in tetrahedral (A) and octahedral (B) sites in spinel structure. It is seen that for x = 0.1 and 0.3 samples, positron trapped within vacancies in A sites, but for x = 0.0 and 0.5, the positrons trapped and annihilated within occupied B sites. The longest lifetime component attributed to annihilation of positrons in the free volume between nanoparticles. The obtained results from coincidence Doppler broadening spectroscopy (CDBS) confirmed the results of positron annihilation lifetime spectroscopy (PALS) and also showed that the vacancy clusters concentration for x = 0.3 is more than those in other samples. Average defect density in the samples, determined from mean lifetime of annihilated positrons reflects that the vacancy concentration for x = 0.3 is maximum. The magnetic measurements showed that the saturation magnetization for x = 0.3 is maximum that can be explained by Néel's theory. The coercivity in nanoparticles increased with increase in copper content. This increase is ascribed to the change in anisotropy constant because of increase of the average defect density due to the substitution of Cu2+ cations and magnetocrystalline anisotropy of Cu2+ cations. Curie temperature of the samples reduces with increase in copper content which

  11. Calculating statistical distributions from operator relations: The statistical distributions of various intermediate statistics

    SciTech Connect

    Dai, Wu-Sheng Xie, Mi

    2013-05-15

    In this paper, we give a general discussion on the calculation of the statistical distribution from a given operator relation of creation, annihilation, and number operators. Our result shows that as long as the relation between the number operator and the creation and annihilation operators can be expressed as a{sup †}b=Λ(N) or N=Λ{sup −1}(a{sup †}b), where N, a{sup †}, and b denote the number, creation, and annihilation operators, i.e., N is a function of quadratic product of the creation and annihilation operators, the corresponding statistical distribution is the Gentile distribution, a statistical distribution in which the maximum occupation number is an arbitrary integer. As examples, we discuss the statistical distributions corresponding to various operator relations. In particular, besides the Bose–Einstein and Fermi–Dirac cases, we discuss the statistical distributions for various schemes of intermediate statistics, especially various q-deformation schemes. Our result shows that the statistical distributions corresponding to various q-deformation schemes are various Gentile distributions with different maximum occupation numbers which are determined by the deformation parameter q. This result shows that the results given in much literature on the q-deformation distribution are inaccurate or incomplete. -- Highlights: ► A general discussion on calculating statistical distribution from relations of creation, annihilation, and number operators. ► A systemic study on the statistical distributions corresponding to various q-deformation schemes. ► Arguing that many results of q-deformation distributions in literature are inaccurate or incomplete.

  12. Optimization of three-dimensional positron annihilation spectroscopy system (3DPASS) for three-dimensional momentum measurements

    NASA Astrophysics Data System (ADS)

    Williams, Christopher S.; Burggraf, Larry W.; Adamson, Paul E.; Petrosky, James C.

    2011-02-01

    A three-dimensional positron annihilation spectroscopy system (3DPASS) was characterized. 3DPASS permits determination of three-dimensional electron-positron ( e-- e+) momentum distributions by simultaneously measuring angles and energies for coincident two-gamma annihilation photons. 3DPASS collects a single dataset of correlated energies and positions for two coincident annihilation photons from a pair of solid-state double-sided strip detectors (DSSDs). Subpixel-interpolated positions are determined by transient charge analysis. 3DPASS performs simultaneous two-dimensional angular correlation of annihilation radiation (2D ACAR) and two-detector coincidence Doppler-broadening of annihilation radiation (CDBAR) measurements, which are typically collected independently. The 2D ACAR response of 3DPASS was measured for single-crystal Cu and 6H-SiC, with and without compensation for subpixel detection efficiency. Variation of efficiency across the width of DSSD charge collection electrodes was dominated by the event selection criteria required by the subpixel interpolation method. The DBAR resolution was optimized by adjusting the energy range of CDBAR events included in the Doppler-broadening (DB) lineshape. 2D ACAR and DBAR spectra from 3DPASS were compared to previously published results for single-crystal Cu and 6H-SiC. Detailed analysis of the ACAR spectra and the DB lineshapes highlighted momentum features not previously reported.

  13. Gamma Spectra Resulting From the Annihilation of Positrons with Electrons in Single, Selected Core Levels of Cu, Ag and Au

    SciTech Connect

    Kim, S; Eshed, A; Goktepeli, S; Sterne, P A; Koymen, A R; Chen, W C; Weiss, A H

    2005-07-25

    The {gamma}-ray energy spectra due to positron annihilation with the 3p core-level of Cu, the 4p core-level of Ag, and 5p core level of Au were obtained separately from the total annihilation spectrum by measuring the energies of {gamma}-rays time coincident with Auger electrons emitted as a result of filling the core-hole left by annihilation. The results of these measurements are compared to the total annihilation spectra and with LDA based theoretical calculations. A comparison of area normalized momentum distributions with the individual cores extracted from the Doppler measurements shows good qualitative agreement, however, in all three spectra, the calculated values of the momentum density appears to fall below the measured values as the momentum increases. The discrepancies between theory and experiment are well outside the statistical uncertainties of the experiment and become more pronounced with increasing Z going down the column from Cu to Ag to Au. The comparison with the experimental results clearly indicates that the calculations are not predicting the correct ratio of high momentum to low momentum spectral weight and suggest the need to improve the treatment of many body electron-positron correlation effects in annihilation as they pertain to core levels.

  14. Element specificity of ortho-positronium annihilation for alkali-metal loaded SiO{sub 2} glasses

    SciTech Connect

    Sato, K.; Hatta, T.

    2015-03-07

    Momentum distributions associated with ortho-positronium (o-Ps) pick-off annihilation photon are often influenced by light elements, as, e.g., carbon, oxygen, and fluorine. This phenomenon, so-called element specificity of o-Ps pick-off annihilation, has been utilized for studying the elemental environment around the open spaces. To gain an insight into the element specificity of o-Ps pick-off annihilation, the chemical shift of oxygen 1s binding energy and the momentum distributions associated with o-Ps pick-off annihilation were systematically investigated for alkali-metal loaded SiO{sub 2} glasses by means of X-ray photoelectron spectroscopy and positron-age-momentum correlation spectroscopy, respectively. Alkali metals introduced into the open spaces surrounded by oxygen atoms cause charge transfer from alkali metals to oxygen atoms, leading to the lower chemical shift for the oxygen 1s binding energy. The momentum distribution of o-Ps localized into the open spaces is found to be closely correlated with the oxygen 1s chemical shift. This correlation with the deepest 1s energy level evidences that the element specificity of o-Ps originates from pick-off annihilation with orbital electrons, i.e., dominantly with oxygen 2p valence electrons and s electrons with lower probability.

  15. Neutrino fluxes from constrained minimal supersymmetric standard model lightest supersymmetric particle annihilations in the Sun

    SciTech Connect

    Ellis, John; Olive, Keith A.; Savage, Christopher; Spanos, Vassilis C.

    2010-04-15

    We evaluate the neutrino fluxes to be expected from neutralino lightest supersymmetric particle (LSP) annihilations inside the Sun, within the minimal supersymmetric extension of the standard model with supersymmetry-breaking scalar and gaugino masses constrained to be universal at the grand unified theory scale [the constrained minimal supersymmetric standard model (CMSSM)]. We find that there are large regions of typical CMSSM (m{sub 1/2},m{sub 0}) planes where the LSP density inside the Sun is not in equilibrium, so that the annihilation rate may be far below the capture rate. We show that neutrino fluxes are dependent on the solar model at the 20% level, and adopt the AGSS09 model of Serenelli et al. for our detailed studies. We find that there are large regions of the CMSSM (m{sub 1/2},m{sub 0}) planes where the capture rate is not dominated by spin-dependent LSP-proton scattering, e.g., at large m{sub 1/2} along the CMSSM coannihilation strip. We calculate neutrino fluxes above various threshold energies for points along the coannihilation/rapid-annihilation and focus-point strips where the CMSSM yields the correct cosmological relic density for tan{beta}=10 and 55 for {mu}>0, exploring their sensitivities to uncertainties in the spin-dependent and -independent scattering matrix elements. We also present detailed neutrino spectra for four benchmark models that illustrate generic possibilities within the CMSSM. Scanning the cosmologically favored parts of the parameter space of the CMSSM, we find that the IceCube/DeepCore detector can probe at best only parts of this parameter space, notably the focus-point region and possibly also at the low-mass tip of the coannihilation strip.

  16. Neutrino fluxes from nonuniversal Higgs mass LSP annihilations in the Sun

    SciTech Connect

    Ellis, John; Olive, Keith A.; Savage, Christopher; Spanos, Vassilis C.

    2011-04-15

    We extend our previous studies of the neutrino fluxes expected from neutralino LSP annihilations inside the Sun to include variants of the minimal supersymmetric extension of the Standard Model (MSSM) with squark, slepton and gaugino masses constrained to be universal at the GUT scale, but allowing one or two nonuniversal supersymmetry breaking parameters contributing to the Higgs masses (NUHM1,2). As in the constrained MSSM (CMSSM) with universal Higgs masses, there are large regions of the NUHM parameter space where the LSP density inside the Sun is not in equilibrium, so that the annihilation rate may be far below the capture rate, and there are also large regions where the capture rate is not dominated by spin-dependent LSP-proton scattering. The spectra possible in the NUHM are qualitatively similar to those in the CMSSM. We calculate neutrino-induced muon fluxes above a threshold energy of 10 GeV, appropriate for the IceCube/DeepCore detector, for points where the NUHM yields the correct cosmological relic density for representative choices of the NUHM parameters. We find that the IceCube/DeepCore detector can probe regions of the NUHM parameter space in addition to analogues of the focus point strip and the tip of the coannihilation strip familiar from the CMSSM. These include regions with enhanced Higgsino-gaugino mixing in the LSP composition, that occurs where neutralino mass eigenstates cross over. On the other hand, rapid-annihilation funnel regions in general yield neutrino fluxes that are unobservably small.

  17. Positron annihilation studies in binary solid solutions and mechanical mixtures of lanthanide dipivaloylmethanate complexes

    NASA Astrophysics Data System (ADS)

    Fulgêncio, F.; Oliveira, F. C.; Windmöller, D.; Araujo, M. H.; Marques-Netto, A.; Machado, J. C.; Magalhães, W. F.

    2015-11-01

    Measurements using positron annihilation lifetime (PALS) and Doppler broadening annihilation radiation lineshape (DBARLS) spectroscopies were performed in several lanthanide dipivaloylmethanate complexes, Ln(dpm)3 where Ln = Sm3+, Gd3+, Tb3+, Ho3+, Er3+, Yb3+ and dpm = 2,2,6,6-tetramethyl-3,5-pentanedionate, and also on their binary solid solutions and mechanical mixtures, biphasic systems, of the general formula Ln1-xEux(dpm)3. Expressive positronium formation was observed in all Ln(dpm)3 complexes, except in Eu(dpm)3 complex. The results indicate formation of solid solutions in the Sm3+, Gd3+and Tb3+ systems, where total inhibition of positronium formation was observed. A Stern-Volmer type equation, I30/I3 = 1 + kx, was used to fit the data, enabling the calculation of the inhibition constants, k. A mechanical mixture behavior, with linear variation of I3 between the I3 values of the pure complexes, was observed in systems containing Ho3+, Er3+ and Yb3+ complexes, where no effective solid solution formation occurred due to differences between the crystalline structures of these complexes and Eu(dpm)3. No positronium quenching reactions were observed in the solid solutions. DBARLS results confirmed those of PALS, evidencing that the positron annihilation spectroscopies are useful techniques to characterize the formation of solid solutions. PALS measurements at 80 K were performed in the Sm1-xEux(dpm)3 and Gd1-xEux(dpm)3 solid solutions. The results indicate that, despite a contraction in the crystalline structures, the solid solution structure remains intact at low temperatures. The temperature dependence of the inhibition constant do not seem to be understood from the positronium formation spur model and might be related to intra and intermolecular energy and charge transfer processes in the solid solutions, which is currently being studied.

  18. Positron annihilation studies of 4-n-butyl-4'-isothiocyanato-1,1'-biphenyl.

    PubMed

    Dryzek, E; Juszyńska, E; Zaleski, R; Jasińska, B; Gorgol, M; Massalska-Arodź, M

    2013-08-01

    Positron annihilation lifetime spectroscopy (PALS) measurements were performed between 93 and 293 K in order to study the supercooled smectic-E (Sm-E) phase of 4-n-butyl-4'-isothiocyanato-1,1'-biphenyl (4TCB), the ordered molecular crystal of 4TCB, and the phase transition between the Sm-E phase and the ordered molecular crystal of 4TCB. The phase transition was well reflected in the abrupt increase of the ortho-positronium (o-Ps) lifetime and intensity. The value of the o-Ps lifetime in the Sm-E liquid crystalline phase of 4TCB, i.e., 2.21 ns at room temperature, was explained by the formation of bubbles induced by Ps atoms, which are created due to a liquidlike state of the butyl chains of 4TCB molecules in the Sm-E phase. The temperature dependence of the o-Ps intensity for the supercooled Sm-E phase can be explained by thermal generation of sites where bubbles are formed; an activation energy equal to 0.30±0.02 eV was estimated. This value was compared with the activation energies of molecular motions. The o-Ps lifetime in the ordered molecular crystal was interpreted as originating from the annihilation of o-Ps confined in molecular vacancy-type imperfections in the crystal lattice. The value of the o-Ps pickoff annihilation between 1.8 and 1.9 ns is in accordance with the size of the molecular vacancy for the 4TCB crystal lattice. Its intensity is lower than 5%. The isothermal crystallization of the 4TCB Sm-E phase was observed by PALS. The low-dimensional crystal growth was concluded from the Avrami equation fitted to the time dependence of the o-Ps intensity, which resulted in an Avrami exponent equal to 1.73. PMID:24032853

  19. Consistent scenarios for cosmic-ray excesses from Sommerfeld-enhanced dark matter annihilation

    NASA Astrophysics Data System (ADS)

    Finkbeiner, Douglas P.; Goodenough, Lisa; Slatyer, Tracy R.; Vogelsberger, Mark; Weiner, Neal

    2011-05-01

    Anomalies in direct and indirect detection have motivated models of dark matter consisting of a multiplet of nearly-degenerate states, coupled by a new GeV-scale interaction. We perform a careful analysis of the thermal freezeout of dark matter annihilation in such a scenario. We compute the range of ``boost factors'' arising from Sommerfeld enhancement in the local halo for models which produce the correct relic density, and show the effect of including constraints on the saturated enhancement from the cosmic microwave background (CMB). We find that boost factors from Sommerfeld enhancement of up to ~ 800 are possible in the local halo. When the CMB bounds on the saturated enhancement are applied, the maximal boost factor is reduced to ~ 400 for 1-2 TeV dark matter and sub-GeV force carriers, but remains large enough to explain the observed Fermi and PAMELA electronic signals. We describe regions in the DM mass-boost factor plane where the cosmic ray data is well fit for a range of final states, and show that Sommerfeld enhancement alone is enough to provide the large annihilation cross sections required to fit the data, although for light mediator masses (mphilesssim200 MeV) there is tension with the CMB constraints in the absence of astrophysical boost factors from substructure. Additionally, we consider the circumstances under which WIMPonium formation is relevant and find for heavy WIMPs (gtrsim2TeV) and soft-spectrum annihilation channels it can be an important consideration; we find regions with mχgtrsim2.8TeV that are consistent with the CMB bounds with Script O(600-700) present-day boost factors.

  20. Dark matter annihilation and decay from non-spherical dark halos in galactic dwarf satellites

    NASA Astrophysics Data System (ADS)

    Hayashi, Kohei; Ichikawa, Koji; Matsumoto, Shigeki; Ibe, Masahiro; Ishigaki, Miho N.; Sugai, Hajime

    2016-09-01

    The dwarf spheroidal galaxies (dSphs) in the Milky Way are the primary targets in the indirect searches for particle dark matter. To set robust constraints on candidate dark matter particles, understanding the dark halo structure of these systems is of substantial importance. In this paper, we first evaluate the astrophysical factors for dark matter annihilation and decay for 24 dSphs, taking into account a non-spherical dark halo, using generalized axisymmetric mass models based on axisymmetric Jeans equations. First, from a fitting analysis of the most recent kinematic data available, our axisymmetric mass models are a much better fit than previous spherical ones, thus, our work should be the most realistic and reliable estimator for astrophysical factors. Secondly, we find that among analysed dSphs, the ultra-faint dwarf galaxies Triangulum II and Ursa Major II are the most promising but large uncertain targets for dark matter annihilation while the classical dSph Draco is the most robust and detectable target for dark matter decay. It is also found that the non-sphericity of luminous and dark components influences the estimate of astrophysical factors, even though these factors largely depend on the sample size, the prior range of parameters and the spatial extent of the dark halo. Moreover, owing to these effects, the constraints on the dark matter annihilation cross-section are more conservative than those of previous spherical works. These results are important for optimizing and designing dark matter searches in current and future multi-messenger observations by space and ground-based telescopes.

  1. Dark Matter Annihilation in The Galactic Center As Seen by the Fermi Gamma Ray Space Telescope

    SciTech Connect

    Hooper, Dan; Goodenough, Lisa; /New York U.

    2010-10-01

    We analyze the first two years of data from the Fermi Gamma Ray Space Telescope from the direction of the inner 10{sup o} around the Galactic Center with the intention of constraining, or finding evidence of, annihilating dark matter. We find that the morphology and spectrum of the emission between 1.25{sup o} and 10{sup o} from the Galactic Center is well described by a the processes of decaying pions produced in cosmic ray collisions with gas, and the inverse Compton scattering of cosmic ray electrons in both the disk and bulge of the Inner Galaxy, along with gamma rays from known points sources in the region. The observed spectrum and morphology of the emission within approximately 1.25{sup o} ({approx}175 parsecs) of the Galactic Center, in contrast, cannot be accounted for by these processes or known sources. We find that an additional component of gamma ray emission is clearly present which is highly concentrated around the Galactic Center, but is not point-like in nature. The observed morphology of this component is consistent with that predicted from annihilating dark matter with a cusped (and possibly adiabatically contracted) halo distribution ({rho} {proportional_to} r{sup -1.34{+-}0.04}). The observed spectrum of this component, which peaks at energies between 2-4 GeV (in E{sup 2} units), is well fit by that predicted for a 7.3-9.2 GeV dark matter particle annihilating primarily to tau leptons with a cross section in the range of <{sigma}{nu}> = 3.3 x 10{sup -27} to 1.5 x 10{sup -26} cm{sup 3}/s, depending on how the dark matter distribution is normalized. We discuss other possible sources for this component, but argue that they are unlikely to account for the observed emission.

  2. A tentative gamma-ray line from Dark Matter annihilation at the Fermi Large Area Telescope

    SciTech Connect

    Weniger, Christoph

    2012-08-01

    The observation of a gamma-ray line in the cosmic-ray fluxes would be a smoking-gun signature for dark matter annihilation or decay in the Universe. We present an improved search for such signatures in the data of the Fermi Large Area Telescope (LAT), concentrating on energies between 20 and 300 GeV. Besides updating to 43 months of data, we use a new data-driven technique to select optimized target regions depending on the profile of the Galactic dark matter halo. In regions close to the Galactic center, we find a 4.6σ indication for a gamma-ray line at E{sub γ} ≈ 130 GeV. When taking into account the look-elsewhere effect the significance of the observed excess is 3.2σ. If interpreted in terms of dark matter particles annihilating into a photon pair, the observations imply a dark matter mass of m{sub χ} = 129.8±2.4 {sup +7}{sub −13} GeV and a partial annihilation cross-section of (σv){sub χχ} {sub →} {sub γγ} = (1.27±0.32 {sup +0.18}{sub −0.28}) × 10{sup −27}cm{sup 3}s{sup −1} when using the Einasto dark matter profile. The evidence for the signal is based on about 50 photons; it will take a few years of additional data to clarify its existence.

  3. Radio and gamma-ray constraints on dark matter annihilation in the Galactic center

    NASA Astrophysics Data System (ADS)

    Crocker, R. M.; Bell, N. F.; Balázs, C.; Jones, D. I.

    2010-03-01

    We determine upper limits on the dark matter (DM) self-annihilation cross section for scenarios in which annihilation leads to the production of electron—positron pairs. In the Galactic center, relativistic electrons and positrons produce a radio flux via synchroton emission, and a gamma-ray flux via bremsstrahlung and inverse Compton scattering. On the basis of archival, interferometric and single-dish radio data, we have determined the radio spectrum of an elliptical region around the Galactic center of extent 3° semimajor axis (along the Galactic plane) and 1° semiminor axis and a second, rectangular region, also centered on the Galactic center, of extent 1.6°×0.6°. The radio spectra of both regions are nonthermal over the range of frequencies for which we have data: 74 MHz-10 GHz. We also consider gamma-ray data covering the same region from the EGRET instrument (about GeV) and from HESS (around TeV). We show how the combination of these data can be used to place robust constraints on DM annihilation scenarios, in a way which is relatively insensitive to assumptions about the magnetic field amplitude in this region. Our results are approximately an order of magnitude more constraining than existing Galactic center radio and gamma-ray limits. For a DM mass of mχ=10GeV, and an Navarro-Frank-White profile, we find ⟨σAv⟩≤few×10-25cm3s-1.

  4. Thermal donor formation and annihilation in oxygen-implanted float-zone silicon

    SciTech Connect

    Hahn, S. ); Stein, H.J. ); Shatas, S.C. ); Ponce, F.A. )

    1992-09-01

    The formation and annihilation behaviors of thermal donors in {sup 16}O{sup +}-, {sup 18}O{sup +}-, or {sup 16}O{sup +}+{sup 12}C{sup +}-implanted float-zone silicon have been investigated with secondary ion mass spectrometry, spreading resistance probe, Hall effect, and transmission electron microscopy. Various oxygen or carbon+oxygen-implanted samples were laser annealed to remove implant damage and subjected to furnace annealing at 450 {degree}C for up to 100 h to activate oxygen-related thermal donors. Oxygen concentrations at the peak of the implanted profiles exceed the maximum for Czochralski Si by an order of magnitude. It is found that the third to fourth power dependence of thermal donor formation on oxygen generally observed for Czochralski Si does not hold for the higher oxygen concentration in the implanted layer. Annihilation characteristics of thermal donors formed in the oxygen implanted layers were investigated by the rapid thermal annealing technique. A rapid thermal anneal at 1150 {degree}C for 30 s was required to remove all the thermal donors. Based upon the annihilation kinetics data, it is tentatively concluded that both old and new thermal donors exist in the oxygen-implanted layer. For carbon+oxygen-coimplanted samples, the data have shown that carbon greatly increases the new thermal donor concentration in the implanted layer. Finally, precipitate morphologies for both oxygen-only- and carbon+oxygen-coimplanted samples after a 450 {degree}C furnace annealing were investigated by high resolution electron microscopy. In the case of oxygen-implant-only samples, predominant precipitate morphologies are needlelike while platelet defects predominate for carbon+oxygen-coimplanted samples. Since carbon increases the formation rate of new thermal donors, it is unlikely that they are distinctly related to needlelike precipitates as claimed in previous studies.

  5. Multistep cascade annihilations of dark matter and the Galactic Center excess

    DOE PAGESBeta

    Elor, Gilly; Rodd, Nicholas L.; Slatyer, Tracy R.

    2015-05-26

    If dark matter is embedded in a non-trivial dark sector, it may annihilate and decay to lighter dark-sector states which subsequently decay to the Standard Model. Such scenarios - with annihilation followed by cascading dark-sector decays - can explain the apparent excess GeV gamma-rays identified in the central Milky Way, while evading bounds from dark matter direct detection experiments. Each 'step' in the cascade will modify the observable signatures of dark matter annihilation and decay, shifting the resulting photons and other final state particles to lower energies and broadening their spectra. We explore, in a model-independent way, the effect ofmore » multi-step dark-sector cascades on the preferred regions of parameter space to explain the GeV excess. We find that the broadening effects of multi-step cascades can admit final states dominated by particles that would usually produce too sharply peaked photon spectra; in general, if the cascades are hierarchical (each particle decays to substantially lighter particles), the preferred mass range for the dark matter is in all cases 20-150 GeV. Decay chains that have nearly-degenerate steps, where the products are close to half the mass of the progenitor, can admit much higher DM masses. We map out the region of mass/cross-section parameter space where cascades (degenerate, hierarchical or a combination) can fit the signal, for a range of final states. In the current paper, we study multi-step cascades in the context of explaining the GeV excess, but many aspects of our results are general and can be extended to other applications.« less

  6. Multistep cascade annihilations of dark matter and the Galactic Center excess

    SciTech Connect

    Elor, Gilly; Rodd, Nicholas L.; Slatyer, Tracy R.

    2015-05-26

    If dark matter is embedded in a non-trivial dark sector, it may annihilate and decay to lighter dark-sector states which subsequently decay to the Standard Model. Such scenarios - with annihilation followed by cascading dark-sector decays - can explain the apparent excess GeV gamma-rays identified in the central Milky Way, while evading bounds from dark matter direct detection experiments. Each 'step' in the cascade will modify the observable signatures of dark matter annihilation and decay, shifting the resulting photons and other final state particles to lower energies and broadening their spectra. We explore, in a model-independent way, the effect of multi-step dark-sector cascades on the preferred regions of parameter space to explain the GeV excess. We find that the broadening effects of multi-step cascades can admit final states dominated by particles that would usually produce too sharply peaked photon spectra; in general, if the cascades are hierarchical (each particle decays to substantially lighter particles), the preferred mass range for the dark matter is in all cases 20-150 GeV. Decay chains that have nearly-degenerate steps, where the products are close to half the mass of the progenitor, can admit much higher DM masses. We map out the region of mass/cross-section parameter space where cascades (degenerate, hierarchical or a combination) can fit the signal, for a range of final states. In the current paper, we study multi-step cascades in the context of explaining the GeV excess, but many aspects of our results are general and can be extended to other applications.

  7. Improving the sensitivity of gamma-ray telescopes to dark matter annihilation in dwarf spheroidal galaxies

    NASA Astrophysics Data System (ADS)

    Carlson, Eric; Hooper, Dan; Linden, Tim

    2015-03-01

    The Fermi-LAT Collaboration has studied the gamma-ray emission from a stacked population of dwarf spheroidal galaxies and used this information to set constraints on the dark matter annihilation cross section. Interestingly, their analysis uncovered an excess with a test statistic (TS) of 8.7. If interpreted naively, this constitutes a 2.95 σ local excess (p -value=0.003 ), relative to the expectations of their background model. In order to further test this interpretation, the Fermi-LAT team studied a large number of blank sky locations and found TS >8.7 excesses to be more common than predicted by their background model, decreasing the significance of their dwarf excess to 2.2 σ (p -value=0.027 ) . We argue that these TS >8.7 blank sky locations are largely the result of unresolved blazars, radio galaxies, and star-forming galaxies, and show that multiwavelength information can be used to reduce the degree to which such sources contaminate the otherwise blank sky. In particular, we show that masking regions of the sky that lie within 1° of sources contained in the BZCAT or CRATES catalogs reduce the fraction of blank sky locations with TS >8.7 by more than a factor of 2. Taking such multiwavelength information into account can enable experiments such as Fermi to better characterize their backgrounds and increase their sensitivity to dark matter in dwarf galaxies, the most important of which remain largely uncontaminated by unresolved point sources. We also note that for the range of dark matter masses and annihilation cross sections currently being tested by studies of dwarf spheroidal galaxies, simulations predict that Fermi should be able to detect a significant number of dark matter subhalos. These subhalos constitute a population of subthreshold gamma-ray point sources and represent an irreducible background for searches for dark matter annihilation in dwarf galaxies.

  8. Dark Matter Capture and Annihilation on the First Stars: Preliminary Estimates

    SciTech Connect

    Iocco, Fabio

    2008-05-02

    Assuming that Dark Matter is dominated by WIMPs, it accretes by gravitational attraction and scattering over baryonic material and annihilates inside celestial objects, giving rise to a 'Dark Luminosity' which may potentially affect the evolution of stars. We estimate the Dark Luminosity achieved by different kinds of stars in a halo with DM properties characteristic of the ones where the first star formation episode occurs. We find that either massive, metal-free and small, galactic-like stars can achieve Dark Luminosities comparable or exceeding their nuclear ones. This might have dramatic effects over the evolution of the very first stars, known as Population III.

  9. Positron annihilation spectroscopy of vacancy-type defects hierarchy in submicrocrystalline nickel during annealing

    SciTech Connect

    Kuznetsov, Pavel V.; Mironov, Yuri P. E-mail: tolmach@ispms.tsc.ru Tolmachev, Aleksey I. E-mail: tolmach@ispms.tsc.ru Rakhmatulina, Tanzilya V. E-mail: tolmach@ispms.tsc.ru; Bordulev, Yuri S. E-mail: laptev.roman@gmail.com Laptev, Roman S. E-mail: laptev.roman@gmail.com Lider, Andrey M. E-mail: laptev.roman@gmail.com Mikhailov, Andrey A. E-mail: laptev.roman@gmail.com; Korznikov, Alexander V.

    2014-11-14

    Positron annihilation and X-ray diffraction analysis have been used to study submicrocrystalline nickel samples prepared by equal channel angular pressing. In the as-prepared samples the positrons are trapped at dislocation-type defects and in vacancy clusters that can include up to 5 vacancies. The study has revealed that the main positron trap centers at the annealing temperature of ΔT= 20°C-180°C are low-angle boundaries enriched by impurities. At ΔT = 180°C-360°C, the trap centers are low-angle boundaries providing the grain growth due to recrystallization in-situ.

  10. Effect of metal ions on positron annihilation characteristics in metal ion containing epoxies

    NASA Technical Reports Server (NTRS)

    Singh, J. J.; St. Clair, A. K.; Stoakley, D. M.; Holt, W. H.; Mock, W., Jr.

    1984-01-01

    In the course of developing improved moisture-resistant epoxy resins, two different types of epoxy resins containing variable mole ratios of chromium ions per polymer repeat unit were developed. Positron annihilation characteristics have been investigated in these resins as a function of their metal ion content. In both cases, the presence of metal ions reduces the lifetime as well as the intensity of the long life component. The long life component intensity reduction is considerably more pronounced than the lifetime reduction. These results have been discussed in terms of increased unpaired electron density at Ps formation sites due to the presence of chromium ions in the matrix.

  11. Positron annihilation studies of the electronic structure and fermiology of the high-{Tc} superconductors

    SciTech Connect

    Smedskjaer, L.C.; Bansil, A.

    1992-09-01

    We discuss the application of the positron annihilation angular correlation (ACAR) spectroscopy for investigating the electronic structure and Fermiology of the high-T{sub c} superconductors, with focus on the YBa{sub 2}Cu{sub 3}O{sub 7} system where most of the experimental and theoretical work has to date been concentrated. Comparisons between measured 2D-ACAR positron spectra and band theory predictions show a remarkable agreement (for the normal state), indicating that the electronic structure and Fermi surface of this material is described reasonably by the conventional picture.

  12. Positron annihilation studies of the electronic structure and fermiology of the high-[Tc] superconductors

    SciTech Connect

    Smedskjaer, L.C. ); Bansil, A. . Dept. of Physics)

    1992-09-01

    We discuss the application of the positron annihilation angular correlation (ACAR) spectroscopy for investigating the electronic structure and Fermiology of the high-T[sub c] superconductors, with focus on the YBa[sub 2]Cu[sub 3]O[sub 7] system where most of the experimental and theoretical work has to date been concentrated. Comparisons between measured 2D-ACAR positron spectra and band theory predictions show a remarkable agreement (for the normal state), indicating that the electronic structure and Fermi surface of this material is described reasonably by the conventional picture.

  13. Gamma-ray lines from novae. [relationship to radioactive decay and positron annihilation

    NASA Technical Reports Server (NTRS)

    Clayton, D. D.; Hoyle, F.

    1974-01-01

    An appropriate gamma-ray telescope could detect the gamma-rays associated with radioactive decays. The observable lines would be the annihilation radiation following the positron emission of N-13, O-14, O-15, and Na-22 and the 2.312-MeV line emitted following the O-14 decay and the 1.274-MeV line emitted following the Na-22 decay. The experimental possibility should be borne in mind for the occurrence of novae within a few kiloparsecs.

  14. Gamma rays from dark matter annihilations strongly constrain the substructure in halos.

    PubMed

    Pinzke, Anders; Pfrommer, Christoph; Bergström, Lars

    2009-10-30

    To fit recent data, e(+/-) from dark matter (DM) needs a boosted annihilation rate. This may imply an observable level of gamma rays from nearby galaxy clusters for the Fermi satellite. Using EGRET data, we limit the minimum mass of DM substructures to be about 5x10(3) times larger than for cold DM, meaning a cutoff similar to, e.g., warm DM. We numerically simulate clusters to reliably model the background. If we assume no anomalous boost factor, we find comparable levels of gamma-ray emission from DM and cosmic ray interactions, giving a chance with future data to characterize the DM. PMID:19905798

  15. Study of the structure of porous silicon via positron annihilation experiments

    NASA Astrophysics Data System (ADS)

    Biasini, M.; Ferro, G.; Monge, M. A.; Di Francia, G.; La Ferrara, V.

    2000-07-01

    We performed two-dimensional angular correlation of the electron-positron annihilation radiation (2D-ACAR) and positron lifetime measurements on a porous Si sample. From the width of the narrow 2D-ACAR component, attributed to the positronium atom, we estimated the average size of the pores to be ~2.4 nm and did not find evidence of a preferential propagation of the pores. Moreover, by comparing the 2D-ACAR spectrum with that observed for a pure Si crystal, we isolated a further isotropic component attributable to crystal defects of unknown origin.

  16. Spin dependent momentum density and Fermi surface of ferromagnetic Ni obtained by positron annihilation experiments

    NASA Astrophysics Data System (ADS)

    Hamid, A. S.; Uedono, A.

    2004-11-01

    The cover picture of this issue, taken from [1], shows a cross section of the Fermi surface in the basal plane of nickel. The measurements were carried out using 2D angular correlation of annihilation radiation (ACAR) experiments. The intersecting plane is normal to the c-axis, passing through the and X points. The light regions correspond to a high electron momentum density. The Fermi surface is presented as two hole surfaces around the point and two electron surfaces around the X point.

  17. Thermalization of positronium atoms studied with time-resolved angular correlation of annihilation radiation

    NASA Astrophysics Data System (ADS)

    Takada, S.; Iwata, T.; Kawashima, K.; Saito, H.; Nagashima, Y.; Hyodo, T.

    2000-06-01

    Time dependence of the kinetic energy of positronium atoms in the free space between the grains of a pressed tablet (1 g/cm 3) of ultrafine silica powder (Cab-O-Sil EH-5) has been measured with time-resolved angular correlation of annihilation radiation (ACAR) apparatus. The apparatus has a momentum resolution of 1.29×10 -3 mc in full width at half maximum and a time resolution of 2.7 ns in full width at half maximum. It is found that the energy of positronium falls below 0.1e V in ˜10 ns after the formation.

  18. Production of {omega}{pi}{sup 0} pairs in electron-positron annihilation

    SciTech Connect

    Arbuzov, A. B.; Kuraev, E. A.; Volkov, M. K.

    2011-04-15

    The process of electron-positron annihilation into a pair of {pi}{sup 0} and {omega} mesons is considered in the framework of the SU(2)xSU(2) Nambu-Jona-Lasinio model. Contributions of intermediate photons, {rho}(770) and {rho}{sup '}(1450) vector mesons are taken into account. It is shown that the bulk of the cross section at energies below 2 GeV is provided by the process with intermediate {rho}{sup '}(1450) state. The contribution due to single photon and {rho}(770) exchange is in agreement with the vector meson dominance model. Numerical results are compared with experimental data.

  19. The Search for Milky Way Halo Substructure WIMP Annihilations Using the GLAST LAT

    SciTech Connect

    Wai, Larry; /SLAC

    2007-02-05

    The GLAST LAT Collaboration is one among several experimental groups, covering a wide range of approaches, pursuing the search for the nature of dark matter. The GLAST LAT has the unique ability to find new sources of high energy gamma radiation emanating directly from WIMP annihilations in situ in the universe. Using it's wide band spectral and full sky spatial capabilities, the GLAST LAT can form ''images'' in high energy gamma-rays of dark matter substructures in the gamma-ray sky. We describe a preliminary feasibility study for indirect detection of milky way dark matter satellites using the GLAST LAT.

  20. Physics cross sections and event generation of e+e- annihilations at the CEPC

    NASA Astrophysics Data System (ADS)

    Mo, Xin; Li, Gang; Ruan, Man-Qi; Lou, Xin-Chou

    2016-03-01

    The cross sections of the Higgs production and the corresponding backgrounds of e+e- annihilations at the CEPC (Circular Electron and Positron Collider) are calculated by a Monte-Carlo method, and the beamstrahlung effect at the CEPC is carefully investigated. The numerical results and the expected number of events for the CEPC are provided. Supported by CAS/SAFEA International Partnership Program for Creative Research Teams, and funding from CAS and IHEP for the Thousand Talent and Hundred Talent programs, as well as grants from the State Key Laboratory of Nuclear Electronics and Particle Detectors

  1. Positron annihilation spectroscopy: a new frontier for understanding nanoparticle-loaded polymer brushes

    NASA Astrophysics Data System (ADS)

    Panzarasa, Guido; Aghion, Stefano; Soliveri, Guido; Consolati, Giovanni; Ferragut, Rafael

    2016-01-01

    Nanoparticle-loaded polymer brushes are powerful tools for the development of innovative devices. However, their characterization is challenging and arrays of different techniques are typically required to gain sufficient insight. Here we demonstrate for the first time the suitability of positron annihilation spectroscopy (PAS) to investigate, with unprecedented detail and without making the least damage to samples, the physico-chemical changes experienced by pH-responsive polymer brushes after protonation and after loading of silver nanoparticles. One of the most important findings is the depth profiling of silver nanoparticles inside the brushes. These results open up a completely new way to understand the structure and behavior of such complex systems.

  2. Annihilation of the scalar pair into a photon in a de Sitter universe

    NASA Astrophysics Data System (ADS)

    Băloi, Mihaela-Andreea

    2016-05-01

    The annihilation of massive scalar particles in one photon in de Sitter expanding universe is studied, using perturbative QED. The amplitude and probability corresponding to this process is computed using the exact solutions of the Klein-Gordon and Maxwell equations on de Sitter geometry. Our results show that the expression of the total probability of photon emission is a function dependent on the ratio mass/expansion factor. We perform a graphical study of the total probability in terms of the parameter mass/expansion factor, showing that this effect is significant only in strong gravitational fields. We also obtain that the total probability for this process vanishes in the Minkowski limit.

  3. Exact Results for a Diffusion-Limited Pair Annihilation Process on a One-Dimensional Lattice

    NASA Astrophysics Data System (ADS)

    Sasaki, Kazuo; Nakagawa, Tomohiro

    2000-05-01

    The process of pair annihilation of particles diffusing on a ring ofone-dimensional lattice is studied analytically.A set of master equations for the distribution functions of particlesare solved exactly for the initial condition of uniform, randomdistribution of particles.An explicit expression for the time dependence of the densityof particles is derived from the distribution functions.In the limit of infinite lattice, the present result agreeswith the one obtained by [Balding, Clifford and Green:Phys. Lett. A 126 (1988) 481].

  4. On the observability of the gamma-ray line flux from dark matter annihilation

    NASA Technical Reports Server (NTRS)

    Rudaz, S.; Stecker, F. W.

    1991-01-01

    The limits on the possible cosmic gamma-ray line flux from the two-photon annihilation of dark matter in the Galaxy are discussed. These limits are derived using both particle physics and cosmological constraints on dark matter candidates which arise in supersymmetric extensions of the standard model of particle physics. Results are given in terms of allowed and prescribed areas in the flux-energy plane. Then these bounds are used to consider the observability of the line flux above continuum background fluxes using future high-resolution gamma-ray telescopes.

  5. Lambda production in electron-positron annihilation at 29 GeV

    SciTech Connect

    Baden, A.R.

    1986-08-01

    The inclusive cross-secton for the production of the singly-strange baryons lambda and anti lambda, along with the differential cross-sections in momentum and energy, are measured by e/sup +/e/sup -/ annihilation at a center-of-mass energy of 29GeV. The charged decay mode lambda ..-->.. p..pi.. is used in a search for polarization. Such a polarization may be used as a check of CP invariance in lambda production. The sample of events with two detected decays is analyzed for correlations in production angle. 43 refs., 44 figs.

  6. Collins effect in semiinclusive deeply inelastic scattering and in electron-positron-annihilation

    SciTech Connect

    Efremov, A.V.; Goeke, K.; Schweitzer, P.

    2006-05-01

    The Collins fragmentation function is extracted from HERMES data on azimuthal single spin asymmetries in semi-inclusive deeply inelastic scattering, and BELLE data on azimuthal asymmetries in e{sup +}e{sup -}-annihilations. A Gaussian model is assumed for the distribution of transverse parton momenta and predictions are used from the chiral quark-soliton model for the transversity distribution function. We find that the HERMES and BELLE data yield a consistent picture of the Collins fragmentation function which is compatible with COMPASS data and the information previously obtained from an analysis of DELPHI data. Estimates for future experiments are made.

  7. Metallophthalocyanines as triplet sensitizers for highly efficient photon upconversion based on sensitized triplet-triplet annihilation.

    PubMed

    Han, J L; You, J; Yonemura, H; Yamada, S; Wang, S R; Li, X G

    2016-08-01

    Soluble palladium and platinum phthalocyanines with coumarin moieties were synthesized with Q bands in the red and near-IR regions, in which the molar extinction coefficients were up to 1.01 × 10(5) cm(-1) mol(-1). These metallophthalocyanines were coupled with rubrene and applied in photon upconversion systems based on triplet-triplet annihilation. The highest upconversion efficiency of the palladium phthalocyanine was 5.6%, which is higher than that of the platinum phthalocyanine-rubrene system. The larger molar extinction coefficient resulted in high upconversion capability (>10(5) cm(-1) mol(-1)) and low saturation incident power (<20 mW cm(-2)). PMID:27431880

  8. p-barp-Annihilation processes in the tree approximation of SU(3) chiral effective theory

    SciTech Connect

    Tarasov, V. E.; Kudryavtsev, A. E. Romanov, A. I.; Weinberg, V. M.

    2012-12-15

    The p-barp-annihilation reactions p-barp {yields} {eta}{eta} {eta} and p-barp {yields} {eta}KK-bar at rest are considered in the tree approximation in the framework of SU(3) chiral effective theory at leading order. The calculated branchings are compared with the data. The results for neutral ({eta}{eta}{eta}, K{sup 0}K-bar{sup 0}{sub {eta}}) and charged (K{sup +}K{sup -}{sub {eta}}) channels are essentially different.

  9. Positronium in Solids: Computer Simulation of Pick-Off and Self-Annihilation

    SciTech Connect

    Bug, A; Muluneh, M; Waldman, J; Sterne, P

    2003-08-01

    Positronium (Ps) is simulated using Path Integral Monte Carlo (PIMC). This method can reproduce the results of previous simple theories in which a single quantum particle is used to represent Ps within an idealized pore. In addition, the calculations treat the e{sup -} and e{sup +} of Ps exactly and realistically model interactions with solid atoms, thereby correcting and extending the simpler theory. They study the pick-off lifetime of o-Ps and the internal contact density, {kappa}, which controls the self-annihilation behavior, for Ps in model voids (spherical pores), defects in a solid (argon), and microporous solids (zeolites).

  10. Annihilation of angular momentum bias during thrusting and spinning-up maneuvers

    NASA Technical Reports Server (NTRS)

    Longuski, J. M.; Kia, T.; Breckenridge, W. G.

    1989-01-01

    During spinning-up and thrusting maneuvers of rockets and spacecraft, undesired transverse torques (from error sources such as thruster misalignment, center-of-mass offset and thruster mismatch) perturb the angular momentum vector from its original orientation. In this paper a maneuver scheme is presented which virtually annihilates the angular momentum vector bias, even though the magnitude and direction of the perturbing body-fixed torques are unknown. In the analysis it is assumed that the torques are small and constant and that the spacecraft or rocket can be approximated by a rigid body, which may be asymmetric. Typical maneuvers of the Galileo spacecraft are simulated to demonstrate the technique.

  11. Diphoton excess at 750 GeV: gluon-gluon fusion or quark-antiquark annihilation?

    NASA Astrophysics Data System (ADS)

    Gao, Jun; Zhang, Hao; Zhu, Hua Xing

    2016-06-01

    Recently, ATLAS and CMS collaborations reported an excess in the measurement of diphoton events, which can be explained by a new resonance with a mass around 750 GeV. In this work, we explored the possibility of identifying if the hypothetical new resonance is produced through gluon-gluon fusion or quark-antiquark annihilation, or tagging the beam. Three different observables for beam tagging, namely the rapidity and transverse-momentum distribution of the diphoton, and one tagged bottom-jet cross section, are proposed. Combining the information gained from these observables, a clear distinction of the production mechanism for the diphoton resonance is promising.

  12. Dynamics of Defects in X-Ray Irradiated Alkali Chloride Crystals Studied by Positron Annihilation.

    NASA Astrophysics Data System (ADS)

    Stern, Stanley Hy.

    This thesis reports first data on the time dependence of positron-electron annihilation characteristics in single crystals of the homologous series NaCl, KCl, RbCl, and CsCl after large doses of x irradiation. A new instrument, the (pi)-radian coincidence apparatus (PICA), recorded the coincidence count rate P of the two 0.5-MeV annihilation (gamma) rays emerging 180(DEGREES) apart from the crystal during isothermal and isochronal heating conditions. In most crystals one observes an initial rapid increase of P to a maximum followed by a slow decline toward the coincidence count rate corresponding to the pre-irradiation state of the crystal. Positron-annihilation data were completed by independent measurements of the optical absorption in KCl and NaCl crystals after various durations of isothermal heating. Absorption spectrophotometry revealed enhancement of the M band in KCl, of the R and N bands in NaCl, at the expense of the F band during the interval of increasing P. The PICA results are consistent with the interpretation that positrons are trapped by radiation-induced color centers in which they annihilate with a higher P than in the bulk of the crystal. The dynamics associated with the incipient rise of P during the initial heating period is attributable to the agglomeration of F centers into aggregate centers. The rise times of P give access to the diffusion rates for agglomeration. At equal temperatures, we observe a strong dependence of the rate of defect diffusion on the size of the cation. For example, it is 100 times faster in CsCl than in NaCl at 120(DEGREES)C. The data must be corrected for the effects of decoloration of the crystals by the positrons during the measurements. Activation energies for defect diffusion annealing are extracted. They test the hypotheses underlying the theories of macroscopic transport properties in these crystals in that they are indicative of the dominant microscopic lattice processes and their dependence on the crystal

  13. Hadron production in e/sup +/e/sup -/ annihilation. QCD and hadronization

    SciTech Connect

    Yamamoto, H.

    1985-12-01

    Recent results on hadron production in e/sup +/e/sup -/ annihilation are summarized. The topics included are: (1) inclusive hadron production, (2) comparison of light (u,d,s) and heavy (c,b) quark jets; (3) p - anti p correlations; (4) gluon vs. quark jets; (5) analysis of 3 jet events; (6) measurement of the strong coupling constant ..cap alpha../sub s/; and (7) forward-backward asymmetries of quarks and leptons. Experimental data are compared with predictions of several models to reveal underlying physics. 62 refs., 22 figs.

  14. Chiral symmetry breaking in three-dimensional quantum electrodynamics as fixed point annihilation

    NASA Astrophysics Data System (ADS)

    Herbut, Igor F.

    2016-07-01

    Spontaneous chiral symmetry breaking in three-dimensional (d =3 ) quantum electrodynamics is understood as annihilation of an infrared-stable fixed point that describes the large-N conformal phase by another unstable fixed point at a critical number of fermions N =Nc. We discuss the root of universality of Nc in this picture, together with some features of the phase boundary in the (d ,N ) plane. In particular, it is shown that as d →4 , Nc→0 with a constant slope, our best estimate of which suggests that Nc=2.89 in d =3 .

  15. Experimental Limits on Weak Annihilation Contributions to b{yields}ul{nu} Decays

    SciTech Connect

    Rosner, J.L.; Adam, N.E.; Alexander, J.P.; Berkelman, K.; Cassel, D.G.; Duboscq, J.E.; Ecklund, K.M.; Ehrlich, R.; Fields, L.; Gibbons, L.; Gray, R.; Gray, S.W.; Hartill, D.L.; Heltsley, B.K.; Hertz, D.; Jones, C.D.; Kandaswamy, J.; Kreinick, D.L.; Kuznetsov, V.E.; Mahlke-Krueger, H.

    2006-03-31

    We present the first experimental limits on high-q{sup 2} contributions to charmless semileptonic B decays of the form expected from the weak annihilation (WA) decay mechanism. Such contributions could bias determinations of vertical bar V{sub ub} vertical bar from inclusive measurements of B{yields}X{sub u}l{nu}. Using a wide range of models based on available theoretical input we set a limit of {gamma}{sub WA}/{gamma}{sub b{yields}}{sub u}<7.4% (90% confidence level) on the WA fraction, and assess the impact on previous inclusive determinations of vertical bar V{sub ub} vertical bar.

  16. Study of gamma irradiation effect on positron annihilation mechanism in PFA

    NASA Astrophysics Data System (ADS)

    Yang, J.; Li, Z. X.; Zhao, B. Z.; Zhang, P.; Lu, E. Y.; Zhang, J.; Yuan, D. Q.; Cao, X. Z.; Yu, R. S.; Wang, B. Y.

    2014-03-01

    Gamma irradiation effect on annihilation characteristics of positronium and free positron in tetrafluoroethylene-perluoro (alkoxy vinyl ether) copolymer (PFA) were studied independently by age momentum correlation (AMOC) and the correlation between Doppler broadening S parameter and o-Ps fraction (S-Io-Ps correlation). AMOC results revealed decreases in S parameter of o-Ps, owing to accumulation of polar atoms around free volume. S-Io-Ps correlation indicated a reduced intrinsic S parameter of free positron in irradiated PFA, which was caused by enhanced positron trapping on polar atoms due to densification of local segments and variation in the elemental environment around free volumes.

  17. Search for gamma rays from dark matter annihilations around intermediate mass black holes with the HESS experiment

    SciTech Connect

    Aharonian, F.; Akhperjanian, A. G.; Sahakian, V.; Barres de Almeida, U.; Brion, E.; Brun, P.; Glicenstein, J. F.; Goret, P.; Moulin, E.; Vivier, M.; Beilicke, M.; Heinzelmann, G.; Horns, D.

    2008-10-01

    The HESS array of Cherenkov telescopes has performed, from 2004 to 2007, a survey of the inner galactic plane at photon energies above 100 GeV. About 400 hours of data have been accumulated in the region between -30 and +60 degrees in galactic longitude, and between -3 and +3 degrees in galactic latitude. Assuming that dark matter is composed of weakly interacting massive particles, we calculate here the HESS sensitivity map for dark matter annihilations, and derive the first experimental constraints on the ('minispikes') scenario, in which a gamma-ray signal arises from dark matter annihilation around intermediate mass black holes. The data exclude the proposed scenario at a 90% confidence level for dark matter particles with velocity-weighted annihilation cross section {sigma}v above 10{sup -28} cm{sup 3} s{sup -1} and mass between 800 GeV and 10 TeV.

  18. Impact of semi-annihilations on dark matter phenomenology. An example of ZN symmetric scalar dark matter

    NASA Astrophysics Data System (ADS)

    Bélanger, Geneviève; Kannike, Kristjan; Pukhov, Alexander; Raidal, Martti

    2012-04-01

    We study the impact of semi-annihilations xixjleftrightarrowxkX and dark matter conversion xixjleftrightarrowxkxl, where xi is any dark matter and X is any standard model particle, on dark matter phenomenology. We formulate minimal scalar dark matter models with an extra doublet and a complex singlet that predict non-trivial dark matter phenomenology with semi-annihilation processes for different discrete Abelian symmetries ZN, N > 2. We implement two such example models with Z3 and Z4 symmetry in micrOMEGAs and work out their phenomenology. We show that both semi-annihilations and dark matter conversion significantly modify the dark matter relic abundance in this type of models. In the Z4 model, there are two stable neutral particles and therefore multi-component dark matter. We also study the possibility of dark matter direct detection in XENON100 in those models.

  19. Impact of semi-annihilation of ℤ{sub 3} symmetric dark matter with radiative neutrino masses

    SciTech Connect

    Aoki, Mayumi; Toma, Takashi

    2014-09-08

    We investigate a ℤ{sub 3} symmetric model with two-loop radiative neutrino masses. Dark matter in the model is either a Dirac fermion or a complex scalar as a result of an unbroken ℤ{sub 3} symmetry. In addition to standard annihilation processes, semi-annihilation of the dark matter contributes to the relic density. We study the effect of the semi-annihilation in the model and find that those contributions are important to obtain the observed relic density. The experimental signatures in dark matter searches are also discussed, where some of them are expected to be different from the signatures of dark matter in ℤ{sub 2} symmetric models.

  20. Modification of steel surfaces induced by turning: non-destructive characterization using Barkhausen noise and positron annihilation

    NASA Astrophysics Data System (ADS)

    Čížek, J.; Neslušan, M.; Čilliková, M.; Mičietová, A.; Melikhova, O.

    2014-11-01

    This paper deals with the characterization of sub-surface damage caused by the machining of 100Cr6 roll bearing steel. The samples turned using tools with variable flank wears were characterized by two non-destructive techniques sensitive to defects introduced by plastic deformation: magnetic Barkhausen noise and positron annihilation. These techniques were combined with light and electron microscopy, x-ray diffraction and microhardness testing. The results of the experiment showed that damage in the sub-surface region increases with increasing flank wear, but from a certain critical value dynamic recovery takes place. The intensity of Barkhausen noise strongly decreases with increasing flank wear due to the increasing density of the dislocations pinning the Bloch walls and suppressing their motion. This was confirmed by positron annihilation spectroscopy, which enables the determination of the dislocation density directly. Hence, a good correlation between Barkhausen noise emission and positron annihilation spectroscopy was found.

  1. Organolead Halide Perovskites for Low Operating Voltage Multilevel Resistive Switching.

    PubMed

    Choi, Jaeho; Park, Sunghak; Lee, Joohee; Hong, Kootak; Kim, Do-Hong; Moon, Cheon Woo; Park, Gyeong Do; Suh, Junmin; Hwang, Jinyeon; Kim, Soo Young; Jung, Hyun Suk; Park, Nam-Gyu; Han, Seungwu; Nam, Ki Tae; Jang, Ho Won

    2016-08-01

    Organolead halide perovskites are used for low-operating-voltage multilevel resistive switching. Ag/CH3 NH3 PbI3 /Pt cells exhibit electroforming-free resistive switching at an electric field of 3.25 × 10(3) V cm(-1) for four distinguishable ON-state resistance levels. The migration of iodine interstitials and vacancies with low activation energies is responsible for the low-electric-field resistive switching via filament formation and annihilation. PMID:27192161

  2. PPPC 4 DMν: a Poor Particle Physicist Cookbook for Neutrinos from Dark Matter annihilations in the Sun

    SciTech Connect

    Baratella, Pietro; Cirelli, Marco; Hektor, Andi; Pata, Joosep; Piibeleht, Morten; Strumia, Alessandro

    2014-03-27

    We provide ingredients and recipes for computing neutrino signals of TeV-scale Dark Matter (DM) annihilations in the Sun. For each annihilation channel and DM mass we present the energy spectra of neutrinos at production, including: state-of-the-art energy losses of primary particles in solar matter, secondary neutrinos, electroweak radiation. We then present the spectra after propagation to the Earth, including (vacuum and matter) flavor oscillations and interactions in solar matter. We also provide a numerical computation of the capture rate of DM particles in the Sun. These results are available in numerical form http://www.marcocirelli.net/PPPC4DMID.html.

  3. A study of vacancy defects related to gray tracks in KTiOPO{sub 4} (KTP) using positron annihilation

    SciTech Connect

    Zhang, Yang; Li, Jing; Wang, Jiyang Jiang, Huaidong; Cao, Xingzhong; Yang, Jing

    2014-12-15

    For the first time to our knowledge, positron annihilation spectroscopy (PAS) was used to study vacancy defects in KTiOPO{sub 4} (KTP) single crystals. Positron annihilation lifetime spectroscopy combined with dielectric measurements identified the existence of oxygen vacancies and reflected the concentration of vacancy defects in three samples. The vacancy defects in KTP do not consist of monovacancies, but rather vacancy complexes. Doppler broadening indicates that the vacancy defects are distributed uniformly. A relationship is established where a crystal with a low oxygen vacancy concentration and a highly balanced stoichiometry has a higher resistance to gray track formation.

  4. A study of vacancy defects related to gray tracks in KTiOPO4 (KTP) using positron annihilation

    NASA Astrophysics Data System (ADS)

    Zhang, Yang; Li, Jing; Cao, Xingzhong; Yang, Jing; Wang, Jiyang; Jiang, Huaidong

    2014-12-01

    For the first time to our knowledge, positron annihilation spectroscopy (PAS) was used to study vacancy defects in KTiOPO4 (KTP) single crystals. Positron annihilation lifetime spectroscopy combined with dielectric measurements identified the existence of oxygen vacancies and reflected the concentration of vacancy defects in three samples. The vacancy defects in KTP do not consist of monovacancies, but rather vacancy complexes. Doppler broadening indicates that the vacancy defects are distributed uniformly. A relationship is established where a crystal with a low oxygen vacancy concentration and a highly balanced stoichiometry has a higher resistance to gray track formation.

  5. Positronium energy levels at order m α7 : Product contributions in the two-photon-annihilation channel

    NASA Astrophysics Data System (ADS)

    Adkins, Gregory S.; Tran, Lam M.; Wang, Ruihan

    2016-05-01

    Ongoing improvements in the measurement of positronium transition intervals motivate the calculation of the O (m α7) corrections to these intervals. In this work we focus on corrections to the spin-singlet parapositronium energies involving virtual annihilation to two photons in an intermediate state. We have evaluated all contributions to the positronium S -state energy levels that can be written as the product of a one-loop correction on one side of the annihilation event and another one-loop correction on the other side. These effects contribute Δ E =-0.561971 (25 ) m α7/π3 to the parapositronium ground-state energy.

  6. PPPC 4 DMν: a Poor Particle Physicist Cookbook for Neutrinos from Dark Matter annihilations in the Sun

    NASA Astrophysics Data System (ADS)

    Baratella, Pietro; Cirelli, Marco; Hektor, Andi; Pata, Joosep; Piibeleht, Morten; Strumia, Alessandro

    2014-03-01

    We provide ingredients and recipes for computing neutrino signals of TeV-scale Dark Matter (DM) annihilations in the Sun. For each annihilation channel and DM mass we present the energy spectra of neutrinos at production, including: state-of-the-art energy losses of primary particles in solar matter, secondary neutrinos, electroweak radiation. We then present the spectra after propagation to the Earth, including (vacuum and matter) flavor oscillations and interactions in solar matter. We also provide a numerical computation of the capture rate of DM particles in the Sun. These results are available in numerical form.

  7. Positron annihilation lifetime studies of changes in free volume on some biorelevant nitrogen heterocyclic compounds and their S-glycosylation.

    PubMed

    Mahmoud, K R; Khodair, A I; Shaban, S Y

    2015-11-01

    A series of N-heterocyclic compounds was investigated by positron annihilation lifetime spectroscopy as well as Doppler broadening of annihilation radiation (DBAR) at room temperature. The results showed that the formation probability and life time of ortho-positronium in this series are structure and electron-donation character dependent, and can give more information about the structure. The DBAR provides direct information about the change of core and valance electrons as well as the number of defect types present in these compounds. PMID:26272166

  8. THE FERMI GAMMA-RAY HAZE FROM DARK MATTER ANNIHILATIONS AND ANISOTROPIC DIFFUSION

    SciTech Connect

    Dobler, Gregory; Cholis, Ilias; Weiner, Neal E-mail: ilias.cholis@sissa.it

    2011-11-01

    Recent full-sky maps of the Galaxy from the Fermi Gamma-Ray Space Telescope have revealed a diffuse component of emission toward the Galactic center and extending up to roughly {+-}50{sup 0} in latitude. This Fermi 'haze' is the inverse Compton emission generated by the same electrons that generate the microwave synchrotron haze at Wilkinson Microwave Anisotropy Probe wavelengths. The gamma-ray haze has two distinct characteristics: the spectrum is significantly harder than emission elsewhere in the Galaxy and the morphology is elongated in latitude with respect to longitude with an axis ratio of {approx}2. If these electrons are generated through annihilations of dark matter (DM) particles in the Galactic halo, this morphology is difficult to realize with a standard spherical halo and isotropic cosmic-ray (CR) diffusion. However, we show that anisotropic diffusion along ordered magnetic field lines toward the center of the Galaxy coupled with a prolate DM halo can easily yield the required morphology without making unrealistic assumptions about diffusion parameters. Furthermore, a Sommerfeld enhancement to the self-annihilation cross-section of {approx}30 yields a good fit to the morphology, amplitude, and spectrum of both the gamma-ray and microwave haze. The model is also consistent with local CR measurements as well as cosmic microwave background constraints.

  9. Dark matter annihilation in Draco: New considerations of the expected gamma flux

    SciTech Connect

    Sanchez-Conde, M. A.; Prada, F.; Moles, M.; Lokas, E. L.; Wojtak, R.; Gomez, M. E.

    2007-12-15

    A new revision of the gamma flux that we expect to detect in imaging atmospheric Cherenkov telescopes from neutralino annihilation in the Draco dwarf spheroidal galaxy is presented in the context of the minimal supersymmetric standard models compatible with the present phenomenological and cosmological constraints, and using the dark matter density profiles compatible with the latest observations. This revision also takes into account the important effect of the point spread function of the telescope, and is valid not only for Draco but also for any other dark matter target. We show that this effect is crucial in the way we will observe and interpret a possible signal detection. Finally, we discuss the prospects to detect a possible gamma signal from Draco for current or planned gamma-ray experiments, i.e., MAGIC, GLAST, and GAW. Even with the large astrophysical and particle physics uncertainties we find that the chances to detect a neutralino annihilation signal in Draco seem to be very scarce for current experiments. However, the prospects for future imaging atmospheric Cherenkov telescopes with upgraded performances (especially lower threshold energies and higher sensitivities) such as those offered by the Cherenkov Telescope Array project, might be substantially better.

  10. Microstructure Evaluation of Fe-BASED Amorphous Alloys Investigated by Doppler Broadening Positron Annihilation Technique

    NASA Astrophysics Data System (ADS)

    Lu, Wei; Huang, Ping; Wang, Yuxin; Yan, Biao

    2013-07-01

    Microstructure of Fe-based amorphous and nanocrystalline soft magnetic alloy has been investigated by X-ray diffraction (XRD), transmission electronic microscopy (TEM) and Doppler broadening positron annihilation technique (PAT). Doppler broadening measurement reveals that amorphous alloys (Finemet, Type I) which can form a nanocrystalline phase have more defects (free volume) than alloys (Metglas, Type II) which cannot form this microstructure. XRD and TEM characterization indicates that the nanocrystallization of amorphous Finemet alloy occurs at 460°C, where nanocrystallites of α-Fe with an average grain size of a few nanometers are formed in an amorphous matrix. With increasing annealing temperature up to 500°C, the average grain size increases up to around 12 nm. During the annealing of Finemet alloy, it has been demonstrated that positron annihilates in quenched-in defect, crystalline nanophase and amorphous-nanocrystalline interfaces. The change of line shape parameter S with annealing temperature in Finemet alloy is mainly due to the structural relaxation, the pre-nucleation of Cu nucleus and the nanocrystallization of α-Fe(Si) phase during annealing. This study throws new insights into positron behavior in the nanocrystallization of metallic glasses, especially in the presence of single or multiple nanophases embedded in the amorphous matrix.

  11. Quantification of stress history in type 304L stainless steel using positron annihilation spectroscopy

    SciTech Connect

    Walters, Thomas W.; Walters, Leon C.; Schoen, Marco P.; Naidu, D. Subbaram; Dickerson, Charles; Perrenoud, Ben C.

    2011-04-15

    Five Type 304L stainless steel specimens were subjected to incrementally increasing values of plastic strain. At each value of strain, the associated static stress was recorded and the specimen was subjected to positron annihilation spectroscopy (PAS) using the Doppler Broadening method. A calibration curve for the 'S' parameter as a function of stress was developed based on the five specimens. Seven different specimens (blind specimens labeled B1-B7) of 304L stainless steel were subjected to values of stress inducing plastic deformation. The values of stress ranged from 310 to 517 MPa. The seven specimens were subjected to PAS post-loading using the Doppler Broadening method, and the results were compared against the developed curve from the previous five specimens. It was found that a strong correlation exists between the 'S' parameter, stress, and strain up to a strain value of 15%, corresponding to a stress value of 500 MPa, beyond which saturation of the 'S' parameter occurs. Research Highlights: {yields} Specimens were initially in an annealed/recrystallized condition. {yields} Calibration results indicate positron annihilation measurements yield correlation. {yields} Deformation produced by cold work was likely larger than the maximum strain.

  12. Double antikaonic nuclear clusters in antiproton-3He annihilation at J-PARC

    NASA Astrophysics Data System (ADS)

    Sakuma, Fuminori; Curceanu, Catalina; Iwasaki, Masahiko; Kienle, Paul; Ohnishi, Hiroaki; Tokuda, Makoto; Tsukada, Kyo; Widmann, Eberhard; Yamazaki, Toshimitsu; Zmeskal, Johannes

    We search for double anti-kaon nuclear bound states in the bar p annihilation reaction in 3He nuclei at rest. In view of the strongly attractive bar K N interaction, the existence of nuclear clusters with more than one K - has been predicted theoretically. The double anti-kaon production in elementary antiproton annihilation at rest is forbidden because of the negative Q-value; however, a double anti-kaon nuclear bound state, such as K - K - pp, with deep binding energy would enable double anti-kaon production in the nuclei. In order to investigate the K - K - pp production in the bar p + ^3He to K^+ + K^0 + X (X = K^-K^-pp) channel, the produced K - K - pp cluster is identified both using missing mass spectroscopy via the K + K 0 channel with a Λ-tag, and invariant mass analysis of the expected decay particles from the K - K - pp cluster such as ΛΛ. We propose to perform the experiment at the existing K1.8BR beam line at J-PARC with the E15 spectrometer.

  13. Double antikaonic nuclear clusters in antiproton-3He annihilation at J-PARC

    NASA Astrophysics Data System (ADS)

    Sakuma, Fuminori; Curceanu, Catalina; Iwasaki, Masahiko; Kienle, Paul; Ohnishi, Hiroaki; Tokuda, Makoto; Tsukada, Kyo; Widmann, Eberhard; Yamazaki, Toshimitsu; Zmeskal, Johannes

    2012-12-01

    We search for double anti-kaon nuclear bound states in the bar p annihilation reaction in 3He nuclei at rest. In view of the strongly attractive bar K N interaction, the existence of nuclear clusters with more than one K - has been predicted theoretically. The double anti-kaon production in elementary antiproton annihilation at rest is forbidden because of the negative Q-value; however, a double anti-kaon nuclear bound state, such as K - K - pp, with deep binding energy would enable double anti-kaon production in the nuclei. In order to investigate the K - K - pp production in the bar p + ^3He to K^+ + K^0 + X (X = K^-K^-pp) channel, the produced K - K - pp cluster is identified both using missing mass spectroscopy via the K + K 0 channel with a Λ-tag, and invariant mass analysis of the expected decay particles from the K - K - pp cluster such as ΛΛ. We propose to perform the experiment at the existing K1.8BR beam line at J-PARC with the E15 spectrometer.

  14. Quantum beats in the 3γ annihilation decay of Positronium observed by perturbed angular distribution

    NASA Astrophysics Data System (ADS)

    Ivanov, Eugeniu; Vata, Ion; Dudu, Dorin; Rusen, Ion; Stefan, Nitisor

    2008-10-01

    We have applied conventional Time Differential Perturbed Angular Correlation (TDPAC) method to observe the anisotropy oscillations in the 3γ annihilation decay of polarized Positronium in a weak magnetic field. The effect, as predicted theoretically and experimentally demonstrated by Barishevsky et al. [V.G. Barishevsky, O.N. Metelitsa, V.V. Tikhomirov, Oscillations of the positronium decay γ-quantum angular distribution in a magnetic field, J. Phys. B: At. Mol. Opt. Phys.22 (1989) 2835], is induced by the coherent admixture of the m = 0 states of ortho-Positronium ( o-Ps) and para-Positronium ( p-Ps) in interaction with the magnetic field. The following experimental characteristics are to be considered: the oscillation frequency corresponds to the difference in energy of the Ps atom levels in magnetic field and is proportional with H2; in a fixed geometry the modulation depth (oscillations amplitude) depends on the mean positron polarization; privileged angles of the polarization vector, magnetic field and detectors are required for optimizing the observed oscillations amplitude. The normalized difference spectrum function ( R( t)) obtained from time spectra measured in vacuum and in different gaseous atmospheres (Ar, H 2, N 2) have the oscillations amplitude constant and we conclude that the Ps atoms are not fully thermalized over a time interval of about 400 ns. The R( t) functions obtained for o-Ps annihilation decays, in dry air or Ar-O mixture, have the oscillations amplitude time dependent due, probably, to the paramagnetism of the Oxygen molecules.

  15. Positronium formation and annihilation in liquid crystalline smectic-E phase revisited

    NASA Astrophysics Data System (ADS)

    Dryzek, E.; Juszyńska-Gałazka, E.

    2016-02-01

    The results of the positron lifetime measurements of the quenched smectic-E (Sm-E ) phase of 4-butyl-4'-isothiocyano-1,1'-biphenyl (4TCB) are revisited. The sites of positronium formation and annihilation, according to the model with nanosegregated layered structure of the Sm-E phase and molten state of alkyl chains of molecules, are identified in the sublayer containing alkyl chains of molecules. The possibility of vitrification of the Sm-E phase for 4TCB consisting in freezing of the alkyl chain motions is considered as a cause of the thermally activated creation of sites where o -Ps is formed and annihilates in the quenched Sm-E phase. The description of the temperature dependence of ortho-positronium intensity is performed using the glass transition model which assumes that the molecules occupy two thermodynamic states: solidlike or liquidlike regarding mobility of their alkyl chains. The equilibrium temperature between solidlike and liquidlike domains of the model obtained from positron lifetime measurements coincides with the exothermic effect in the temperature dependence of the heat capacity.

  16. Preorganized Chromophores Facilitate Triplet Energy Migration, Annihilation and Upconverted Singlet Energy Collection.

    PubMed

    Mahato, Prasenjit; Yanai, Nobuhiro; Sindoro, Melinda; Granick, Steve; Kimizuka, Nobuo

    2016-05-25

    Photon upconversion (UC) based on triplet-triplet annihilation (TTA) has the potential to enhance significantly photovoltaic and photocatalytic efficiencies by harnessing sub-bandgap photons, but the progress of this field is held back by the chemistry problem of how to preorganize multiple chromophores for efficient UC under weak solar irradiance. Recently, the first maximization of UC quantum yield at solar irradiance was achieved using fast triplet energy migration (TEM) in metal-organic frameworks (MOFs) with ordered acceptor arrays, but at the same time, a trade-off between fast TEM and high fluorescence efficiency was also found. Here, we provide a solution for this trade-off issue by developing a new strategy, triplet energy migration, annihilation and upconverted singlet energy collection (TEM-UPCON). The porous structure of acceptor-based MOF crystals allows triplet donor molecules to be accommodated without aggregation. The surface of donor-doped MOF nanocrystals is modified with highly fluorescent energy collectors through coordination bond formation. Thanks to the higher fluorescence quantum yield of surface-bound collectors than parent MOFs, the implementation of the energy collector greatly improves the total UC quantum yield. The UC quantum yield maximization behavior at ultralow excitation intensity was retained because the TTA events take place only in the MOF acceptors. The TEM-UPCON concept may be generalized to collectors with various functions and would lead to quantitative harvesting of upconverted energy, which is difficult to achieve in common molecular diffusion-based systems. PMID:27163784

  17. Positron annihilation signatures associated with the outburst of the microquasar V404 Cygni

    NASA Astrophysics Data System (ADS)

    Siegert, Thomas; Diehl, Roland; Greiner, Jochen; Krause, Martin G. H.; Beloborodov, Andrei M.; Bel, Marion Cadolle; Guglielmetti, Fabrizia; Rodriguez, Jerome; Strong, Andrew W.; Zhang, Xiaoling

    2016-03-01

    Microquasars are stellar-mass black holes accreting matter from a companion star and ejecting plasma jets at almost the speed of light. They are analogues of quasars that contain supermassive black holes of 106 to 1010 solar masses. Accretion in microquasars varies on much shorter timescales than in quasars and occasionally produces exceptionally bright X-ray flares. How the flares are produced is unclear, as is the mechanism for launching the relativistic jets and their composition. An emission line near 511 kiloelectronvolts has long been sought in the emission spectrum of microquasars as evidence for the expected electron-positron plasma. Transient high-energy spectral features have been reported in two objects, but their positron interpretation remains contentious. Here we report observations of γ-ray emission from the microquasar V404 Cygni during a recent period of strong flaring activity. The emission spectrum around 511 kiloelectronvolts shows clear signatures of variable positron annihilation, which implies a high rate of positron production. This supports the earlier conjecture that microquasars may be the main sources of the electron-positron plasma responsible for the bright diffuse emission of annihilation γ-rays in the bulge region of our Galaxy. Additionally, microquasars could be the origin of the observed megaelectronvolt continuum excess in the inner Galaxy.

  18. Measurement of the hadronic cross section in electron-positron annihilation

    SciTech Connect

    Clearwater, S.

    1983-11-01

    This thesis describes the most precise measurement to date of the ratio R, the hadronic cross section in lowest order electron-positron annihilation to the cross section for muon pair production in lowest order electron-positron annihilation. This experiment is of interest because R is a fundamental parameter that tests in a model independent way the basic assumptions of strong interaction theories. According to the assumptions of one of these theories the value of R is determined simply from the electric charges, spin, and color assignments of the produced quark-pairs. The experiment was carried out with the MAgnetic Calorimeter using collisions of 14.5 GeV electrons and positrons at the 2200m circumference PEP storage ring at SLAC. The MAC detector is one of the best-suited collider detectors for measuring R due to its nearly complete coverage of the full angular range. The data for this experiment were accumulated between February 1982 and April 1983 corresponding to a total event sample of about 40,000 hadronic events. About 5% of the data were taken with 14 GeV beams and the rest of the data were taken with 14.5 GeV beams. A description of particle interactions and experimental considerations is given.

  19. Cascade model of gamma-ray bursts: Power-law and annihilation-line components

    NASA Technical Reports Server (NTRS)

    Harding, A. K.; Sturrock, P. A.; Daugherty, J. K.

    1988-01-01

    If, in a neutron star magnetosphere, an electron is accelerated to an energy of 10 to the 11th or 12th power eV by an electric field parallel to the magnetic field, motion of the electron along the curved field line leads to a cascade of gamma rays and electron-positron pairs. This process is believed to occur in radio pulsars and gamma ray burst sources. Results are presented from numerical simulations of the radiation and photon annihilation pair production processes, using a computer code previously developed for the study of radio pulsars. A range of values of initial energy of a primary electron was considered along with initial injection position, and magnetic dipole moment of the neutron star. The resulting spectra was found to exhibit complex forms that are typically power law over a substantial range of photon energy, and typically include a dip in the spectrum near the electron gyro-frequency at the injection point. The results of a number of models are compared with data for the 5 Mar., 1979 gamma ray burst. A good fit was found to the gamma ray part of the spectrum, including the equivalent width of the annihilation line.

  20. Correlated Pair States Formed by Singlet Fission and Exciton-Exciton Annihilation.

    PubMed

    Scholes, Gregory D

    2015-12-24

    Singlet fission to form a pair of triplet excitations on two neighboring molecules and the reverse process, triplet-triplet annihilation to upconvert excitation, have been extensively studied. Comparatively little work has sought to examine the properties of the intermediate state in both of these processes-the bimolecular pair state. Here, the eigenstates constituting the manifold of 16 bimolecular pair excitations and their relative energies in the weak-coupling regime are reported. The lowest-energy states obtained from the branching diagram method are the triplet pairs with overall singlet spin |X1⟩ ≈ (1)[TT] and quintet spin |Q⟩ ≈ (5)[TT]. It is shown that triplet pair states can be separated by a triplet-triplet energy-transfer mechanism to give a separated, yet entangled triplet pair (1)[T···T]. Independent triplets are produced by decoherence of the separated triplet pair. Recombination of independent triplets by exciton-exciton annihilation to form the correlated triplet pair (i.e., nongeminate recombination) happens with 1/3 of the rate of either triplet migration or recombination of the separated correlated triplet pair (geminate recombination). PMID:26595530

  1. Dwarf Galaxy Annihilation and Decay Emission Profiles for Dark Matter Experiments

    NASA Astrophysics Data System (ADS)

    Geringer-Sameth, Alex; Koushiappas, Savvas M.; Walker, Matthew

    2015-03-01

    Gamma-ray searches for dark matter annihilation and decay in dwarf galaxies rely on an understanding of the dark matter density profiles of these systems. Conversely, uncertainties in these density profiles propagate into the derived particle physics limits as systematic errors. In this paper we quantify the expected dark matter signal from 20 Milky Way dwarfs using a uniform analysis of the most recent stellar-kinematic data available. Assuming that the observed stellar populations are equilibrium tracers of spherically symmetric gravitational potentials that are dominated by dark matter, we find that current stellar-kinematic data can predict the amplitudes of annihilation signals to within a factor of a few for the ultra-faint dwarfs of greatest interest. On the other hand, the expected signal from several classical dwarfs (with high-quality observations of large numbers of member stars) can be localized to the ~20% level. These results are important for designing maximally sensitive searches in current and future experiments using space and ground-based instruments.

  2. Novel time-of-flight spectrometer for the analysis of positron annihilation induced Auger electrons

    SciTech Connect

    Hugenschmidt, Christoph; Legl, Stefan

    2006-10-15

    Positron annihilation induced Auger-electron spectroscopy (PAES) has several advantages over conventional Auger-electron spectroscopy such as extremely high surface sensitivity and outstanding signal-to-noise ratio at the Auger-transition energy. In order to benefit from these prominent features a low-energy positron beam of high intensity is required for surface sensitive PAES studies. In addition, an electron energy analyzer is required, which efficiently detects the Auger electrons with acceptable energy resolution. For this reason a novel time-of-flight (TOF) spectrometer has been developed at the intense positron source NEPOMUC that allows PAES studies within short measurement time. This TOF-PAES setup combines a trochoidal filter and a flight tube in a Faraday cage in order to achieve an improved energy resolution of about 1 eV at high electron energies up to E{approx_equal}1000 eV. The electron flight time is the time between the annihilation radiation at the sample and when the electron hits a microchannel plate detector at the end of the flight tube.

  3. Cosmological and astrophysical signatures of dark matter annihilations into pseudo-Goldstone bosons

    SciTech Connect

    Garcia-Cely, Camilo; Ibarra, Alejandro; Molinaro, Emiliano E-mail: alejandro.ibarra@ph.tum.de

    2014-02-01

    We investigate a model where the dark matter particle is a chiral fermion field charged under a global U(1) symmetry which is assumed to be spontaneously broken, leading to a pseudo-Goldstone boson (PGB). We argue that the dark matter annihilation into PGBs determine the dark matter relic abundance. Besides, we also note that experimental searches for PGBs allow either for a very long lived PGB, with a lifetime much longer than the age of the Universe, or a relatively short lived PGB, with a lifetime shorter than one minute. Hence, two different scenarios arise, producing very different signatures. In the long lived PGB scenario, the PGB might contribute significantly to the radiation energy density of the Universe. On the other hand, in the short lived PGB scenario, and since the decay length is shorter than one parsec, the s-wave annihilation into a PGB and a CP even dark scalar in the Galactic center might lead to an intense box feature in the gamma-ray energy spectrum, provided the PGB decay branching ratio into two photons is sizable. We also analyze the constraints on these two scenarios from thermal production, the Higgs invisible decay width and direct dark matter searches.

  4. Study of positrons from cosmic rays interactions and cold dark matter annihilations in the galactic environment

    NASA Astrophysics Data System (ADS)

    Lineros, Roberto A.

    2008-12-01

    Positron and electron cosmic rays provide a complementary way to study the galactic environment. The actual cosmic rays experiments, for instance PAMELA and HEAT, have presented very exciting results in this field. The observed positron fraction appears larger than the actual theoretical predictions for energies larger than 10 GeV. The indirect evidences of Dark Matter in connection with Beyond the Standard Model theories would suggest the existence of an extra contribution present in the cosmic ray signal. We study and calculate the positron signal produced by the annihilation of a generic Dark Matter candidate. Especially, We analyze typical annihilation signatures and the impact of CR propagation physics on the positron signal. In addition, we study the positron signal related to spallation processes between nuclei cosmic--rays and the interstellar gas. We analyze the effects of uncertainties present in nuclear cross section, nuclei cosmic--ray and CR propagation physics. The propagation of positrons is modeled according to the Two--Zone Propagation Model which has been successfully tested in the study of nuclei cosmic--ray and present an analytical approach to study the cosmic--ray physics.

  5. Annihilating Filter-Based Low-Rank Hankel Matrix Approach for Image Inpainting.

    PubMed

    Jin, Kyong Hwan; Ye, Jong Chul

    2015-11-01

    In this paper, we propose a patch-based image inpainting method using a low-rank Hankel structured matrix completion approach. The proposed method exploits the annihilation property between a shift-invariant filter and image data observed in many existing inpainting algorithms. In particular, by exploiting the commutative property of the convolution, the annihilation property results in a low-rank block Hankel structure data matrix, and the image inpainting problem becomes a low-rank structured matrix completion problem. The block Hankel structured matrices are obtained patch-by-patch to adapt to the local changes in the image statistics. To solve the structured low-rank matrix completion problem, we employ an alternating direction method of multipliers with factorization matrix initialization using the low-rank matrix fitting algorithm. As a side product of the matrix factorization, locally adaptive dictionaries can be also easily constructed. Despite the simplicity of the algorithm, the experimental results using irregularly subsampled images as well as various images with globally missing patterns showed that the proposed method outperforms existing state-of-the-art image inpainting methods. PMID:26087492

  6. Exciton-Exciton Annihilation in Copper-Phthalocyanine Single-Crystal Nanowires

    SciTech Connect

    Ma, Yingzhong; Xiao, Kai; Shaw, Robert W

    2012-01-01

    Femtosecond one-color pump-probe spectroscopy was applied to study exciton dynamics in single-crystal copper-phthalocyanine (CuPc) nanowires grown on an opaque silicon substrate. The transient reflectance kinetics measured at different pump fluences exhibit a remarkable intensity-dependent decay behavior which accelerates significantly with increasing pump pulse intensity. All the kinetic decays can be satisfactorily described using a bi-exponential decay function with lifetimes of 22 and 204 ps, and corresponding relative amplitudes depending on the pump intensity. The accelerated decay behavior observed at high pump intensities arises from a nonlinear exciton-exciton annihilation process. While this phenomenon has been found previously in crystalline metallophthalocyanine (MPc) polymorphs such as colloidal particles and thin films, the results obtained using the CuPc nanowires are markedly distinct, namely, much longer decay times and a linear intensity dependence of the initial peak amplitudes. Despite these differences, detailed data analysis further shows that, as found for other metal-phthalocyanine polymorphs, exciton-exciton annihilation in the CuPc nanowires is one-dimensional (1D) diffusion-limited, which possibly involves intra-chain exciton diffusion along 1D molecular stacks. The significantly long-lived excitons of CuPc nanowires in comparison to those of other crystalline polymorphs make them particularly suitable for photovoltaic applications.

  7. Self-diffusion and defect annihilation in nanocrystalline Fe films probed by neutron reflectometry

    NASA Astrophysics Data System (ADS)

    Chakravarty, Sujoy; Schmidt, Harald; Tietze, Ursula; Lott, Dieter; Lalla, N. P.; Gupta, Ajay

    2009-07-01

    Self-diffusion in ion-beam-sputtered nanocrystalline Fe is studied between 310 and 510°C , using neutron reflectometry on [Fnate(7nm)/F57e(3nm)]15 isotope multilayers. Neutron reflectometry has the advantage over other methods of diffusivity determination, that diffusion lengths on the order of 1 nm and below can be determined. This enables diffusion experiments in a nanostructure which is not significantly modified by grain growth during annealing. The determined diffusivities are time depended and decrease by more than two orders of magnitude during isothermal annealing. In early stages, diffusion is controlled by frozen-in nonequilibrium point defects (interstitials or vacancies) present after deposition. The decrease in the diffusivities can be attributed to the annihilation of these point defects. For very long annealing times the diffusivities above 400°C are in good agreement with volume diffusivities measured in single crystals given in literature. However, at a temperature of 400°C and below the diffusivities are still higher than extrapolated literature data also after more than 8 days of annealing, indicating that defect annihilation is still going on.

  8. Positron annihilation in the hydrogenated granular superconductor of YBa 2Cu 3O 7-δ

    NASA Astrophysics Data System (ADS)

    Lam, C. C.; Shao, L. W.; Jin, X.; Chen, W. M.; Xiong, H. Q.; Feng, J.; Qi, S. R.; Hung, K. C.

    1996-02-01

    In this paper, we have used the sputtering neutral-particles mass spectroscopy (SNMS) and positron-annihilation technique to investigate the effect of hydrogenation on the physical properties of different oxygenated YBa 2Cu 3O 7-δ superconductors. Under the same of hydrogenation treatment, the hydrogenation effects on the superconductors are compared to the non-superconductors. It was shown that the hydrogen concentration in the superconductors is about eight times of the non-superconductor's. It was proven that the long lifetime of positrons in the annihilation process is determined by the variation of the concentrations of monovacancies and microvoids, which takes place in both of intragrain and intergrain samples. The hydrogenation effect can be classified into four stages. At the first stage, the hydrogen atoms fill both monovacancy and microvoid. At the end of the first stage, the long lifetime τ2 reaches the maximum value which is determined by the lifetime of the positron in the monovacancy-free and nearly microvoid-exhausted YBCO sample. In the second stage, the hydrogen charging will lead to creation of new monovacancies; this will make the long lifetime τ2 drop monotonically to its minimum value. In the third stage, further hydrogen charging promotes the formation of microvoids, and leads to an increasing τ2 up to a saturation value, which indicates the equilibrium concentrations of monovacancy and microvoid at that temperature.

  9. Challenges in detecting gamma-rays from dark matter annihilations in the galactic center

    SciTech Connect

    Zaharijas, Gabrijela; Hooper, Dan

    2006-05-15

    Atmospheric Cerenkov Telescopes, including HESS and MAGIC, have detected a spectrum of gamma-rays from the galactic center region which extends from {approx}200 GeV or lower, to at least {approx}10 TeV. Although the source of this radiation is not yet known, the spectrum appears to behave as a simple power-law, which is not the expectation for gamma-rays generated through the annihilation of dark matter particles. If instead we conclude that the source of these gamma-rays is astrophysical in origin, this spectrum will constitute a background for future dark matter searches using gamma-rays from this region. In this paper we study how this background will affect the prospects for experiments such as GLAST to detect dark matter in the galactic center. We find that only a narrow range of dark matter annihilation rates are potentially observable by GLAST given this newly discovered background and considering current constraints from EGRET and HESS. We also find that a detection of line emission, while not completely ruled out, is only possible for a very narrow range of dark matter models and halo profiles.

  10. New signature of dark matter annihilations: Gamma rays from intermediate-mass black holes

    SciTech Connect

    Bertone, Gianfranco; Zentner, Andrew R.; Silk, Joseph

    2005-11-15

    We study the prospects for detecting gamma rays from dark matter (DM) annihilations in enhancements of the DM density (mini-spikes) around intermediate-mass black holes (IMBH) with masses in the range 10{sup 2} < or approx. M/M{sub {center_dot}} < or approx. 10{sup 6}. Focusing on two different IMBH formation scenarios, we show that, for typical values of mass and cross section of common DM candidates, mini-spikes, produced by the adiabatic growth of DM around pregalactic IMBHs, would be bright sources of gamma rays, which could be easily detected with large field-of-view gamma-ray experiments such as GLAST, and further studied with smaller field-of-view, larger-area experiments like Air Cherenkov Telescopes CANGAROO, HESS, MAGIC, and VERITAS. The detection of many gamma-ray sources not associated with a luminous component of the Local Group, and with identical cutoffs in their energy spectra at the mass of the DM particle, would provide a potential smoking-gun signature of DM annihilations and shed new light on the nature of intermediate and supermassive black holes.

  11. Search for photon-linelike signatures from dark matter annihilations with H.E.S.S.

    PubMed

    Abramowski, A; Acero, F; Aharonian, F; Akhperjanian, A G; Anton, G; Balenderan, S; Balzer, A; Barnacka, A; Becherini, Y; Becker Tjus, J; Bernlöhr, K; Birsin, E; Biteau, J; Bochow, A; Boisson, C; Bolmont, J; Bordas, P; Brucker, J; Brun, F; Brun, P; Bulik, T; Carrigan, S; Casanova, S; Cerruti, M; Chadwick, P M; Chaves, R C G; Cheesebrough, A; Colafrancesco, S; Cologna, G; Conrad, J; Couturier, C; Dalton, M; Daniel, M K; Davids, I D; Degrange, B; Deil, C; deWilt, P; Dickinson, H J; Djannati-Ataï, A; Domainko, W; Drury, L O'C; Dubus, G; Dutson, K; Dyks, J; Dyrda, M; Egberts, K; Eger, P; Espigat, P; Fallon, L; Farnier, C; Fegan, S; Feinstein, F; Fernandes, M V; Fernandez, D; Fiasson, A; Fontaine, G; Förster, A; Füßling, M; Gajdus, M; Gallant, Y A; Garrigoux, T; Gast, H; Giebels, B; Glicenstein, J F; Glück, B; Göring, D; Grondin, M-H; Häffner, S; Hague, J D; Hahn, J; Hampf, D; Harris, J; Heinz, S; Heinzelmann, G; Henri, G; Hermann, G; Hillert, A; Hinton, J A; Hofmann, W; Hofverberg, P; Holler, M; Horns, D; Jacholkowska, A; Jahn, C; Jamrozy, M; Jung, I; Kastendieck, M A; Katarzyński, K; Katz, U; Kaufmann, S; Khélifi, B; Klepser, S; Klochkov, D; Kluźniak, W; Kneiske, T; Komin, Nu; Kosack, K; Kossakowski, R; Krayzel, F; Krüger, P P; Laffon, H; Lamanna, G; Lefaucheur, J; Lemoine-Goumard, M; Lenain, J-P; Lennarz, D; Lohse, T; Lopatin, A; Lu, C-C; Marandon, V; Marcowith, A; Masbou, J; Maurin, G; Maxted, N; Mayer, M; McComb, T J L; Medina, M C; Méhault, J; Menzler, U; Moderski, R; Mohamed, M; Moulin, E; Naumann, C L; Naumann-Godo, M; de Naurois, M; Nedbal, D; Nekrassov, D; Nguyen, N; Niemiec, J; Nolan, S J; Ohm, S; de Oña Wilhelmi, E; Opitz, B; Ostrowski, M; Oya, I; Panter, M; Parsons, R D; Paz Arribas, M; Pekeur, N W; Pelletier, G; Perez, J; Petrucci, P-O; Peyaud, B; Pita, S; Pühlhofer, G; Punch, M; Quirrenbach, A; Raue, M; Reimer, A; Reimer, O; Renaud, M; de Los Reyes, R; Rieger, F; Ripken, J; Rob, L; Rosier-Lees, S; Rowell, G; Rudak, B; Rulten, C B; Sahakian, V; Sanchez, D A; Santangelo, A; Schlickeiser, R; Schulz, A; Schwanke, U; Schwarzburg, S; Schwemmer, S; Sheidaei, F; Skilton, J L; Sol, H; Spengler, G; Stawarz, L; Steenkamp, R; Stegmann, C; Stinzing, F; Stycz, K; Sushch, I; Szostek, A; Tavernet, J-P; Terrier, R; Tluczykont, M; Trichard, C; Valerius, K; van Eldik, C; Vasileiadis, G; Venter, C; Viana, A; Vincent, P; Völk, H J; Volpe, F; Vorobiov, S; Vorster, M; Wagner, S J; Ward, M; White, R; Wierzcholska, A; Wouters, D; Zacharias, M; Zajczyk, A; Zdziarski, A A; Zech, A; Zechlin, H-S

    2013-01-25

    Gamma-ray line signatures can be expected in the very-high-energy (E(γ)>100 GeV) domain due to self-annihilation or decay of dark matter (DM) particles in space. Such a signal would be readily distinguishable from astrophysical γ-ray sources that in most cases produce continuous spectra that span over several orders of magnitude in energy. Using data collected with the H.E.S.S. γ-ray instrument, upper limits on linelike emission are obtained in the energy range between ∼ 500 GeV and ∼ 25 TeV for the central part of the Milky Way halo and for extragalactic observations, complementing recent limits obtained with the Fermi-LAT instrument at lower energies. No statistically significant signal could be found. For monochromatic γ-ray line emission, flux limits of (2 × 10(-7) -2 × 10(-5)) m(-2) s(-1) sr(-1) and (1 × 10(-8) -2 × 10(-6)) m(-2) s(-1)sr(-1) are obtained for the central part of the Milky Way halo and extragalactic observations, respectively. For a DM particle mass of 1 TeV, limits on the velocity-averaged DM annihilation cross section ⟨σv⟩(χχ → γγ) reach ∼ 10(-27) cm(3)s(-1), based on the Einasto parametrization of the Galactic DM halo density profile. PMID:25166149

  12. Positron annihilation signatures associated with the outburst of the microquasar V404 Cygni.

    PubMed

    Siegert, Thomas; Diehl, Roland; Greiner, Jochen; Krause, Martin G H; Beloborodov, Andrei M; Bel, Marion Cadolle; Guglielmetti, Fabrizia; Rodriguez, Jerome; Strong, Andrew W; Zhang, Xiaoling

    2016-03-17

    Microquasars are stellar-mass black holes accreting matter from a companion star and ejecting plasma jets at almost the speed of light. They are analogues of quasars that contain supermassive black holes of 10(6) to 10(10) solar masses. Accretion in microquasars varies on much shorter timescales than in quasars and occasionally produces exceptionally bright X-ray flares. How the flares are produced is unclear, as is the mechanism for launching the relativistic jets and their composition. An emission line near 511 kiloelectronvolts has long been sought in the emission spectrum of microquasars as evidence for the expected electron-positron plasma. Transient high-energy spectral features have been reported in two objects, but their positron interpretation remains contentious. Here we report observations of γ-ray emission from the microquasar V404 Cygni during a recent period of strong flaring activity. The emission spectrum around 511 kiloelectronvolts shows clear signatures of variable positron annihilation, which implies a high rate of positron production. This supports the earlier conjecture that microquasars may be the main sources of the electron-positron plasma responsible for the bright diffuse emission of annihilation γ-rays in the bulge region of our Galaxy. Additionally, microquasars could be the origin of the observed megaelectronvolt continuum excess in the inner Galaxy. PMID:26934231

  13. The gamma-ray spectra of 5-carbon alkane isomers in the positron annihilation process

    NASA Astrophysics Data System (ADS)

    Ma, Xiaoguang; Zhu, Yinghao; Liu, Yang

    2016-05-01

    The gamma-ray spectra of pentane (C5H12) and its two isomers, i.e., 2-Methylbutane (CH3C(CH3)HC2H5) and 2,2-Dimethylpropane (C(CH3)4) have been studied theoretically in the present work. The recent experimental gamma-ray spectra of these three molecules show that they have the same Doppler shifts, although their molecular structures are dramatically different. In order to reveal why the gamma-ray spectra of these molecules are less sensitive to the molecular structures, the one-dimensional gamma-ray spectra and spherically averaged momentum (SAM) distributions, the two-dimensional angular correlation of annihilation radiation (ACAR), and the three-dimensional momentum distributions of the positron-electron pair are studied. The one-centered momentum distributions of the electrons are found to play more important role than the multi-centered coordinate distributions. The present theoretical predictions have confirmed the experimental findings for the first time. The dominance of the inner valence electrons in the positron-electron annihilation process has also been suggested in the present work.

  14. W/Z bremsstrahlung as the dominant annihilation channel for dark matter

    SciTech Connect

    Bell, Nicole F.; Jacques, Thomas D.; Dent, James B.; Weiler, Thomas J.

    2011-01-01

    Dark matter annihilation to leptons, {chi}{chi}{yields}ll, is necessarily accompanied by electroweak radiative corrections, in which a W or Z boson is radiated from a final-state particle. Given that the W and Z gauge bosons decay dominantly via hadronic channels, it is thus impossible to produce final-state leptons without accompanying protons, antiprotons, and gamma rays. Significantly, while many dark matter models feature a helicity-suppressed annihilation rate to fermions, radiating a massive gauge boson from a final-state fermion removes this helicity suppression, such that the branching ratios Br(l{nu}W), Br(l{sup +}l{sup -}Z), and Br({nu}{nu}Z) dominate over Br(ll). W/Z bremsstrahlung thus allows indirect detection of many weakly interacting massive particle models that would otherwise be helicity suppressed, or v{sup 2} suppressed. Antiprotons and even antideuterons become consequential final-state particles. This is an important result for future dark matter searches. We discuss the implications of W/Z bremsstrahlung for 'leptonic' dark matter models which aim to fit recent cosmic ray positron and antiproton data.

  15. Two-photon annihilation of thermal pairs in strong magnetic fields

    NASA Technical Reports Server (NTRS)

    Baring, Matthew G.; Harding, Alice K.

    1992-01-01

    The annihilation spectrum of pairs with 1-D thermal distributions in the presence of a strong magnetic field is calculated. Numerical analysis of the spectrum are performed for mildly relativistic temperatures and for different angles of emission with respect to field lines. Teragauss magnetic fields are assumed so that conditions are typical of gamma ray burst and pulsar environments. The spectra at each viewing angle reveal asymmetric line profiles that are signatures of the magnetic broadening and red shifting of the line: these asymmetries are more prominent for small viewing angles. Thermal Doppler broadening tends to dominate in the right wing of the line and obscures the magnetic broadening more at high temperatures and smaller viewing angles. This angular dependence of the line asymmetry may prove a valuable diagnostic tool. For low temperatures and magnetic field strengths, useful analytic expressions are presented for the line width, and also for the annihilation spectrum at zero viewing angle. The results presented find application in gamma ray burst and pulsar models, and may prove very helpful in deducing field strengths and temperatures of the emission regions of these objects from line observations made by Compton GRO and future missions.

  16. Probing spectator scattering and annihilation corrections in Bs→P V decays

    NASA Astrophysics Data System (ADS)

    Chang, Qin; Hu, Xiaohui; Sun, Junfeng; Yang, Yueling

    2015-04-01

    Motivated by the recent LHCb measurements on B¯s→π-K*+ and B¯s→K±K*∓ decay modes, we revisit the Bs→P V decays within QCD factorization framework. The effects of hard-spectator scattering and annihilation corrections are studied in detail. After performing a χ2-fit on the end-point parameters XAi ,f(ρAi ,f,ϕAi ,f) and XH(ρH,ϕH) with available data, it is found that although some possible mismatches exist, the universalities of XAi ,f and XH in Bs and Bu ,d systems are still allowed within theoretical uncertainties and experimental errors. With the end-point parameters obtained from Bu ,d→P V decays, the numerical results and detailed analyses for the observables of B¯s→π K*, ρ K , π ρ , π ϕ , and K ϕ decay modes are presented. In addition, we have identified a few useful observables, especially the ones of B¯s→π0ϕ decay for instance, for probing hard-spectator scattering and annihilation contributions.

  17. Segmented scintillation detectors with silicon photomultiplier readout for measuring antiproton annihilations.

    PubMed

    Sótér, A; Todoroki, K; Kobayashi, T; Barna, D; Horváth, D; Hori, M

    2014-02-01

    The Atomic Spectroscopy and Collisions Using Slow Antiprotons experiment at the Antiproton Decelerator (AD) facility of CERN constructed segmented scintillators to detect and track the charged pions which emerge from antiproton annihilations in a future superconducting radiofrequency Paul trap for antiprotons. A system of 541 cast and extruded scintillator bars were arranged in 11 detector modules which provided a spatial resolution of 17 mm. Green wavelength-shifting fibers were embedded in the scintillators, and read out by silicon photomultipliers which had a sensitive area of 1 × 1 mm(2). The photoelectron yields of various scintillator configurations were measured using a negative pion beam of momentum p ≈ 1 GeV/c. Various fibers and silicon photomultipliers, fiber end terminations, and couplings between the fibers and scintillators were compared. The detectors were also tested using the antiproton beam of the AD. Nonlinear effects due to the saturation of the silicon photomultiplier were seen at high annihilation rates of the antiprotons. PMID:24593349

  18. Segmented scintillation detectors with silicon photomultiplier readout for measuring antiproton annihilations

    SciTech Connect

    Sótér, A.; Todoroki, K.; Kobayashi, T.; Barna, D.; Wigner Research Center of Physics, H-1525 Budapest ; Horváth, D.; Hori, M.; Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033

    2014-02-15

    The Atomic Spectroscopy and Collisions Using Slow Antiprotons experiment at the Antiproton Decelerator (AD) facility of CERN constructed segmented scintillators to detect and track the charged pions which emerge from antiproton annihilations in a future superconducting radiofrequency Paul trap for antiprotons. A system of 541 cast and extruded scintillator bars were arranged in 11 detector modules which provided a spatial resolution of 17 mm. Green wavelength-shifting fibers were embedded in the scintillators, and read out by silicon photomultipliers which had a sensitive area of 1 × 1 mm{sup 2}. The photoelectron yields of various scintillator configurations were measured using a negative pion beam of momentum p ≈ 1 GeV/c. Various fibers and silicon photomultipliers, fiber end terminations, and couplings between the fibers and scintillators were compared. The detectors were also tested using the antiproton beam of the AD. Nonlinear effects due to the saturation of the silicon photomultiplier were seen at high annihilation rates of the antiprotons.

  19. DARK MATTER DECAY AND ANNIHILATION IN THE LOCAL UNIVERSE: CLUES FROM FERMI

    SciTech Connect

    Cuesta, A. J.; Zandanel, F.; Prada, F.; Jeltema, T. E.; Yepes, G.; Klypin, A.; Hoffman, Y.; Gottloeber, S.; Sanchez-Conde, M. A.; Pfrommer, C. E-mail: fabio@iaa.es

    2011-01-01

    We present all-sky simulated Fermi maps of {gamma}-rays from dark matter (DM) decay and annihilation in the local universe. The DM distribution is obtained from a constrained cosmological simulation of the neighboring large-scale structure provided by the CLUES project. The DM fields of density and density squared are then taken as an input for the Fermi observation simulation tool to predict the {gamma}-ray photon counts that Fermi would detect in 5 years of an all-sky survey for given DM models. Signal-to-noise ratio (S/N) sky maps have also been obtained by adopting the current Galactic and isotropic diffuse background models released by the Fermi Collaboration. We point out the possibility for Fermi to detect a DM {gamma}-ray signal in local extragalactic structures. In particular, we conclude here that Fermi observations of nearby clusters (e.g., Virgo and Coma) and filaments are expected to give stronger constraints on decaying DM compared to previous studies. As an example, we find a significant S/N in DM models with a decay rate fitting the positron excess as measured by PAMELA. This is the first time that DM filaments are shown to be promising targets for indirect detection of DM. On the other hand, the prospects for detectability of annihilating DM in local extragalactic structures are less optimistic even with extreme cross-sections. We make the DM density and density squared maps publicly available online.

  20. Bright gamma-ray Galactic Center excess and dark dwarfs: Strong tension for dark matter annihilation despite Milky Way halo profile and diffuse emission uncertainties

    NASA Astrophysics Data System (ADS)

    Abazajian, Kevork N.; Keeley, Ryan E.

    2016-04-01

    We incorporate Milky Way dark matter halo profile uncertainties, as well as an accounting of diffuse gamma-ray emission uncertainties in dark matter annihilation models for the Galactic Center Extended gamma-ray excess (GCE) detected by the Fermi Gamma Ray Space Telescope. The range of particle annihilation rate and masses expand when including these unknowns. However, two of the most precise empirical determinations of the Milky Way halo's local density and density profile leave the signal region to be in considerable tension with dark matter annihilation searches from combined dwarf galaxy analyses for single-channel dark matter annihilation models. The GCE and dwarf tension can be alleviated if: one, the halo is very highly concentrated or strongly contracted; two, the dark matter annihilation signal differentiates between dwarfs and the GC; or, three, local stellar density measures are found to be significantly lower, like that from recent stellar counts, increasing the local dark matter density.

  1. Hydrodynamic and kinetic models for spin-1/2 electron-positron quantum plasmas: Annihilation interaction, helicity conservation, and wave dispersion in magnetized plasmas

    NASA Astrophysics Data System (ADS)

    Andreev, Pavel A.

    2015-06-01

    We discuss the complete theory of spin-1/2 electron-positron quantum plasmas, when electrons and positrons move with velocities mach smaller than the speed of light. We derive a set of two fluid quantum hydrodynamic equations consisting of the continuity, Euler, spin (magnetic moment) evolution equations for each species. We explicitly include the Coulomb, spin-spin, Darwin and annihilation interactions. The annihilation interaction is the main topic of the paper. We consider the contribution of the annihilation interaction in the quantum hydrodynamic equations and in the spectrum of waves in magnetized electron-positron plasmas. We consider the propagation of waves parallel and perpendicular to an external magnetic field. We also consider the oblique propagation of longitudinal waves. We derive the set of quantum kinetic equations for electron-positron plasmas with the Darwin and annihilation interactions. We apply the kinetic theory to the linear wave behavior in absence of external fields. We calculate the contribution of the Darwin and annihilation interactions in the Landau damping of the Langmuir waves. We should mention that the annihilation interaction does not change number of particles in the system. It does not related to annihilation itself, but it exists as a result of interaction of an electron-positron pair via conversion of the pair into virtual photon. A pair of the non-linear Schrodinger equations for the electron-positron plasmas including the Darwin and annihilation interactions is derived. Existence of the conserving helicity in electron-positron quantum plasmas of spinning particles with the Darwin and annihilation interactions is demonstrated. We show that the annihilation interaction plays an important role in the quantum electron-positron plasmas giving the contribution of the same magnitude as the spin-spin interaction.

  2. Hydrodynamic and kinetic models for spin-1/2 electron-positron quantum plasmas: Annihilation interaction, helicity conservation, and wave dispersion in magnetized plasmas

    SciTech Connect

    Andreev, Pavel A.

    2015-06-15

    We discuss the complete theory of spin-1/2 electron-positron quantum plasmas, when electrons and positrons move with velocities mach smaller than the speed of light. We derive a set of two fluid quantum hydrodynamic equations consisting of the continuity, Euler, spin (magnetic moment) evolution equations for each species. We explicitly include the Coulomb, spin-spin, Darwin and annihilation interactions. The annihilation interaction is the main topic of the paper. We consider the contribution of the annihilation interaction in the quantum hydrodynamic equations and in the spectrum of waves in magnetized electron-positron plasmas. We consider the propagation of waves parallel and perpendicular to an external magnetic field. We also consider the oblique propagation of longitudinal waves. We derive the set of quantum kinetic equations for electron-positron plasmas with the Darwin and annihilation interactions. We apply the kinetic theory to the linear wave behavior in absence of external fields. We calculate the contribution of the Darwin and annihilation interactions in the Landau damping of the Langmuir waves. We should mention that the annihilation interaction does not change number of particles in the system. It does not related to annihilation itself, but it exists as a result of interaction of an electron-positron pair via conversion of the pair into virtual photon. A pair of the non-linear Schrodinger equations for the electron-positron plasmas including the Darwin and annihilation interactions is derived. Existence of the conserving helicity in electron-positron quantum plasmas of spinning particles with the Darwin and annihilation interactions is demonstrated. We show that the annihilation interaction plays an important role in the quantum electron-positron plasmas giving the contribution of the same magnitude as the spin-spin interaction.

  3. Positron Annihilation Spectroscopy as a Probe of Microscopic Structure and Physical Aging in Polymer.

    NASA Astrophysics Data System (ADS)

    Yu, Minzi

    Positron annihilation is studied as a characterization method for the properties of polymers. Previous studies indicate that the ortho-positronium lifetime tau _3 and intensity I_3 is correlated to the free volume "hole" size and number density of holes in a polymer. Positron annihilation lifetime (PAL) studies in polymers measure the change in free volume, and they are sensitive to different physical environments. PAL studies of the temperature dependence of a bisphenol-A polycarbonate shows that the free volume increases with increasing temperature, and it also obtains the transition temperatures T_{rm g} and T_beta^', from the tau_3 curve and the I_3 curve, respectively. The isothermal aging in polycarbonate shows that: I_3 decreases while tau_3 remains constant during a long-time annealing at a temperature far below T_{rm g}; and I_3 remains constant while tau_3 goes through a "over shooting" in the first few hours after quenching and annealing at a temperature just below T_{rm g}. The free volume in polycarbonate increases (as a result of an increase in tau_3 ) with applied tensile strain up to 4%, then levels off. Similarly, the free volume in polymethyl methacrylate (PMMA) decreases (as the result of tau_3 ) with applied compressional strain also up to -4% then levels off. A negative change in both tau_3 and I _3 has been observed when polycarbonate is under 3% tensile strain and after release of strain. A more advance technique of positron annihilation, PAL-momentum correlation which can give more detailed information about free volume structure in polymers, has also been studied and improved. Two 5-cm-diameter, 5-cm-long CsF scintillation detectors for lifetime measurement, and a 30-cm-diameter Anger camera whose y-analog pulse gives one-dimensional ACAR information, comprise a new experimental arrangement of PAL-momentum correlation system. Its triple -coincidence counting rate is about 2.5 per minute per microcurie of positron source and system time

  4. Interaction of positronium atoms, with paramagnetic molecules, measured by perturbed angular distribution in 3γ annihilation decay

    NASA Astrophysics Data System (ADS)

    Ivanov, Eugeniu; Vata, Ion; Teodorian, Stefan; Rusen, Ion; Stefan, Nitisor

    2009-01-01

    Positronium in the triplet spin state (S = 1) decays by 3γ annihilation having a life time of about 140 ns in vacuum. Positronium annihilation is affected by magnetic fields which mix the M = 0 state of ortho-positronium with the M = 0 state of para-positronium. The mixing fraction depends on the magnetic field intensity and causes quantum beats in the time distribution of γ annihilation decay. This effect was predicted by Barishevsky et al. [V.G. Barishevsky, O.N. Metelitsa, V.V. Tikhomirov, J. Phys. B Atom. Mol. Opt. Phys. 22 (1989) 2835]. The time differential perturbed angular correlation method (TDPAC), combined with long-lived positron life time spectroscopy (PLTS), has been used to observe these quantum beats. It is found that the characteristics of the annihilation time distribution are not influenced by the presence of diamagnetic species such as Ar, N2 and H2 but are affected by the presence of the paramagnetic O2 molecule. Our results are encouraging in developing a new method for investigating magnetic fields on an atomic scale.

  5. The Characterization of the Gamma-Ray Signal from the Central Milky Way: A Compelling Case for Annihilating Dark Matter

    SciTech Connect

    Daylan, Tansu; Finkbeiner, Douglas P.; Hooper, Dan; Linden, Tim; Portillo, Stephen K. N.; Rodd, Nicholas L.; Slatyer, Tracy R.

    2014-02-26

    Past studies have identified a spatially extended excess of ~1-3 GeV gamma rays from the region surrounding the Galactic Center, consistent with the emission expected from annihilating dark matter. We revisit and scrutinize this signal with the intention of further constraining its characteristics and origin. By applying cuts to the Fermi event parameter CTBCORE, we suppress the tails of the point spread function and generate high resolution gamma-ray maps, enabling us to more easily separate the various gamma-ray components. Within these maps, we find the GeV excess to be robust and highly statistically significant, with a spectrum, angular distribution, and overall normalization that is in good agreement with that predicted by simple annihilating dark matter models. For example, the signal is very well fit by a 31-40 GeV dark matter particle annihilating to b quarks with an annihilation cross section of sigma v = (1.4-2.0) x 10^-26 cm^3/s (normalized to a local dark matter density of 0.3 GeV/cm^3). Furthermore, we confirm that the angular distribution of the excess is approximately spherically symmetric and centered around the dynamical center of the Milky Way (within ~0.05 degrees of Sgr A*), showing no sign of elongation along or perpendicular to the Galactic Plane. The signal is observed to extend to at least 10 degrees from the Galactic Center, disfavoring the possibility that this emission originates from millisecond pulsars.

  6. Tachyon Condensation and Brane Annihilation in Bose-Einstein Condensates: Spontaneous Symmetry Breaking in Restricted Lower-Dimensional Subspace

    NASA Astrophysics Data System (ADS)

    Takeuchi, Hiromitsu; Kasamatsu, Kenichi; Tsubota, Makoto; Nitta, Muneto

    2013-05-01

    In brane cosmology, the Big Bang is hypothesized to occur by the annihilation of the brane-anti-brane pair in a collision, where the branes are three-dimensional objects in a higher-dimensional Universe. Spontaneous symmetry breaking accompanied by the formation of lower-dimensional topological defects, e.g. cosmic strings, is triggered by the so-called `tachyon condensation', where the existence of tachyons is attributable to the instability of the brane-anti-brane system. Here, we discuss the closest analogue of the tachyon condensation in atomic Bose-Einstein condensates. We consider annihilation of domain walls, namely branes, in strongly segregated two-component condensates, where one component is sandwiched by two domains of the other component. In this system, the process of the brane annihilation can be projected effectively as ferromagnetic ordering dynamics onto a two-dimensional space. Based on this correspondence, three-dimensional formation of vortices from a domain-wall annihilation is considered to be a kink formation due to spontaneous symmetry breaking in the two-dimensional space. We also discuss a mechanism to create a `vorton' when the sandwiched component has a vortex string bridged between the branes. We hope that this study motivates experimental researches to realize this exotic phenomenon of spontaneous symmetry breaking in superfluid systems.

  7. Photon-induced positron annihilation lifetime spectroscopy using ultrashort laser-Compton-scattered gamma-ray pulses

    SciTech Connect

    Taira, Y.; Toyokawa, H.; Kuroda, R.; Yamamoto, N.; Adachi, M.; Tanaka, S.; Katoh, M.

    2013-05-15

    High-energy ultrashort gamma-ray pulses can be generated via laser Compton scattering with 90 Degree-Sign collisions at the UVSOR-II electron storage ring. As an applied study of ultrashort gamma-ray pulses, a new photon-induced positron annihilation lifetime spectroscopy approach has been developed. Ultrashort gamma-ray pulses with a maximum energy of 6.6 MeV and pulse width of 2.2 ps created positrons throughout bulk lead via pair production. Annihilation gamma rays were detected by a BaF{sub 2} scintillator mounted on a photomultiplier tube. A positron lifetime spectrum was obtained by measuring the time difference between the RF frequency of the electron storage ring and the detection time of the annihilation gamma rays. We calculated the response of the BaF{sub 2} scintillator and the time jitter caused by the variation in the total path length of the ultrashort gamma-ray pulses, annihilation gamma rays, and scintillation light using a Monte Carlo simulation code. The positron lifetime for bulk lead was successfully measured.

  8. Photon-induced positron annihilation lifetime spectroscopy using ultrashort laser-Compton-scattered gamma-ray pulses.

    PubMed

    Taira, Y; Toyokawa, H; Kuroda, R; Yamamoto, N; Adachi, M; Tanaka, S; Katoh, M

    2013-05-01

    High-energy ultrashort gamma-ray pulses can be generated via laser Compton scattering with 90° collisions at the UVSOR-II electron storage ring. As an applied study of ultrashort gamma-ray pulses, a new photon-induced positron annihilation lifetime spectroscopy approach has been developed. Ultrashort gamma-ray pulses with a maximum energy of 6.6 MeV and pulse width of 2.2 ps created positrons throughout bulk lead via pair production. Annihilation gamma rays were detected by a BaF2 scintillator mounted on a photomultiplier tube. A positron lifetime spectrum was obtained by measuring the time difference between the RF frequency of the electron storage ring and the detection time of the annihilation gamma rays. We calculated the response of the BaF2 scintillator and the time jitter caused by the variation in the total path length of the ultrashort gamma-ray pulses, annihilation gamma rays, and scintillation light using a Monte Carlo simulation code. The positron lifetime for bulk lead was successfully measured. PMID:23742543

  9. On the nature of high-mass states observed in {bar N}N annihilation at rest into 3 pseudoscalars

    SciTech Connect

    Grigoryan, A.A.; Montanet, L.

    1994-09-01

    The peaks at large masses of systems {pi}{pi}, {pi}{eta}, and {eta}{eta} produced in {bar N}N annihilation at rest into 3 pseudoscalars are shown to be connected to the dynamics of the nucleon-exchange mechanism. 13 refs., 4 figs.

  10. Search for Neutrinos from Annihilation of Captured Low-Mass Dark Matter Particles in the Sun by Super-Kamiokande

    NASA Astrophysics Data System (ADS)

    Choi, K.; Abe, K.; Haga, Y.; Hayato, Y.; Iyogi, K.; Kameda, J.; Kishimoto, Y.; Miura, M.; Moriyama, S.; Nakahata, M.; Nakano, Y.; Nakayama, S.; Sekiya, H.; Shiozawa, M.; Suzuki, Y.; Takeda, A.; Tomura, T.; Wendell, R. A.; Irvine, T.; Kajita, T.; Kametani, I.; Kaneyuki, K.; Lee, K. P.; Nishimura, Y.; Okumura, K.; McLachlan, T.; Labarga, L.; Kearns, E.; Raaf, J. L.; Stone, J. L.; Sulak, L. R.; Berkman, S.; Tanaka, H. A.; Tobayama, S.; Goldhaber, M.; Carminati, G.; Kropp, W. R.; Mine, S.; Renshaw, A.; Smy, M. B.; Sobel, H. W.; Ganezer, K. S.; Hill, J.; Hong, N.; Kim, J. Y.; Lim, I. T.; Akiri, T.; Himmel, A.; Scholberg, K.; Walter, C. W.; Wongjirad, T.; Ishizuka, T.; Tasaka, S.; Jang, J. S.; Learned, J. G.; Matsuno, S.; Smith, S. N.; Hasegawa, T.; Ishida, T.; Ishii, T.; Kobayashi, T.; Nakadaira, T.; Nakamura, K.; Oyama, Y.; Sakashita, K.; Sekiguchi, T.; Tsukamoto, T.; Suzuki, A. T.; Takeuchi, Y.; Bronner, C.; Hirota, S.; Huang, K.; Ieki, K.; Ikeda, M.; Kikawa, T.; Minamino, A.; Nakaya, T.; Suzuki, K.; Takahashi, S.; Fukuda, Y.; Itow, Y.; Mitsuka, G.; Mijakowski, P.; Hignight, J.; Imber, J.; Jung, C. K.; Yanagisawa, C.; Ishino, H.; Kibayashi, A.; Koshio, Y.; Mori, T.; Sakuda, M.; Yano, T.; Kuno, Y.; Tacik, R.; Kim, S. B.; Okazawa, H.; Choi, Y.; Nishijima, K.; Koshiba, M.; Totsuka, Y.; Yokoyama, M.; Martens, K.; Marti, Ll.; Vagins, M. R.; Martin, J. F.; de Perio, P.; Konaka, A.; Wilking, M. J.; Chen, S.; Zhang, Y.; Wilkes, R. J.; Super-Kamiokande Collaboration

    2015-04-01

    Super-Kamiokande (SK) can search for weakly interacting massive particles (WIMPs) by detecting neutrinos produced from WIMP annihilations occurring inside the Sun. In this analysis, we include neutrino events with interaction vertices in the detector in addition to upward-going muons produced in the surrounding rock. Compared to the previous result, which used the upward-going muons only, the signal acceptances for light (few-GeV /c2-200 -GeV /c2 ) WIMPs are significantly increased. We fit 3903 days of SK data to search for the contribution of neutrinos from WIMP annihilation in the Sun. We found no significant excess over expected atmospheric-neutrino background and the result is interpreted in terms of upper limits on WIMP-nucleon elastic scattering cross sections under different assumptions about the annihilation channel. We set the current best limits on the spin-dependent WIMP-proton cross section for WIMP masses below 200 GeV /c2 (at 10 GeV /c2 , 1.49 ×10-39 cm2 for χ χ →b b ¯ and 1.31 ×10-40 cm2 for χ χ →τ+τ- annihilation channels), also ruling out some fraction of WIMP candidates with spin-independent coupling in the few-GeV /c2 mass range.

  11. Photon-induced positron annihilation lifetime spectroscopy using ultrashort laser-Compton-scattered gamma-ray pulses

    NASA Astrophysics Data System (ADS)

    Taira, Y.; Toyokawa, H.; Kuroda, R.; Yamamoto, N.; Adachi, M.; Tanaka, S.; Katoh, M.

    2013-05-01

    High-energy ultrashort gamma-ray pulses can be generated via laser Compton scattering with 90° collisions at the UVSOR-II electron storage ring. As an applied study of ultrashort gamma-ray pulses, a new photon-induced positron annihilation lifetime spectroscopy approach has been developed. Ultrashort gamma-ray pulses with a maximum energy of 6.6 MeV and pulse width of 2.2 ps created positrons throughout bulk lead via pair production. Annihilation gamma rays were detected by a BaF2 scintillator mounted on a photomultiplier tube. A positron lifetime spectrum was obtained by measuring the time difference between the RF frequency of the electron storage ring and the detection time of the annihilation gamma rays. We calculated the response of the BaF2 scintillator and the time jitter caused by the variation in the total path length of the ultrashort gamma-ray pulses, annihilation gamma rays, and scintillation light using a Monte Carlo simulation code. The positron lifetime for bulk lead was successfully measured.

  12. Search for neutrinos from annihilation of captured low-mass dark matter particles in the sun by super-kamiokande.

    PubMed

    Choi, K; Abe, K; Haga, Y; Hayato, Y; Iyogi, K; Kameda, J; Kishimoto, Y; Miura, M; Moriyama, S; Nakahata, M; Nakano, Y; Nakayama, S; Sekiya, H; Shiozawa, M; Suzuki, Y; Takeda, A; Tomura, T; Wendell, R A; Irvine, T; Kajita, T; Kametani, I; Kaneyuki, K; Lee, K P; Nishimura, Y; Okumura, K; McLachlan, T; Labarga, L; Kearns, E; Raaf, J L; Stone, J L; Sulak, L R; Berkman, S; Tanaka, H A; Tobayama, S; Goldhaber, M; Carminati, G; Kropp, W R; Mine, S; Renshaw, A; Smy, M B; Sobel, H W; Ganezer, K S; Hill, J; Hong, N; Kim, J Y; Lim, I T; Akiri, T; Himmel, A; Scholberg, K; Walter, C W; Wongjirad, T; Ishizuka, T; Tasaka, S; Jang, J S; Learned, J G; Matsuno, S; Smith, S N; Hasegawa, T; Ishida, T; Ishii, T; Kobayashi, T; Nakadaira, T; Nakamura, K; Oyama, Y; Sakashita, K; Sekiguchi, T; Tsukamoto, T; Suzuki, A T; Takeuchi, Y; Bronner, C; Hirota, S; Huang, K; Ieki, K; Ikeda, M; Kikawa, T; Minamino, A; Nakaya, T; Suzuki, K; Takahashi, S; Fukuda, Y; Itow, Y; Mitsuka, G; Mijakowski, P; Hignight, J; Imber, J; Jung, C K; Yanagisawa, C; Ishino, H; Kibayashi, A; Koshio, Y; Mori, T; Sakuda, M; Yano, T; Kuno, Y; Tacik, R; Kim, S B; Okazawa, H; Choi, Y; Nishijima, K; Koshiba, M; Totsuka, Y; Yokoyama, M; Martens, K; Marti, Ll; Vagins, M R; Martin, J F; de Perio, P; Konaka, A; Wilking, M J; Chen, S; Zhang, Y; Wilkes, R J

    2015-04-10

    Super-Kamiokande (SK) can search for weakly interacting massive particles (WIMPs) by detecting neutrinos produced from WIMP annihilations occurring inside the Sun. In this analysis, we include neutrino events with interaction vertices in the detector in addition to upward-going muons produced in the surrounding rock. Compared to the previous result, which used the upward-going muons only, the signal acceptances for light (few-GeV/c^{2}-200-GeV/c^{2}) WIMPs are significantly increased. We fit 3903 days of SK data to search for the contribution of neutrinos from WIMP annihilation in the Sun. We found no significant excess over expected atmospheric-neutrino background and the result is interpreted in terms of upper limits on WIMP-nucleon elastic scattering cross sections under different assumptions about the annihilation channel. We set the current best limits on the spin-dependent WIMP-proton cross section for WIMP masses below 200  GeV/c^{2} (at 10  GeV/c^{2}, 1.49×10^{-39}  cm^{2} for χχ→bb[over ¯] and 1.31×10^{-40}  cm^{2} for χχ→τ^{+}τ^{-} annihilation channels), also ruling out some fraction of WIMP candidates with spin-independent coupling in the few-GeV/c^{2} mass range. PMID:25910107

  13. SEARCH FOR DARK MATTER ANNIHILATION SIGNALS FROM THE FORNAX GALAXY CLUSTER WITH H.E.S.S

    SciTech Connect

    Abramowski, A.; Acero, F.; Akhperjanian, A. G.; Anton, G.; Balzer, A.; Brucker, J.; Barnacka, A.; Barres de Almeida, U.; Becherini, Y.; Becker, J.; Behera, B.; Birsin, E.; Biteau, J.; Brun, F.; Bolmont, J.; Collaboration: H.E.S.S. Collaboration; and others

    2012-05-10

    The Fornax galaxy cluster was observed with the High Energy Stereoscopic System for a total live time of 14.5 hr, searching for very high energy (VHE; E > 100GeV) {gamma}-rays from dark matter (DM) annihilation. No significant signal was found in searches for point-like and extended emissions. Using several models of the DM density distribution, upper limits on the DM velocity-weighted annihilation cross-section ({sigma}v) as a function of the DM particle mass are derived. Constraints are derived for different DM particle models, such as those arising from Kaluza-Klein and supersymmetric models. Various annihilation final states are considered. Possible enhancements of the DM annihilation {gamma}-ray flux, due to DM substructures of the DM host halo, or from the Sommerfeld effect, are studied. Additional {gamma}-ray contributions from internal bremsstrahlung and inverse Compton radiation are also discussed. For a DM particle mass of 1 TeV, the exclusion limits at 95% of confidence level reach values of ({sigma}v){sup 95%C.L.} {approx} 10{sup -23} cm{sup 3} s{sup -1}, depending on the DM particle model and halo properties. Additional contribution from DM substructures can improve the upper limits on ({sigma}v) by more than two orders of magnitude. At masses around 4.5 TeV, the enhancement by substructures and the Sommerfeld resonance effect results in a velocity-weighted annihilation cross-section upper limit at the level of ({sigma}v){sup 95%C.L.} {approx}10{sup -26} cm{sup 3} s{sup -1}.

  14. Three-dimensional positron annihilation momentum measurement technique applied to measure oxygen-atom defects in 6H silicon carbide

    NASA Astrophysics Data System (ADS)

    Williams, Christopher S.

    A three-dimensional Positron Annihilation Spectroscopy System (3DPASS) capable to simultaneously measure three-dimensional electron-positron (e--e+) momentum densities measuring photons derived from e--e+ annihilation events was designed and characterized. 3DPASS simultaneously collects a single data set of correlated energies and positions for two coincident annihilation photons using solid-state double-sided strip detectors (DSSD). Positions of photons were determined using an interpolation method which measures a figure-of-merit proportional to the areas of transient charges induced on both charge collection strips directly adjacent to the charge collection strips interacting with the annihilation photons. The subpixel resolution was measured for both double-sided strip detectors (DSSD) and quantified using a new method modeled after a Gaussian point-spread function with a circular aperture. Error associated with location interpolation within an intrinsic pixel in each of the DSSDs, the subpixel resolution, was on the order of +/- 0.20 mm (this represents one-standard deviation). The subpixel resolution achieved was less than one twenty-fifth of the 25-mm2 square area of an intrinsic pixel created by the intersection of the DSSDs' orthogonal charge collection strips. The 2D ACAR and CDBAR response for single-crystal copper and 6H silicon carbide (6H SiC) was compared with results in the literature. Two additional samples of 6H SiC were irradiated with 24 MeV O+ ions, one annealed and one un-annealed, and measured using 3DPASS. Three-dimensional momentum distributions with correlated energies and coincident annihilation photons' positions were presented for all three 6H SiC samples. 3DPASS was used for the first experimental measurement of the structure of oxygen defects in bulk 6H SiC.

  15. FERMI-LAT SENSITIVITY TO DARK MATTER ANNIHILATION IN VIA LACTEA II SUBSTRUCTURE

    SciTech Connect

    Anderson, Brandon; Johnson, Robert P.; Madau, Piero; Kuhlen, Michael; Diemand, Juerg E-mail: mqk@astro.berkeley.ed

    2010-08-01

    We present a study of the ability of the Fermi Gamma-ray Space Telescope to detect dark matter (DM) annihilation signals from the Galactic subhalos predicted by the Via Lactea II N-body simulation. We implement an improved formalism for estimating the boost factor needed to account for the effect of DM clumping on scales below the resolution of the simulation, and we incorporate a detailed Monte Carlo simulation of the response of the Fermi-LAT, including a simulation of its all-sky observing mode integrated over a 10 year mission. We find that for WIMP masses up to about 150 GeV c {sup -2} in standard supersymmetric models with ({sigma}v) = 3 x 10{sup -26} cm{sup 3} s{sup -1}, a few subhalos could be detectable with >5 standard deviation significance and would likely deviate significantly from the appearance of a point source.

  16. Photon upconversion: from two-photon absorption (TPA) to triplet-triplet annihilation (TTA).

    PubMed

    Ye, Changqing; Zhou, Liwei; Wang, Xiaomei; Liang, Zuoqin

    2016-04-20

    Organic upconversion is a unique process in which low-energy light (usually NIR light) is converted to high-energy light through either the two-photon absorption (TPA) mechanism or the triplet-triplet annihilation (TTA) mechanism. Both TPA upconversion (TPA-UC) and TTA upconversion (TTA-UC) have been actively investigated in recent years due to their intriguing applications in optics, biophotonics, and solar energy utilization. Although they show some similarity (i.e., belonging to the nonlinear two-quantum process and needing focused excitation light), TPA-UC and TTA-UC are very different, such as in mechanism, characteristics involved, molecular design and potential applications. Here, we collectively reviewed these two kinds of upconversion processes and compared their respective characteristics and merits. We also present recent advances made in the areas of TPA- and TTA-UC, the remaining challenges and opportunities, with particular emphasis on molecular engineering of these two active upconversion materials. PMID:26843136

  17. Triplet-triplet annihilation photon-upconversion: towards solar energy applications.

    PubMed

    Gray, Victor; Dzebo, Damir; Abrahamsson, Maria; Albinsson, Bo; Moth-Poulsen, Kasper

    2014-06-14

    Solar power production and solar energy storage are important research areas for development of technologies that can facilitate a transition to a future society independent of fossil fuel based energy sources. Devices for direct conversion of solar photons suffer from poor efficiencies due to spectrum losses, which are caused by energy mismatch between the optical absorption of the devices and the broadband irradiation provided by the sun. In this context, photon-upconversion technologies are becoming increasingly interesting since they might offer an efficient way of converting low energy solar energy photons into higher energy photons, ideal for solar power production and solar energy storage. This perspective discusses recent progress in triplet-triplet annihilation (TTA) photon-upconversion systems and devices for solar energy applications. Furthermore, challenges with evaluation of the efficiency of TTA-photon-upconversion systems are discussed and a general approach for evaluation and comparison of existing systems is suggested. PMID:24733519

  18. Gamma-induced positron annihilation spectroscopy and application to radiation-damaged alloys

    NASA Astrophysics Data System (ADS)

    Wells, D. P.; Hunt, A. W.; Tchelidze, L.; Kumar, J.; Smith, K.; Thompson, S.; Selim, F.; Williams, J.; Harmon, J. F.; Maloy, S.; Roy, A.

    2006-06-01

    Radiation damage and other defect studies of materials are limited to thin samples because of inherent limitations of well-established techniques such as diffraction methods and traditional positron annihilation spectroscopy (PAS) [P. Hautojarvi, et al., Positrons in Solids, Springer, Berlin, 1979, K.G. Lynn, et al., Appl. Phys. Lett. 47 (1985) 239]. This limitation has greatly hampered industrial and in-situ applications. ISU has developed new methods that use pair-production to produce positrons throughout the volume of thick samples [F.A. Selim, D.P. Wells, et al., Nucl. Instr. and Meth. B 192 (2002) 197, F.A. Selim, D.P. Wells, et al., Nucl. Instru. Meth. A 495 (2002) 154, F.A. Selim, et al., J. Rad. Phys. Chem. 68 (2004) 427, F.A. Selim, D.P. Wells, et al., Nucl. Instr. and Meth. B 241 (2005) 253, A.W. Hunt, D.P. Wells, et al., Nucl. Instr. and Meth. B. 241 (2005) 262]. Unlike prior work at other laboratories that use bremsstrahlung beams to create positron beams (via pair-production) that are then directed at a sample of interest, we produce electron-positron pairs directly in samples of interest, and eliminate the intermediate step of a positron beam and its attendant penetrability limitations. Our methods include accelerator-based bremsstrahlung-induced pair-production in the sample for positron annihilation energy spectroscopy measurements (PAES), coincident proton-capture gamma-rays (where one of the gammas is used for pair-production in the sample) for positron annihilation lifetime spectroscopy (PALS), or photo-nuclear activation of samples for either type of measurement. The positrons subsequently annihilate with sample electrons, emitting coincident 511 keV gamma-rays [F.A. Selim, D.P. Wells, et al., Nucl. Instr. and Meth. B 192 (2002) 197, F.A. Selim, D.P. Wells, et al., Nucl. Instru. Meth. A 495 (2002) 154, F.A. Selim, et al., J. Rad. Phys. Chem. 68 (2004) 427, F.A. Selim, D.P. Wells, et al., Nucl. Instr. and Meth. B 241 (2005) 253, A.W. Hunt, D

  19. Search for the Rare Quark-annihilation Decays B->Ds(*)Phi

    SciTech Connect

    Aubert, B.; Barate, R.; Boutigny, D.; Couderc, F.; Karyotakis, Y.; Lees, J.P.; Poireau, V.; Tisserand, V.; Zghiche, A.; Grauges, E.; Palano, A.; Pappagallo, M.; Pompili, A.; Chen, J.C.; Qi, N.D.; Rong, G.; Wang, P.; Zhu, Y.S.; Eigen, G.; Ofte, I.; Stugu, B.; /Annecy, LAPP /Barcelona, Autonoma U. /Bari U. /Beijing, Inst. High Energy Phys. /Bergen U. /LBL, Berkeley /Birmingham U. /Ruhr U., Bochum /Bristol U. /British Columbia U. /Brunel U. /Novosibirsk, IYF /UC, Irvine /UCLA /UC, Riverside /UC, San Diego /UC, Santa Barbara /UC, Santa Cruz /Caltech /Cincinnati U. /Colorado U.

    2005-12-19

    We report on searches for B{sup -} {yields} D{sub s}{sup -} {phi} and B{sup -} {yields} D*{sub s}{sup -} {phi}. In the context of the Standard Model, these decays are expected to be highly suppressed since they proceed through annihilation of the b and {bar u} quarks in the B{sup -} meson. Our results are based on 234 million {Upsilon}(4S) {yields} B{bar B} decays collected with the BABAR detector at SLAC. We find no evidence for these decays, and we set Bayesian 90% confidence level upper limits on the branching fractions {Beta}(B{sup -} {yields} D{sub s}{sup -}{phi}) < 1.9 x 10{sup -6} and {Beta}(B{sup -} {yields} D*{sub s}{sup -} {phi}) < 1.2 x 10{sup -5}. These results are consistent with Standard Model expectations.

  20. On the detectability of Galactic dark matter annihilation into monochromatic gamma-rays

    NASA Astrophysics Data System (ADS)

    Tang, Zhi-Cheng; Yuan, Qiang; Bi, Xiao-Jun; Chen, Guo-Ming

    2011-08-01

    Monochromatic γ-rays are thought to be the smoking gun signal for identifying dark matter annihilation. However, the flux of monochromatic γ-rays is usually suppressed by virtual quantum effects since dark matter should be neutral and does not couple with γ-rays directly. In this work, we study the detection strategy of the monochromatic γ-rays in a future space-based detector. The flux of monochromatic γ-rays between 50 GeV and several TeV is calculated by assuming the supersymmetric neutralino as a typical dark matter candidate. The detection both by focusing on the Galactic center and in a scan mode that detects γ-rays from the whole Galactic halo are compared. The detector performance for the purpose of monochromatic γ-ray detection, with different energy and angular resolution, field of view, and background rejection efficiencies, is carefully studied with both analytical and fast Monte-Carlo methods.

  1. Threshold and Other Properties of U Particle Production in e{sup +}e{sup -} Annihilation

    DOE R&D Accomplishments Database

    Perl, M. L.

    1976-05-01

    The anomalous e..mu.. events produced in e{sup +}e{sup -} annihilation, e{sup +} + e{sup -} ..-->.. e/sup + -/ + ..mu..{sup - +} + missing energy, (1) was explained as the decay products of a pair of U particles produced in the reaction e{sup +} + e{sup -} ..-->.. U{sup +} + U{sup -}. (2) New data is presented on the U particles in the energy region just above their production threshold and results of a study of the nature of the particles carrying off the missing energy in Eq. (1). While presenting these new results the present status of knowledge of the anomalous e..mu.. events and their U particle explanation is briefly reviewed. (JFP)

  2. Analyzing the scalar top co-annihilation region at the ILC

    SciTech Connect

    Carena, M.; Finch, A.; Freitas, A.; Milstene, C.; Nowak, H.; Sopczak, A.; /Lancaster U.

    2005-08-01

    The Minimal Supersymmetric Standard Model opens the possibility of electroweak baryogenesis provided that the light scalar top quark (stop) is lighter than the top quark. In addition, the lightest neutralino is an ideal candidate to explain the existence of dark matter. For a light stop with mass close to the lightest neutralino, the stop-neutralino co-annihilation mechanism becomes efficient, thus rendering the predicted dark matter density compatible with observations. Such a stop may however remain elusive at hadron colliders. Here it is shown that a future linear collider provides a unique opportunity to detect and study the light stop. The production of stops with small stop-neutralino mass differences is studied in a detailed experimental analysis with a realistic detector simulation including a CCD vertex detector for flavor tagging. Furthermore, the linear collider, by precision measurements of superpartner masses and mixing angles, also allows to determine the dark matter relic density with an accuracy comparable to recent astrophysical observations.

  3. Neutralino annihilation into {gamma} rays in the Milky Way and in external galaxies

    SciTech Connect

    Fornengo, N.; Pieri, L.; Scopel, S.

    2004-11-15

    We discuss the gamma-ray signal from dark matter annihilation in our Galaxy and in external objects, namely, the Large Magellanic Cloud, the Andromeda Galaxy (M31), and M87. We derive predictions for the fluxes in a low energy realization of the minimal supersymmetric standard model and compare them with current data from EGRET, CANGAROO-II, and HEGRA and with the capabilities of new-generation satellite-borne experiments, like GLAST, and ground-based Cerenkov telescopes, like VERITAS. We find fluxes below the level required to explain the possible indications of a {gamma}-ray excess shown by CANGAROO-II (toward the galactic center) and HEGRA (from M87). As far as future experiments are concerned, we show that only the signal from the galactic center could be accessible to both satellite-borne experiments and to atmospheric Cerenkov telescopes (ACTs), even though this requires very steep dark matter density profiles.

  4. Identifying Dark Matter Annihilation Products In The Diffuse Gamma Ray Background

    SciTech Connect

    Dodelson, Scott; Belikov, Alexander V.; Hooper, Dan; Serpico, Pasquale

    2009-03-01

    Annihilation of cosmologically distributed dark matter is predicted to produce a potentially observable flux of high energy photons. Neglecting the contribution from local structure, this signal is predicted to be virtually uniform on the sky and, in order to be identified, must compete with various extragalactic backgrounds. We focus here on unresolved blazars and discuss several techniques for separating the dark matter signal from this background. First, the spectral shapes of the signal and background are expected to differ, a feature which can be exploited with the Fisher Matrix formalism. Second, in any given angular pixel, the number of photons from blazars is drawn from a distribution which is far from Poisson. A knowledge of this distribution enhances one's ability to extract the dark matter signal, while ignorance of it can lead to the introduction of a large systematic error.

  5. Time-resolved positron annihilation spectroscopy study of relaxation dynamics of ion damage in fused quartz

    NASA Astrophysics Data System (ADS)

    Tsuchida, Hidetsugu; Mizuno, Shohei; Tsutsumi, Hironori; Kinomura, Atsushi; Suzuki, Ryoichi; Itoh, Akio

    2016-05-01

    Relaxation dynamics of ion damage in fused quartz is investigated by our newly developed pump–probe technique combining energetic ions (pump) with slow positrons (probe). This method enables determination of time-resolved positron lifetime. We study the time-dependent relaxation of ion damage, by analyzing the intensity variation in the ortho-positronium lifetime component associated with irradiation damage. For irradiation with 160 keV He ions in the temperature range of 300–573 K, the positron annihilation lifetime spectra are obtained as a function of time after ion irradiation. We observe that the relaxation time of ion damage is strongly influenced by specimen temperatures; the relaxation time constant is approximately 400 ms at room temperature (300 K) and becomes smaller with an increasing temperature. Analysis for the effect of temperature on damage accumulation reveals that the activation energy for thermal annealing of the observed damage is approximately 0.1 eV.

  6. Three-Photon-Annihilation Contributions to Positronium Energies at Order mα^{7}.

    PubMed

    Adkins, Gregory S; Kim, Minji; Parsons, Christian; Fell, Richard N

    2015-12-01

    Positronium spectroscopy (n=1 hyperfine splitting, n=2 fine structure, and the 2S-1S interval) has reached a precision of order 1 MHz. Vigorous ongoing efforts to improve the experimental results motivate the calculation of the positronium energy levels at order mα^{7}. In this Letter, we present the result for a complete class of such contributions-those involving virtual annihilation of positronium to three photons in an intermediate state. We find an energy shift of 2.6216(11)mα^{7}/(nπ)^{3}=11.5/n^{3}  kHz for the spin-triplet S state with principal quantum number n. The corresponding energy shift for true muonium (the μ^{+}μ^{-} bound state) is 2.38/n^{3}  MHz with an additional -5.33/n^{3}  MHz coming from electronic vacuum polarization. PMID:26684116

  7. Study on the Enhanced Contribution in Noble Metals from Positron Annihilation

    NASA Astrophysics Data System (ADS)

    Hamid, A. S.; Ahmed, M. M.; Abu-Elmagd, M. S. M.; Rizk, R. A. M.

    2007-02-01

    Our motivations in the current work were to inspect various enhancement formulae along with to classify the electronic structure of noble metals Cu, Ag and Au. The measurements were performed via the two dimensional angular correlation of annihilation radiation 2D-ACAR apparatus. The electron density in momentum space ρ(p) was reconstructed and it displayed the following features. Initially, the reciprocal lattice points underscored the calculations, and they revealed Fermi surface features. Additionally, enhanced anisotropy exposed nearby Fermi momentum. They attributed to enhancement of the electronic wave function at the position of the positron. Finally, the high momentum contributions, due to interaction of positron with core-like-state, conducted the electronic structure of the metals under investigations. From another viewpoint, the features of Fermi surface of Cu, Ag and Au showed an expected analogous behavior as multiply connected sphere inside the first Brillouin zone.

  8. Two magnetic states of iron atoms in Invar Fe-Ni alloys and positron annihilation

    NASA Astrophysics Data System (ADS)

    Sedov, V. L.; Tsigel'nik, O. A.

    1999-11-01

    The temperature dependence of angular correlation annihilation radiation (ACAR) in Invar Fe-Ni alloys is investigated. It is found that the ACAR distribution in the Curie temperature region TC depends on temperature. This effect is created only by those positrons that are trapped by vacancies. The effect is enhanced if the positrons trapped by vacancy-hydrogen complexes. The ACAR distribution is changed due to enhanced interaction of these positrons with 3d electrons. A simple interpretation of this phenomenon can be given on the basis of the model of two magnetic states of Fe atoms in Invar alloys. According to this model the enhancement of the electron-positron correlation interaction in the TC region occurs as a result of the convergence of the energy levels εHS and εLS corresponding to the high-spin (HS) and low-spin (LS) states of Fe atoms.

  9. Identification of vacancy-type defects in ZnTe using positron annihilation spectroscopy

    NASA Astrophysics Data System (ADS)

    Hamid, A. S.; Shaban, H.; Mansour, B. A.; Uedono, A.

    2005-08-01

    The species of defects in Mg0.5Zn0.5Te, Li-doped and P-doped ZnTe samples were investigated by using positron-based experiments. The positron lifetime experiments along with the atomic superposition (AT-SUP) method were used to predict the positron trapping centers in the samples. The results of lifetime of positron were combined with the 2D angular correlation of annihilation radiation (ACAR) experiments to get information on the electronic structure of these defects. The momentum density distributions permitted the vacancy-type defect to be distinguished in each sample. In addition, the results of the 2D-ACAR experiments disclosed a relaxation of the atoms around the vacancy in the P-doped ZnTe sample.

  10. Time of flight spectrometer for background-free positron annihilation induced Auger electron spectroscopy.

    PubMed

    Mukherjee, S; Shastry, K; Anto, C V; Joglekar, P V; Nadesalingam, M P; Xie, S; Jiang, N; Weiss, A H

    2016-03-01

    We describe a novel spectrometer designed for positron annihilation induced Auger electron spectroscopy employing a time-of-flight spectrometer. The spectrometer's new configuration enables us to implant monoenergetic positrons with kinetic energies as low as 1.5 eV on the sample while simultaneously allowing for the detection of electrons emitted from the sample surface at kinetic energies ranging from ∼500 eV to 0 eV. The spectrometer's unique characteristics made it possible to perform (a) first experiments demonstrating the direct transition of a positron from an unbound scattering state to a bound surface state and (b) the first experiments demonstrating that Auger electron spectra can be obtained down to 0 eV without the beam induced secondary electron background obscuring the low energy part of the spectra. Data are presented which show alternative means of estimating positron surface state binding energy and background-free Auger spectra. PMID:27036826

  11. Relative Defect Density Measurements of Laser Shock Peened 316L Stainless Steel Using Positron Annihilation Spectroscopy

    SciTech Connect

    Marcus A. Gagliardi; Bulent H. Sencer; A. W. Hunt; Stuart A. Maloy; George T. Gray III

    2011-12-01

    The surface of an annealed 316L stainless steel coupon was laser shock peened and Vickers hardness measurements were subsequently taken of its surface. This Vickers hardness data was compared with measurements taken using the technique of positron annihilation Doppler broadening spectroscopy. When compared, a correlation was found between the Vickers hardness data measurements and those made using Doppler broadening spectroscopy. Although materials with a high defect density can cause the S-parameter measurements to saturate, variations in the Sparameter measurements suggest that through further research the Doppler broadening technique could be used as a viable alternative to measuring a material's hardness. In turn, this technique, could be useful in industrial settings where surface hardness and surface defects are used to predict lifetime of components.

  12. In Situ Visualization of Birth and Annihilation of Grain Boundaries in an Au Nanocrystal

    NASA Astrophysics Data System (ADS)

    Zheng, He; Wang, Jianbo; Huang, Jian Yu; Cao, Ajing; Mao, Scott X.

    2012-11-01

    The formation and vanishing processes of a low angle grain boundary (GB) in nanosized Au during tension and release of stress, respectively, were obsvered by in situ high resolution transmission electron microscopy. The nucleation of perfect dislocations led to the formation of a 15° low angle GB inside an Au nanocrystal upon off-axial tensile loading (coupled uniaxial tensile and bending stress). Strikingly, the dislocations were completely annihilated accompanied with the disappearance of the GB after the removal of external stress, indicating that plastic bending is recoverable in the nanocrystal. The back force and surface stress played important roles in such a pseudoelastic behavior. This transient GB dynamics cannot be captured in ex situ experimental investigations. Such pseudoelastic bending deformation in nanosized crystals will have an important impact on the designing of nanomechanical devices with ultrahigh bending capability.

  13. Searching for dark matter annihilation to monoenergetic neutrinos with liquid scintillation detectors

    SciTech Connect

    Kumar, J.; Sandick, P.

    2015-06-22

    We consider searches for dark matter annihilation to monoenergetic neutrinos in the core of the Sun. We find that liquid scintillation neutrino detectors have enhanced sensitivity to this class of dark matter models, due to the energy and angular resolution possible for electron neutrinos and antineutrinos that scatter via charged-current interactions. In particular we find that KamLAND, utilizing existing data, could provide better sensitivity to such models than any current direct detection experiment for m{sub X}≲15 Gev. KamLAND’s sensitivity is signal-limited, and future liquid scintillation or liquid argon detectors with similar energy and angular resolution, but with larger exposure, will provide significantly better sensitivity. These detectors may be particularly powerful probes of dark matter with mass O(10) GeV.

  14. Study of microvoids in high-rate a-Si:H using positron annihilation

    SciTech Connect

    Zou, X.; Webb, D.P.; Lin, S.H.; Lam, Y.W.; Chan, Y.C.; Hu, Y.F.; Beling, C.D.; Fung, S.

    1997-07-01

    In this paper, the authors have carried out the positron annihilation measurement on high-rate and low-rate a-Si:H thin films deposited by PECVD. By means of the slow positron beam Doppler-broadening technique, the depth profiles of microvoids in a-Si:H have been determined. They have also studied the vacancy-type defect in the surface region in high-rate grown a-Si:H, making comparison between high-rate and low-rate a-Si:H. By plotting S and W parameters in the (S, W) plane, they have shown that the vacancies in all of the high-rate and low-rate deposited intrinsic samples, and in differently doped low-rate samples are of the same nature.

  15. On the theory of Gamma Ray Amplification through Stimulated Annihilation Radiation (GRASAR)

    NASA Technical Reports Server (NTRS)

    Ramaty, R.; Mckinley, J. M.; Jones, F. C.

    1981-01-01

    The theory of photon emission, absorption, and scattering in a relativistic plasma of positrons, electrons, and photon was studied. Expressions for the emissivities and absorption coefficients of pair annihilation, pair production, and Compton scattering are given and evaluated numerically. The conditions for negative absorption were investigated. In a system of photons and e(+) - e(-) pairs, an emission line at at approximately 0.43 MeV can be produced by grasar action provided that the pair chemical potential exceeds approximately 1 MeV. At a temperature of approximately 10 to the 9th power. This requires a pair density approximately 10 to the 30th power cm to the (-3) power a value much larger than the thermodynamic equilbrium pair density at this temperature. This emission line could account without a gravitational redshift for the observed lines at this energy from gamma ray bursts.

  16. Effects of TMD evolution and partonic flavor on e + e - annihilation into hadrons

    NASA Astrophysics Data System (ADS)

    Bacchetta, Alessandro; Echevarria, Miguel G.; Mulders, Piet J. G.; Radici, Marco; Signori, Andrea

    2015-11-01

    We calculate the transverse momentum dependence in the production of two back-to-back hadrons in electron-positron annihilations at the medium/large energy scales of B es-III and B elle experiments. We use the parameters of the transverse-momentum-dependent (TMD) fragmentation functions that were recently extracted from the semi-inclusive deep-inelastic-scattering multiplicities at low energy from H ermes. TMD evolution is applied according to different approaches and using different parameters for the nonperturbative part of the evolution kernel, thus exploring the sensitivity of our results to these different choices and to the flavor dependence of parton fragmentation functions. We discuss how experimental measurements could discriminate among the various scenarios.

  17. Exciton–exciton annihilation and biexciton stimulated emission in graphene nanoribbons

    DOE PAGESBeta

    Soavi, Giancarlo; Dal Conte, Stefano; Manzoni, Cristian; Viola, Daniele; Narita, Akimitsu; Hu, Yunbin; Feng, Xinliang; Hohenester, Ulrich; Molinari, Elisa; Prezzi, Deborah; et al

    2016-03-17

    Graphene nanoribbons display extraordinary optical properties due to one-dimensional quantum-confinement, such as width-dependent bandgap and strong electron–hole interactions, responsible for the formation of excitons with extremely high binding energies. Here we use femtosecond transient absorption spectroscopy to explore the ultrafast optical properties of ultranarrow, structurally well-defined graphene nanoribbons as a function of the excitation fluence, and the impact of enhanced Coulomb interaction on their excited states dynamics. We show that in the high-excitation regime biexcitons are formed by nonlinear exciton–exciton annihilation, and that they radiatively recombine via stimulated emission. We obtain a biexciton binding energy of ≈250meV, in very goodmore » agreement with theoretical results from quantum Monte Carlo simulations. As a result, these observations pave the way for the application of graphene nanoribbons in photonics and optoelectronics.« less

  18. Self-annihilation of inversion domains by high energy defects in III-Nitrides

    SciTech Connect

    Koukoula, T.; Kioseoglou, J. Kehagias, Th.; Komninou, Ph.; Ajagunna, A. O.; Georgakilas, A.

    2014-04-07

    Low-defect density InN films were grown on Si(111) by molecular beam epitaxy over an ∼1 μm thick GaN/AlN buffer/nucleation layer. Electron microscopy observations revealed the presence of inverse polarity domains propagating across the GaN layer and terminating at the sharp GaN/InN (0001{sup ¯}) interface, whereas no inversion domains were detected in InN. The systematic annihilation of GaN inversion domains at the GaN/InN interface is explained in terms of indium incorporation on the Ga-terminated inversion domains forming a metal bonded In-Ga bilayer, a structural instability known as the basal inversion domain boundary, during the initial stages of InN growth on GaN.

  19. Study of radiation damage in ODS steels by positron annihilation spectroscopy

    NASA Astrophysics Data System (ADS)

    Bartošová, I.; Bouhaddane, A.; Dománková, M.; Slugeň, V.; Wall, D.; Selim, F. A.

    2016-01-01

    Microstructure of various oxide-dispersion-strengthened (ODS) steels with 15% chromium content was studied in term of vacancy defects presence and their accumulation after defined irradiation treatment, respectively. Studied materials originated from Kyoto University and studied via IAEA collaborative project. Samples were characterized “as received” by positron annihilation lifetime spectroscopy and their microstructure was examined by transmission electron microscopy as well. Samples were afterwards irradiated in Washington State University Nuclear Radiation Center via a strong gamma source (6TBq). Damage induced by gamma irradiation was evaluated by positron lifetime measurements in emphasis on defect accumulation in the materials. We have demonstrated strong defect production induced by gamma irradiation which results from positron measurement data.

  20. Anodic, cathodic, and annihilation electrochemiluminescence emissions from hydrophilic conjugated polymer dots in aqueous medium.

    PubMed

    Dai, Ruiping; Wu, Fanmin; Xu, Huifeng; Chi, Yuwu

    2015-07-22

    Hydrophilic poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) conjugated polymer dots (CP-dots) capped by Triton X-100 were synthesized. For the first time, the electrochemiluminescence (ECL) emission of CP-dots was investigated in aqueous solution. At the glassy carbon/water interface, the CP-dots have excellent and multichannel ECL properties, such as having annihilation ECL activity in the absence of coreactants, and give bright anodic and cathodic ECL emission (590 nm) in the presence of tri-n-propylamine (TPrA) and peroxydisulfate (S2O8(2-)), respectively. The versatile ECL properties of the hydrophilic CP-dots combined with their low cytotoxicity, good biocompatibility, and easy bioconjugation may suggest promising applications of this new type of ECL nanomaterial in novel biosensing and bioimaging, and new types of light-emitting devices. PMID:26115552