Electron positron pair production at RHIC and LHC
Cem Gueclue, M.
2008-11-11
The STAR Collaboration at the Relativistic Heavy Ion Collider present data on electron-positron pair production accompanied by nuclear breakup at small impact parameters where the simultaneous excitation of the two ions, mainly the giant dipole resonance GDR, can occur. We calculate the electron-positron pair production cross section relevant for the STAR experimental setup, and compare our results with the other calculations. We have also predictions for the LHC energies.
Towards laboratory produced relativistic electron-positron pair plasmas
NASA Astrophysics Data System (ADS)
Chen, Hui; Meyerhofer, D. D.; Wilks, S. C.; Cauble, R.; Dollar, F.; Falk, K.; Gregori, G.; Hazi, A.; Moses, E. I.; Murphy, C. D.; Myatt, J.; Park, J.; Seely, J.; Shepherd, R.; Spitkovsky, A.; Stoeckl, C.; Szabo, C. I.; Tommasini, R.; Zulick, C.; Beiersdorfer, P.
2011-12-01
We review recent experimental results on the path to producing electron-positron pair plasmas using lasers. Relativistic pair-plasmas and jets are believed to exist in many astrophysical objects and are often invoked to explain energetic phenomena related to Gamma Ray Bursts and Black Holes. On earth, positrons from radioactive isotopes or accelerators are used extensively at low energies (sub-MeV) in areas related to surface science positron emission tomography and basic antimatter science. Experimental platforms capable of producing the high-temperature pair-plasma and high-flux jets required to simulate astrophysical positron conditions have so far been absent. In the past few years, we performed extensive experiments generating positrons with intense lasers where we found that relativistic electron and positron jets are produced by irradiating a solid gold target with an intense picosecond laser pulse. The positron temperatures in directions parallel and transverse to the beam both exceeded 0.5 MeV, and the density of electrons and positrons in these jets are of order 10 16 cm -3 and 10 13 cm -3, respectively. With the increasing performance of high-energy ultra-short laser pulses, we expect that a high-density, up to 10 18 cm -3, relativistic pair-plasma is achievable, a novel regime of laboratory-produced hot dense matter.
Electron-positron pairs production in a macroscopic charged core
NASA Astrophysics Data System (ADS)
Ruffini, Remo; Xue, She-Sheng
2011-02-01
Classical and semi-classical energy states of relativistic electrons bounded by a massive and charged core with the charge-mass radio Q/M and macroscopic radius R are discussed. We show that the energies of semi-classical (bound) states can be much smaller than the negative electron mass-energy (-mc2), and energy-level crossing to negative energy continuum occurs. Electron-positron pair production takes place by quantum tunneling, if these bound states are not occupied. Electrons fill into these bound states and positrons go to infinity. We explicitly calculate the rate of pair-production, and compare it with the rates of electron-positron production by the Sauter-Euler-Heisenberg-Schwinger in a constant electric field. In addition, the pair-production rate for the electro-gravitational balance ratio Q/M=10-19 is much larger than the pair-production rate due to the Hawking processes.
Neutrino annihilation of an electron-positron pair
Samsonenko, N.V.; Lal, K.C.
1987-01-01
In this study the authors carry out the analysis of the differential cross sections of the electron-positron pair annihilation process by simultaneously taking into account the spin effects, the interference of the charged and neutral currents, and also the possible nonzero neutrino rest mass. The differential cross sections are calculated in the COM system to first order in the weak interaction coupling constant with arbitrary electron and positron spin orientations and arbitrary neutrino and antineutrino polarizations.
Progress toward positron-electron pair plasma experiments
Stenson, E. V.; Stanja, J.; Hergenhahn, U.; Saitoh, H.; Niemann, H.; Pedersen, T. Sunn; Marx, G. H.; Schweikhard, L.; Danielson, J. R.; Surko, C. M.; Hugenschmidt, C.
2015-06-29
Electron-positron plasmas have been of theoretical interest for decades, due to the unique plasma physics that arises from all charged particles having precisely identical mass. It is only recently, though, that developments in non-neutral plasma physics (both in linear and toroidal geometries) and in the flux of sources for cold positrons have brought the goal of conducting electron-positron pair plasma experiments within reach. The APEX/PAX collaboration is working on a number of projects in parallel toward that goal; this paper provides an overview of recent, current, and upcoming activities.
Progress toward positron-electron pair plasma experiments
NASA Astrophysics Data System (ADS)
Stenson, E. V.; Saitoh, H.; Stanja, J.; Niemann, H.; Hergenhahn, U.; Pedersen, T. Sunn; Marx, G. H.; Schweikhard, L.; Danielson, J. R.; Surko, C. M.; Hugenschmidt, C.
2015-06-01
Electron-positron plasmas have been of theoretical interest for decades, due to the unique plasma physics that arises from all charged particles having precisely identical mass. It is only recently, though, that developments in non-neutral plasma physics (both in linear and toroidal geometries) and in the flux of sources for cold positrons have brought the goal of conducting electron-positron pair plasma experiments within reach. The APEX/PAX collaboration is working on a number of projects in parallel toward that goal; this paper provides an overview of recent, current, and upcoming activities.
Electron-positron pair equilibrium in strongly magnetized plasmas
Harding, A.K.
1984-11-01
Steady states of thermal electron-positron pair plasmas at mildly relativistic temperatures and in strong magnetic fields are investigated. The pair density in steady-state equilibrium, where pair production balances annihilation, is found as a function of temperature, magnetic field strength and source size, by a numerical calculation which includes pair production attenuation and Compton scattering of the photons. It is found that there is a maximum pair density for each value of temperature and field strength, and also a source size above which optically thin equilibrium states do not exist. (ESA)
Search for bound-state electron+positron pair decay
NASA Astrophysics Data System (ADS)
Bosch, F.; Hagmann, S.; Hillenbrand, P.-M.; Lane, G. J.; Litvinov, Yu. A.; Reed, M. W.; Sanjari, M. S.; Stöhlker, Th.; Torilov, S. Yu.; Tu, X. L.; Walke, P. M.
2016-09-01
The heavy ion storage rings coupled to in-flight radioactive-ion beam facilities, namely the ability to produce and store for extended periods of time radioactive nuclides in high atomic charge states, for the searchof yet unobserved decay mode - bound-state electron-positron pair decay.
Pumping Electron-Positron Pairs from a Well Potential
NASA Astrophysics Data System (ADS)
Wang, Qiang; Liu, Jie; Fu, Li-Bin
2016-04-01
In the presence of very deep well potential, electrons will spontaneously occupy the empty embedded bound states and electron-positron pairs are created by means of a non-perturbative tunneling process. In this work, by slowly oscillating the width or depth, the population transfer channels are opened and closed periodically. We find and clearly show that by the non-synchronous ejections of particles, the saturation of pair number in a static super-critical well can be broken, and electrons and positrons can be pumped inexhaustibly from vacuum with a constant production rate. In the adiabatic limit, final pair number after a single cycle has quantized values as a function of the upper boundary of the oscillating, and the critical upper boundaries indicate the diving points of the bound states.
Pumping Electron-Positron Pairs from a Well Potential
Wang, Qiang; Liu, Jie; Fu, Li-bin
2016-01-01
In the presence of very deep well potential, electrons will spontaneously occupy the empty embedded bound states and electron-positron pairs are created by means of a non-perturbative tunneling process. In this work, by slowly oscillating the width or depth, the population transfer channels are opened and closed periodically. We find and clearly show that by the non-synchronous ejections of particles, the saturation of pair number in a static super-critical well can be broken, and electrons and positrons can be pumped inexhaustibly from vacuum with a constant production rate. In the adiabatic limit, final pair number after a single cycle has quantized values as a function of the upper boundary of the oscillating, and the critical upper boundaries indicate the diving points of the bound states. PMID:27125998
Progress toward positron-electron pair plasma experiments
NASA Astrophysics Data System (ADS)
Stanja, J.; Hergenhahn, U.; Niemann, H.; Paschkowski, N.; Sunn Pedersen, T.; Saitoh, H.; Stenson, E. V.; Hugenschmidt, Ch.; Marx, G. H.; Schweikhard, L.; Danielson, J. R.; Surko, C. M.
2014-10-01
Matter-antimatter pair plasmas have been of great theoretical and astrophysical interest for a long time. A Positron-Electron Experiment (APEX) aims for the creation and study of such a plasma in the laboratory. It will be operated at the NEPOMUC facility which provides a cold and high-intensity positron beam. To achieve at least 10 Debye length within APEX's flux surfaces the beam needs to initially pass through several stages of manipulation. Presented here is an overview of work from the APEX team. Topics include E-> × B-> beam handling for separation into multiple beams in order to reduce the energy spread of the positron beam; injection and trapping of electrons in a prototype dipole field device with a permanent magnet; and design plans for the next generation of confinement device. on behalf of the APEX/PAX Team and Collaborators.
A constraint on the pair-density ratio (Z+) in an electron-positron pair wind
NASA Technical Reports Server (NTRS)
Moscoso, M. D.; Wheeler, J. C.
1994-01-01
We derive a constraint on the pair density ratio, z(sub +) = n(sub +)/n(sub p), in an electron-positron pair wind flowing away from the central region of an accretion disk around a compact object under the assumption of a coupling between electrons, positrons, and protons. The minimum rate at which positrons are injected into the annihilation volume is given by the observed annihilation flux per unit volume. This rate is then used to determine a minimum mass loss rate per unit area, M(dot)(sub *) for a given pair density ratio at the base of the streamline. The requirement that M(dot)(sub *) less than M(dot)(sub *)(sub Edd) (the mean Eddington mass loss rate per unit area) then places a lower limit on the pair density ratio, z(sub +,)(sub min). A positron annihilation line was observed in Nova Muscae 1991 by GRANAT/SIGMA. The narrow width and redshift of the line suggest that the pair production and annihilation regions are physically distinct. We hypothesize that an electron-positron pair wind transports the pairs from the production to the annihilation region and calculate z(sub +),(sub min). We then determine constraints on the physical parameters on the pair production region by comparing z(sub +),(sub min) with previous studies of two-temperature and one-temperature accretion disks with electron-positron pairs.
Electron-Positron Pair Production in the Deep Quantum Regime
Thompson, Kathleen A
1998-10-06
Electron-positron pair production via real and virtual photons is significant to the design of linear colliders, especially in the deep quantum regime (i.e., beamstrahlung parameter Upsilon >> 1). In this regime, pair production via a virtual photon (the trident process) can become comparable in rate to pair production via a real beamstrahlung photon. We derive characteristics of the e+e- pairs produced via the trident process, using the quasi-classical approach of Baier, Katkov, and Strakhovenko. We have also examined some of the implications of e+e- pair production for the design of very high energy (several TeV in the center of mass) linear colliders in the deep quantum regime.
Correlations in laser-induced electron-positron pair creation
Krajewska, K.; Kaminski, J. Z.
2011-09-15
Probability rates of electron-positron pair creation in head-on laser-beam-proton collisions are investigated, using an exact treatment of the colliding proton as a finite-mass particle. We observe that the recoil effects become more important when passing from the perturbative multiphoton regime to the nonperturbative above-threshold regime of laser-matter coupling. Thus we concentrate on the latter case. In this regime, our detailed analysis shows that energy supplied by the colliding proton makes the process more effective, and that the electrons and positrons that are created during the collision are more energetic than in the case when the momentum transfer from the proton is neglected. A number of similarities to above-threshold atomic ionization are also illustrated.
The effect of direct electron-positron pair production on relativistic feedback rates
NASA Astrophysics Data System (ADS)
Vodopiyanov, I. B.; Dwyer, J. R.; Cramer, E. S.; Lucia, R. J.; Rassoul, H. K.
2015-01-01
Runaway electron avalanches developing in thunderclouds in high electric field become self-sustaining due to relativistic feedback via the production of backward propagating positrons and backscattered X-rays. To date, only positrons created from pair production by gamma rays interacting with the air have been considered. In contrast, direct electron-positron pair production, also known as "trident process," occurs from the interaction of energetic runaway electrons with atomic nuclei, and so it does not require the generation of a gamma ray mediator. The positrons produced in this process contribute to relativistic feedback and become especially important when the feedback factor value approaches unity. Then the steady state flux of runaway electrons increases significantly. In certain cases, when the strong electrostatic field forms in a narrow area, the direct positrons become one of processes dominating relativistic feedback. Calculations of the direct positron production contribution to relativistic feedback are presented for different electric field configurations.
The magnetic toroidal sector: a broad-band electron-positron pair spectrometer
NASA Astrophysics Data System (ADS)
Hagmann, Siegbert; Hillenbrand, Pierre-Michel; Litvinov, Yuri; Spillmann, Uwe
2016-05-01
At the future relativistic storage-ring HESR at FAIR the study of electron-positron pairs from non-nuclear, atomic processes will be one of the goals of the experimental program with kinematically complete experiments focusing on momentum spectroscopy of coincident emission of electrons and positrons from free-free pairs and corresponding recoil ions. The underlying production mechanisms belong to central topics of QED in strong fields. We present first results on the electron-optical properties of a magnetic toroidal sector configuration enabling coincident detection of free-free electron-positron pairs; this spectrometer is suitable for implementation into a storage ring with a supersonic jet target and covering a wide range of lepton emission into the forward hemisphere. The simulation calculations are performed using the OPERA code.
Monte Carlo analysis of electron-positron pair creation by powerful laser-ion impact
Kaminski, J. Z.; Krajewska, K.; Ehlotzky, F.
2006-09-15
We consider electron-positron pair creation by the impact of very powerful laser pulses with highly charged ions. In contrast to our foregoing work with rather limited angular configurations of pair creation, we extend these calculations to even higher laser intensities, and we use the Monte Carlo method to numerically analyze the rates of pair creation for arbitrary angular distributions. We also evaluate the intensity dependence of the total rates of pair creation. Thus we demonstrate that our laser-induced process shows stabilization, because beyond a specific laser power the total rates of pair creation decreases. Our analysis of the angular distributions of the created electron-positron pairs leads to the conclusion that pairs are predominantly emitted in the direction of laser pulse propagation.
NASA Technical Reports Server (NTRS)
Wu, Jianshi; Derrickson, J. H.; Parnell, T. A.; Strayer, M. R.
1999-01-01
We study the screening effects of the atomic electrons in the electromagnetic production of electron-positron pairs in relativistic nucleus-atom collisions for fixed target experiments. Our results are contrasted with those obtained in bare collisions, with particular attention given to its dependence on the beam energy and the target atom.
Enhanced electron-positron pair production by ultra intense laser irradiating a compound target
NASA Astrophysics Data System (ADS)
Liu, Jian-Xun; Ma, Yan-Yun; Yu, Tong-Pu; Zhao, Jun; Yang, Xiao-Hu; Gan, Long-Fei; Zhang, Guo-Bo; Zhao, Yuan; Zhang, Shi-Jie; Liu, Jin-Jin; Zhuo, Hong-Bin; Shao, Fu-Qiu; Kawata, Shigeo
2016-12-01
High-energy-density electron-positron pairs play an increasingly important role in many potential applications. Here, we propose a scheme for enhanced positron production by an ultra intense laser irradiating a gas-Al compound target via the multi-photon Breit-Wheeler (BW) process. The laser pulse first ionizes the gas and interacts with a near-critical-density plasma, forming an electron bubble behind the laser pulse. A great deal of electrons are trapped and accelerated in the bubble, while the laser front hole-bores the Al target and deforms its front surface. A part of the laser wave is thus reflected by the inner curved target surface and collides with the accelerated electron bunch. Finally, a large number of γ photons are emitted in the forward direction via the Compton back-scattering process and the BW process is initiated. Dense electron-positron pairs are produced with a maximum density of 6.02× {{10}27} m-3. Simulation results show that the positron generation is greatly enhanced in the compound target, where the positron yield is two orders of magnitude greater than that in only the solid slab case. The influences of the laser intensity, gas density and length on the positron beam quality are also discussed, which demonstrates the feasibility of the scheme in practice.
Cross section for production of low-energy electron-positron pairs by relativistic heavy ions
NASA Technical Reports Server (NTRS)
Eby, P. B.
1991-01-01
Starting with the lowest-order unscreened QED matrix element for electron-positron pair production by heavy charged particles, the paper calculates the cross section for this process differential in all independent variables and valid for all pair energies small compared to the incident particle energy. Integration over the possible emission angles of one of the pair members gives an expression that is valid for low-energy pairs that can be compared with previous work based on the Weizsaecker-Williams method. Integration over the possible angles of the other pair member then yields an expression identical to one derived by Racah. The high energy-transfer limit of the expression for the cross section integrated over electron and positron angles is found to be identical to that of Kelner in the unscreened case.
Electron positron pair winds and the Eddington limit
NASA Technical Reports Server (NTRS)
Leighly, K. M.; Tsuruta, S.
1989-01-01
The dynamics of pair winds in the environment of the central engine of Active Galactic Nuclei (AGN) are investigated assuming super Eddington accretion onto black holes. If the accretion is assumed to be spherically symmetric with the accreting matter occurring in discrete cool blobs, and pairs are produced by a nonthermal mechanism, these pairs are blown out by radiation pressure if the coupling between the pairs and accreting blobs is not complete. The coupling also determines the escaping luminosity. If the maximal coupling constraint is relaxed, then a qualitative argument shows that the classical Eddington limit may be exceeded. When the pairs are considered to be noninteracting particles, the outflow is optically thin. Frame dependent effects are considered. Equations are derived considering pair production in the rest frame of the wind and also in the rest frame of the accreting cool blobs. The hydrodynamic equations are integrated numerically.
Nonperturbative multiphoton processes and electron-positron pair production
Hatsagortsyan, K. Z.; Mueller, C.; Keitel, C. H.
2006-04-07
Various regimes of pair production in laser fields are analyzed. Particularly, the question of the observability of pair production in a nonperturbative multiphoton regime is discussed. A simple heuristic method is employed which gives order-of-magnitude estimates for probabilities of multiphoton processes and allows to describe its main features. The method is initially probed upon the known process of pair production in a Coulomb and a strong laser field. Then it is applied to the nonperturbative multiphoton regime of the pair production process in a standing laser wave.
Nonperturbative multiphoton processes and electron-positron pair production
NASA Astrophysics Data System (ADS)
Hatsagortsyan, K. Z.; Müller, C.; Keitel, C. H.
2006-04-01
Various regimes of pair production in laser fields are analyzed. Particularly, the question of the observability of pair production in a nonperturbative multiphoton regime is discussed. A simple heuristic method is employed which gives order-of-magnitude estimates for probabilities of multiphoton processes and allows to describe its main features. The method is initially probed upon the known process of pair production in a Coulomb and a strong laser field. Then it is applied to the nonperturbative multiphoton regime of the pair production process in a standing laser wave.
Electron-positron pair production in the Aharonov-Bohm potential
Skarzhinsky, V.D. |; Audretsch, J.; Jasper, U.
1996-02-01
In the framework of QED we evaluate the cross section for electron-positron pair production by a single photon in the presence of the external Aharonov-Bohm potential in first order of perturbation theory. We analyze energy, angular, and polarization distributions at different energy regines: near the threshold and at high photon energies. {copyright} {ital 1996 The American Physical Society.}
Dynamics of electron-positron pairs in a vacuum polarized by an external radiation field
NASA Astrophysics Data System (ADS)
Apostol, M.
2011-04-01
The polarization of the vacuum under the action of an external classical field of electromagnetic radiation is investigated in the stationary regime. The electron-positron pairs interact both with the external field and with their own polarization field. For a macroscopic piece of vacuum the pairs are condensed on the low-momenta states and tend to form a quasi-localized electron-positron plasma of pairs, with single-particle states labeled by the position vector. In the polarization process under the action of a classical field of radiation the electron-positron and photon dynamics can be treated by means of classical fields. Under these circumstances, the corresponding coupled non-linear equations of motion are solved. It is shown that the pair dynamics consists of quasi-stationary single-particle states, while the polarization field reduces to a static magnetic field. The single-particle 'energy' (temporal phase) due to a monochromatic external field exhibits a spatial distribution characteristic of a stationary wave. Both the pair energy and the polarization energy are computed. Their values are extremely small, even for highly focused, reasonably high, external fields. The number of pairs is determined by the external energy. Under the action of a classical field the polarized vacuum is magnetized, and the corresponding (very low) magnetic susceptibility (the refractive index of the vacuum) is computed.
Bound-free electron-positron pair production in relativistic heavy-ion collisions
NASA Astrophysics Data System (ADS)
Şengül, M. Y.; Güçlü, M. C.; Fritzsche, S.
2009-10-01
The bound-free electron-positron pair production is considered for relativistic heavy ion collisions. In particular, cross sections are calculated for the pair production with the simultaneous capture of the electron into the 1s ground state of one of the ions and for energies that are relevant for the relativistic heavy ion collider and the large hadron colliders. In the framework of perturbation theory, we applied Monte Carlo integration techniques to compute the lowest-order Feynman diagrams amplitudes by using Darwin wave functions for the bound states of the electrons and Sommerfeld-Maue wave functions for the continuum states of the positrons. Calculations were performed especially for the collision of Au+Au at 100 GeV/nucleon and Pb+Pb at 3400 GeV/nucleon.
NASA Astrophysics Data System (ADS)
Makkonen, Ilja; Ervasti, Mikko M.; Siro, Topi; Harju, Ari
2014-01-01
The correlated motion of a positron surrounded by electrons is a fundamental many-body problem. We approach this by modeling the momentum density of annihilating electron-positron pairs using the framework of reduced density matrices, natural orbitals, and natural geminals (electron-positron pair wave functions) of the quantum theory of many-particle systems. We find that an expression based on the natural geminals provides an exact, unique, and compact expression for the momentum density. The natural geminals can be used to define and to determine enhancement factors for enhancement models going beyond the independent-particle model for a better understanding of the results of positron annihilation experiments.
Bound free electron-positron pair production accompanied by giant dipole resonances
Senguel, M. Y.; Gueclue, M. C.
2011-01-15
At the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC), for example, virtual photons produce many particles. At small impact parameters where the colliding nuclei make peripheral collisions, photon fluxes are very large and these are responsible for the multiple photonuclear interactions. Free pair productions, bound free pair productions, and nuclear Coulomb excitations are important examples of such interactions, and these processes play important roles in the beam luminosity at RHIC and LHC. Here we obtained the impact parameter dependence of bound free pair production cross sections and by using this probability we obtained bound free electron-positron pair production with nuclear breakup for heavy ion collisions at RHIC and LHC. We also compared our results to the other calculations.
Coherent electron-positron pair production in ultra-peripheral AuAu collisions at STAR
NASA Astrophysics Data System (ADS)
Rehbein, Matthew; STAR Collaboration
2016-09-01
The focus of this study is coherent photoproduction of electron-positron pairs in 200 GeV ultraperipheral AuAu collisions detected by STAR, with an integrated luminosity of 1.9 inverse nanobarns. Because hadronic interactions are suppressed in ultra-peripheral collisions, these events provide an opportunity to study purely electromagnetic interaction in the non-perturbative regime. This presentation will provide a description of the techniques used to select exclusive electron-positron events, as well as the resulting kinematic distributions for pair invariant mass greater than 0.35 GeV, pair transverse momentum less than 0.1 GeV, and absolute value of pair pseudorapidity less than 0.8. Efficiency correction techniques will also be discussed. In previous measurements at the same energy at STAR, the shape of the transverse momentum distribution could not be fully described by the equivalent photon approximation (EPA). Measurements at the LHC indicate that the cross section is reduced by approximately 25 percent compared to the EPA. This study ultimately seeks to examine these effects in more detail at RHIC energies. Partial funding provided by DOE Grant #DE-FG02-96ER40991.
Electron-positron pairs in physics and astrophysics: From heavy nuclei to black holes
NASA Astrophysics Data System (ADS)
Ruffini, Remo; Vereshchagin, Gregory; Xue, She-Sheng
2010-02-01
scales. What has become clear in the last ten years is that all the three above mentioned processes, duly extended in the general relativistic framework, are necessary for the understanding of the physics of the gravitational collapse to a black hole. Vice versa, the natural arena where these processes can be observed in mutual interaction and on an unprecedented scale, is indeed the realm of relativistic astrophysics. We systematically analyze the conceptual developments which have followed the basic work of Dirac and Breit-Wheeler. We also recall how the seminal work of Born and Infeld inspired the work by Sauter, Heisenberg and Euler on effective Lagrangian leading to the estimate of the rate for the process of electron-positron production in a constant electric field. In addition to reviewing the intuitive semi-classical treatment of quantum mechanical tunneling for describing the process of electron-positron production, we recall the calculations in Quantum Electro-Dynamics of the Schwinger rate and effective Lagrangian for constant electromagnetic fields. We also review the electron-positron production in both time-alternating electromagnetic fields, studied by Brezin, Itzykson, Popov, Nikishov and Narozhny, and the corresponding processes relevant for pair production at the focus of coherent laser beams as well as electron-beam-laser collision. We finally report some current developments based on the general JWKB approach which allows us to compute the Schwinger rate in spatially varying and time varying electromagnetic fields. We also recall the pioneering work of Landau and Lifshitz, and Racah on the collision of charged particles as well as the experimental success of AdA and ADONE in the production of electron-positron pairs. We then turn to the possible experimental verification of these phenomena. We review: (A) the experimental verification of the e+e-→2γ process studied by Dirac. We also briefly recall the very successful experiments of e
NASA Technical Reports Server (NTRS)
Derrickson, J. H.; Eby, P. B.; Moon, K. H.; Parnell, T. A.; King, D. T.; Gregory, J. C.; Takahashi, Y.; Ogata, T.
1995-01-01
Measurements of direct Coulomb electron-positron pair production have been made on the tracks of relativistic heavy ions in nuclear track emulsion. Tracks of 0(16) and S(32) at 200 GeV/nucleon were studied. The measured total cross sections and energy and emission angle distributions for the pair members are compared to theoretical predictions. The data are consistent with some recent calculations when knock-on electron contamination is accounted for.
Progress towards a laser produced relativistic electron-positron pair plasma
Chen, Hui; Bonlie, J.; Cauble, R.; ...
2016-04-01
Here, a set of experiments has been performed exploring unique characteristics of pair jets and plasmas at several energetic short-pulse laser facilities including Titan at Livermore and OMEGA EP in Rochester, as well as the Osaka LFEX and AWE Orion lasers. New results are summarized, including positron beam emittance, scaling of pair production vs. laser energy, and initial results on the pair jet collimation using electromagnetic fields.
Progress towards a laser produced relativistic electron-positron pair plasma
Chen, Hui; Bonlie, J.; Cauble, R.; Fiuza, F.; Goldstein, W.; Hazi, A.; Keane, C.; Link, A.; Marley, E.; Nagel, S. R.; Park, J.; Shepherd, R.; Williams, G. J.; Meyerhofer, D. D.; Fiksel, G.; Barnak, D.; Chang, P. Y.; Nakai, M.; Arikawa, Y.; Azechi, H.; Fujioka, S.; Kojima, S.; Miyanaga, N.; Morita, T.; Nagai, T.; Nishimura, H.; Ozaki, T.; Sakawa, Y.; Takabe, H.; Zhang, Z.; Kerr, S.; Fedosejevs, R.; Sentoku, Y.; Hill, M. P.; Hoarty, D. J.; Hobbs, L. M. R.; James, S. F.
2016-03-01
Here, a set of experiments has been performed exploring unique characteristics of pair jets and plasmas at several energetic short-pulse laser facilities including Titan at Livermore and OMEGA EP in Rochester, as well as the Osaka LFEX and AWE Orion lasers. New results are summarized, including positron beam emittance, scaling of pair production vs. laser energy, and initial results on the pair jet collimation using electromagnetic fields.
Progress Towards a Laser Produced Relativistic Electron-Positron Pair Plasma
NASA Astrophysics Data System (ADS)
Chen, Hui; Bonlie, J.; Cauble, R.; Fiuza, F.; Goldstein, W.; Hazi, A.; Keane, C.; Link, A.; Marley, E.; Nagel, S. R.; Park, J.; Shepherd, R.; Williams, G. J.; Meyerhofer, D. D.; Fiksel, G.; Barnak, D.; Chang, P. Y.; Nakai, M.; Arikawa, Y.; Azechi, H.; Fujioka, S.; Kojima, S.; Miyanaga, N.; Morita, T.; Nagai, T.; Nishimura, H.; Ozaki, T.; Sakawa, Y.; Takabe, H.; Zhang, Z.; Kerr, S.; Fedosejevs, R.; Sentoku, Y.; Hill, M. P.; Hoarty, D. J.; Hobbs, L. M. R.; James, S. F.
2016-03-01
A set of experiments has been performed exploring unique characteristics of pair jets and plasmas at several energetic short-pulse laser facilities including Titan at Livermore and OMEGA EP in Rochester, as well as the Osaka LFEX and AWE Orion lasers. New results are summarized, including positron beam emittance, scaling of pair production vs. laser energy, and initial results on the pair jet collimation using electromagnetic fields.
NASA Astrophysics Data System (ADS)
Abdrashitov, S. V.; Bogdanov, O. V.; Dabagov, S. B.; Pivovarov, Yu L.; Tukhfatullin, T. A.
2016-07-01
We consider the radiator-converter approach at 200 MeV channeled electrons (the SPARC_LAB LNF facility energies) for the case of using W crystalline radiator and W amorphous converter. A comparison of the positron production by the axial channeling radiation and the bremsstrahlung is performed. The positron stopping in the convertor is studied by means of computer simulations. It is shown that for the maximum yield of positrons the thickness of the W amorphous converter should be taken 0.35 cm in the case of using the axial channeling radiation resulting to total yield of positrons 5 10-3 e+/e- and 0.71 cm in the case of using the bremsstrahlung resulting to total yield of positrons 3.3 10-3 e+/e-.
NASA Astrophysics Data System (ADS)
Lotze, K.-H.
We present, based upon quantum electrodynamics in Robertson-Walker flat universes, a thorough analysis of the creation of mutually interacting electron-positron pairs and photons from vacuum. Therefore we discuss at least qualitatively all processes contributing to the number densities of created particles up to the second order in the coupling constant. For two particular expansion laws with Minkowskian in respectively in and out regions, we obtain exact solutions to the Dirac equation and investigate in detail the process of simultaneous creation of electron-positron pairs and photons and the related attenuation effect for fermionic particles. This is done for electrons and positrons which have nonrelativistic momenta at Compton time in rapidly expanding universes. The results are compared with the zeroth-order creation of electron-positron pairs. Despite being smaller by a factor of roughly e02 /4π ≈ 1 /137, the interacting-particle creation is important mainly as a source of photons even in conformally flat universes.
Creation of electron-positron pairs at excited Landau levels by neutrino in a strong magnetic field
NASA Astrophysics Data System (ADS)
Kuznetsov, A. V.; Rumyantsev, D. A.; Savin, V. N.
2014-10-01
The process of neutrino production of electron-positron pairs in a magnetic field of arbitrary strength, where electrons and positrons can be created in the states corresponding to excited Landau levels, is analyzed. The mean value of the neutrino energy loss due to the process ν → νe-e+ is calculated. The result can be applied for calculating the efficiency of the electron-positron plasma production by neutrinos in the conditions of the Kerr black hole accretion disk considered by experts as the most possible source of a short cosmological gamma burst. The presented research can also be useful for further development of the calculation technique for an analysis of quantum processes in external active medium, and in part in the conditions of moderately strong magnetic field, when taking account of the ground Landau level appears to be insufficient.
Pair creation induced by transitions between electronic and positronic bound states
NASA Astrophysics Data System (ADS)
Liu, Y.; Lv, Q. Z.; Li, Y. T.; Grobe, R.; Su, Q.
2015-05-01
We study the creation process of electron-positron pairs from the quantum electrodynamical vacuum under very strong electric fields by solving the quantum field theoretical Dirac equation on a space-time grid. We investigate the role of bound-bound state mixing in such a process, which can be studied if the external force can be modeled by a combination of a potential barrier and a potential well. By increasing the magnitude of the two potentials, discrete states that originate from the positive and negative energy continua can become quasidegenerate in the mass gap region (between -mc 2 and mc 2). We show that this bound-bound state mixing is quite different from the usual bound-continuum state mixing where the particles are created until the Pauli exclusion principle inhibits this process. In the case of bound-bound mixing the particle number exhibits a characteristic oscillatory behavior that in principle can last forever. These findings can be modeled by an effective two-state model.
Production of electron-positron pairs by a photon in the radiation-dominated universe
Tsaregorodtsev, L.I.
1995-12-01
The production of an arbitrary number of electron-positron pairs by a photon in a spatially flat Robertson-Walker universe with expansion law a(t) = a{sub o}{radical}t is considered. In Minkowski space, this process is forbidden by conservation laws. The total probability of the process and the mean number of Dirac particles produced as the result of photon decay are calculated and analyzed as functions of the primary-photon energy. The expressions obtained in this study are compared with the results of calculation of photon emission from the vacuum. The massless limit of the total probability of the process is considered. Numerical estimates are obtained for the mean number of particles produced in photon decays in the early universe. These estimates show that the production of Dirac particles in photon decays dominates over their production in photon emission from the vacuum and over their production from the vacuum of a free spinor field. 21 refs., 2 figs.
NASA Astrophysics Data System (ADS)
Wiktor, Julia; Jomard, Gérald; Torrent, Marc; Bertolus, Marjorie
2017-01-01
We performed first-principles calculations of the momentum distributions of annihilating electron-positron pairs in vacancies in uranium dioxide. Full atomic relaxation effects (due to both electronic and positronic forces) were taken into account and self-consistent two-component density functional theory schemes were used. We present one-dimensional momentum distributions (Doppler-broadened annihilation radiation line shapes) along with line-shape parameters S and W. We studied the effect of the charge state of the defect on the Doppler spectra. The effect of krypton incorporation in the vacancy was also considered and it was shown that it should be possible to observe the fission gas incorporation in defects in UO2 using positron annihilation spectroscopy. We suggest that the Doppler broadening measurements can be especially useful for studying impurities and dopants in UO2 and of mixed actinide oxides.
Lapidus, K. O.
2010-06-15
The inclusive production of electron-positron pairs in proton-proton and deuteron-proton collisions at a beam kinetic energy of 1.25 GeV per nucleon was studied with the HADES (High Acceptance Dielectron Spectrometer) detector. The main objective of the deuteron-proton experiment was to investigate pair production in quasifree neutron-proton collisions. In the invariant-mass region M > 140 MeV/c{sup 2}, the invariant-mass spectrum determined in this channel shows a significant enhancement of the pair yield in relation to that in the case of proton-proton collisions.
NASA Astrophysics Data System (ADS)
Jiang, M.; Lv, Q. Z.; Sheng, Z. M.; Grobe, R.; Su, Q.
2013-04-01
We study the creation of electron-positron pairs induced by two spatially separated electric fields that vary periodically in time. The results are based on large-scale computer simulations of the time-dependent Dirac equation in reduced spatial dimensions. When the separation of the fields is very large, the pair creation is caused by multiphoton transitions and mainly determined by the frequency of the fields. However, for small spatial separations a coherence effect can be observed that can enhance or reduce the particle yield compared to the case of two infinitely separated fields. If the travel time for a created electron or positron between both field locations becomes comparable to the period of the oscillating fields, we observe peaks in the energy spectrum which can be explained in terms of field-induced transient bound states.
Electroweak measurements in electron-positron collisions at W-boson-pair energies at LEP
NASA Astrophysics Data System (ADS)
ALEPH Collaboration; DELPHI Collaboration; L3 Collaboration; OPAL Collaboration; LEP Electroweak Working Group 1
2013-11-01
Electroweak measurements performed with data taken at the electron-positron collider LEP at CERN from 1995 to 2000 are reported. The combined data set considered in this report corresponds to a total luminosity of about 3 fb-1 collected by the four LEP experiments ALEPH, DELPHI, L3 and OPAL, at centre-of-mass energies ranging from 130 GeV to 209 GeV.
Dense GeV electron-positron pairs generated by lasers in near-critical-density plasmas
NASA Astrophysics Data System (ADS)
Zhu, Xing-Long; Yu, Tong-Pu; Sheng, Zheng-Ming; Yin, Yan; Turcu, Ion Cristian Edmond; Pukhov, Alexander
2016-12-01
Pair production can be triggered by high-intensity lasers via the Breit-Wheeler process. However, the straightforward laser-laser colliding for copious numbers of pair creation requires light intensities several orders of magnitude higher than possible with the ongoing laser facilities. Despite the numerous proposed approaches, creating high-energy-density pair plasmas in laboratories is still challenging. Here we present an all-optical scheme for overdense pair production by two counter-propagating lasers irradiating near-critical-density plasmas at only ~1022 W cm-2. In this scheme, bright γ-rays are generated by radiation-trapped electrons oscillating in the laser fields. The dense γ-photons then collide with the focused counter-propagating lasers to initiate the multi-photon Breit-Wheeler process. Particle-in-cell simulations indicate that one may generate a high-yield (1.05 × 1011) overdense (4 × 1022 cm-3) GeV positron beam using 10 PW scale lasers. Such a bright pair source has many practical applications and could be basis for future compact high-luminosity electron-positron colliders.
Dense GeV electron-positron pairs generated by lasers in near-critical-density plasmas.
Zhu, Xing-Long; Yu, Tong-Pu; Sheng, Zheng-Ming; Yin, Yan; Turcu, Ion Cristian Edmond; Pukhov, Alexander
2016-12-14
Pair production can be triggered by high-intensity lasers via the Breit-Wheeler process. However, the straightforward laser-laser colliding for copious numbers of pair creation requires light intensities several orders of magnitude higher than possible with the ongoing laser facilities. Despite the numerous proposed approaches, creating high-energy-density pair plasmas in laboratories is still challenging. Here we present an all-optical scheme for overdense pair production by two counter-propagating lasers irradiating near-critical-density plasmas at only ∼10(22) W cm(-2). In this scheme, bright γ-rays are generated by radiation-trapped electrons oscillating in the laser fields. The dense γ-photons then collide with the focused counter-propagating lasers to initiate the multi-photon Breit-Wheeler process. Particle-in-cell simulations indicate that one may generate a high-yield (1.05 × 10(11)) overdense (4 × 10(22) cm(-3)) GeV positron beam using 10 PW scale lasers. Such a bright pair source has many practical applications and could be basis for future compact high-luminosity electron-positron colliders.
Studies of positron electron pair production in {sup 238}U + {sup 232}Th
Ahmad, I.; Back, B.B.; Betts, R.R.
1995-08-01
Following the non-observation of sharp sum-energy lines in our earlier {sup 238}U + {sup 181}Ta measurements, it was decided to pursue measurements of the {sup 238}U + {sup 232}Th system which, in the previously published work, showed the most striking evidence for near-equal-energy back-to-back pairs leading to sharp sum-energy lines. Following the refurbishing of the APEX silicon arrays and extensive tests of the rotating target wheel assembly, a major positron run took place in November 1994. Rolled 1-mg/cm{sub 2} {sup 232}Th targets were bombarded with 5.95-MeV/u {sup 238}U. The target rotation allowed up to 2 pnA of beam to be used without serious deterioration of the targets. Over 300,000 pairs were accumulated, representing an order-of-magnitude improvement in statistics over the previously published results. Preliminary analysis shows no evidence for the sharp lines at a cross section level orders of magnitude below those previously reported. The analysis of these data is currently being completed in preparation for publication.
Gamma-ray bursts: Modeling electron-positron pair plasmas in cataclysmic astrophysical phenomena
NASA Astrophysics Data System (ADS)
Salmonson, Jay David
Despite three decades of intense scientific scrutiny, gamma-ray bursts have remained one of astronomy's biggest unsolved mysteries. Recent observational breakthroughs have allowed us to learn much about these big, brief, brilliant bangs seen from across the cosmos, but their origin remains a mystery. In this work we study three progenitor models: a neutron star binary system near its last stable orbit, a charged black hole, and the collapse of a globular star cluster. All of these scenarios result in a common theme; the relativistic expansion of a super- heated electron-positron-photon plasma. Thus we study the evolution of, and emission from, this plasma as it might result from these three progenitors using numerical general relativistic hydrodynamic simulations. This emission is then compared with that of gamma-ray bursts to test the feasibility of each of these models as a gamma-ray burst progenitor.
NASA Astrophysics Data System (ADS)
Nagirner, D. I.
1999-01-01
The kinematics of electron-positron pair production and annihilation, i.e., the determination and transformation of the momenta and energies of particles and photons upon the transition from an arbitrary reference frame to the center-of-mass frame of the particles and back, is analyzed in detail. It is found that the magnitudes of the particle momenta in certain directions in pair production may be ambiguous. An interpretation of this ambiguity and a way of circumventing it are given. Invariant quantities and the most convenient variables for calculating various integrals are found. Then the differential and total cross sections are given and the mean frequencies and dispersions of the frequencies of photons produced during annihilation are calculated.
NASA Astrophysics Data System (ADS)
Aguilar, M.; Aisa, D.; Alvino, A.; Ambrosi, G.; Andeen, K.; Arruda, L.; Attig, N.; Azzarello, P.; Bachlechner, A.; Barao, F.; Barrau, A.; Barrin, L.; Bartoloni, A.; Basara, L.; Battarbee, M.; Battiston, R.; Bazo, J.; Becker, U.; Behlmann, M.; Beischer, B.; Berdugo, J.; Bertucci, B.; Bigongiari, G.; Bindi, V.; Bizzaglia, S.; Bizzarri, M.; Boella, G.; de Boer, W.; Bollweg, K.; Bonnivard, V.; Borgia, B.; Borsini, S.; Boschini, M. J.; Bourquin, M.; Burger, J.; Cadoux, F.; Cai, X. D.; Capell, M.; Caroff, S.; Casaus, J.; Cascioli, V.; Castellini, G.; Cernuda, I.; Cervelli, F.; Chae, M. J.; Chang, Y. H.; Chen, A. I.; Chen, H.; Cheng, G. M.; Chen, H. S.; Cheng, L.; Chikanian, A.; Chou, H. Y.; Choumilov, E.; Choutko, V.; Chung, C. H.; Clark, C.; Clavero, R.; Coignet, G.; Consolandi, C.; Contin, A.; Corti, C.; Coste, B.; Cui, Z.; Dai, M.; Delgado, C.; Della Torre, S.; Demirköz, M. B.; Derome, L.; Di Falco, S.; Di Masso, L.; Dimiccoli, F.; Díaz, C.; von Doetinchem, P.; Du, W. J.; Duranti, M.; D'Urso, D.; Eline, A.; Eppling, F. J.; Eronen, T.; Fan, Y. Y.; Farnesini, L.; Feng, J.; Fiandrini, E.; Fiasson, A.; Finch, E.; Fisher, P.; Galaktionov, Y.; Gallucci, G.; García, B.; García-López, R.; Gast, H.; Gebauer, I.; Gervasi, M.; Ghelfi, A.; Gillard, W.; Giovacchini, F.; Goglov, P.; Gong, J.; Goy, C.; Grabski, V.; Grandi, D.; Graziani, M.; Guandalini, C.; Guerri, I.; Guo, K. H.; Habiby, M.; Haino, S.; Han, K. C.; He, Z. H.; Heil, M.; Hoffman, J.; Hsieh, T. H.; Huang, Z. C.; Huh, C.; Incagli, M.; Ionica, M.; Jang, W. Y.; Jinchi, H.; Kanishev, K.; Kim, G. N.; Kim, K. S.; Kirn, Th.; Kossakowski, R.; Kounina, O.; Kounine, A.; Koutsenko, V.; Krafczyk, M. S.; Kunz, S.; La Vacca, G.; Laudi, E.; Laurenti, G.; Lazzizzera, I.; Lebedev, A.; Lee, H. T.; Lee, S. C.; Leluc, C.; Li, H. L.; Li, J. Q.; Li, Q.; Li, Q.; Li, T. X.; Li, W.; Li, Y.; Li, Z. H.; Li, Z. Y.; Lim, S.; Lin, C. H.; Lipari, P.; Lippert, T.; Liu, D.; Liu, H.; Lomtadze, T.; Lu, M. J.; Lu, Y. S.; Luebelsmeyer, K.; Luo, F.; Luo, J. Z.; Lv, S. S.; Majka, R.; Malinin, A.; Mañá, C.; Marín, J.; Martin, T.; Martínez, G.; Masi, N.; Maurin, D.; Menchaca-Rocha, A.; Meng, Q.; Mo, D. C.; Morescalchi, L.; Mott, P.; Müller, M.; Ni, J. Q.; Nikonov, N.; Nozzoli, F.; Nunes, P.; Obermeier, A.; Oliva, A.; Orcinha, M.; Palmonari, F.; Palomares, C.; Paniccia, M.; Papi, A.; Pedreschi, E.; Pensotti, S.; Pereira, R.; Pilo, F.; Piluso, A.; Pizzolotto, C.; Plyaskin, V.; Pohl, M.; Poireau, V.; Postaci, E.; Putze, A.; Quadrani, L.; Qi, X. M.; Rancoita, P. G.; Rapin, D.; Ricol, J. S.; Rodríguez, I.; Rosier-Lees, S.; Rozhkov, A.; Rozza, D.; Sagdeev, R.; Sandweiss, J.; Saouter, P.; Sbarra, C.; Schael, S.; Schmidt, S. M.; Schuckardt, D.; von Dratzig, A. Schulz; Schwering, G.; Scolieri, G.; Seo, E. S.; Shan, B. S.; Shan, Y. H.; Shi, J. Y.; Shi, X. Y.; Shi, Y. M.; Siedenburg, T.; Son, D.; Spada, F.; Spinella, F.; Sun, W.; Sun, W. H.; Tacconi, M.; Tang, C. P.; Tang, X. W.; Tang, Z. C.; Tao, L.; Tescaro, D.; Ting, Samuel C. C.; Ting, S. M.; Tomassetti, N.; Torsti, J.; Türkoǧlu, C.; Urban, T.; Vagelli, V.; Valente, E.; Vannini, C.; Valtonen, E.; Vaurynovich, S.; Vecchi, M.; Velasco, M.; Vialle, J. P.; Wang, L. Q.; Wang, Q. L.; Wang, R. S.; Wang, X.; Wang, Z. X.; Weng, Z. L.; Whitman, K.; Wienkenhöver, J.; Wu, H.; Xia, X.; Xie, M.; Xie, S.; Xiong, R. Q.; Xin, G. M.; Xu, N. S.; Xu, W.; Yan, Q.; Yang, J.; Yang, M.; Ye, Q. H.; Yi, H.; Yu, Y. J.; Yu, Z. Q.; Zeissler, S.; Zhang, J. H.; Zhang, M. T.; Zhang, X. B.; Zhang, Z.; Zheng, Z. M.; Zhuang, H. L.; Zhukov, V.; Zichichi, A.; Zimmermann, N.; Zuccon, P.; Zurbach, C.; AMS Collaboration
2014-09-01
Precision measurements by the Alpha Magnetic Spectrometer on the International Space Station of the primary cosmic-ray electron flux in the range 0.5 to 700 GeV and the positron flux in the range 0.5 to 500 GeV are presented. The electron flux and the positron flux each require a description beyond a single power-law spectrum. Both the electron flux and the positron flux change their behavior at ˜30 GeV but the fluxes are significantly different in their magnitude and energy dependence. Between 20 and 200 GeV the positron spectral index is significantly harder than the electron spectral index. The determination of the differing behavior of the spectral indices versus energy is a new observation and provides important information on the origins of cosmic-ray electrons and positrons.
Aguilar, M; Aisa, D; Alvino, A; Ambrosi, G; Andeen, K; Arruda, L; Attig, N; Azzarello, P; Bachlechner, A; Barao, F; Barrau, A; Barrin, L; Bartoloni, A; Basara, L; Battarbee, M; Battiston, R; Bazo, J; Becker, U; Behlmann, M; Beischer, B; Berdugo, J; Bertucci, B; Bigongiari, G; Bindi, V; Bizzaglia, S; Bizzarri, M; Boella, G; de Boer, W; Bollweg, K; Bonnivard, V; Borgia, B; Borsini, S; Boschini, M J; Bourquin, M; Burger, J; Cadoux, F; Cai, X D; Capell, M; Caroff, S; Casaus, J; Cascioli, V; Castellini, G; Cernuda, I; Cervelli, F; Chae, M J; Chang, Y H; Chen, A I; Chen, H; Cheng, G M; Chen, H S; Cheng, L; Chikanian, A; Chou, H Y; Choumilov, E; Choutko, V; Chung, C H; Clark, C; Clavero, R; Coignet, G; Consolandi, C; Contin, A; Corti, C; Coste, B; Cui, Z; Dai, M; Delgado, C; Della Torre, S; Demirköz, M B; Derome, L; Di Falco, S; Di Masso, L; Dimiccoli, F; Díaz, C; von Doetinchem, P; Du, W J; Duranti, M; D'Urso, D; Eline, A; Eppling, F J; Eronen, T; Fan, Y Y; Farnesini, L; Feng, J; Fiandrini, E; Fiasson, A; Finch, E; Fisher, P; Galaktionov, Y; Gallucci, G; García, B; García-López, R; Gast, H; Gebauer, I; Gervasi, M; Ghelfi, A; Gillard, W; Giovacchini, F; Goglov, P; Gong, J; Goy, C; Grabski, V; Grandi, D; Graziani, M; Guandalini, C; Guerri, I; Guo, K H; Habiby, M; Haino, S; Han, K C; He, Z H; Heil, M; Hoffman, J; Hsieh, T H; Huang, Z C; Huh, C; Incagli, M; Ionica, M; Jang, W Y; Jinchi, H; Kanishev, K; Kim, G N; Kim, K S; Kirn, Th; Kossakowski, R; Kounina, O; Kounine, A; Koutsenko, V; Krafczyk, M S; Kunz, S; La Vacca, G; Laudi, E; Laurenti, G; Lazzizzera, I; Lebedev, A; Lee, H T; Lee, S C; Leluc, C; Li, H L; Li, J Q; Li, Q; Li, Q; Li, T X; Li, W; Li, Y; Li, Z H; Li, Z Y; Lim, S; Lin, C H; Lipari, P; Lippert, T; Liu, D; Liu, H; Lomtadze, T; Lu, M J; Lu, Y S; Luebelsmeyer, K; Luo, F; Luo, J Z; Lv, S S; Majka, R; Malinin, A; Mañá, C; Marín, J; Martin, T; Martínez, G; Masi, N; Maurin, D; Menchaca-Rocha, A; Meng, Q; Mo, D C; Morescalchi, L; Mott, P; Müller, M; Ni, J Q; Nikonov, N; Nozzoli, F; Nunes, P; Obermeier, A; Oliva, A; Orcinha, M; Palmonari, F; Palomares, C; Paniccia, M; Papi, A; Pedreschi, E; Pensotti, S; Pereira, R; Pilo, F; Piluso, A; Pizzolotto, C; Plyaskin, V; Pohl, M; Poireau, V; Postaci, E; Putze, A; Quadrani, L; Qi, X M; Rancoita, P G; Rapin, D; Ricol, J S; Rodríguez, I; Rosier-Lees, S; Rozhkov, A; Rozza, D; Sagdeev, R; Sandweiss, J; Saouter, P; Sbarra, C; Schael, S; Schmidt, S M; Schuckardt, D; Schulz von Dratzig, A; Schwering, G; Scolieri, G; Seo, E S; Shan, B S; Shan, Y H; Shi, J Y; Shi, X Y; Shi, Y M; Siedenburg, T; Son, D; Spada, F; Spinella, F; Sun, W; Sun, W H; Tacconi, M; Tang, C P; Tang, X W; Tang, Z C; Tao, L; Tescaro, D; Ting, Samuel C C; Ting, S M; Tomassetti, N; Torsti, J; Türkoğlu, C; Urban, T; Vagelli, V; Valente, E; Vannini, C; Valtonen, E; Vaurynovich, S; Vecchi, M; Velasco, M; Vialle, J P; Wang, L Q; Wang, Q L; Wang, R S; Wang, X; Wang, Z X; Weng, Z L; Whitman, K; Wienkenhöver, J; Wu, H; Xia, X; Xie, M; Xie, S; Xiong, R Q; Xin, G M; Xu, N S; Xu, W; Yan, Q; Yang, J; Yang, M; Ye, Q H; Yi, H; Yu, Y J; Yu, Z Q; Zeissler, S; Zhang, J H; Zhang, M T; Zhang, X B; Zhang, Z; Zheng, Z M; Zhuang, H L; Zhukov, V; Zichichi, A; Zimmermann, N; Zuccon, P; Zurbach, C
2014-09-19
Precision measurements by the Alpha Magnetic Spectrometer on the International Space Station of the primary cosmic-ray electron flux in the range 0.5 to 700 GeV and the positron flux in the range 0.5 to 500 GeV are presented. The electron flux and the positron flux each require a description beyond a single power-law spectrum. Both the electron flux and the positron flux change their behavior at ∼30 GeV but the fluxes are significantly different in their magnitude and energy dependence. Between 20 and 200 GeV the positron spectral index is significantly harder than the electron spectral index. The determination of the differing behavior of the spectral indices versus energy is a new observation and provides important information on the origins of cosmic-ray electrons and positrons.
NASA Astrophysics Data System (ADS)
Lobet, M.; Davoine, X.; d'Humières, E.; Gremillet, L.
2017-04-01
Generation of electron-positron pairs via the multiphoton Breit-Wheeler process in an all-optical scheme will be made possible on forthcoming high-power laser facilities through the collision of wakefield-accelerated GeV electrons with a counter-propagating laser pulse of 1 022- 1 023 W cm-2 peak intensity. By means of integrated 3D particle-in-cell simulations, we show that the production of high-density sources of ultrarelativistic electron-positron pairs is within the reach of soon-to-be-available laser systems. Under physical conditions accessible to the dual-beam CILEX-Apollon facility, we find that the generated positrons can carry a total charge of 0.05-1 nC, with a mean energy of 100-400 MeV and an angular divergence of 0.01-0.1 rad. The variations of the positron source's properties with respect to the laser parameters are also examined.
NASA Astrophysics Data System (ADS)
Kawakatu, Nozomu; Kino, Motoki; Takahara, Fumio
2016-03-01
We examine the plasma composition of relativistic jets in four Fanaroff-Riley type II (FRII) radio galaxies by analysing the total cocoon pressure in terms of partial pressures of thermal and non-thermal electrons/positrons and protons. The total cocoon pressure is determined by cocoon dynamics via comparison of theoretical model with the observed cocoon shape. By inserting the observed number density of non-thermal electrons/positrons and the upper limit of thermal electron/positron number density into the equation of state, the number density of protons is constrained. We apply this method to four FRII radio galaxies (Cygnus A, 3C 219, 3C 223 and 3C 284), for which the total cocoon pressures have been already evaluated. We find that the positron-free plasma comprising protons and electrons is ruled out, when we consider plausible particle distribution functions. In other words, the mixture of positrons is required for all four FRII radio galaxies; the number density ratio of electrons/positrons to protons is larger than 2. Thus, we find that the plasma composition is independent of the jet power and the size of cocoons. We also investigate the additional contribution of thermal electrons/positrons and protons on the cocoon dynamics. When thermal electrons/positrons are absent, the cocoon is supported by the electron/proton plasma pressure, while both electron/positron pressure supported and electron/proton plasma pressure supported cocoons are allowed if the number density of thermal electrons/positrons is about 10 times larger than that of non-thermal ones.
Electron-positron pairs beaming in the Breit-Wheeler process
NASA Astrophysics Data System (ADS)
Ribeyre, X.; d'Humières, E.; Jansen, O.; Jequier, S.; Tikhonchuk, V. T.
2017-01-01
The pair creation from the Breit-Wheeler process is one of the basic processes in the universe. Laser induced intense γ-ray sources will allow a direct observation of this process in the laboratory for the first time. In this paper we demonstrate the effect of pair beaming in the collision of two photon beams which may facilitate the experimental observation of the Breit-Wheeler process.
Electron-positron pair production from vacuum in the field of high-intensity laser radiation
NASA Astrophysics Data System (ADS)
Popov, V. S.; Mur, V. D.; Narozhnyi, N. B.; Popruzhenko, S. V.
2016-03-01
The works dealing with the theory of e + e - pair production from vacuum under the action of highintensity laser radiation are reviewed. The following problems are discussed: pair production in a constant electric field E and time-variable homogeneous field E( t); the dependence of the number of produced pairs {N_{{e^ + }{e^ - }}} on the shape of a laser pulse (dynamic Schwinger effect); and a realistic three-dimensional model of a focused laser pulse, which is based on exact solution of Maxwell's equations and contains parameters such as focal spot radius R, diffraction length L, focusing parameter Δ, pulse duration τ, and pulse shape. This model is used to calculate {N_{{e^ + }{e^ - }}} for both a single laser pulse ( n = 1) and several ( n ≥ 2) coherent pulses with a fixed total energy that simultaneously "collide" in a laser focus. It is shown that, at n ≫ 1, the number of pairs increases by several orders of magnitude as compared to the case of a single pulse. The screening of a laser field by the vapors that are generated in vacuum, its "depletion," and the limiting fields to be achieved in laser experiments are considered. The relation between pair production, the problem of a quantum frequency-variable oscillator, and the theory of groups SU(1, 1) and SU(2) is discussed. The relativistic version of the imaginary time method is used in calculations. In terms of this version, a relativistic theory of tunneling is developed and the Keldysh theory is generalized to the case of ionization of relativistic bound systems, namely, atoms and ions. The ionization rate of a hydrogen-like ion with a charge 1 ≤ Z ≤ 92 is calculated as a function of laser radiation intensity ( F and ellipticity ρ.
Nonthermal electron-positron pairs and cold matter in the central engines of active galactic nuclei
NASA Technical Reports Server (NTRS)
Zdziarski, Andrzej A.
1992-01-01
The nonthermal e(+/-) pair model of the central engine of active galactic nuclei (AGNs) is discussed. The model assumes that nonthermal e(+/-) pairs are accelerated to highly relativistic energies in a compact region close to the central black hole and in the vicinity of some cold matter. The model has a small number of free parameters and explains a large body of AGN observations from EUV to soft gamma-rays. In particular, the model explains the existence of the UV bump, the soft X-rays excess, the canonical hard X-ray power law, the spectral hardening above about 10 keV, and some of the variability patterns in the soft and hard X-rays. In addition, the model explains the spectral steepening above about 50 keV seen in NGC 4151.
Electron-Positron Pair Production in Strong Fields Characterized by Conversion Energy
NASA Astrophysics Data System (ADS)
Sitiwaldi, Ibrahim; Li, Zi-Liang; Xie, Bai-Song
2017-01-01
It is demonstrated that the production mechanism of a pair which is produced from vacuum under an external field can be characterized by its conversion energy, a quantity defined as total mass-energy of this pair. The value of this quantity is checked with quantum field theoretical simulations for several field configurations and it is found that conversion energy can show all the production channels and give the yields of each channel specifically. We detect signatures of effective mass, combination of different photons as well as dynamically assisted Schwinger mechanism and represented more features of these processes in the view of conversion energy. Supported by the National Natural Science Foundation of China under Grant No. 11475026
Nonthermal electron-positron pairs and cold matter in the central engines of active galactic nuclei
NASA Technical Reports Server (NTRS)
Zdziarski, Andrzej A.
1992-01-01
The nonthermal e(+/-) pair model of the central engine of active galactic nuclei (AGNs) is discussed. The model assumes that nonthermal e(+/-) pairs are accelerated to highly relativistic energies in a compact region close to the central black hole and in the vicinity of some cold matter. The model has a small number of free parameters and explains a large body of AGN observations from EUV to soft gamma-rays. In particular, the model explains the existence of the UV bump, the soft X-rays excess, the canonical hard X-ray power law, the spectral hardening above about 10 keV, and some of the variability patterns in the soft and hard X-rays. In addition, the model explains the spectral steepening above about 50 keV seen in NGC 4151.
Investigation into electron cloud effects in the International Linear Collider positron damping ring
Crittenden, J. A.; Conway, J.; Dugan, G. F.; Palmer, M. A.; Rubin, D. L.; Shanks, J.; Sonnad, K. G.; Boon, L.; Harkay, K.; Ishibashi, T.; Furman, M. A.; Guiducci, S.; Pivi, M. T. F.; Wang, L.
2014-03-01
We report modeling results for electron cloud buildup and instability in the International Linear Collider positron damping ring. Updated optics, wiggler magnets, and vacuum chamber designs have recently been developed for the 5 GeV, 3.2-km racetrack layout. An analysis of the synchrotron radiation profile around the ring has been performed, including the effects of diffuse and specular photon scattering on the interior surfaces of the vacuum chamber. The results provide input to the cloud buildup simulations for the various magnetic field regions of the ring. The modeled cloud densities thus obtained are used in the instability threshold calculations. We conclude that the mitigation techniques employed in this model will suffice to allow operation of the damping ring at the design operational specifications
Coherent pair creation as a positron source for linear colliders
Chen, P. ); Palmer, R.B. Brookhaven National Lab., Upton, NY )
1992-11-01
We propose a positron source for future linear colliders which uses the mechanism of coherent pair creation process from the collision of a high energy electron beam and a monochromatic photon beam. We show that there is a sharp spike in the pair-produced positron energy spectrum at an energy much lower than the primary beam energy. The transverse emittance is damped'', yielding final positrons with lower normalized emittance than the initial electrons. Numerical examples invoking conventional lasers and Free Electron Lasers (FEL) for the photon beams are considered.
Coherent pair creation as a positron source for linear colliders
Chen, P.; Palmer, R.B. |
1992-11-01
We propose a positron source for future linear colliders which uses the mechanism of coherent pair creation process from the collision of a high energy electron beam and a monochromatic photon beam. We show that there is a sharp spike in the pair-produced positron energy spectrum at an energy much lower than the primary beam energy. The transverse emittance is ``damped``, yielding final positrons with lower normalized emittance than the initial electrons. Numerical examples invoking conventional lasers and Free Electron Lasers (FEL) for the photon beams are considered.
Studies of positron electron pair production in {sup 238}U + {sup 181}Ta
Ahmad, I.; Back, B.B.; Betts, R.R.
1995-08-01
Following the completion of APEX in late 1993, a two-week run on the {sup 238}U + {sup 181}Ta system at 6.1 and 6.3 MeV/u with 1 mg/cm{sup 2} targets provided, for the first time, data in which the expected sharp sum-energy lines should appear. Data from previous experiments show evidence for sharp sum-energy lines at 625, 748 and 805 keV, observed at bombarding energies from 5.9 to 6.3 MeV/u. The 625- and 809-keV lines display the characteristics of equal-energy back-to-back emission whereas the 748-keV line shows a rather different behavior. In our measurements, average beam currents of 2-3 pnA from the ATLAS accelerator were used to bombard 1-mg/cm{sup 2} rolled {sup 181}Ta targets, the energy loss in which corresponds to the ranges of bombarding energies over which the sharp sum-energy lines were previously reported. A run at 5.95 MeV/u for {sup 238}U + {sup 181}Ta followed in May 1994. These data were analyzed extensively. Sum-energy spectra measured in coincidence with scattered ions in the range 20{degrees} < {theta} < 68{degrees}. No evidence is found for the sharp sum-energy lines reported previously and, depending on the scenario assumed for the production mechanism and kinematics of the pairs, upper limits on cross sections at the 90% confidence limit range from 10-100 times smaller than the values that can be deduced from the earlier reports. We are in the process of refining the data analysis and simulations of the apparatus in order to finalize these numbers for publication.
Towards laboratory produced relativistic electron–positron pair plasmas
Chen, Hui; Meyerhofer, D. D.; Wilks, S. C.; Cauble, R.; Dollar, F.; Falk, K.; Gregori, G.; Hazi, A.; Moses, E. I.; Murphy, C. D.; Myatt, J.; Park, J.; Seely, J.; Shepherd, R.; Spitkovsky, A.; Stoeckl, C.; Szabo, C. I.; Tommasini, R.; Zulick, C.; Beiersdorfer, P.
2011-12-01
We review recent experimental results on the path to producing electron–positron pair plasmas using lasers. Relativistic pair-plasmas and jets are believed to exist in many astrophysical objects and are often invoked to explain energetic phenomena related to Gamma Ray Bursts and Black Holes. On earth, positrons from radioactive isotopes or accelerators are used extensively at low energies (sub-MeV) in areas related to surface science positron emission tomography and basic antimatter science. Experimental platforms capable of producing the high-temperature pair-plasma and high-flux jets required to simulate astrophysical positron conditions have so far been absent. In the past few years, we performed extensive experiments generating positrons with intense lasers where we found that relativistic electron and positron jets are produced by irradiating a solid gold target with an intense picosecond laser pulse. The positron temperatures in directions parallel and transverse to the beam both exceeded 0.5 MeV, and the density of electrons and positrons in these jets are of order 1016 cm^{-3} and 1013 cm^{-3}, respectively. With the increasing performance of high-energy ultra-short laser pulses, we expect that a high-density, up to 1018 cm^{-3}, relativistic pair-plasma is achievable, a novel regime of laboratory-produced hot dense matter.
Chang, H X; Qiao, B; Xu, Z; Xu, X R; Zhou, C T; Yan, X Q; Wu, S Z; Borghesi, M; Zepf, M; He, X T
2015-11-01
A scheme for enhanced quantum electrodynamics (QED) production of electron-positron-pair plasmas is proposed that uses two ultraintense lasers irradiating a thin solid foil from opposite sides. In the scheme, under a proper matching condition, in addition to the skin-depth emission of γ-ray photons and Breit-Wheeler creation of pairs on each side of the foil, a large number of high-energy electrons and photons from one side can propagate through it and interact with the laser on the other side, leading to much enhanced γ-ray emission and pair production. More importantly, the created pairs can be collected later and confined to the center by opposite laser radiation pressures when the foil becomes transparent, resulting in the formation of unprecedentedly overdense and high-energy pair plasmas. Two-dimensional QED particle-in-cell simulations show that electron-positron-pair plasmas with overcritical density 10(22) cm(-3) and a high energy of 100s of MeV are obtained with 10 PW lasers at intensities 10(23) W/cm(2), which are of key significance for laboratory astrophysics studies.
Electron and positron induced processes. POSMOL 2013
NASA Astrophysics Data System (ADS)
Limão-Vieira, Paulo; Campeanu, Radu; Hoshino, Masamitsu; Ingólfsson, Oddur; Mason, Nigel; Nagashima, Yasuyuki; Tanuma, Hajime
2014-09-01
POSMOL 2013, the international meeting on electron and positron induced processes comprising the XVII International Workshop on Low-Energy Positron and Positronium Physics and the XVIII International Symposium on Electron-Molecule Collisions and Swarms, was held at Kanazawa Bunka Hall, Kanazawa, Ishikawa, Japan, from 19-21 July 2013. The XVII Workshop encompassed all aspects of positron, positronium and antiproton interactions with electrons, atoms, molecules and solid surfaces, and topics related to these, whereas the XVIII Symposium encompassed all aspects of electron interactions with molecules in both gaseous and condensed phases. Particular topics include studies of electron interactions with biomolecules, electron induced surface chemistry and the study of plasma processes. Recent research on the study of electron swarms was also highlighted. Contribution to the Topical Issue "Electron and Positron Induced Processes", edited by Michael Brunger, Radu Campeanu, Masamitsu Hoshino, Oddur Ingólfsson, Paulo Limão-Vieira, Nigel Mason, Yasuyuki Nagashima and Hajime Tanuma.
Electron Cloud in the Wigglers of the Positron Damping Ring of the International Linear Collider
Wang, L.; /SLAC
2007-07-06
The ILC positron damping ring comprises hundreds of meters of wiggler sections, where many more photons than in the arcs are emitted, and with the smallest beampipe aperture of the ring. A significant electron-cloud density can therefore be accumulated via photo-emission and via beam-induced multipacting. In field-free regions the electron-cloud build up may be suppressed by adding weak solenoid fields, but the electron cloud remaining in the wigglers as well as in the arc dipole magnets can still drive single-bunch and multi-bunch beam instabilities. This paper studies the electron-cloud formation in an ILC wiggler section for various scenarios, as well as its character, and possible mitigation schemes.
Enhanced production of low-mass electron-positron pairs in 40-AGeV Pb-Au collisions at the CERN SPS.
Adamová, D; Agakichiev, G; Appelshäuser, H; Belaga, V; Braun-Munzinger, P; Cherlin, A; Damjanović, S; Dietel, T; Dietrich, L; Drees, A; Esumi, S I; Filimonov, K; Fomenko, K; Fraenkel, Z; Garabatos, C; Glässel, P; Hering, G; Holeczek, J; Kushpil, V; Lenkeit, B; Maas, A; Marín, A; Milosević, J; Milov, A; Miśkowiec, D; Panebrattsev, Yu; Petchenova, O; Petrácek, V; Pfeiffer, A; Rak, J; Ravinovich, I; Rehak, P; Richter, M; Sako, H; Schmitz, W; Sedykh, S; Seipp, W; Sharma, A; Shimansky, S; Slívová, J; Specht, H J; Stachel, J; Sumbera, M; Tilsner, H; Tserruya, I; Wessels, J P; Wienold, T; Windelband, B; Wurm, J P; Xie, W; Yurevich, S; Yurevich, V
2003-07-25
We report on first measurements of low-mass electron-positron pairs in Pb-Au collisions at the CERN SPS beam energy of 40 AGeV. The observed pair yield integrated over the range of invariant masses 0.2
Energy loss of relativistic electrons and positrons traversing cosmic matter
NASA Technical Reports Server (NTRS)
Gould, R. J.
1975-01-01
Questions of adiabatic expansion are considered along with aspects of Compton scattering, bremsstrahlung, electronic excitation, synchrotron radiation, and electron-positron pair production. It is found that, unless the intergalactic magnetic field is very small, synchrotron radiation will dominate all other energy loss processes at ultrahigh electron and positron energies. The dependence of the loss rates on the cosmic epoch is also discussed.
NASA Astrophysics Data System (ADS)
Kovács, Z.; Harko, T.
2011-11-01
We present a full general relativistic numerical code for estimating the energy-momentum deposition rate (EMDR) from neutrino pair annihilation (?). The source of the neutrinos is assumed to be a neutrino-cooled accretion disc around neutron and quark stars. We calculate the neutrino trajectories by using a ray-tracing algorithm with the general relativistic Hamilton's equations for neutrinos and derive the spatial distribution of the EMDR due to the annihilations of neutrinos and antineutrinos around rotating neutron and quark stars. We obtain the EMDR for several classes of rotating neutron stars, described by different equations of state of the neutron matter, and for quark stars, described by the Massachusetts Institute of Technology (MIT) bag model equation of state and in the colour-flavour-locked (CFL) phase. The distribution of the total annihilation rate of the neutrino-antineutrino pairs around rotating neutron and quark stars is studied for isothermal discs and accretion discs in thermodynamical equilibrium. We demonstrate both the differences in the equations of state for neutron and quark matter and rotation with the general relativistic effects significantly modify the EMDR of the electrons and positrons generated by the neutrino-antineutrino pair annihilation around compact stellar objects, as measured at infinity.
Alternative positron-target design for electron-positron colliders
Donahue, R.J. ); Nelson, W.R. )
1991-04-01
Current electron-positron linear colliders are limited in luminosity by the number of positrons which can be generated from targets presently used. This paper examines the possibility of using an alternate wire-target geometry for the production of positrons via an electron-induced electromagnetic cascade shower. 39 refs., 38 figs., 5 tabs.
Electron-positron pair production near the Galactic Centre and the 511 keV emission line
NASA Astrophysics Data System (ADS)
Chan, Man Ho
2016-02-01
Recent observations indicate that a high production rate of positrons (strong 511 keV line) and a significant amount of excess GeV gamma-ray exist in our Galactic bulge. The latter issue can be explained by ˜40 GeV dark matter annihilation through b bar{b} channel while the former one remains a mystery. On the other hand, recent studies reveal that a large amount of high-density gas might exist near the Galactic Centre million years ago to account for the young, massive stars extending from 0.04-7 pc. In this Letter, I propose a new scenario and show that the 40 GeV dark matter annihilation model can also explain the required positron production rate (511 keV line) in the bulge due to the existence of the high-density gas cloud near the supermassive black hole long time ago.
Progress toward positron accumulation for use in pair plasmas
NASA Astrophysics Data System (ADS)
Stenson, E. V.; Hergenhahn, U.; Niemann, H.; Paschkowski, N.; Pedersen, T. Sunn; Saitoh, H.; Stanja, J.; Marx, G. H.; Schweikhard, L.; Hugenschmidt, C.; Danielson, J. R.; Surko, C. M.
2014-10-01
A Positron-Electron Experiment (APEX) is being developed to create and investigate magnetically confined matter-antimatter pair plasmas in the laboratory. These plasmas, whose oppositely charged species have precisely equal mass, have long been a topic of theoretical and astrophysical interest. The accompanying Positron Accumulation Experiment (PAX) comprises a series of non-neutral plasma traps. PAX will provide a bridge between the parameters of the NEPOMUC (Neutron-Induced Positron Source Munich) beam, from which APEX will receive its positrons, and the parameters needed to achieve at least 10 Debye lengths within APEX's flux surfaces. Presented here is an overview of work from the PAX team. Topics include the following: diagnostics for non-neutral plasmas, including a comparison of phosphor luminescence in response to electrons versus positrons, as well as work on a nonperturbative potential probe; progress to date on injection into and trapping within various sub-components of the experiment (buffer gas trap, accumulator, and high-field trap); and a discussion of design considerations for the next-generation, multi-cell trap to be built for the high-field magnet. on behalf of the APEX/PAX Team and Collaborators.
Positron source position sensing detector and electronics
Burnham, Charles A.; Bradshaw, Jr., John F.; Kaufman, David E.; Chesler, David A.; Brownell, Gordon L.
1985-01-01
A positron source, position sensing device, particularly with medical applications, in which positron induced gamma radiation is detected using a ring of stacked, individual scintillation crystals, a plurality of photodetectors, separated from the scintillation crystals by a light guide, and high resolution position interpolation electronics. Preferably the scintillation crystals are several times more numerous than the photodetectors with each crystal being responsible for a single scintillation event from a received gamma ray. The light guide will disperse the light emitted from gamma ray absorption over several photodetectors. Processing electronics for the output of the photodetectors resolves the location of the scintillation event to a fraction of the dimension of each photodetector. Because each positron absorption results in two 180.degree. oppositely traveling gamma rays, the detection of scintillation in pairs permits location of the positron source in a manner useful for diagnostic purposes. The processing electronics simultaneously responds to the outputs of the photodetectors to locate the scintillations to the source crystal. While it is preferable that the scintillation crystal include a plurality of stacked crystal elements, the resolving power of the processing electronics is also applicable to continuous crystal scintillators.
Advances in positron and electron scattering*
NASA Astrophysics Data System (ADS)
Limão-Vieira, Paulo; García, Gustavo; Krishnakumar, E.; Petrović, Zoran; Sullivan, James; Tanuma, Hajime
2016-10-01
The topical issue on Advances in Positron and Electron Scattering" combines contributions from POSMOL 2015 together with others devoted to celebrate the unprecedented scientific careers of our loyal colleagues and trusted friends Steve Buckman (Australian National University, Australia) and Michael Allan (University of Fribourg, Switzerland) on the occasion of their retirements. POSMOL 2015, the XVIII International Workshop on Low-Energy Positron and Positronium Physics and the XIX International Symposium on Electron-Molecule Collisions and Swarms, was held at Universidade NOVA de Lisboa, Lisboa, Portugal, from 17-20 July 2015. The international workshop and symposium allowed to achieve a very privileged forum of sharing and developing our scientific expertise on current aspects of positron, positronium and antiproton interactions with electrons, atoms, molecules and solid surfaces, and related topics, as well as electron interactions with molecules in both gaseous and condensed phases. Particular topics include studies of electron interactions with biomolecules, electron induced surface chemistry and the study of plasma processes. Recent developments in the study of swarms are also fully addressed.
Monte-Carlo-based studies of a polarized positron source for International Linear Collider (ILC)
NASA Astrophysics Data System (ADS)
Dollan, Ralph; Laihem, Karim; Schälicke, Andreas
2006-04-01
The full exploitation of the physics potential of an International Linear Collider (ILC) requires the development of a polarized positron beam. New concepts of polarized positron sources are based on the development of circularly polarized photon sources. The polarized photons create electron-positron pairs in a thin target and transfer their polarization state to the outgoing leptons. To achieve a high level of positron polarization the understanding of the production mechanisms in the target is crucial. Therefore, a general framework for the simulation of polarized processes with GEANT4 is under development. In this contribution the current status of the project and its application to a study of the positron production process for the ILC is presented.
Positron accumulation for the fueling of matter-antimatter pair plasmas
NASA Astrophysics Data System (ADS)
Stenson, E. V.; Pedersen, T. Sunn; Hergenhahn, U.; Saitoh, H.; Sarasola, X.; Paschkowski, N.; Schauer, F.; Marx, G. H.; Schweikhard, L.; Hugenschmidt, C.; Danielson, J. R.; Surko, C. M.
2013-10-01
Pair plasmas have been a topic of theoretical and astrophysical interest for decades. APEX (A Positron-Electron Experiment) aims to create them in the laboratory by building upon recent advancements in several areas: devices that can magnetically confine both quasi-neutral and non-neutral plasmas, the strength of positron beams, and the manipulation of non-neutral plasmas. This last is the focus of the Positron Accumulation Experiment (PAX). PAX will provide a necessary bridge between the source of APEX's positrons (Neutron-Induced Positron Source Munich) and the magnetic confinement device for the pair plasma. PAX will cool and store incoming positrons over a 10-15 minute period, thereby accumulating them at sufficiently low energies and in sufficiently high numbers that the resulting plasma will extend at least 10 Debye lengths. The current status of PAX's construction and tests will be presented.
The Clic Electron and Positron Polarized Sources
NASA Astrophysics Data System (ADS)
Rinolfi, L.
2011-01-01
The CLIC polarized electron source is based on a DC gun where the photocathode is illuminated by a laser beam. Each micro-bunch has a charge of 6 × 109 e-, a width of 100 ps and a repetition rate of 2 GHz. A peak current of 10 A in the micro-bunch is a challenge for the surface charge limit of the photo-cathode. Two options are feasible to generate the 2 GHz e- bunch train: 100 ps micro-bunches can be extracted from the photo-cathode either by a 2 GHz laser system or by generating a macro-bunch using a ~200 ns laser pulse and a subsequent RF bunching system to produce the appropriate micro-bunch structure. Recent results obtained by SLAC, for the latter case, are presented. The polarized positron source is based on a positron production scheme in which polarized photons are produced by a laser Compton scattering process. The resulting circularly-polarized gamma photons are sent onto a target, producing pairs of longitudinally polarized electrons and positrons. The Compton backscattering process occurs either in a Compton ring, where a 1 GeV electron beam interacts with circularly-polarized photons in an optical resonator or in a 1.8 GeV Compton Energy Recovery Linac (ERL) or in a 6 GeV Linac with several optical cavities. The undulator scheme is also studied. The nominal CLIC e+ bunch population is 6.7 × 109 particles per bunch at 200 MeV. The tradeoff between e+ yield and level of polarization is an important topic. The overall scheme for both polarized electron and positron beams is described.
Recent Advances in Electron and Positron Sources
Clendenin, James E
2000-07-20
Recent advances in electron and positron sources have resulted in new capabilities driven in most cases by the increasing demands of advanced accelerating systems. Electron sources for brighter beams and for high average-current beams are described. The status and remaining challenges for polarized electron beams are also discussed. For positron sources, recent activity in the development of polarized positron beams for future colliders is reviewed. Finally, a new proposal for combining laser cooling with beam polarization is presented.
Electron pairing without superconductivity.
Cheng, Guanglei; Tomczyk, Michelle; Lu, Shicheng; Veazey, Joshua P; Huang, Mengchen; Irvin, Patrick; Ryu, Sangwoo; Lee, Hyungwoo; Eom, Chang-Beom; Hellberg, C Stephen; Levy, Jeremy
2015-05-14
Strontium titanate (SrTiO3) is the first and best known superconducting semiconductor. It exhibits an extremely low carrier density threshold for superconductivity, and possesses a phase diagram similar to that of high-temperature superconductors--two factors that suggest an unconventional pairing mechanism. Despite sustained interest for 50 years, direct experimental insight into the nature of electron pairing in SrTiO3 has remained elusive. Here we perform transport experiments with nanowire-based single-electron transistors at the interface between SrTiO3 and a thin layer of lanthanum aluminate, LaAlO3. Electrostatic gating reveals a series of two-electron conductance resonances-paired electron states--that bifurcate above a critical pairing field Bp of about 1-4 tesla, an order of magnitude larger than the superconducting critical magnetic field. For magnetic fields below Bp, these resonances are insensitive to the applied magnetic field; for fields in excess of Bp, the resonances exhibit a linear Zeeman-like energy splitting. Electron pairing is stable at temperatures as high as 900 millikelvin, well above the superconducting transition temperature (about 300 millikelvin). These experiments demonstrate the existence of a robust electronic phase in which electrons pair without forming a superconducting state. Key experimental signatures are captured by a model involving an attractive Hubbard interaction that describes real-space electron pairing as a precursor to superconductivity.
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.
Electron and Positron Stopping Powers of Materials
National Institute of Standards and Technology Data Gateway
SRD 7 NIST Electron and Positron Stopping Powers of Materials (PC database for purchase) The EPSTAR database provides rapid calculations of stopping powers (collisional, radiative, and total), CSDA ranges, radiation yields and density effect corrections for incident electrons or positrons with kinetic energies from 1 keV to 10 GeV, and for any chemically defined target material.
Positron annihilation induced Auger electron emission
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.
Electron- and positron-proton elastic scattering in CLAS
Weinstein, L. B.
2009-09-02
There is a significant disagreement between measurements of the proton electric form factor, G{sup p}{sub E}, using Rosenbluth separations and polarization transfer. This disagreement, if not explained, could pose a fundamental challenge to our understanding of electron scattering or proton structure. Two-photon exchange (TPE) processes, although not fully calculable, are the most likely explanation of this disagreement. We will definitively test this assertion by comparing the electron-proton and positron-proton elastic scattering cross section in the Jefferson Lab CLAS. We will make a mixed identical electron and positron tertiary beam by passing a 5.5 GeV primary electron beam through a radiator to make a photon beam and then passing the photon beam through a converter to make electron-positron pairs. Measuring the elastic cross sections simultaneously using identical lepton beams should significantly reduce systematic uncertainties.
Electron- and positron-proton elastic scattering in CLAS
L.B. Weinstein
2009-08-01
There is a significant disagreement between measurements of the proton electric form factor, G{sup p}{sub E}, using Rosenbluth separations and polarization transfer. This disagreement, if not explained, could pose a fundamental challenge to our understanding of electron scattering or proton structure. Two-photon exchange (TPE) processes, although not fully calculable, are the most likely explanation of this disagreement. We will definitively test this assertion by comparing the electron-proton and positron-proton elastic scattering cross section in the Jefferson Lab CLAS. We will make a mixed identical electron and positron tertiary beam by passing a 5.5 GeV primary electron beam through a radiator to make a photon beam and then passing the photon beam through a converter to make electron-positron pairs. Measuring the elastic cross sections simultaneously using identical lepton beams should significantly reduce systematic uncertainties.
PEPPo: Using a Polarized Electron Beam to Produce Polarized Positrons
Adeyemi, Adeleke H.
2015-09-01
Polarized positron beams have been identified as either an essential or a significant ingredient for the experimental program of both the present and next generation of lepton accelerators (JLab, Super KEK B, ILC, CLIC). An experiment demonstrating a new method for producing polarized positrons has been performed at the Continuous Electron Beam Accelerator Facility at Jefferson Lab. The PEPPo (Polarized Electrons for Polarized Positrons) concept relies on the production of polarized e⁻/e⁺ pairs from the bremsstrahlung radiation of a longitudinally polarized electron beam interacting within a high-Z conversion target. PEPPo demonstrated the effective transfer of spin-polarization of an 8.2 MeV/c polarized (P~85%) electron beam to positrons produced in varying thickness tungsten production targets, and collected and measured in the range of 3.1 to 6.2 MeV/c. In comparison to other methods this technique reveals a new pathway for producing either high-energy or thermal polarized positron beams using a relatively low polarized electron beam energy (~10MeV) .This presentation will describe the PEPPo concept, the motivations of the experiment and high positron polarization achieved.
Relativistic electron-positron beams in gamma-ray bursters
NASA Technical Reports Server (NTRS)
Smith, I. A.; Epstein, Richard I.
1993-01-01
Beams of relativistic electrons and/or positrons leaving the surface of a strongly magnetized neutron star may give rise to gamma-ray bursts. The beams could be accelerated by strong, magnetically aligned electric fields that are produced by oscillations of the stellar surface. Here we investigate the particle acceleration in these electric fields, the resulting electron-positron pair cascade, and the gamma-ray emission. We find that beams of electrons and positrons moving parallel to the magnetic field are generated, with a reported differential energy distribution. These beams produce the bulk of the gamma-ray burst radiation below about 1 MeV by the resonant Compton scattering of thermal photons emitted from the stellar surface. The escaping synchrotron radiation from the cascade dominates the radiation spectrum above about 1 MeV.
NASA Astrophysics Data System (ADS)
Uddin, M. J.; Alam, M. S.; Mamun, A. A.
2015-02-01
Nonplanar (cylindrical and spherical) positron-acoustic (PA) Gardner solitary waves (SWs) in an unmagnetized plasma system consisting of immobile positive ions, mobile cold positrons, and superthermal (kappa distributed) hot positrons and electrons are investigated. The modified Gardner equation is derived by using the reductive perturbation technique. The effects of cylindrical and spherical geometries, superthermal parameter of hot positrons and electrons, relative temperature ratios, and relative number density ratios on the PA Gardner SWs are studied by using the numerical simulations. The implications of our results in various space and laboratory plasma environments are briefly discussed.
Uddin, M. J. Alam, M. S.; Mamun, A. A.
2015-02-15
Nonplanar (cylindrical and spherical) positron-acoustic (PA) Gardner solitary waves (SWs) in an unmagnetized plasma system consisting of immobile positive ions, mobile cold positrons, and superthermal (kappa distributed) hot positrons and electrons are investigated. The modified Gardner equation is derived by using the reductive perturbation technique. The effects of cylindrical and spherical geometries, superthermal parameter of hot positrons and electrons, relative temperature ratios, and relative number density ratios on the PA Gardner SWs are studied by using the numerical simulations. The implications of our results in various space and laboratory plasma environments are briefly discussed.
Electron capture from solids by positrons
Howell, R.
1987-08-01
The capture of electrons in solids is modified from that in gasses by several factors. The most important is the collective interaction of the electrons which results in a density of electron states in the solid in wide bands. Also the high density of electrons in many solids gives a high frequency of interaction as compared to gasses, and quickly destroys any electron-positron states in the metal matrix. Consequently, most positrons implanted in a metal will rapidly thermalize, and unless they reach the surface will annihilate with an electron in an uncorrelated state. Positronium formation from positrons scattered at a metal surface is analogous to ion neutralization however, most of the positronium comes from positrons passing through the surface from the bulk. The dominant motivation for studying positronium formation has been the hope that the distribution of the electrons at the surface would be obtained through the annihilation properties of positrons trapped at the surface or through analysis of the energy and angular distributions of the positronium emitted into the vacuum. These distributions have been measured and are included in this paper. 17 refs.
A conventional positron source for international linear collider
NASA Astrophysics Data System (ADS)
Omori, Tsunehiko; Takahashi, Tohru; Riemann, Sabine; Gai, Wei; Gao, Jie; Kawada, Shin-ichi; Liu, Wanming; Okuda, Natsuki; Pei, Guoxi; Urakawa, Junji; Ushakov, Andriy
2012-04-01
A possible solution to realize a conventional positron source driven by a several-GeV electron beam for the International Linear Collider is proposed. A 300 Hz electron linac is employed to create positrons with stretching pulse length in order to cure target thermal load. ILC requires about 2600 bunches in a train which pulse length is 1 ms. Each pulse of the 300 Hz linac creates about 130 bunches, then 2600 bunches are created in 63 ms. Optimized parameters such as drive beam energy, beam size, and target thickness, are discussed assuming a L-band capture system to maximize the capture efficiency and to mitigate the target thermal load. A slow rotating tungsten disk is employed as positron generation target.
Internal Pair Decay of Giant Resonances in Hot LEAD-200.
NASA Astrophysics Data System (ADS)
Adami, Susan
Electron-positron pairs emitted during the de -excitation of the hot ^{200}Pb were detected with the Stony Brook pair detector, a phoswich array, in order to observe the internal pair decay of giant resonances (GR) built on excited states. These collective excitations are particularly well defined in heavy nuclei, and the full GR sum rule had been found in the ground state excitations of both the giant dipole resonance and the isoscalar monopole resonance. The excited compound nucleus was formed by bombarding a ^{181} Ta target with a 95 MeV pulsed ^ {19}F beam. While the gamma-decay from giant resonances of multipolarities L >=q 1 results in cross-sections 3-4 orders of magnitudes bigger than the internal pair decay, the decay of giant monopole resonances via a collective E0 transition can only be observed in the e^+ - e^ --decay channel. Another advantage of investigating electro-magnetic transitions via the pair decay channel is the fact that the correlation angle (and also the energy sharing) between the electron and the positron provides insight in the multipolarity of the observed transition. Especially the angular correlation distribution of an L = 0 transition is easily distinguished from the L >=q 1 cases. In the data analysis, the pair spectra were compared to calculations using the statistical model code CASCADE, which was modified to include the internal pair decay of giant resonances from the compound nucleus as well as from the fission fragments. In addition, gamma measurements from the same reaction at a comparable excitation energy (93 MeV) were available. The extracted pair spectra confirmed the CASCADE prediction that the giant dipole resonance dominates the pair decay from a hot, heavy nucleus. Superior statistics would be necessary in order to extract weaker modes like the monopole or quadrupole resonances and due to the lack in statistics this work can only offer a rough estimate for the width and position of the isoscalar giant monopole
Electron--positron beam--plasma experiments
NASA Astrophysics Data System (ADS)
Gilbert, S. J.; Kurz, C. K.; Greaves, R. G.; Surko, C. M.
1997-11-01
Electron-positron plasmas possess unique properties due to inherent symmetries between the charge species. The ability to accumulate large numbers of positron.html>cold positrons in Penning-Malmberg traps has made the study of such plasmas possible in the laboratory.(R.G. Greaves, M.D. Tinkle and C.M. Surko, Phys. Plas.) 1 1439 (1994) In the first experiment of this type we studied a beam-plasma system by transmitting an electron beam through a positron plasma in a Penning trap.(R.G. Greaves and C.M. Surko, Phys. Rev. Lett.), 74 3846 (1995) These earlier measurements were obtained using a hot cathode electron source, for which the large beam energy spreads ( ~ 0.5 eV) made it impossible to explore the low energy regime of this beam-plasma system, where the strongest interaction occurs. We report new growth rate measurements obtained using a novel low-energy, cold (Δ E ≈ 0.05 eV) electron beam based on the extraction of electrons stored in a Penning trap.(S.J. Gilbert et al.), Appl. Phys. Lett., 70 1944 (1997). The measured growth rates for a transit time instability are found to be in excellent agreement with a cold fluid theory by D.H.E. Dubin over the range of accessible energies (0.1--3 eV).
Kovermann, J.; Stahl, A.; Mikhailichenko, A.A.; Scott, D.; Moortgat-Pick, G.A.; Gharibyan, V.; Pahl, P.; Poschl, R.; Schuler, K.P.; Laihem, K.; Riemann, S.; Schalicke, A.; Dollan, R.; Kolanoski, H.; Lohse, T.; Schweizer, T.; McDonald, K.T.; Batygin, Y.; Bharadwaj, V.; Bower, G.; Decker, F.J.; /SLAC /Tel Aviv U. /Tennessee U.
2011-11-14
A longitudinal polarized positron beam is foreseen for the international linear collider (ILC). A proof-of-principle experiment has been performed in the final focus test beam at SLAC to demonstrate the production of polarized positrons for implementation at the ILC. The E166 experiment uses a 1 m long helical undulator in a 46.6 GeV electron beam to produce a few MeV photons with a high degree of circular polarization. These photons are then converted in a thin target to generate longitudinally polarized e{sup +} and e{sup -}. The positron polarization is measured using a Compton transmission polarimeter. The data analysis has shown asymmetries in the expected vicinity of 3.4% and {approx}1% for photons and positrons respectively and the expected positron longitudinal polarization is covering a range from 50% to 90%. The full exploitation of the physics potential of an international linear collider (ILC) will require the development of polarized positron beams. Having both e{sup +} and e{sup -} beams polarized will provide new insight into structures of couplings and thus give access to physics beyond the standard model [1]. The concept for a polarized positron source is based on circularly polarized photon sources. These photons are then converted to longitudinally polarized e{sup +} and e{sup -} pairs. While in an experiment at KEK [1a], Compton backscattering is used [2], the E166 experiment uses a helical undulator to produce polarized photons. An undulator-based positron source for the ILC has been proposed in [3,4]. The proposed scheme for an ILC positron source is illustrated in figure 1. In this scheme, a 150 GeV electron beam passes through a 120 m long helical undulator to produce an intense photon beam with a high degree of circular polarization. These photons are converted in a thin target to e{sup +} e{sup -} pairs. The polarized positrons are then collected, pre-accelerated to the damping ring and injected to the main linac. The E166 experiment is
Uddin, M. J. Alam, M. S.; Mamun, A. A.
2015-06-15
A theoretical investigation is made on the positron-acoustic (PA) shock waves (SHWs) in an unmagnetized electron-positron-ion plasma containing immobile positive ions, cold mobile positrons, and hot positrons and electrons following the kappa (κ) distribution. The cold positron kinematic viscosity is taken into account, and the reductive perturbation method is used to derive the Burgers equation. It is found that the viscous force acting on cold mobile positron fluid is a source of dissipation and is responsible for the formation of the PA SHWs. It is also observed that the fundamental properties of the PA SHWs are significantly modified by the effects of different parameters associated with superthermal (κ distributed) hot positrons and electrons.
Many-body aspects of positron annihilation in the electron gas
NASA Astrophysics Data System (ADS)
Apaja, V.; Denk, S.; Krotscheck, E.
2003-11-01
We investigate positron annihilation in the electron gas as a case study for many-body theory, in particular, the Fermi-hypernetted-chain Euler-Lagrange (FHNC-EL) method. We examine several approximation schemes and show that one has to go up to the most sophisticated implementation of the theory available at the moment in order to get annihilation rates that agree reasonably well with experimental data. Even though there is basically just one number we look at, namely, the electron-positron pair-distribution function at zero distance, it is exactly this number that dictates how the full pair distribution behaves: in most cases, it falls off monotonously towards unity as the distance increases. Cases where the electron-positron pair distribution exhibits a dip are precursors to the formation of bound electron-positron pairs. The formation of electron-positron pairs is indicated by a divergence of the FHNC-EL equations; from this we can estimate the density regime where positrons must be localized. This occurs in our calculations in the range 9.4⩽rs⩽10, where rs is the dimensionless density parameter of the electron liquid.
Positron-electron decay of 28Si at an excitation energy of 50 MeV
NASA Astrophysics Data System (ADS)
Buda, A.; Bacelar, J. C.; Balanda, A.; van der Ploeg, H.; Sujkowski, Z.; van der Woude, A.
1993-03-01
The electron-position pair decay of 28Si at 50 MeV excitation produced by the isospin T=0 (α + 24Mg) and the mixed isospin T=0,1 (3He + 25Mg) reactions has been studied using a special designed Positron-Electron pair spectrometer PEPSI.
Veramendi, Gregory Francisco
2003-01-01
The authors present a measurement of the mass dependence of the forward-backward charge asymmetry for e^{+}e^{-} pairs resulting from γ*/Z decays with mass M_{ee} > 40 GeV/c^{2}. The Run II data sample consists of 72 pb^{-1} of data, which was collected by the CDF detector in $\\bar{p}$p collisions at √s = 1.96 TeV at the Fermilab Tevatron. The measurement is compared with predictions from the Standard Model.
NASA Astrophysics Data System (ADS)
Smith, Bryan R.
For the process e+e/sp-/rightarrow μ+/mu/sp- (nγ), the cross section and forward-backward charge asymmetry are measured at the highest ever center of mass energies which ranged from 130 to 183GeV. The data originates from 85pb-1 of integrated luminosity collected with the L3 detector at LEP. The measured muon pair cross section and forward-backward asymmetry agree with the Standard Model prediction with a χ SM2/N =.61 with 10 degrees of freedom. A mass limit on an additional heavy, neutral gauge boson of M Z' > 315GeV is set using muon pair production alone, rising to M Z' > 805GeV when all final states are considered. A search for an excited lepton decaying via /mu*/rightarrow/mu/gamma excludes such objects with electromagnetic coupling up to 183GeV. (Copies available exclusively from MIT Libraries, RM. 14- 0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.)
Shah, Asif; Mahmood, S.; Haque, Q.
2011-11-15
Electrostatic ion acoustic solitary waves are studied in a plasma system comprising of relativistic ions, kappa distributed electrons, and positrons. The increase in the relativistic streaming factor and positron and electron kappa parameters cause the soliton amplitude to thrive. However, the soliton amplitude diminishes as the positron concentration is increased in the system. Our results are general and may be helpful, in understanding nonlinear phenomena in the presence of kappa distibuted electrons, positrons, and relativistically streaming ions.
New generation electron-positron factories
NASA Astrophysics Data System (ADS)
Zobov, Mikhail
2011-09-01
In 2010 we celebrate 50 years since commissioning of the first particle storage ring ADA in Frascati (Italy) that also became the first electron-positron collider in 1964. After that date the particle colliders have increased their intensity, luminosity and energy by several orders of magnitude. Namely, because of the high stored beam currents and high rate of useful physics events (luminosity) the modern electron-positron colliders are called "factories". However, the fundamental physics has required luminosities by 1-2 orders of magnitudes higher with respect to those presently achieved. This task can be accomplished by designing a new generation of factories exploiting the potential of a new collision scheme based on the Crab Waist (CW) collision concept recently proposed and successfully tested at Frascati. In this paper we discuss the performance and limitations of the present generation electron-positron factories and give a brief overview of new ideas and collision schemes proposed for further collider luminosity increase. In more detail we describe the CW collision concept and the results of the crab waist collision tests in DAϕNE, the Italian ϕ-factory. Finally, we briefly describe most advanced projects of the next generation factories based on the CW concept: SuperB in Italy, SuperKEKB in Japan and SuperC-Tau in Russia.
Tuning laser produced electron-positron jets for lab-astrophysics experiment
Chen, Hui; Fiuza, F.; Hazi, A.; Kemp, A.; Link, A.; Pollock, B.; Marley, E.; Nagel, S. R.; Park, J.; Schneider, M.; Shepherd, R.; Tommasini, R.; Wilks, S. C.; Williams, G. J.; Barnak, D.; Chang, P-Y.; Fiksel, G.; Glebov, V.; Meyerhofer, D. D.; Myatt, J. F.; Stoeckel, C.; Nakai, M.; Arikawa, Y.; Azechi, H.; Fujioka, S.; Hosoda, H.; Kojima, S.; Miyanga, N.; Morita, T.; Moritaka, T.; Nagai, T.; Namimoto, T.; Nishimura, H.; Ozaki, T.; Sakawa, Y.; Takabe, H.; Zhang, Z.
2015-02-23
This paper reviews the experiments on the laser produced electron-positron jets using large laser facilities worldwide. The goal of the experiments was to optimize the parameter of the pair jets for their potential applications in laboratory-astrophysical experiment. Results on tuning the pair jet’s energy, number, emittance and magnetic collimation will be presented.
Electronic pairing in exotic superconductors
Cox, D.L. ); Maple, M.B. )
1995-02-01
Superconductivity in heavy-fermion materials and high T[sub c] cuprates may involve electronic pairing with unconventional symmetries and mechanisms. Although there has been no smoking-gun proof, numerous pieces of circumstantial evidence combined with heuristic theoretical arguments make a compelling case that these materials have pairs with exotic symmetry bound by nonphonon glue. 20 refs., 5 figs.
Positron annihilation lifetime spectroscopy at a superconducting electron accelerator
NASA Astrophysics Data System (ADS)
Wagner, A.; Anwand, W.; Attallah, A. G.; Dornberg, G.; Elsayed, M.; Enke, D.; Hussein, A. E. M.; Krause-Rehberg, R.; Liedke, M. O.; Potzger, K.; Trinh, T. T.
2017-01-01
The Helmholtz-Zentrum Dresden-Rossendorf operates a superconducting linear accelerator for electrons with energies up to 35 MeV and average beam currents up to 1.6 mA. The electron beam is employed for production of several secondary beams including X-rays from bremsstrahlung production, neutrons, and positrons. The secondary positron beam after moderation feeds the Monoenergetic Positron Source (MePS) where positron annihilation lifetime (PALS) and positron annihilation Doppler-broadening experiments in materials science are performed in parallel. The adjustable repetition rate of the continuous-wave electron beams allows matching of the pulse separation to the positron lifetime in the sample under study. The energy of the positron beam can be set between 0.5 keV and 20 keV to perform depth resolved defect spectroscopy and porosity studies especially for thin films.
ELECTRON-POSITRON FLOWS AROUND MAGNETARS
Beloborodov, Andrei M.
2013-11-10
The twisted magnetospheres of magnetars must sustain a persistent flow of electron-positron plasma. The flow dynamics is controlled by the radiation field around the hot neutron star. The problem of plasma motion in the self-consistent radiation field is solved using the method of virtual beams. The plasma and radiation exchange momentum via resonant scattering and self-organize into the 'radiatively locked' outflow with a well-defined, decreasing Lorentz factor. There is an extended zone around the magnetar where the plasma flow is ultra-relativistic; its Lorentz factor is self-regulated so that it can marginally scatter thermal photons. The flow becomes slow and opaque in an outer equatorial zone, where the decelerated plasma accumulates and annihilates; this region serves as a reflector for the thermal photons emitted by the neutron star. The e {sup ±} flow carries electric current, which is sustained by a moderate induced electric field. The electric field maintains a separation between the electron and positron velocities, against the will of the radiation field. The two-stream instability is then inevitable, and the induced turbulence can generate low-frequency emission. In particular, radio emission may escape around the magnetic dipole axis of the star. Most of the flow energy is converted to hard X-ray emission, which is examined in an accompanying paper.
Electron-Positron Flows around Magnetars
NASA Astrophysics Data System (ADS)
Beloborodov, Andrei M.
2013-11-01
The twisted magnetospheres of magnetars must sustain a persistent flow of electron-positron plasma. The flow dynamics is controlled by the radiation field around the hot neutron star. The problem of plasma motion in the self-consistent radiation field is solved using the method of virtual beams. The plasma and radiation exchange momentum via resonant scattering and self-organize into the "radiatively locked" outflow with a well-defined, decreasing Lorentz factor. There is an extended zone around the magnetar where the plasma flow is ultra-relativistic; its Lorentz factor is self-regulated so that it can marginally scatter thermal photons. The flow becomes slow and opaque in an outer equatorial zone, where the decelerated plasma accumulates and annihilates; this region serves as a reflector for the thermal photons emitted by the neutron star. The e ± flow carries electric current, which is sustained by a moderate induced electric field. The electric field maintains a separation between the electron and positron velocities, against the will of the radiation field. The two-stream instability is then inevitable, and the induced turbulence can generate low-frequency emission. In particular, radio emission may escape around the magnetic dipole axis of the star. Most of the flow energy is converted to hard X-ray emission, which is examined in an accompanying paper.
Optimization of positrons generation based on laser wakefield electron acceleration
NASA Astrophysics Data System (ADS)
Wu, Yuchi; Han, Dan; Zhang, Tiankui; Dong, Kegong; Zhu, Bin; Yan, Yonghong; Gu, Yuqiu
2016-08-01
Laser based positron represents a new particle source with short pulse duration and high charge density. Positron production based on laser wakefield electron acceleration (LWFA) has been investigated theoretically in this paper. Analytical expressions for positron spectra and yield have been obtained through a combination of LWFA and cascade shower theories. The maximum positron yield and corresponding converter thickness have been optimized as a function of driven laser power. Under the optimal condition, high energy (>100 MeV ) positron yield up to 5 ×1011 can be produced by high power femtosecond lasers at ELI-NP. The percentage of positrons shows that a quasineutral electron-positron jet can be generated by setting the converter thickness greater than 5 radiation lengths.
NASA Astrophysics Data System (ADS)
Bulanov, S. S.; Schroeder, C. B.; Esarey, E.; Leemans, W. P.
2013-06-01
The interaction of high-energy electrons, positrons, and photons with intense laser pulses is studied in head-on collision geometry. It is shown that electrons and/or positrons undergo a cascade-type process involving multiple emissions of photons. These photons can consequently convert into electron-positron pairs. As a result charged particles quickly lose their energy developing an exponentially decaying energy distribution, which suppresses the emission of high-energy photons, thus reducing the number of electron-positron pairs being generated. Therefore, this type of interaction suppresses the development of the electromagnetic avalanche-type discharge, i.e., the exponential growth of the number of electrons, positrons, and photons does not occur in the course of interaction. The suppression will occur when three-dimensional effects can be neglected in the transverse particle orbits, i.e., for sufficiently broad laser pulses with intensities that are not too extreme. The final distributions of electrons, positrons, and photons are calculated for the case of a high-energy e-beam interacting with a counterstreaming, short intense laser pulse. The energy loss of the e-beam, which requires a self-consistent quantum description, plays an important role in this process, as well as provides a clear experimental observable for the transition from the classical to quantum regime of interaction.
Polarized positrons and electrons at the linear collider
NASA Astrophysics Data System (ADS)
Moortgat-Pick, G.; Abe, T.; Alexander, G.; Ananthanarayan, B.; Babich, A. A.; Bharadwaj, V.; Barber, D.; Bartl, A.; Brachmann, A.; Chen, S.; Clarke, J.; Clendenin, J. E.; Dainton, J.; Desch, K.; Diehl, M.; Dobos, B.; Dorland, T.; Dreiner, H. K.; Eberl, H.; Ellis, J.; Flöttmann, K.; Fraas, H.; Franco-Sollova, F.; Franke, F.; Freitas, A.; Goodson, J.; Gray, J.; Han, A.; Heinemeyer, S.; Hesselbach, S.; Hirose, T.; Hohenwarter-Sodek, K.; Juste, A.; Kalinowski, J.; Kernreiter, T.; Kittel, O.; Kraml, S.; Langenfeld, U.; Majerotto, W.; Martinez, A.; Martyn, H.-U.; Mikhailichenko, A.; Milstene, C.; Menges, W.; Meyners, N.; Mönig, K.; Moffeit, K.; Moretti, S.; Nachtmann, O.; Nagel, F.; Nakanishi, T.; Nauenberg, U.; Nowak, H.; Omori, T.; Osland, P.; Pankov, A. A.; Paver, N.; Pitthan, R.; Pöschl, R.; Porod, W.; Proulx, J.; Richardson, P.; Riemann, S.; Rindani, S. D.; Rizzo, T. G.; Schälicke, A.; Schüler, P.; Schwanenberger, C.; Scott, D.; Sheppard, J.; Singh, R. K.; Sopczak, A.; Spiesberger, H.; Stahl, A.; Steiner, H.; Wagner, A.; Weber, A. M.; Weiglein, G.; Wilson, G. W.; Woods, M.; Zerwas, P.; Zhang, J.; Zomer, F.
2008-05-01
The proposed International Linear Collider (ILC) is well-suited for discovering physics beyond the Standard Model and for precisely unraveling the structure of the underlying physics. The physics return can be maximized by the use of polarized beams. This report shows the paramount role of polarized beams and summarizes the benefits obtained from polarizing the positron beam, as well as the electron beam. The physics case for this option is illustrated explicitly by analyzing reference reactions in different physics scenarios. The results show that positron polarization, combined with the clean experimental environment provided by the linear collider, allows to improve strongly the potential of searches for new particles and the identification of their dynamics, which opens the road to resolve shortcomings of the Standard Model. The report also presents an overview of possible designs for polarizing both beams at the ILC, as well as for measuring their polarization.
Pair Creation in QED-Strong Pulsed Laser Fields Interacting with Electron Beams
Sokolov, Igor V.; Naumova, Natalia M.; Nees, John A.; Mourou, Gerard A.
2010-11-05
QED effects are known to occur in a strong laser pulse interaction with a counterpropagating electron beam, among these effects being electron-positron pair creation. We discuss the range of laser pulse intensities of J{>=}5x10{sup 22} W/cm{sup 2} combined with electron beam energies of tens of GeV. In this regime multiple pairs may be generated from a single beam electron, some of the newborn particles being capable of further pair production. Radiation backreaction prevents avalanche development and limits pair creation. The system of integro-differential kinetic equations for electrons, positrons and {gamma} photons is derived and solved numerically.
Pair creation in QED-strong pulsed laser fields interacting with electron beams.
Sokolov, Igor V; Naumova, Natalia M; Nees, John A; Mourou, Gérard A
2010-11-05
QED effects are known to occur in a strong laser pulse interaction with a counterpropagating electron beam, among these effects being electron-positron pair creation. We discuss the range of laser pulse intensities of J≥5×10(22) W/cm2 combined with electron beam energies of tens of GeV. In this regime multiple pairs may be generated from a single beam electron, some of the newborn particles being capable of further pair production. Radiation backreaction prevents avalanche development and limits pair creation. The system of integro-differential kinetic equations for electrons, positrons and γ photons is derived and solved numerically.
Dynamics of the positron acoustic waves in electron-positron-ion magnetoplasmas
NASA Astrophysics Data System (ADS)
Ali, Rustam; Saha, Asit; Chatterjee, Prasanta
2017-01-01
Dynamics of the positron acoustic waves in electron-positron-ion (e-p-i) magnetoplasmas with κ-distributed hot electrons and positrons is investigated in the frameworks of the Kadomtsev-Petviashili (KP) and modified Kadomtsev-Petviashili (mKP) equations. Employing the reductive perturbation technique, the KP and mKP equations are derived. Using the bifurcation theory of planar dynamical systems, the positron acoustic solitary wave solutions, the kink and anti-kink wave solutions are obtained. Considering an external periodic perturbation in the electron-positron-ion magnetoplasmas, the perturbed KP and mKP equations are studied via some qualitative and quantitative approaches. To corroborate in the fact that the perturbed KP and mKP equations can indeed give rise to the quasiperiodic and chaotic motions, the phase plane plots, time series plots, and the Poincaré section are used. The quasiperiodic and developed chaos can be observed for the perturbed positron acoustic waves. The frequency (ω ) of the external periodic perturbation plays the role of the switching parameter in chaotic motions of the perturbed positron acoustic waves through quasiperiodic route to chaos. This work can be useful to understand the dynamics of nonlinear electromagnetic perturbations in space and laboratory plasmas consisting of κ-distributed hot electrons and positrons.
Investigation of Positron Moderator Materials for Electron-Linac-Based Slow Positron Beamlines
NASA Astrophysics Data System (ADS)
Suzuki, Ryoichi; Ohdaira, Toshiyuki; Uedono, Akira; Cho, Yang; Yoshida, Sadafumi; Ishida, Yuuki; Ohshima, Takeshi; Itoh, Hisayoshi; Chiwaki, Mitsukuni; Mikado, Tomohisa; Yamazaki, Tetsuo; Tanigawa, Shoichiro
1998-08-01
Positron re-emission properties were studied on moderator materials in order to improve the positron moderation system of electron-linac-based intense slow positron beamlines. The re-emitted positron fraction was measured on tungsten, SiC, GaN, SrTiO3, and hydrogen-terminated Si with a variable-energy pulsed positron beam. The results suggested that tungsten is the best material for the primary moderator of the positron beamlines while epitaxially grown n-type 6H SiC is the best material for the secondary moderator. Defect characterization by monoenergetic positron beams and surface characterization by Auger electron spectroscopy were carried out to clarify the mechanism of tungsten moderator degradation induced by high-energy electron irradiation. The characterization experiments revealed that the degradation is due to both radiation-induced vacancy clusters and surface carbon impurities. For the restoration of degraded tungsten moderators, oxygen treatment at ˜900°C is effective. Furthermore, it was found that oxygen at the tungsten surface inhibits positronium formation; as a result, it can increase the positron re-emission fraction.
Recent status of A Positron-Electron Experiment (APEX)
NASA Astrophysics Data System (ADS)
Saitoh, H.; Pedersen, T. S.; Hergenhahn, U.; Stenson, E. V.; Paschkowski, N.; Hugenschmidt, C.
2014-04-01
A project is underway to generate an electron-positron plasma by using the NEPOMUC positron source at the FRM-II facility combined with a multicell-type Penning trap (PAX) and a superconducting dipole magnetic field trap (APEX). In the APEX project, proof-of principle experiments are proposed for the development of efficient injection methods of positrons by using a small dipole magnetic field trap with a permanent magnet. Plans for the APEX project and its recent status are reported.
The stationary non-equilibrium plasma of cosmic-ray electrons and positrons
NASA Astrophysics Data System (ADS)
Tomaschitz, Roman
2016-06-01
The statistical properties of the two-component plasma of cosmic-ray electrons and positrons measured by the AMS-02 experiment on the International Space Station and the HESS array of imaging atmospheric Cherenkov telescopes are analyzed. Stationary non-equilibrium distributions defining the relativistic electron-positron plasma are derived semi-empirically by performing spectral fits to the flux data and reconstructing the spectral number densities of the electronic and positronic components in phase space. These distributions are relativistic power-law densities with exponential cutoff, admitting an extensive entropy variable and converging to the Maxwell-Boltzmann or Fermi-Dirac distributions in the non-relativistic limit. Cosmic-ray electrons and positrons constitute a classical (low-density high-temperature) plasma due to the low fugacity in the quantized partition function. The positron fraction is assembled from the flux densities inferred from least-squares fits to the electron and positron spectra and is subjected to test by comparing with the AMS-02 flux ratio measured in the GeV interval. The calculated positron fraction extends to TeV energies, predicting a broad spectral peak at about 1 TeV followed by exponential decay.
Electrons and positrons from expanding supernova envelopes in dense clouds
NASA Technical Reports Server (NTRS)
Stephens, S. A.
1985-01-01
If antiprotons in cosmic rays are produced as secondary particles in sources, it is expected that positrons are also created by the same process. The interstellar spectra of positrons and electrons are calculated by taking into account such sources. Spectra are then compared with observations.
Fragmentation production of charmed hadrons in electron-positron annihilation
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.
Langmuir oscillations in a nonthermal nonextensive electron-positron plasma
NASA Astrophysics Data System (ADS)
El-Taibany, W. F.; Zedan, N. A.
2017-02-01
The high-frequency Langmuir-type oscillations in a pure pair plasma are studied using Vlasov-Poisson's equations in the presence of hybrid nonthermal nonextensive distributed species. The characteristics of the Langmuir oscillations, Landau damping, and growing unstable modes in a nonthermal nonextensive electron-positron (EP) plasma are remarkably modified. It is found that the phase velocity of the Langmuir waves increases by decreasing (increasing) the value of nonextensive (nonthermal) parameter, q ( α). In particular, depending on the degree of nonthermality and nonextensivity, both damping and growing oscillations are predicted in the proposed EP plasma. It is seen that the Langmuir waves suffer from Landau damping in two different q regions. Furthermore, the mechanism that leads to unstable modes is established in the context of the nonthermal nonextensive formalism, yet the damping mechanism is the same developed by Landau. The present study is useful in the regions where such mixed distributions in space or laboratory plasmas exist.
Positron-electron autocorrelation function study of E-center in silicon
NASA Astrophysics Data System (ADS)
Ho, K. F.; Ching, H. M.; Beling, C. D.; Fung, S.; Ng, K. P.; Biasini, M.; Ferro, G.; Gong, M.
2003-11-01
Two-dimensional angular correlation of annihilation radiation (2D-ACAR) spectra have been taken for 1019cm-3 phosphorus-doped Si in the as-grown state after having been subjected to 1.8 MeV electron fluences of 1×1018 and 2×1018 cm-2. Positron annihilation lifetime spectroscopy confirms, in accordance with previous works, that positrons are saturation trapping into (VSi:P) pair defect (E-center) monovacancy sites in the electron irradiated samples. In the as-grown case, the positron-electron autocorrelation functions along the [111] and [1-10] directions, obtained through Fourier transformation of the 2D-ACAR data, reveal zero-crossings that deviate only slightly from the lattice points, in a manner consistent with positron-electron correlation effects. Conversely, in the spectra of the irradiated samples, the zero-crossing points are observed to move outward further by between 0.15 and 0.50 Å. This displacement is associated with positron annihilation with electrons in localized orbitals at the defect site. An attempt is made to extract just the component of the defect's positron-electron autocorrelation function that relates to the localized defect orbitals. In doing this features are found that correspond to the expected atomic positions at the vacancy defect site suggesting that this real-space function may provide a convenient means for obtaining a mapping of localized orbitals. The observed approximate separability of positron and electron wave-function autocorrelates leads to an estimate of 0.22 eV for the positron binding energy to the E-center.
Andreev, Pavel A; Iqbal, Z
2016-03-01
We consider the separate spin evolution of electrons and positrons in electron-positron and electron-positron-ion plasmas. We consider the oblique propagating longitudinal waves in these systems. Working in a regime of high-density n(0) ∼ 10(27) cm(-3) and high-magnetic-field B(0)=10(10) G, we report the presence of the spin-electron acoustic waves and their dispersion dependencies. In electron-positron plasmas, similarly to the electron-ion plasmas, we find one spin-electron acoustic wave (SEAW) at the propagation parallel or perpendicular to the external field and two spin-electron acoustic waves at the oblique propagation. At the parallel or perpendicular propagation of the longitudinal waves in electron-positron-ion plasmas, we find four branches: the Langmuir wave, the positron-acoustic wave, and a pair of waves having spin nature, they are the SEAW and the wave discovered in this paper, called the spin-electron-positron acoustic wave (SEPAW). At the oblique propagation we find eight longitudinal waves: the Langmuir wave, the Trivelpiece--Gould wave, a pair of positron-acoustic waves, a pair of SEAWs, and a pair of SEPAWs. Thus, for the first time, we report the existence of the second positron-acoustic wave existing at the oblique propagation and the existence of SEPAWs.
NASA Astrophysics Data System (ADS)
Abdikian, A.; Mahmood, S.
2016-12-01
The obliquely nonlinear acoustic solitary propagation in a relativistically quantum magnetized electron-positron (e-p) plasma in the presence of the external magnetic field as well as the stationary ions for neutralizing the plasma background was studied. By considering the dynamic of the fluid e-p quantum and by using the quantum hydrodynamics model and the standard reductive perturbation technique, the Zakharov-Kuznetsov (ZK) equation is derived for small but finite amplitude waves and the solitary wave solution for the parameters relevant to dense astrophysical objects such as white dwarf stars is obtained. The numerical results show that the relativistic effects lead to propagate the electrostatic bell shape structures in quantum e-p plasmas like those in classical pair-ion or pair species for relativistic plasmas. It is also observed that by increasing the relativistic effects, the amplitude and width of the e-p acoustic solitary wave will decrease. In addition, the wave amplitude increases as positron density decreases in magnetized e-p plasmas. It is indicated that by increasing the strength of the magnetic field, the width of the soliton reduces and it becomes sharper. At the end, we have analytically and numerically shown that the pulse soliton solution of the ZK equation is unstable and have traced the dependence of the instability growth rate on electron density. It is found that by considering the relativistic pressure, the instability of the soliton pulse can be reduced. The results can be useful to study the obliquely nonlinear propagation of small amplitude localized structures in magnetized quantum e-p plasmas and be applicable to understand the particle and energy transport mechanism in compact stars such as white dwarfs, where the effects of relativistic electron degeneracy become important.
Scattering of positrons and electrons by alkali atoms
NASA Technical Reports Server (NTRS)
Stein, T. S.; Kauppila, W. E.; Kwan, C. K.; Lukaszew, R. A.; Parikh, S. P.; Wan, Y. J.; Zhou, S.; Dababneh, M. S.
1990-01-01
Absolute total scattering cross sections (Q sub T's) were measured for positrons and electrons colliding with sodium, potassium, and rubidium in the 1 to 102 eV range, using the same apparatus and experimental approach (a beam transmission technique) for both projectiles. The present results for positron-sodium and -rubidium collisions represent the first Q sub T measurements reported for these collision systems. Features which distinguish the present comparisons between positron- and electron-alkali atom Q sub T's from those for other atoms and molecules (room-temperature gases) which have been used as targets for positrons and electrons are the proximity of the corresponding positron- and electron-alkali atom Q sub T's over the entire energy range of overlap, with an indication of a merging or near-merging of the corresponding positron and electron Q sub T's near (and above) the relatively low energy of about 40 eV, and a general tendency for the positron-alkali atom Q sub T's to be higher than the corresponding electron values as the projectile energy is decreased below about 40 eV.
NASA Astrophysics Data System (ADS)
Saha, Asit
2017-03-01
Positron acoustic shock waves (PASHWs) in unmagnetized electron-positron-ion (e-p-i) plasmas consisting of mobile cold positrons, immobile positive ions, q-nonextensive distributed electrons, and hot positrons are studied. The cold positron kinematic viscosity is considered and the reductive perturbation technique is used to derive the Burgers equation. Applying traveling wave transformation, the Burgers equation is transformed to a one dimensional dynamical system. All possible vector fields corresponding to the dynamical system are presented. We have analyzed the dynamical system with the help of potential energy, which helps to identify the stability and instability of the equilibrium points. It is found that the viscous force acting on cold mobile positron fluid is a source of dissipation and is responsible for the formation of the PASHWs. Furthermore, fully nonlinear arbitrary amplitude positron acoustic waves are also studied applying the theory of planar dynamical systems. It is also observed that the fundamental features of the small amplitude and arbitrary amplitude PASHWs are significantly affected by the effect of the physical parameters q e , q h , μ e , μ h , σ , η , and U. This work can be useful to understand the qualitative changes in the dynamics of nonlinear small amplitude and fully nonlinear arbitrary amplitude PASHWs in solar wind, ionosphere, lower part of magnetosphere, and auroral acceleration regions.
NASA Astrophysics Data System (ADS)
Hashemzadeh, M.; Niknam, A. R.
2017-06-01
Nonlinear space charge dynamics and modulational instability in the interaction between ultrashort, intense laser pulses and electron-positron pair plasmas are investigated taking into account the relativistic ponderomotive force and the relativistic mass of electrons and positrons. By coupling Maxwell's equations and hydrodynamic model, the electron and positron density distributions and the dispersion relation for the modulational instability are obtained. Moreover, two coupled nonlinear equations for the scalar and vector potentials are derived and numerically solved. The results show that the growth rate of instability increases with the decrease in the electron and positron temperatures. Moreover, it is shown that when the temperatures of electrons and positrons are not equal to each other, the profiles of scalar potential are similar to bright-like or dark-like solitons.
NASA Technical Reports Server (NTRS)
Hoshino, Masahiro; Arons, Jonathan
1991-01-01
A new process of the preferential strong heating of positrons through the ion synchrotron maser instability in positron-electron-proton magnetized plasmas is investigated using particle-in-cell simulations. It is shown that the positrons form a nonthermal power-law-like energy distribution via their gyroresonant interaction with the extraordinary modes emitted by the ions. It is noted that this process may be of significance in connection with the shock excitation of nonthermal synchrotron radiation from astrophysical systems powered by relativistic outflows from compact central objects, e.g., supernova remnants powered by pulsars and jets from active galactic nuclei.
Extracting the Size of the Cosmic Electron-Positron Anomaly
NASA Astrophysics Data System (ADS)
Auchettl, Katie; Balazs, C.
2011-09-01
Over the last few decades, numerous observations have hinted at an excess of high energy positrons in our locality. The most recent of these experiments has been the positron fraction measured by the PAMELA satellite and the electron plus positron spectrum as measured by the Fermi-LAT satellite. Since the release of these measurements, there have been a plethora of papers where authors invoke new physics ranging from, modification of the cosmic ray propagation, supernova remnants and dark matter annihilation. Using a Bayesian likelihood analysis, we isolate the anomalous contribution of the cosmic electron-positron flux. A significant tension was found between the electron positron related data and non-electron-positron cosmic ray fluxes. Using 219 recent cosmic ray datum, we extracted the preferred values of the selected cosmic ray propagation parameters from the non-electron-positron related measurements. Based on these parameter values we calculated background predictions with uncertainties for PAMELA and Fermi-LAT. We found a deviation between the PAMELA and Fermi-LAT data and the predicted background even when uncertainties, including systematics, were taken into account. Interpreting this as a hint of new physics, we subtracted the background from the data extracting the size, shape and uncertainty of the anomalous contribution in a model independent fashion. We briefly compared the extracted signal to some theoretical results predicting such an anomaly.
Study of electron-positron interactions
Abashian, A.; Gotow, K.; Philonen, L.
1990-09-15
For the past seven years, this group has been interested in the study of tests of the Standard Model of Electroweak interactions. The program has centered about the AMY experiment which examines the nature of the final state products in electron-positron collisions in the center of mass energy range near 60 GeV. Results of these measurements have shown a remarkable consistency with the predictions of the minimal model of 3 quark and lepton generations and single charged and neutral intermediate bosons. No new particles or excited states have been observed nor has any evidence for departures in cross sections or angular asymmetries from expectations been observed. These conclusions have been even more firmly established by the higher energy results from the LEP and SLC colliders at center of mass energies of about 90 GeV. Our focus is shifting to the neutrino as a probe to electroweak interactions. The relative merit of attempting to observe neutrinos from point sources versus observing neutrinos generally is not easy to predict. The improved ability to interpret is offset by the probably episodic nature of the emission and irreproducibility of the results. In this phase of development, it is best to be sensitive to both sources of neutrinos. As a second phase of our program at Virginia Tech, we are studying the feasibility of detecting cosmic ray neutrinos in a proposed experiment which we have called NOVA. the results of the test setup will be instrumental in developing an optimum design. A third program we are involved in is the MEGA experiment at Los Alamos, an experiment to place a limit on the rate of muon decay to electron plus photon which is forbidden by the Standard Model.
Intense positron beam as a source for production of electron-positron plasma
NASA Astrophysics Data System (ADS)
Stoneking, M. R.; Horn-Stanja, J.; Stenson, E. V.; Pedersen, T. Sunn; Saitoh, H.; Hergenhahn, U.; Niemann, H.; Paschkowski, N.; Hugenschmidt, C.; Piochacz, C.
2016-10-01
We aim to produce magnetically confined, short Debye length electron-positron plasma and test predicted properties for such systems. A first challenge is obtaining large numbers of positrons; a table-top experiment (system size 5 cm) with a temperature less than 5 eV requires about 1010 positrons to have more than 10 Debye lengths in the system. The NEPOMUC facility at the FRM II research reactor in Germany is one of the world's most intense positron sources. We report on characterization (using a retarding field energy analyzer with magnetic field gradient) of the NEPOMUC beam as delivered to the open beam port at various beam energies and in both the re-moderated and primary beam configurations in order to design optimal trapping (and accumulation) schemes for production of electron-positron plasma. The intensity of the re-moderated (primary) beam is in the range 2 -3 x 107 /s (1 - 5 x 108 /s). The re-moderated beam is currently the most promising for direct injection and confinement experiments; it has a parallel energy spread of 15 - 35% and the transverse energy spread is 6 - 15% of the parallel energy. We report on the implications for injection and trapping in a dipole magnetic field as well as plans for beam development, in situ re-moderation, and accumulation. We also report results demonstrating a difference in phosphor luminescent response to low energy positrons versus electrons.
The Calibration of the PEPPo Polarimeter for Electrons and Positrons
Adeyemi, Adeleke Hakeem; Voutier, Eric J-.M.
2013-06-01
The PEPPo (Polarized Electrons for Polarized Positrons) experiment at Jefferson Laboratory investigated the polarization transfer from longitudinally polarized electrons to longitudinally polarized positrons, with the aim of developing this technology for a low energy (~MeV) polarized positron source. Polarization of the positrons was measured by means of a Compton transmission polarimeter where incoming positrons transfer their polarization into circularly polarized photons that were subsequently analyzed by a thick polarized iron target. The measurement of the transmitted photon flux with respect to the orientation of the target polarization (+-) or the helicity (+-) of the incoming leptons provided the measurement of their polarization. Similar measurements with a known electron beam were also performed for calibration purposes. This presentation will describe the apparatus and calibrations performed at the injector at the Jefferson Laboratory to measure positron polarization in the momentum range 3.2-6.2 MeV/c, specifically to quantify the positron analyzing power from electron experimental data measured over a comparable momentum range.
Positron trapping at vacancies in electron-irradiated Si at low temperatures
Maekinen, J.; Corbel, C.; Hautojaervi, P.; Moser, P.; Pierre, F.
1989-05-15
Experimental results on positron trapping at vacancies in electron-irradiated silicon are presented. The positron lifetimes 273 +- 3 and 248 +- 2 ps in pure Si and heavily-phosphorus-doped Si ((P) = 10/sup 20/ cm/sup -3/) are assigned to a negative monovacancy V/sup -/ and a negative vacancy-phosphorus pair (V-P)/sup -/, respectively. In pure Si, positron trapping displays a strong negative temperature dependence, and the specific trapping rate reaches very large values (10/sup 17//sup --/10/sup 18/ s/sup -1/) at low temperatures. In Si:P the trapping rate is independent of temperature. These different temperature behaviors are attributed to different positron-trapping mechanisms, a cascade of one-phonon transitions in pure Si, and an Auger process in Si:P.
Dipole configuration for confinement of positrons and electron-positron plasma
NASA Astrophysics Data System (ADS)
Stenson, E. V.; Saitoh, H.; Horn-Stanja, J.; Hergenhahn, U.; Paschkowski, N.; Sunn Pedersen, T.; Stoneking, M. R.; Dickmann, M.; Singer, M.; Vohburger, S.; Hugenschmidt, C.; Schweikhard, L.; Danielson, J. R.; Surko, C. M.
2016-10-01
Laboratory creation and confinement of electron-positron plasmas, which are expected to exhibit atypical plasma physics characteristics, would enable tests of many theory and simulation predictions (e.g., the stabilization of anomalous transport mechanisms). This is the goal of APEX/PAX (A Positron-Electron eXperiment/Positron Accumulation eXperiment). Following demonstration of efficient (38%) E ×B injection and subsequent confinement (τ = 3-5 ms) of cold positrons in a dipole magnetic field, the system is undergoing upgrades from a supported permanent magnet to a supported HTSC (high-temperature superconductor) coil, then to a levitated HTSC coil suitable for the simultaneous confinement of electrons and positrons. This contribution will report on the design and testing of the new systems and subsystems (e.g., for cooling, excitation, and levitation) and, if available, on results of upcoming experiments using a ``rotating wall'' to generate inward particle flux deeper into the confinement region. on behalf of the APEX/PAX team and collaborators.
New fast beam profile monitor for electron-positron colliders
Bogomyagkov, A. V.; Gurko, V. F.; Zhuravlev, A. N.; Zubarev, P. V.; Kiselev, V. A.; Meshkov, O. I.; Muchnoi, N. Yu.; Selivanov, A. N.; Smaluk, V. V.; Khilchenko, A. D.
2007-04-15
A new fast beam profile monitor has been developed at the Budker Institute of Nuclear Physics. This monitor is based on the Hamamatsu multianode photomultiplier with 16 anode strips and provides turn-by-turn measurement of the transverse beam profile. The device is equipped with an internal memory, which has enough capacity to store 131 072 samples of the beam profile. The dynamic range of the beam profile monitor allows us to study turn-by-turn beam dynamics within the bunch charge range from 1 pC up to 10 nC. Using this instrument, we have investigated at the VEPP-4M electron-positron collider a number of beam dynamics effects which cannot be observed by other beam diagnostics tools.
Positron/Electron Annihilation via the Two-Photon Pathway
NASA Astrophysics Data System (ADS)
Gauthier, Isabelle
When a positron/electron pair annihilate via the two-photon pathway, the emitted photons are momentum correlated. This correlation ensures that they move along a straight line path in opposite directions. An experiment performed in 2004 by Dr. V.D. Irby measured the time interval between detection of the photons. He observed a decay in the number of counts with increasing detection time interval, which he described using a Lorentzian, the line width of which at full-width half-maximum is measured to be 120ps. The data collected by Irby is interesting because current theory predicts that because the source is so localized (the effective source width used by Irby is safely within 5rnrn) the photons should be detected within a time interval of Deltat=d/c where d is the thickness of the source. This time interval corresponds to 17ps. This thesis fits the results to an exponential, and shows that this exponentially decaying nature of the coincidence time interval is characteristic of the entanglement of the two photons. We find that the wavefunctions of the photons decoheres in space according to how long the particle pair took to decay (which is exponential), and that the probability of simultaneous detection depends on the exponential of the product of the lifetime of positronium and the detection time interval.
Dense GeV electron–positron pairs generated by lasers in near-critical-density plasmas
Zhu, Xing-Long; Yu, Tong-Pu; Sheng, Zheng-Ming; Yin, Yan; Turcu, Ion Cristian Edmond; Pukhov, Alexander
2016-01-01
Pair production can be triggered by high-intensity lasers via the Breit–Wheeler process. However, the straightforward laser–laser colliding for copious numbers of pair creation requires light intensities several orders of magnitude higher than possible with the ongoing laser facilities. Despite the numerous proposed approaches, creating high-energy-density pair plasmas in laboratories is still challenging. Here we present an all-optical scheme for overdense pair production by two counter-propagating lasers irradiating near-critical-density plasmas at only ∼1022 W cm−2. In this scheme, bright γ-rays are generated by radiation-trapped electrons oscillating in the laser fields. The dense γ-photons then collide with the focused counter-propagating lasers to initiate the multi-photon Breit–Wheeler process. Particle-in-cell simulations indicate that one may generate a high-yield (1.05 × 1011) overdense (4 × 1022 cm−3) GeV positron beam using 10 PW scale lasers. Such a bright pair source has many practical applications and could be basis for future compact high-luminosity electron–positron colliders. PMID:27966530
Anisotropies in the flux of cosmic ray electrons and positrons
NASA Astrophysics Data System (ADS)
Manconi, S.; Di Mauro, M.; Donato, F.
2017-05-01
High energy cosmic ray electrons and positrons probe the local properties of our galaxy. In fact, regardless of the production mechanism, electromagnetic energy losses limit the typical propagation scale of GeV-TeV electrons and positrons to a few kpc. In the diffusion model, the presence of nearby and dominant sources may produce an observable dipole anisotropy in the cosmic ray fluxes. We present a detailed study on the role of anisotropies from nearby sources in the interpretation of present cosmic ray electron and positrons fluxes. Predictions for the dipole anisotropy from known astrophysical sources as Supernova Remnants (SNRs) and pulsars taken from the Green and the Australia Telescope National Facility (ATNF) catalogs are shown. The results are obtained from models compatible with the most recent AMS-02 data on electrons and positrons fluxes. In particular, anisotropies for single sources as well as for a distribution of catalog sources are discussed. We compare our results with current anisotropy upper limits from the Fermi-LAT and PAMELA experiments, showing that the search of anisotropy in the electron and positron fluxes represents a complementary tool to inspect the properties of close SNRs, as for example the Vela SNR.
Interpretation of AMS-02 electrons and positrons data
Mauro, M. Di; Donato, F.; Fornengo, N.; Vittino, A.; Lineros, R. E-mail: donato@to.infn.it E-mail: rlineros@ific.uv.es
2014-04-01
We perform a combined analysis of the recent AMS-02 data on electrons, positrons, electrons plus positrons and positron fraction, in a self-consistent framework where we realize a theoretical modeling of all the astrophysical components that can contribute to the observed fluxes in the whole energy range. The primary electron contribution is modeled through the sum of an average flux from distant sources and the fluxes from the local supernova remnants in the Green catalog. The secondary electron and positron fluxes originate from interactions on the interstellar medium of primary cosmic rays, for which we derive a novel determination by using AMS-02 proton and helium data. Primary positrons and electrons from pulsar wind nebulae in the ATNF catalog are included and studied in terms of their most significant (while loosely known) properties and under different assumptions (average contribution from the whole catalog, single dominant pulsar, a few dominant pulsars). We obtain a remarkable agreement between our various modeling and the AMS-02 data for all types of analysis, demonstrating that the whole AMS-02 leptonic data admit a self-consistent interpretation in terms of astrophysical contributions.
Gamma-induced Positron Spectroscopy (GiPS) at a superconducting electron linear accelerator
NASA Astrophysics Data System (ADS)
Butterling, Maik; Anwand, Wolfgang; Cowan, Thomas E.; Hartmann, Andreas; Jungmann, Marco; Krause-Rehberg, Reinhard; Krille, Arnold; Wagner, Andreas
2011-11-01
A new and unique setup for Positron Annihilation Spectroscopy has been established and optimized at the superconducting linear electron accelerator ELBE at Helmholtz-Zentrum Dresden-Rossendorf (Germany). The intense, pulsed (26 MHz) photon source (bremsstrahlung with energies up to 16 MeV) is used to generate positrons by means of pair production throughout the entire sample volume. Due to the very short gamma bunches (< 5 ps temporal length), the facility for Gamma-induced Positron Spectroscopy (GiPS) is suitable for positron lifetime spectroscopy using the accelerator's radiofrequency as time reference. Positron lifetime and Doppler broadening Spectroscopy are employed by a coincident measurement (Age-Momentum Correlation) of the time-of-arrival and energy of the annihilation photons which in turn significantly reduces the background of scattered photons resulting in spectra with high signal to background ratios. Simulations of the setup using the GEANT4 framework have been performed to yield optimum positron generation rates for various sample materials and improved background conditions.
Saha, Asit E-mail: prasantachatterjee1@rediffmail.com; Pal, Nikhil; Chatterjee, Prasanta E-mail: prasantachatterjee1@rediffmail.com
2014-10-15
The dynamic behavior of ion acoustic waves in electron-positron-ion magnetoplasmas with superthermal electrons and positrons has been investigated in the framework of perturbed and non-perturbed Kadomtsev-Petviashili (KP) equations. Applying the reductive perturbation technique, we have derived the KP equation in electron-positron-ion magnetoplasma with kappa distributed electrons and positrons. Bifurcations of ion acoustic traveling waves of the KP equation are presented. Using the bifurcation theory of planar dynamical systems, the existence of the solitary wave solutions and the periodic traveling wave solutions has been established. Two exact solutions of these waves have been derived depending on the system parameters. Then, using the Hirota's direct method, we have obtained two-soliton and three-soliton solutions of the KP equation. The effect of the spectral index κ on propagations of the two-soliton and the three-soliton has been shown. Considering an external periodic perturbation, we have presented the quasi periodic behavior of ion acoustic waves in electron-positron-ion magnetoplasmas.
Timelike Virtual Compton Scattering from Electron-Positron Radiative Annihilation
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.
Timelike Virtual Compton Scattering from Electron-Positron Radiative Annihilation
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.
Generation of neutral and high-density electron–positron pair plasmas in the laboratory
Sarri, G.; Poder, K.; Cole, J. M.; Schumaker, W.; Di Piazza, A.; Reville, B.; Dzelzainis, T.; Doria, D.; Gizzi, L. A.; Grittani, G.; Kar, S.; Keitel, C. H.; Krushelnick, K.; Kuschel, S.; Mangles, S. P. D.; Najmudin, Z.; Shukla, N.; Silva, L. O.; Symes, D.; Thomas, A. G. R.; Vargas, M.; Vieira, J.; Zepf, M.
2015-01-01
Electron–positron pair plasmas represent a unique state of matter, whereby there exists an intrinsic and complete symmetry between negatively charged (matter) and positively charged (antimatter) particles. These plasmas play a fundamental role in the dynamics of ultra-massive astrophysical objects and are believed to be associated with the emission of ultra-bright gamma-ray bursts. Despite extensive theoretical modelling, our knowledge of this state of matter is still speculative, owing to the extreme difficulty in recreating neutral matter–antimatter plasmas in the laboratory. Here we show that, by using a compact laser-driven setup, ion-free electron–positron plasmas with unique characteristics can be produced. Their charge neutrality (same amount of matter and antimatter), high-density and small divergence finally open up the possibility of studying electron–positron plasmas in controlled laboratory experiments. PMID:25903920
Alam, M S; Uddin, M J; Masud, M M; Mamun, A A
2014-09-01
Positron-acoustic (PA) solitary waves (SWs) and double layers (DLs) in four-component plasmas consisting of immobile positive ions, mobile cold positrons, and superthermal (kappa distributed) hot positrons and electrons are investigated both numerically and analytically by deriving Korteweg-de Vries (K-dV), modified K-dV (mK-dV), and Gardner equations along with their DLs solutions using the reductive perturbation method. It is examined that depending on the plasma parameters, the K-dV SWs, Gardner SWs, and DLs support either compressive or rarefactive structures, whereas mK-dV SWs support only compressive structure. It is also found that the presence of superthermal (kappa distributed) hot positrons and hot electrons significantly modify the basic features of PA SWs as well as PA DLs. Besides, the critical number density ratio of hot positrons and cold positrons play an important role in the polarity of PA SWs and DLs. The implications of our results in different space as well as laboratory plasma environments are briefly discussed.
NASA Astrophysics Data System (ADS)
Feng, Lei; Yang, Rui-Zhi; He, Hao-Ning; Dong, Tie-Kuang; Fan, Yi-Zhong; Chang, Jin
2014-01-01
The data collected by ATIC, CREAM and PAMELA all display remarkable cosmic ray nuclei spectrum hardening above the magnetic rigidity ∼240 GV. One natural speculation is that the primary electron spectrum also gets hardened (possibly at ∼80 GV) and the hardening partly accounts for the electron/positron total spectrum excess discovered by ATIC, HESS and Fermi-LAT. If it is the case, the increasing behavior of the subsequent positron-to-electron ratio will get flattened and the spectrum hardening should be taken into account in the joint fit of the electron/positron data otherwise the inferred parameters will be biased. Our joint fits of the latest AMS-02 positron fraction data together with the PAMELA/Fermi-LAT electron/positron spectrum data suggest that the primary electron spectrum hardening is needed in most though not all modelings. The bounds on dark matter models have also been investigated. In the presence of spectrum hardening of primary electrons, the amount of dark-matter-originated electron/positron pairs needed in the modeling is smaller. Even with such a modification, the annihilation channel χχ→μ+μ- has been tightly constrained by the Fermi-LAT Galactic diffuse emission data. The decay channel χ→μ+μ- is found to be viable.
NASA Astrophysics Data System (ADS)
Zhang, Wen-Shuai; Gu, Bing-Chuan; Han, Xiao-Xi; Liu, Jian-Dang; Ye, Bang-Jiao
2015-10-01
We make a gradient correction to a new local density approximation form of positron-electron correlation. The positron lifetimes and affinities are then probed by using these two approximation forms based on three electronic-structure calculation methods, including the full-potential linearized augmented plane wave (FLAPW) plus local orbitals approach, the atomic superposition (ATSUP) approach, and the projector augmented wave (PAW) approach. The differences between calculated lifetimes using the FLAPW and ATSUP methods are clearly interpreted in the view of positron and electron transfers. We further find that a well-implemented PAW method can give near-perfect agreement on both the positron lifetimes and affinities with the FLAPW method, and the competitiveness of the ATSUP method against the FLAPW/PAW method is reduced within the best calculations. By comparing with the experimental data, the new introduced gradient corrected correlation form is proved to be competitive for positron lifetime and affinity calculations. Project supported by the National Natural Science Foundation of China (Grant Nos. 11175171 and 11105139).
Plasma Focusing of High Energy Density Electron and Positron Beams
Ng, Johnny S.T.
2000-10-09
We present results from the SLAC E-150 experiment on plasma focusing of high energy density electron and, for the first time, positron beams. We also present results on plasma lens-induced synchrotron radiation, longitudinal dynamics of plasma focusing, and laser- and beam-plasma interactions.
Simulation of tail distributions in electron-positron circular colliders
Irwin, J.
1992-02-01
In addition to the Gaussian shaped core region, particle bunches in electron-positron circular colliders have a rarefied halo region of importance in determining beam lifetimes and backgrounds in particle detectors. A method is described which allows simulation of halo particle distributions.
Simulation of tail distributions in electron-positron circular colliders
Irwin, J.
1992-02-01
In addition to the Gaussian shaped core region, particle bunches in electron-positron circular colliders have a rarefied halo region of importance in determining beam lifetimes and backgrounds in particle detectors. A method is described which allows simulation of halo particle distributions.
Statistical correlation between atomic electron pairs
NASA Astrophysics Data System (ADS)
Sagar, Robin P.; Laguna, Humberto G.; Guevara, Nicolais L.
2011-10-01
The statistical correlation between a pair of electrons in Hartree-Fock orbitals is measured by mutual information and studied in position and in momentum space. We show that there are same- and opposite-spin orbital pairs where the correlation is larger in momentum space. Among these are opposite-spin valence shell pairs where the correlation arises from the indistinguishability of electron spins.
PREFACE: XV International Workshop on Low Energy Positron and Positronium Physics
NASA Astrophysics Data System (ADS)
Campeanu, R. I.; Darewych, J. W.; Stauffer, A. D.
2010-01-01
This volume of Journal of Physics: Conference Series contains the Proceedings of the XV International Workshop on Low Energy Positron and Positronium Physics, which was held at York University, Toronto, Canada, between 29 July and 1 August 2009. This Workshop was one of the official satellites of the XXVI International Conference on Photonic, Electronic and Atomic Collisions, held at Kalamazoo, MI, USA between 22 and 28 July 2009. Our Workshop was run in parallel with the XVI International Conference on Electron-Molecule Collisions and Swarms, enabling delegates to select talks from either meeting. The proceedings of the XVI International Conference on Electron-Molecule Collisions and Swarms are being published in a separate volume of Journal of Physics: Conference Series. The combined attendance at the two meetings was 110, from 19 countries, with interest being roughly split between the two areas. There were 5 plenary lectures addressed to all participants and on the Positron Workshop side there were 20 invited talks and 40 posters presented in two poster sessions. The subjects covered antihydrogen, positron collisions with atoms and molecules, annihilation, bound and resonant states, positronium and positronium negative ion, plasmas and swarms. The talks and posters highlighted the vigour of the field and underlined the impressive new developments now in progress and which promise to transform the subject. The next Workshop of this biennial series of meetings will be held in July 2011 at Maynooth University in Ireland. R I Campeanu J W Darewych A D Stauffer Guest Editors
Production of Highly Polarized Positrons Using Polarized Electrons at MeV Energies
Abbott, D.; Adderley, P.; Adeyemi, A.; Aguilera, P.; Ali, M.; Areti, H.; Baylac, M.; Benesch, J.; Bosson, G.; Cade, B.; Camsonne, A.; Cardman, L. S.; Clark, J.; Cole, P.; Covert, S.; Cuevas, C.; Dadoun, O.; Dale, D.; Dong, H.; Dumas, J.; Fanchini, E.; Forest, T.; Forman, E.; Freyberger, A.; Froidefond, E.; Golge, S.; Grames, J.; Guèye, P.; Hansknecht, J.; Harrell, P.; Hoskins, J.; Hyde, C.; Josey, B.; Kazimi, R.; Kim, Y.; Machie, D.; Mahoney, K.; Mammei, R.; Marton, M.; McCarter, J.; McCaughan, M.; McHugh, M.; McNulty, D.; Mesick, K. E.; Michaelides, T.; Michaels, R.; Moffit, B.; Moser, D.; Muñoz Camacho, C.; Muraz, J. -F.; Opper, A.; Poelker, M.; Réal, J. -S.; Richardson, L.; Setiniyaz, S.; Stutzman, M.; Suleiman, R.; Tennant, C.; Tsai, C.; Turner, D.; Ungaro, M.; Variola, A.; Voutier, E.; Wang, Y.; Zhang, Y.
2016-05-27
The Polarized Electrons for Polarized Positrons experiment at the injector of the Continuous Electron Beam Accelerator Facility has demonstrated for the first time the efficient transfer of polarization from electrons to positrons produced by the polarized bremsstrahlung radiation induced by a polarized electron beam in a high-Z target. Positron polarization up to 82% have been measured for an initial electron beam momentum of 8.19~MeV/c, limited only by the electron beam polarization. We report that this technique extends polarized positron capabilities from GeV to MeV electron beams, and opens access to polarized positron beam physics to a wide community.
Production of Highly Polarized Positrons Using Polarized Electrons at MeV Energies
Abbott, D.; Adderley, P.; Adeyemi, A.; ...
2016-05-27
The Polarized Electrons for Polarized Positrons experiment at the injector of the Continuous Electron Beam Accelerator Facility has demonstrated for the first time the efficient transfer of polarization from electrons to positrons produced by the polarized bremsstrahlung radiation induced by a polarized electron beam in a high-Z target. Positron polarization up to 82% have been measured for an initial electron beam momentum of 8.19~MeV/c, limited only by the electron beam polarization. We report that this technique extends polarized positron capabilities from GeV to MeV electron beams, and opens access to polarized positron beam physics to a wide community.
Inelastic collisions of positrons with one-valence-electron targets
NASA Technical Reports Server (NTRS)
Abdel-Raouf, Mohamed Assad
1990-01-01
The total elastic and positronium formation cross sections of the inelastic collisions between positrons and various one-valence-electron atoms, (namely hydrogen, lithium, sodium, potassium and rubidium), and one-valence-electron ions, (namely hydrogen-like, lithium-like and alkaline-earth positive ions) are determined using an elaborate modified coupled-static approximation. Special attention is devoted to the behavior of the Ps cross sections at the energy regions lying above the Ps formation thresholds.
Monte carlo simulation of positron induced secondary electrons in thin carbon foils
NASA Astrophysics Data System (ADS)
Cai, L. H.; Yang, B.; Ling, C. C.; Beling, C. D.; Fung, S.
2011-01-01
Emission of secondary electrons induced by the passage of low energy positrons through thin carbon foils was studied by the Monte Carlo method. The positron and electron elastic cross sections were calculated by partial wave analysis. The inelastic positron-valence-electron was described by the energy loss function obtained from dielectric theory. The positron-core-electron interaction was modelled by the Gryzinski's excitation function. Positron transport inside the carbon foil was simulated in detail. Secondary electrons created by positrons and high energy secondary electrons through inelastic interactions were tracked through the foil. The positron transmission coefficient and secondary electron yielded in forward and backward geometry are calculated and dependences on positron energy and carbon foil thickness are discussed.
NASA Astrophysics Data System (ADS)
Kovermann, J.; Stahl, A.; Mikhailichenko, A. A.; Scott, D.; Moortgat-Pick, G. A.; Gharibyan, V.; Pahl, P.; Põschl, R.; Schüler, K. P.; Laihem, K.; Riemann, S.; Schälicke, A.; Dollan, R.; Kolanoski, H.; Lohse, T.; Schweizer, T.; McDonald, K. T.; Batygin, Y.; Bharadwaj, V.; Bower, G.; Decker, F.-J.; Hast, C.; Iverson, R.; Sheppard, J. C.; Szalata, Z.; Walz, D.; Weidemann, A.; Alexander, G.; Reinherz-Aronis, E.; Berridge, S.; Bugg, W.; Efrimenko, Y.
2007-12-01
A longitudinal polarized positron beam is foreseen for the international linear collider (ILC). A proof-of-principle experiment has been performed in the final focus test beam at SLAC to demonstrate the production of polarized positrons for implementation at the ILC. The E166 experiment uses a 1 m long helical undulator in a 46.6 GeV electron beam to produce a few MeV photons with a high degree of circular polarization. These photons are then converted in a thin target to generate longitudinally polarized e^+ and e^-. The positron polarization is measured using a Compton transmission polarimeter. The data analysis has shown asymmetries in the expected vicinity of 3.4% and ˜1% for photons and positrons respectively and the expected positron longitudinal polarization is covering a range from 50% to 90%.
NASA Astrophysics Data System (ADS)
Saha, Asit; Tamang, Jharna
2017-08-01
Qualitative analysis of the positron acoustic (PA) waves in a four-component plasma system consisting of static positive ions, mobile cold positron, and Kaniadakis distributed hot positrons and electrons is investigated. Using the reductive perturbation technique, the Korteweg-de Vries (K-dV) equation and the modified KdV equation are derived for the PA waves. Variations of the total energy of the conservative systems corresponding to the KdV and mKdV equations are presented. Applying numerical computations, effect of parameter (κ), number density ratio (μ1) of electrons to ions and number density (μ2) of hot positrons to ions, and speed (U) of the traveling wave are discussed on the positron acoustic solitary wave solutions of the KdV and mKdV equations. Furthermore, it is found that the parameter κ has no effect on the solitary wave solution of the KdV equation, whereas it has significant effect on the solitary wave solution of the modified KdV equation. Considering an external periodic perturbation, the perturbed dynamical systems corresponding to the KdV and mKdV equations are analyzed by employing three dimensional phase portrait analysis, time series analysis, and Poincare section. Chaotic motions of the perturbed PA waves occur through the quasiperiodic route to chaos.
Measurement of the hadronic cross section in electron-positron annihilation
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.
Electron and Positron Scattering from C3H6 Isomers
NASA Astrophysics Data System (ADS)
Makochekanwa, Casten; Sueoka, Osamu; Kimura, Mineo; Hoshino, Masamitsu; Tanaka, Takahiro; Kitajima, Masashi; Tanaka, Hiroshi
2004-09-01
Hydrocarbons play an important role in high temperature plasmas in Tokamak fusion devices in plasma processing and many other fields [1]. In this paper we report experiments for 0.4-1000 eV electron and 0.2-1000 eV positron total cross sections (TCS) measured using a linear time-of-flight apparatus [2], and electron differential cross sections (DCS) for elastic, vibrational and electronic excitations covering the ranges 1.5 to 100 eV and 15 deg to 130 deg, measured using the crossed beam and relative flow method [3]. The continuum multiple scattering (CMS) [4] calculations have also been performed for the theoretical analysis of the observed features in our cross sections. We observe the isomer effect in both electron and positron TCSs and DCSs. The presence of a dipole moment in propene molecules shows up in enhanced forward scattering in DCSs, leading to larger TCSs and integral cross sections compared to cyclopropane at energies less than 20 eV. However, both electron and positron TCSs for these two molecules nearly equal each other above 100 eV, i.e. the molecular size effect. [1] W. L. Moragn, Adv. At. Mol. Opt. Phys. 43, 79 (2000). [2] O. Sueoka, S. Mori and A. Hamada, J. Phys. B 27, 1453 (1994). [3] H. Tanaka, L. Boesten, D. Matsunaga and T. Kudo, J. Phys. B 21, 1255 (1988). [4] M. Kimura and H. Sato, Comments At. Mol. Phys. 26, 333 (1991).
Low energy lepton scattering -- recent results for electron and positron interactions
NASA Astrophysics Data System (ADS)
Sullivan, J. P.; Vizcaino, V.; Mondal, S.; Lower, J. C.; Jones, A.; Caradonna, P.; Makochekanwa, C.; Buckman, S. J.
2008-07-01
The interaction of low energy electrons with atoms, molecules and materials underpin a large number of technological, environmental and biomedical processes that impact on our everyday lives. Many of these areas have been well studied over the years and in some cases a large body of important and relevant cross section data has been gathered to assist in the understanding and development of the technology or phenomena. A perfect example of this is the area of low energy gaseous electronics where microscopic cross section information for a whole host of scattering processes (vibrational and electronic excitation, dissociation, ionization) have been critical to an understanding of the macroscopic behaviour of a range of gas discharge environments -- large area plasma processing discharges being a case in point. More recently there has been a realisation that fundamental information about both low energy electron and positron interactions also have significant bearing on issues of radiation damage in biological materials. Low energy electrons have been shown to cause significant damage to DNA strands, for instance, as a result of processes such as dissociative attachment -- a process which can occur at energies down to 0 eV. These processes result from the production of copious low energy electrons (< 20 eV) when high energy ionizing radiation thermalises in the body. This realisation has provided an enormous boost to the field of low energy electron physics and spawned an enormous number of new studies of interactions with biologically relevant molecules. In a similar fashion, low energy positron interactions are thought to be fundamentally important for an understanding of the atomic and molecular processes that underpin technologies such as Positron Emission Tomography (PET). PET scans image the coincident 511 keV gamma-rays that arise form the annihilation of an electron-positron pair. During a PET scan, high energy positrons thermalise in the body through
Bruno Touschek: From Betatrons to Electron-Positron Colliders
NASA Astrophysics Data System (ADS)
Bernardini, Carlo; Pancheri, Giulia; Pellegrini, Claudio
Bruno Touschek’s life as a physicist spanned the period from World War II to the 1970s. He was a key figure in the developments of electron-positron colliders and storage rings, and made important contributions to theoretical high energy physics. Storage rings, initially developed for high energy physics, are being widely used in many countries as synchrotron radiation sources and are a tool for research in physics, chemistry, biology, environmental sciences and cultural heritage studies. We describe Touschek’s life in Austria, where he was born, in Germany, where he participated in the construction of a betatron during WWII, and in Italy, where he proposed and led to completion the first electron-positron storage ring in 1960, in Frascati. We highlight how his central European culture influenced his lifestyle and work, and his main contributions to physics, such as the discovery of the Touschek effect and beam instabilities in the larger storage ring ADONE.
Bruno Touschek: From Betatrons to Electron-Positron Colliders
NASA Astrophysics Data System (ADS)
Bernardini, Carlo; Pancheri, Giulia; Pellegrini, Claudio
Bruno Touschek's life as a physicist spanned the period from World War II to the 1970s. He was a key figure in the developments of electron-positron colliders and storage rings, and made important contributions to theoretical high energy physics. Storage rings, initially developed for high energy physics, are being widely used in many countries as synchrotron radiation sources and are a tool for research in physics, chemistry, biology, environmental sciences and cultural heritage studies. We describe Touschek's life in Austria, where he was born, in Germany, where he participated in the construction of a betatron during WWII, and in Italy, where he proposed and led to completion the first electron-positron storage ring in 1960, in Frascati. We highlight how his central European culture influenced his lifestyle and work, and his main contributions to physics, such as the discovery of the Touschek effect and beam instabilities in the larger storage ring ADONE.
Nonlinear Electromagnetic Waves in a Degenerate Electron-Positron Plasma
NASA Astrophysics Data System (ADS)
El-Labany, S. K.; El-Taibany, W. F.; El-Samahy, A. E.; Hafez, A. M.; Atteya, A.
2015-08-01
Using the reductive perturbation technique (RPT), the nonlinear propagation of magnetosonic solitary waves in an ultracold, degenerate (extremely dense) electron-positron (EP) plasma (containing ultracold, degenerate electron, and positron fluids) is investigated. The set of basic equations is reduced to a Korteweg-de Vries (KdV) equation for the lowest-order perturbed magnetic field and to a KdV type equation for the higher-order perturbed magnetic field. The solutions of these evolution equations are obtained. For better accuracy and searching on new features, the new solutions are analyzed numerically based on compact objects (white dwarf) parameters. It is found that including the higher-order corrections results as a reduction (increment) of the fast (slow) electromagnetic wave amplitude but the wave width is increased in both cases. The ranges where the RPT can describe adequately the total magnetic field including different conditions are discussed.
Langmuir rogue waves in electron-positron plasmas
Moslem, W. M.
2011-03-15
Progress in understanding the nonlinear Langmuir rogue waves which accompany collisionless electron-positron (e-p) plasmas is presented. The nonlinearity of the system results from the nonlinear coupling between small, but finite, amplitude Langmuir waves and quasistationary density perturbations in an e-p plasma. The nonlinear Schroedinger equation is derived for the Langmuir waves' electric field envelope, accounting for small, but finite, amplitude quasistationary plasma slow motion describing the Langmuir waves' ponderomotive force. Numerical calculations reveal that the rogue structures strongly depend on the electron/positron density and temperature, as well as the group velocity of the envelope wave. The present study might be helpful to understand the excitation of nonlinear rogue pulses in astrophysical environments, such as in active galactic nuclei, in pulsar magnetospheres, in neutron stars, etc.
Transparency of an instantaneously created electron-positron-photon plasma
NASA Astrophysics Data System (ADS)
Bégué, D.; Vereshchagin, G. V.
2014-03-01
The problem of the expansion of a relativistic plasma generated when a large amount of energy is released in a small volume has been considered by many authors. We use the analytical solution of Bisnovatyi-Kogan and Murzina for the spherically symmetric relativistic expansion. The light curves and the spectra from transparency of an electron-positron-photon plasma are obtained. We compare our results with the work of Goodman.
Collisionless Reconnection in an Electron-Positron Plasma
Bessho, N.; Bhattacharjee, A.
2005-12-09
Electromagnetic particle-in-cell simulations of fast collisionless reconnection in a two-dimensional electron-positron plasma (without an equilibrium guide field) are presented. A generalized Ohm's law in which the Hall current cancels out exactly is given. It is suggested that the key to fast reconnection in this plasma is the localization caused by the off-diagonal components of the pressure tensors, which produce an effect analogous to a spatially localized resistivity.
Magnetic field induced by strong transverse plasmons in ultra-relativistic electron-positron plasmas
NASA Astrophysics Data System (ADS)
Liu, Y.; Li, X. Q.; Liu, S. Q.
2012-08-01
Context. We investigated the generation of localized magnetic fields in an ultra-relativistic non-isothermal electron-positron plasma by strong electromagnetic plasmons. Aims: The results obtained can be used to explain the origin of small-scale magnetic fields in the internal shock region of gamma-ray bursts with ultra-relativistic electron positron plasmas. Methods: The generation of magnetic fields was investigated with kinetic Vlasov Maxwell equations. Results: The self-generated magnetic field will collapse for modulation instability, leading to spatially highly intermittent magnetic fluxes, whose characteristic scale is much larger than relativistic plasma skin depth, which in turn is conducive to the generation of the long-life small-scale magnetic fields in the internal shock region of gamma-ray bursts.
NASA Astrophysics Data System (ADS)
Katsouleas, Thomas; Sahai, Aakash
2015-11-01
The excitation of a non-linear ion-wake by a train of non-linear electron wake of an electron and a positron beam is modeled and its use for positron acceleration is explored. The ion-wake is shown to be a driven non-linear ion-acoustic wave in the form of a cylindrical ion-soliton similar to the solution of the cKdV equation. The phases of the oscillating radial electric fields of the slowly-propagating electron wake are asymmetric in time and excite time-averaged inertial ion motion radially. The radial field of the electron compression region sucks-in the ions and the field of space-charge region of the wake expels them, driving a cylindrical ion-soliton structure with on-axis and bubble-edge density-spikes. Once formed, the channel-edge density-spike is driven radially outwards by the thermal pressure of the thermalized wake energy. Its channel-like structure due to the flat-residue left behind by the propagating ion-soliton, is independent of the energy-source driving the non-linear electron wake. We explore the use of the partially-filled channel formed by the cylindrical ion-soliton for a novel regime of positron acceleration. PIC simulations are used to study the ion-wake soliton structure, its driven propagation and its use for positron acceleration (arXiv:1504.03735). Work supported by the US Department of Energy under DE-SC0010012 and the National Science Foundation under NSF-PHY-0936278.
NASA Astrophysics Data System (ADS)
Callewaert, Vincent; Saniz, Rolando; Barbiellini, Bernardo; Bansil, Arun; Partoens, Bart
2017-08-01
We discuss positron-annihilation lifetimes for a set of illustrative bulk materials within the framework of the weighted-density approximation (WDA). The WDA can correctly describe electron-positron correlations in strongly inhomogeneous systems, such as surfaces, where the applicability of (semi-)local approximations is limited. We analyze the WDA in detail and show that the electrons which cannot screen external charges efficiently, such as the core electrons, cannot be treated accurately via the pair correlation of the homogeneous electron gas. We discuss how this problem can be addressed by reducing the screening in the homogeneous electron gas by adding terms depending on the gradient of the electron density. Further improvements are obtained when core electrons are treated within the LDA and the valence electron using the WDA. Finally, we discuss a semiempirical WDA-based approach in which a sum rule is imposed to reproduce the experimental lifetimes.
Resonant generation of an electron–positron pair by two photons to excited Landau levels
Diachenko, M. M. Novak, O. P.; Kholodov, R. I.
2015-11-15
We consider the resonant generation of an electron–positron pair by two polarized photons to arbitrarily low Landau levels. The resonance occurs when the energy of one photon exceeds the one-photon generation threshold, and the energy of the other photon is multiple to the spacing between the levels. The cross section of the process is determined taking into account the spins of particles. The order of magnitude of the cross section is the highest when the magnetic moments of the particles are oriented along the magnetic field.
NASA Astrophysics Data System (ADS)
Ali Shan, S.; El-Tantawy, S. A.
2016-07-01
In this work, we examine the nonlinear propagation of planar ion-acoustic freak waves in an unmagnetized plasma consisting of cold positive ions and superthermal electrons subjected to cold positrons beam. For this purpose, the reductive perturbation method is used to derive a nonlinear Schrödinger equation (NLSE) for the evolution of electrostatic potential wave. We determine the domain of the plasma parameters where the rogue waves exist. The effect of the positron beam on the modulational instability of the ion-acoustic rogue waves is discussed. It is found that the region of the modulational stability is enhanced with the increase of positron beam speed and positron population. Second as positrons beam increases the nonlinearities of the plasma system, large amplitude ion acoustic rogue waves are pointed out. The present results will be helpful in providing a good fit between the theoretical analysis and real applications in future laboratory plasma experiments.
Ali Shan, S.; El-Tantawy, S. A.
2016-07-15
In this work, we examine the nonlinear propagation of planar ion-acoustic freak waves in an unmagnetized plasma consisting of cold positive ions and superthermal electrons subjected to cold positrons beam. For this purpose, the reductive perturbation method is used to derive a nonlinear Schrödinger equation (NLSE) for the evolution of electrostatic potential wave. We determine the domain of the plasma parameters where the rogue waves exist. The effect of the positron beam on the modulational instability of the ion-acoustic rogue waves is discussed. It is found that the region of the modulational stability is enhanced with the increase of positron beam speed and positron population. Second as positrons beam increases the nonlinearities of the plasma system, large amplitude ion acoustic rogue waves are pointed out. The present results will be helpful in providing a good fit between the theoretical analysis and real applications in future laboratory plasma experiments.
Model of electron pairs in electron-doped cuprates
NASA Astrophysics Data System (ADS)
Singh, R. J.; Khan, Shakeel
2016-07-01
In the order parameter of hole-doped cuprate superconductors in the pseudogap phase, two holes enter the order parameter from opposite sides and pass through various CuO2 cells jumping from one O2- to the other under the influence of magnetic field offered by the Cu2+ ions in that CuO2 cell and thus forming hole pairs. In the pseudogap phase of electron-doped cuprates, two electrons enter the order parameter at Cu2+ sites from opposite ends and pass from one Cu2+ site to the diagonally opposite Cu2+ site. Following this type of path, they are subjected to high magnetic fields from various Cu2+ ions in that cell. They do not travel from one Cu2+ site to the other along straight path but by helical path. As they pass through the diagonal, they face high to low to very high magnetic field. Therefore, frequency of helical motion and pitch goes on changing with the magnetic field. Just before reaching the Cu2+ ions at the exit points of all the cells, the pitch of the helical motion is enormously decreased and thus charge density at these sites is increased. So the velocity of electrons along the diagonal path is decreased. Consequently, transition temperature of electron-doped cuprates becomes less than that of hole-doped cuprates. Symmetry of the order parameter of the electron-doped cuprates has been found to be of 3dx2-y2 + iS type. It has been inferred that internal magnetic field inside the order parameter reconstructs the Fermi surface, which is requisite for superconductivity to take place. Electron pairs formed in the pseudogap phase are the precursors of superconducting order parameter when cooled below Tc.
Nonlinear electromagnetic perturbations in a degenerate ultrarelativistic electron-positron plasma.
El-Taibany, W F; Mamun, A A
2012-02-01
Nonlinear propagation of fast and slow magnetosonic perturbation modes in an ultrarelativistic, ultracold, degenerate (extremely dense) electron positron (EP) plasma (containing ultrarelativistic, ultracold, degenerate electron and positron fluids) has been investigated by the reductive perturbation method. The Alfvén wave velocity is modified due to the presence of the enthalpy correction in the fluid equations of motion. The degenerate EP plasma system (under consideration) supports the Korteweg-de Vries (KdV) solitons, which are associated with either fast or slow magnetosonic perturbation modes. It is found that the ultrarelativistic model leads to compressive (rarefactive) electromagnetic solitons corresponding to the fast (slow) wave mode. There are certain critical angles, θ(c), at which no soliton solution is found corresponding to the fast wave mode. For the slow mode, the magnetic-field intensity affects both the soliton amplitude and width. It is also illustrated that the basic features of the electromagnetic solitary structures, which are found to exist in such a degenerate EP plasma, are significantly modified by the effects of enthalpy correction, electron and positron degeneracy, magnetic-field strength, and the relativistic effect. The applications of the results in a pair-plasma medium, which occurs in many astrophysical objects (e.g., pulsars, white dwarfs, and neutron stars) are briefly discussed.
Threshold for Trapping Positrons in the Wake Driven by a Ultra-relativistic Electron Bunch
Wang, X.; Muggli, P.; Katsouleas, T.; Ischebeck, R.; Hogan, M. J.; Joshi, C.; Mori, W. B.
2009-01-22
We have recently proposed a new concept for generating, injecting and accelerating positrons in a plasma using a double-pulse electron bunch. Monte Carlo simulations show that the number of the positrons produced in a foil target has an exponentially decay energy spectrum. The energy threshold for the trapping of these positrons in a ultra-relativistic electron wake is investigated numerically. For a typical 28.5 GeV electron drive bunch, the trapping threshold for the positrons is a few MeV, and therefore a majority of positrons generated in the foil target are focused and accelerated by the plasma wake.
High energy electrons, positrons and photonuclear reactions in petawatt laser-solid experiments
Cowan, T E; Hunt, A W; Johnson, J; Perry, M D; Fountain, W; Hatchett, S; Key, M H; Kuehl, T; Parnell, T; Pennington, D M; Phillips, T W; Roth, M; Takahashi, Y; Wilks, S C
1999-09-09
The Petawatt laser at LLNL has opened a new regime of high-energy laser-matter interactions in which the quiver motion of plasma electrons is fully relativistic with energies extending well above the threshold for nuclear processes. We have observed that, in addition to the large flux of several MeV electrons ponderomotively expelled from the ultra-intense laser focus, there is a high energy component of electrons extending to -100 MeV, apparently from relativistic self-focusing and plasma acceleration in the underdense pre-formed plasma. The generation of hard bremsstrahlung cascade as these electrons traverse the solid target material, and the resulting photo-nuclear reactions, nuclear fission, and positron-electron pair production are described.
PREFACE 12th International Workshop on Slow Positron Beam Techniques
NASA Astrophysics Data System (ADS)
Buckman, Stephen; Sullivan, James; White, Ronald
2011-01-01
Preface These proceedings arose from the 12th International Workshop on Slow Positron Beam Techniques (SLOPOS12), which was held on Magnetic Island, North Queensland, Australia, between 1-6th August 2010. Meetings in the SLOPOS series are held (roughly) every three years and have now been held on (almost) all continents, indicating the truly international nature of the field. SLOPOS12 marked the second time that the Workshop had been held in the southern hemisphere, and the first time in Australia. SLOPOS12 attracted 122 delegates from 16 countries. Most encouraging was the attendance of 28 student delegates, and that about half of the overall delegates were early career researchers - a good sign for the future of our field. We also enjoyed the company of more than a dozen partners and families of delegates. In a slight departure from previous SLOPOS meetings, the International Advisory Committee approved a broader scope of scientific topics for inclusion in the program for the 2010 Workshop. This broader scope was intended to capture the applications of positrons in atomic, molecular and biomedical areas and was encapsulated in the byeline for SLOPOS-12: The 12th International Workshop on Slow Positron Beam Techniques for Solids, Surfaces, Atoms and Molecules. The scientific and social program for the meeting ran over 6 days with delegates gathering on Sunday August 1st and departing on August 6th. The scientific program included plenary, invited, contributed and student lectures, the latter being the subject of a student prize. In all there were 53 oral presentations during the week. There were also two poster sessions, with 63 posters exhibited, and a prize was awarded for the best poster by a student delegate. The standard of the student presentations, both oral and posters, was outstanding, so much so that the judging panel recommended an additional number of prizes be awarded. Topics that were the focus of invited presentations and contributed papers at
Pulse shape optimization for electron-positron production in rotating fields
NASA Astrophysics Data System (ADS)
Fillion-Gourdeau, François; Hebenstreit, Florian; Gagnon, Denis; MacLean, Steve
2017-07-01
We optimize the pulse shape and polarization of time-dependent electric fields to maximize the production of electron-positron pairs via strong field quantum electrodynamics processes. The pulse is parametrized in Fourier space by a B -spline polynomial basis, which results in a relatively low-dimensional parameter space while still allowing for a large number of electric field modes. The optimization is performed by using a parallel implementation of the differential evolution, one of the most efficient metaheuristic algorithms. The computational performance of the numerical method and the results on pair production are compared with a local multistart optimization algorithm. These techniques allow us to determine the pulse shape and field polarization that maximize the number of produced pairs in computationally accessible regimes.
Shock formation in magnetised electron-positron plasmas: mechanism and timing
NASA Astrophysics Data System (ADS)
Stockem Novo, A.; Bret, A.; Sinha, U.
2016-10-01
The shock formation process in electron-positron pair plasmas is investigated in the presence of an ambient perpendicular magnetic field. In initially unmagnetised plasmas, which are dominated by the Weibel or filamentation instability, the shock formation time is a multiple of the saturation time of the linear instability. While in weakly magnetised plasmas the mechanism is still the same, higher magnetisations induce synchrotron maser modes such that the shock formation is dominated by magnetic reflection. As a consequence the formation times are reduced. The focus is on the detailed picture of the particle kinetics, in which the transition between Weibel and magneto-hydrodynamic shocks can be clearly identified.
Acceleration of positrons by a relativistic electron beam in the presence of quantum effects
Niknam, A. R.; Aki, H.; Khorashadizadeh, S. M.
2013-09-15
Using the quantum magnetohydrodynamic model and obtaining the dispersion relation of the Cherenkov and cyclotron waves, the acceleration of positrons by a relativistic electron beam is investigated. The Cherenkov and cyclotron acceleration mechanisms of positrons are compared together. It is shown that growth rate and, therefore, the acceleration of positrons can be increased in the presence of quantum effects.
Nonlinear electrostatic drift waves in dense electron-positron-ion plasmas
Haque, Q.; Mahmood, S.; Mushtaq, A.
2008-08-15
The Korteweg-de Vries-Burgers (KdVB)-type equation is obtained using the quantum hydrodynamic model in an inhomogeneous electron-positron-ion quantum magnetoplasma with neutral particles in the background. The KdV-type solitary waves, Burgers-type monotonic, and oscillatory shock like solutions are discussed in different limits. The quantum parameter is also dependent on the positron concentration in dense multicomponent plasmas. It is found that both solitary hump and dip are formed and their amplitude and width are dependent on percentage presence of positrons in electron-ion plasmas. The height of the monotonic shock is decreased with the increase of positron concentration and it is independent of the quantum parameter in electron-positron-ion magnetized quantum plasmas. However, the amplitude of the oscillatory shock is dependent on positron concentration and quantum parameter in electron-positron-ion plasmas.
Electron and Positron Beam-Driven Plasma Acceleration
NASA Astrophysics Data System (ADS)
Hogan, Mark J.
Particle accelerators are the ultimate microscopes. They produce high energy beams of particles — or, in some cases, generate X-ray laser pulses — to probe the fundamental particles and forces that make up the universe and to explore the building blocks of life. But it takes huge accelerators, like the Large Hadron Collider or the two-mile-long SLAC linac, to generate beams with enough energy and resolving power. If we could achieve the same thing with accelerators just a few meters long, accelerators and particle colliders could be much smaller and cheaper. Since the first theoretical work in the early 1980s, an exciting series of experiments have aimed at accelerating electrons and positrons to high energies in a much shorter distance by having them "surf" on waves of hot, ionized gas like that found in fluorescent light tubes. Electron-beam-driven experiments have measured the integrated and dynamic aspects of plasma focusing, the bright flux of high energy betatron radiation photons, particle beam refraction at the plasma-neutral-gas interface, and the structure and amplitude of the accelerating wakefield. Gradients spanning kT/m to MT/m for focusing and 100MeV/m to 50 GeV/m for acceleration have been excited in meter-long plasmas with densities of 1014-1017 cm-3, respectively. Positron-beam-driven experiments have evidenced the more complex dynamic and integrated plasma focusing, 100MeV/m to 5 GeV/m acceleration in linear and nonlinear plasma waves, and explored the dynamics of hollow channel plasma structures. Strongly beam-loaded plasma waves have accelerated beams of electrons and positrons with hundreds of pC of charge to over 5 GeV in meter scale plasmas with high efficiency and narrow energy spread. These "plasma wakefield acceleration" experiments have been mounted by a diverse group of accelerator, laser and plasma researchers from national laboratories and universities around the world. This article reviews the basic principles of plasma wakefield
Electron and Positron Beam-Driven Plasma Acceleration
NASA Astrophysics Data System (ADS)
Hogan, Mark J.
Particle accelerators are the ultimate microscopes. They produce high energy beams of particles — or, in some cases, generate X-ray laser pulses — to probe the fundamental particles and forces that make up the universe and to explore the building blocks of life. But it takes huge accelerators, like the Large Hadron Collider or the two-mile-long SLAC linac, to generate beams with enough energy and resolving power. If we could achieve the same thing with accelerators just a few meters long, accelerators and particle colliders could be much smaller and cheaper. Since the first theoretical work in the early 1980s, an exciting series of experiments have aimed at accelerating electrons and positrons to high energies in a much shorter distance by having them “surf” on waves of hot, ionized gas like that found in fluorescent light tubes. Electron-beam-driven experiments have measured the integrated and dynamic aspects of plasma focusing, the bright flux of high energy betatron radiation photons, particle beam refraction at the plasma-neutral-gas interface, and the structure and amplitude of the accelerating wakefield. Gradients spanning kT/m to MT/m for focusing and 100MeV/m to 50GeV/m for acceleration have been excited in meter-long plasmas with densities of 1014-1017cm-3, respectively. Positron-beam-driven experiments have evidenced the more complex dynamic and integrated plasma focusing, 100MeV/m to 5GeV/m acceleration in linear and nonlinear plasma waves, and explored the dynamics of hollow channel plasma structures. Strongly beam-loaded plasma waves have accelerated beams of electrons and positrons with hundreds of pC of charge to over 5GeV in meter scale plasmas with high efficiency and narrow energy spread. These “plasma wakefield acceleration” experiments have been mounted by a diverse group of accelerator, laser and plasma researchers from national laboratories and universities around the world. This article reviews the basic principles of plasma
Optical distortions in electron/positron storage rings
Brown, K.L.; Donald, M.; Servranckx, R.
1983-01-01
We have studied the optical distortions in the PEP electron/positron storage ring for various optical configurations using the computer programs DIMAT, HARMON, PATRICIA, and TURTLE. The results are shown graphically by tracing several thousand trajectories from one interaction region to the next using TURTLE and by tracing a few selected rays several hundred turns using the programs DIMAT and PATRICIA. The results show an interesting correlation between the calculated optical cleanliness of a particular lattice configuration and the observed operating characteristics of the machine.
Low-energy scattering of electrons and positrons in liquids
NASA Technical Reports Server (NTRS)
Schrader, D. M.
1990-01-01
The scattering of low energy electrons and positrons is described for the liquid phase and compared and contrasted with that for the gas phase. Similarities as well as differences are noted. The loci of scattering sites, called spurs in the liquid phase, are considered in detail. In particular, their temporal and spatial evolution is considered from the point of view of scattering. Two emphases are made: one upon the stochastic calculation of the distribution of distances required for slowing down to thermal velocities, and the other upon the calculation of cross sections for energy loss by means of quantum mechanics.
Acosta, D.; The CDF Collaboration
2005-02-23
We report a measurement of the forward-backward charge asymmetry of electrons from W boson decays in p{bar p} collisions at {radical}s = 1.96 TeV using a data sample of 170 pb{sup -1} collected by the Collider Detector at Fermilab. The asymmetry is measured as a function of electron rapidity and transverse energy and provides new input on the momentum fraction dependence of the u and d quark parton distribution functions within the proton.
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.
DEPFET detectors for future electron-positron colliders
NASA Astrophysics Data System (ADS)
Marinas, C.
2015-11-01
The DEPFET Collaboration develops highly granular, ultra-thin pixel detectors for outstanding vertex reconstruction at future electron-positron collider experiments. A DEPFET sensor, by the integration of a field effect transistor on a fully depleted silicon bulk, provides simultaneous position sensitive detector capabilities and in pixel amplification. The characterization of the latest DEPFET prototypes has proven that a adequate signal-to-noise ratio and excellent single point resolution can be achieved for a sensor thickness of 50 micrometers. The close to final auxiliary ASICs have been produced and found to operate a DEPFET pixel detector of the latest generation with the required read-out speed. A complete detector concept is being developed for the Belle II experiment at the new Japanese super flavor factory. DEPFET is not only the technology of choice for the Belle II vertex detector, but also a prime candidate for the ILC. Therefore, in this contribution, the status of DEPFET R&D project is reviewed in the light of the requirements of the vertex detector at a future electron-positron collider.
Small Explorer (SMEX) POsitron Electron Magnet Spectrometer (POEMS)
NASA Technical Reports Server (NTRS)
LHeureux, Jacques; Evenson, Paul A.; Aleman, R. (Technical Monitor)
1995-01-01
This report covers the activities of Louisiana State University (LSU) under subcontract 26053-EX between LSU and the Bartol Research Institute (Bartol), which began January 1, 1994. The purpose of this subcontract was for LSU to participate in and support Bartol in the work to define the SMEX (Small Explorer)/POEMS (Positron Electron Magnet Spectrometer) spaceflight mission under NASA Contract NAS5-38098 between NASA and Bartol. The conclusions of this study were that for a 1998 launch into a 600km altitude, 98 degrees, approximately sun synchronous orbit, (a) the total radiation dose would be typically a few k-rad per year, certainly less than 20 k-rad per year for the anticipated shielding and potential solar flare environment, (b) detector counting rates would be dominated by the South Atlantic Anomaly (SAA) and the horns of the Van Allen belts, (c) the galactic electron and positron 'signal' can be extracted from the albedo background and the trapped populations by detailed evaluation of the geomagnetic transmission function (cut-off) for each event, (d) POEMS could make significant contributions to magnetospheric science if sufficient downlink capacity were provided and, (e) a fully functioning, cost efficient, data processing and analysis facility design was developed for the mission. Overall, POEMS was found to be a relatively simple experiment to manifest, operate and analyze and had potential for fundamental new discoveries in cosmic, heliospheric, solar and magnetospheric science.
Application of conservation laws in electron-positron annihilation
NASA Astrophysics Data System (ADS)
Aryal, Bijaya
2014-03-01
Electron-positron annihilation and creation of gamma rays involve various conservation principles. The least possible number of gamma rays produced in an annihilation event for low energy case can be generally explained using energy and momentum conservation. For this purpose, we choose a convenient frame of reference in which the system has zero linear momentum just before the annihilation event occurs. A learning activity was designed to help introductory level physics students understand and apply some of these conservation principles in the context of electron-positron annihilation. This study presents the students' spontaneous application of prior learning resources while explaining the annihilation process and predicting the least possible number of gamma rays produced in an annihilation event. Qualitative and quantitative data were gathered from students' interviews and written responses from several semesters. Data analysis has revealed students' use of macroscopic analogies during these applications. Moreover, this study has shown that analogical mechanical models seemed to improve student performance. However, a majority of the students using such models provided incorrect reasoning in their explanations.
Current Issues in Electron and Positron Transport Theory
NASA Astrophysics Data System (ADS)
Robson, Robert
2007-10-01
In this paper we review the current status of transport theory for low energy electrons or positrons in gases, in the context of both kinetic theory and fluid modelling. In particular, we focus on the following issues: (i) Muliterm vs two-term representation of the velocity distribution function in solution of Boltzmann's equation; (ii) the effect of non-conservative collisions (attachment, ionization, positron annihilation) on transport properties; (iii) the enduring electron- hydrogen vibrational cross section controversy and possible implications for the Boltzmann equation itself; (iv) closure of the fluid equations and the heat flux ansatz; and (v) correct use of swarm transport coefficients in fluid modelling of low temperature plasmas. Both hydrodynamic and non-hydrodynamic examples will be given, with attention focussed on the Franck-Hertz experiment, particularly the ``window'' of fields in which oscillations of transport properties are produced, and the way in which electric and magnetic fields combine to affect transport properties. In collaboration with co-authors Z. LJ. Petrovi'c, Institute of Physics Belgrade, and R.D. White, James Cook University.
Relativistic, perpendicular shocks in electron-positron plasmas
NASA Technical Reports Server (NTRS)
Gallant, Yves A.; Hoshino, Masahiro; Langdon, A. B.; Arons, Jonathan; Max, Claire E.
1992-01-01
One-dimensional particle-in-cell plasma simulations are used to examine the mechanical structure and thermalization properties of collisionless relativistic shock waves in electron-positron plasmas. Shocks propagating perpendicularly to the magnetic field direction are considered. It is shown that these shock waves exist, and that they are completely parameterized by the ratio of the upstream Poynting flux to the upstream kinetic energy flux. The way in which the Rankine-Hugoniot shock jump conditions are modified by the presence of wave fluctuations is shown, and they are used to provide a macroscopic description of these collisionless shock flows. The results of a 2D simulation that demonstrates the generality of these results beyond the assumption of the 1D case are discussed. It is suggested that the thermalization mechanism is the formation of a synchrotron maser by the coherently reflected particles in the shock front. Because the downstream medium is thermalized, it is argued that perpendicular shocks in pure electron-positron plasmas are not candidates as nonthermal particle accelerators.
Total yield and spectra of positrons produced by channeling radiation from 0.1 ÷ 1.6 GeV electrons
NASA Astrophysics Data System (ADS)
Abdrashitov, S. V.; Bogdanov, O. V.; Dabagov, S. B.; Pivovarov, Yu. L.; Tukhfatullin, T. A.
2017-07-01
The hybrid scheme of positron source involving channeling radiation from 0.1 ÷ 1.6 GeV <1 0 0> channeled electrons in a crystalline W target (radiator) and subsequent electron-positron pair production in a downstream thick amorphous W target (converter) is investigated by means of computer simulation using the BCM-1 code. Computer simulation is carried out taking into account positron energy loss in a thick converter. Total yield of positrons as a function of the thickness of the converter as well as the energy spectrum of positrons for the chosen converter thickness are obtained. According to the calculations, the total yield of positrons produced by channeling radiation from 0.1 ÷ 1.6 GeV electrons in a 10 μm W crystal equals 0.5 ÷ 160 positrons per 103 incident electrons, respectively, with the maximum of positron energy spectrum in the energy range 1 ÷ 3 MeV. Calculations are performed within the framework of the planned experimental program at SPARC_LAB LNF.
Moortgat-Pick, G.; Abe, T.; Alexander, G.; Ananthanarayan, B.; Babich, A.A.; Bharadwaj, V.; Barber, D.; Bartl, A.; Brachmann, A.; Chen, S.; Clarke, J.; Clendenin, J.E.; Dainton, J.; Desch, K.; Diehl, M.; Dobos, B.; Dorland, T.; Eberl, H.; Ellis, John R.; Flottman, K.; Frass, H.; /CERN /Durham U., IPPP /Colorado U. /Tel-Aviv U. /Bangalore, Indian Inst. Sci. /Gomel State Tech. U. /SLAC /DESY /Vienna U. /Daresbury /Liverpool U. /Freiburg U. /Vienna, OAW /Wurzburg U. /Fermilab /Uppsala U. /Waseda U., RISE /Warsaw U. /Bonn U. /Aachen, Tech. Hochsch. /Cornell U., Phys. Dept.
2005-07-01
The proposed International Linear Collider (ILC) is well-suited for discovering physics beyond the Standard Model and for precisely unraveling the structure of the underlying physics. The physics return can be maximized by the use of polarized beams. This report shows the paramount role of polarized beams and summarizes the benefits obtained from polarizing the positron beam, as well as the electron beam. The physics case for this option is illustrated explicitly by analyzing reference reactions in different physics scenarios. The results show that positron polarization, combined with the clean experimental environment provided by the linear collider, allows to improve strongly the potential of searches for new particles and the identification of their dynamics, which opens the road to resolve shortcomings of the Standard Model. The report also presents an overview of possible designs for polarizing both beams at the ILC, as well as for measuring their polarization.
Moortgat-Pick, G.; Abe, T.; Alexander, G.; Ananthanarayan, B.; Babich, A.A.; Bharadwaj, V.; Barber, D.; Bartl, A.; Brachmann, A.; Chen, S.; Clarke, J.; Clendenin, J.E.; Dainton, J.; Desch, K.; Diehl, M.; Dobos, B.; Dorland, T.; Eberl, H.; Ellis, John R.; Flottman, K.; Frass, H.; /CERN /Durham U., IPPP /Colorado U. /Tel-Aviv U. /Bangalore, Indian Inst. Sci. /Gomel State Tech. U. /SLAC /DESY /Vienna U. /Daresbury /Liverpool U. /Freiburg U. /Vienna, OAW /Wurzburg U. /Fermilab /Uppsala U. /Waseda U., RISE /Warsaw U. /Bonn U. /Aachen, Tech. Hochsch. /Cornell U., Phys. Dept.
2005-07-06
The proposed International Linear Collider (ILC) is well-suited for discovering physics beyond the Standard Model and for precisely unraveling the structure of the underlying physics. The physics return can be maximized by the use of polarized beams. This report shows the paramount role of polarized beams and summarizes the benefits obtained from polarizing the positron beam, as well as the electron beam. The physics case for this option is illustrated explicitly by analyzing reference reactions in different physics scenarios. The results show that positron polarization, combined with the clean experimental environment provided by the linear collider, allows to improve strongly the potential of searches for new particles and the identification of their dynamics, which opens the road to resolve shortcomings of the Standard Model. The report also presents an overview of possible designs for polarizing both beams at the ILC, as well as for measuring their polarization.
NASA Astrophysics Data System (ADS)
Kanazawa, I.; Sasaki, T.; Yamada, K.; Imai, E.
2014-04-01
We have discussed positron and ion diffusions in liquids by using the gauge-invariant effection Lagrange density with the spontaneously broken density (the hedgehog-like density) with the internal non-linear gauge fields (Yaug-Mills gauge fields), and have presented the relation to the Hubbard-Onsager theory.
Secondary electron spectra of Au and Cu under bombardment by very low energy positrons
NASA Astrophysics Data System (ADS)
Mukherjee, S.; Weiss, A. H.; Nadesalingam, M. P.; Guagliardo, P.; Sergeant, A.; Williams, J.
2008-03-01
Measurements of the secondary electron energy spectra resulting from very low energy positron bombardment of a polycrystalline Au and Cu (100) surfaces are presented. The low energy part of the secondary spectra contain significant contributions from two processes: 1. annihilation induced Auger electrons that have lost energy before leaving the surface and 2. secondary electrons resulting from direct energy exchange with an incident positron. Our data indicate that the second process (direct energy exchange with the primary positron) is still important at and below 3 eV incident beam energy. Since energy conservation precludes secondary electron generation below an incident beam energy equal to the difference between the electron and positron work functions (˜3eV), the fact that we still observe significant secondary electron emission at energies at or below this value provides strong evidence that the incident positrons are falling directly into the surface state and transferring all of the energy difference to an outgoing secondary electron.
NASA Astrophysics Data System (ADS)
Aguilar, M.; Alberti, G.; Alpat, B.; Alvino, A.; Ambrosi, G.; Andeen, K.; Anderhub, H.; Arruda, L.; Azzarello, P.; Bachlechner, A.; Barao, F.; Baret, B.; Barrau, A.; Barrin, L.; Bartoloni, A.; Basara, L.; Basili, A.; Batalha, L.; Bates, J.; Battiston, R.; Bazo, J.; Becker, R.; Becker, U.; Behlmann, M.; Beischer, B.; Berdugo, J.; Berges, P.; Bertucci, B.; Bigongiari, G.; Biland, A.; Bindi, V.; Bizzaglia, S.; Boella, G.; de Boer, W.; Bollweg, K.; Bolmont, J.; Borgia, B.; Borsini, S.; Boschini, M. J.; Boudoul, G.; Bourquin, M.; Brun, P.; Buénerd, M.; Burger, J.; Burger, W.; Cadoux, F.; Cai, X. D.; Capell, M.; Casadei, D.; Casaus, J.; Cascioli, V.; Castellini, G.; Cernuda, I.; Cervelli, F.; Chae, M. J.; Chang, Y. H.; Chen, A. I.; Chen, C. R.; Chen, H.; Cheng, G. M.; Chen, H. S.; Cheng, L.; Chernoplyiokov, N.; Chikanian, A.; Choumilov, E.; Choutko, V.; Chung, C. H.; Clark, C.; Clavero, R.; Coignet, G.; Commichau, V.; Consolandi, C.; Contin, A.; Corti, C.; Costado Dios, M. T.; Coste, B.; Crespo, D.; Cui, Z.; Dai, M.; Delgado, C.; Della Torre, S.; Demirkoz, B.; Dennett, P.; Derome, L.; Di Falco, S.; Diao, X. H.; Diago, A.; Djambazov, L.; Díaz, C.; von Doetinchem, P.; Du, W. J.; Dubois, J. M.; Duperay, R.; Duranti, M.; D'Urso, D.; Egorov, A.; Eline, A.; Eppling, F. J.; Eronen, T.; van Es, J.; Esser, H.; Falvard, A.; Fiandrini, E.; Fiasson, A.; Finch, E.; Fisher, P.; Flood, K.; Foglio, R.; Fohey, M.; Fopp, S.; Fouque, N.; Galaktionov, Y.; Gallilee, M.; Gallin-Martel, L.; Gallucci, G.; García, B.; García, J.; García-López, R.; García-Tabares, L.; Gargiulo, C.; Gast, H.; Gebauer, I.; Gentile, S.; Gervasi, M.; Gillard, W.; Giovacchini, F.; Girard, L.; Goglov, P.; Gong, J.; Goy-Henningsen, C.; Grandi, D.; Graziani, M.; Grechko, A.; Gross, A.; Guerri, I.; de la Guía, C.; Guo, K. H.; Habiby, M.; Haino, S.; Hauler, F.; He, Z. H.; Heil, M.; Heilig, J.; Hermel, R.; Hofer, H.; Huang, Z. C.; Hungerford, W.; Incagli, M.; Ionica, M.; Jacholkowska, A.; Jang, W. Y.; Jinchi, H.; Jongmanns, M.; Journet, L.; Jungermann, L.; Karpinski, W.; Kim, G. N.; Kim, K. S.; Kirn, Th.; Kossakowski, R.; Koulemzine, A.; Kounina, O.; Kounine, A.; Koutsenko, V.; Krafczyk, M. S.; Laudi, E.; Laurenti, G.; Lauritzen, C.; Lebedev, A.; Lee, M. W.; Lee, S. C.; Leluc, C.; León Vargas, H.; Lepareur, V.; Li, J. Q.; Li, Q.; Li, T. X.; Li, W.; Li, Z. H.; Lipari, P.; Lin, C. H.; Liu, D.; Liu, H.; Lomtadze, T.; Lu, Y. S.; Lucidi, S.; Lübelsmeyer, K.; Luo, J. Z.; Lustermann, W.; Lv, S.; Madsen, J.; Majka, R.; Malinin, A.; Mañá, C.; Marín, J.; Martin, T.; Martínez, G.; Masciocchi, F.; Masi, N.; Maurin, D.; McInturff, A.; McIntyre, P.; Menchaca-Rocha, A.; Meng, Q.; Menichelli, M.; Mereu, I.; Millinger, M.; Mo, D. C.; Molina, M.; Mott, P.; Mujunen, A.; Natale, S.; Nemeth, P.; Ni, J. Q.; Nikonov, N.; Nozzoli, F.; Nunes, P.; Obermeier, A.; Oh, S.; Oliva, A.; Palmonari, F.; Palomares, C.; Paniccia, M.; Papi, A.; Park, W. H.; Pauluzzi, M.; Pauss, F.; Pauw, A.; Pedreschi, E.; Pensotti, S.; Pereira, R.; Perrin, E.; Pessina, G.; Pierschel, G.; Pilo, F.; Piluso, A.; Pizzolotto, C.; Plyaskin, V.; Pochon, J.; Pohl, M.; Poireau, V.; Porter, S.; Pouxe, J.; Putze, A.; Quadrani, L.; Qi, X. N.; Rancoita, P. G.; Rapin, D.; Ren, Z. L.; Ricol, J. S.; Riihonen, E.; Rodríguez, I.; Roeser, U.; Rosier-Lees, S.; Rossi, L.; Rozhkov, A.; Rozza, D.; Sabellek, A.; Sagdeev, R.; Sandweiss, J.; Santos, B.; Saouter, P.; Sarchioni, M.; Schael, S.; Schinzel, D.; Schmanau, M.; Schwering, G.; Schulz von Dratzig, A.; Scolieri, G.; Seo, E. S.; Shan, B. S.; Shi, J. Y.; Shi, Y. M.; Siedenburg, T.; Siedling, R.; Son, D.; Spada, F.; Spinella, F.; Steuer, M.; Stiff, K.; Sun, W.; Sun, W. H.; Sun, X. H.; Tacconi, M.; Tang, C. P.; Tang, X. W.; Tang, Z. C.; Tao, L.; Tassan-Viol, J.; Ting, Samuel C. C.; Ting, S. M.; Titus, C.; Tomassetti, N.; Toral, F.; Torsti, J.; Tsai, J. R.; Tutt, J. C.; Ulbricht, J.; Urban, T.; Vagelli, V.; Valente, E.; Vannini, C.; Valtonen, E.; Vargas Trevino, M.; Vaurynovich, S.; Vecchi, M.; Vergain, M.; Verlaat, B.; Vescovi, C.; Vialle, J. P.; Viertel, G.; Volpini, G.; Wang, D.; Wang, N. H.; Wang, Q. L.; Wang, R. S.; Wang, X.; Wang, Z. X.; Wallraff, W.; Weng, Z. L.; Willenbrock, M.; Wlochal, M.; Wu, H.; Wu, K. Y.; Wu, Z. S.; Xiao, W. J.; Xie, S.; Xiong, R. Q.; Xin, G. M.; Xu, N. S.; Xu, W.; Yan, Q.; Yang, J.; Yang, M.; Ye, Q. H.; Yi, H.; Yu, Y. J.; Yu, Z. Q.; Zeissler, S.; Zhang, J. G.; Zhang, Z.; Zhang, M. M.; Zheng, Z. M.; Zhuang, H. L.; Zhukov, V.; Zichichi, A.; Zuccon, P.; Zurbach, C.
2013-04-01
A precision measurement by the Alpha Magnetic Spectrometer on the International Space Station of the positron fraction in primary cosmic rays in the energy range from 0.5 to 350 GeV based on 6.8×106 positron and electron events is presented. The very accurate data show that the positron fraction is steadily increasing from 10 to ˜250GeV, but, from 20 to 250 GeV, the slope decreases by an order of magnitude. The positron fraction spectrum shows no fine structure, and the positron to electron ratio shows no observable anisotropy. Together, these features show the existence of new physical phenomena.
The Design of the Positron Source for the International Linear Collider
Clarke, J.A.; Malyshev, O.B.; Scott, D.J.; Bailey, I.R.; Dainton, J.B.; Hock, K.M.; Jenner, L.J.; Malysheva, L.I.; Zang, L.; Baynham, E.; Bradshaw, T.W.; Brummitt, A.J.; Carr, F.S.; Lintern, A.J.; Rochford, J.; Bharadwaj, V.; Sheppard, J.; Bungau, A.; Collomb, N.A.; Dollan, R.; Gai, W.; /Argonne /LLNL, Livermore /Unlisted /Durham U. /DESY /Humboldt U., Berlin /Cornell U., Phys. Dept. /Bristol U.
2011-11-04
The high luminosity requirements and the option of a polarized positron beam present a great challenge for the positron source of a future linear collider. This paper provides a comprehensive overview of the latest proposed design for the baseline positron source of the International Linear Collider (ILC). We report on recent progress and results concerning the main components of the source: including the undulator, capture optics, and target.
Novel Cosmic-Ray Electron and Positron Constraints on MeV Dark Matter Particles
NASA Astrophysics Data System (ADS)
Boudaud, Mathieu; Lavalle, Julien; Salati, Pierre
2017-07-01
MeV dark matter (DM) particles annihilating or decaying to electron-positron pairs cannot, in principle, be observed via local cosmic-ray (CR) measurements because of the shielding solar magnetic field. In this Letter, we take advantage of spacecraft Voyager 1's capacity for detecting interstellar CRs since it crossed the heliopause in 2012. This opens up a new avenue to probe DM in the sub-GeV energy/mass range that we exploit here for the first time. From a complete description of the transport of electrons and positrons at low energy, we derive predictions for both the secondary astrophysical background and the pair production mechanisms relevant to DM annihilation or decay down to the MeV mass range. Interestingly, we show that reacceleration may push positrons up to energies larger than the DM particle mass. We combine the constraints from the Voyager and AMS-02 data to get novel limits covering a very extended DM particle mass range, from MeV to TeV. In the MeV mass range, our limits reach annihilation cross sections of order ⟨σ v ⟩˜10-28 cm3/s . An interesting aspect is that these limits barely depend on the details of cosmic-ray propagation in the weak reacceleration case, a configuration which seems to be favored by the most recent B /C data. Though extracted from a completely different and new probe, these bounds have a strength similar to those obtained with the cosmic microwave background—they are even more stringent for p -wave annihilation.
Novel Cosmic-Ray Electron and Positron Constraints on MeV Dark Matter Particles.
Boudaud, Mathieu; Lavalle, Julien; Salati, Pierre
2017-07-14
MeV dark matter (DM) particles annihilating or decaying to electron-positron pairs cannot, in principle, be observed via local cosmic-ray (CR) measurements because of the shielding solar magnetic field. In this Letter, we take advantage of spacecraft Voyager 1's capacity for detecting interstellar CRs since it crossed the heliopause in 2012. This opens up a new avenue to probe DM in the sub-GeV energy/mass range that we exploit here for the first time. From a complete description of the transport of electrons and positrons at low energy, we derive predictions for both the secondary astrophysical background and the pair production mechanisms relevant to DM annihilation or decay down to the MeV mass range. Interestingly, we show that reacceleration may push positrons up to energies larger than the DM particle mass. We combine the constraints from the Voyager and AMS-02 data to get novel limits covering a very extended DM particle mass range, from MeV to TeV. In the MeV mass range, our limits reach annihilation cross sections of order ⟨σv⟩∼10^{-28} cm^{3}/s. An interesting aspect is that these limits barely depend on the details of cosmic-ray propagation in the weak reacceleration case, a configuration which seems to be favored by the most recent B/C data. Though extracted from a completely different and new probe, these bounds have a strength similar to those obtained with the cosmic microwave background-they are even more stringent for p-wave annihilation.
Numerical analysis of electrostatic ion cyclotron instability in an electron-positron-ion plasma
Khorashadizadeh, S. M. Barati Moqadam Niyat, M.; Niknam, A. R.
2016-06-15
This paper presents a theoretical study of the effects of positron density on the electrostatic ion cyclotron instability in an electron-positron-ion plasma using the kinetic theory approach. It is supposed that positrons and electrons can drift parallel to the magnetic field either in the same or the opposite directions. The dispersion relation for the electrostatic ion cyclotron waves in an electron-positron-ion plasma is derived, and the numerical results are investigated. It is found that an increase in positron concentration increases the critical drift velocity for excitation of the instability in both configurations. It is also found that as the positron concentration increases the growth rate of instability decreases. In addition, it is shown that at low velocities the maximum instability growth rate for the unidirectional case is higher than the counter-streaming case; however, after a certain velocity, the maximum growth rate in the counter-streaming case dominates that of the unidirectional case.
NASA Astrophysics Data System (ADS)
Zhang, Xilin; Miller, Gerald A.
2017-01-01
Recently, the experimentalists in [Phys.Rev.Lett.116.042501(2016)] claimed seeing unexpected enhancement of the internal electron-positron pair (e+-e-) production in the large e+-e- relative angle region in the EM transition from the Beryllium-8 nucleus's second lowest 1+ state to its ground state. According to the experimentalists, the signal can be explained by a new neutral boson weighted around 17 MeV. This has stipulated significant interests in the particle physics community [e.g. Phys. Rev. Lett. 117, 071803 (2016)]. In this talk, I will present our latest study of the underlying nuclear physics, and emphasize several pieces of physics that haven't been well studied theoretically and not been included in the current experimental analysis, including the interferences between the dominant E1 and M1 transitions, two extra angular dependences, possible impact of E2 transition and its interferences with E1 and M1, and nuclear form factor. I will also point out that the previously measured on-shell photon production constrains the ratio between E1 and M1 contributions in the pair production, which however haven't been checked in the current experimental analysis. In the end, I will discuss the possibility of nuclear physics being the origin of the observed anomaly. The work is supported by the U.S. Department of Energy under Grant DE-FG02-97ER-41014.
Linear tearing modes in an electron-positron plasma
NASA Astrophysics Data System (ADS)
Guiliang, SONG; Huishan, CAI
2017-04-01
The general dispersion of tearing modes due to the effects of electron inertia and resistivity in pair plasmas is derived analytically, and is discussed in two cases: \\bigtriangleup \\prime \\gg 1 and \\bigtriangleup \\prime \\ll 1, where {{Δ }}\\prime is the instability criterion of the tearing mode. It is found that the conditions under which either resistivity or electron inertia dominates depend strongly on the limit of {{Δ }}\\prime considered.
Electron-positron collision physics: 1 MeV to 2 TeV
Perl, M.L.
1988-07-01
An overview of electron-positron collision physics is presented. It begins at 1 MeV, the energy region of positronium formation, and extends to 2 TeV, the energy region which requires an electron- positron linear collider. In addition, the concept of searching for a lepton-specific forces is discussed. 18 refs., 15 figs., 1 tab.
Design Considerations for High Energy Electron -- Positron Storage Rings
DOE R&D Accomplishments Database
Richter, B.
1966-11-01
High energy electron-positron storage rings give a way of making a new attack on the most important problems of elementary particle physics. All of us who have worked in the storage ring field designing, building, or using storage rings know this. The importance of that part of storage ring work concerning tests of quantum electrodynamics and mu meson physics is also generally appreciated by the larger physics community. However, I do not think that most of the physicists working tin the elementary particle physics field realize the importance of the contribution that storage ring experiments can make to our understanding of the strongly interacting particles. I would therefore like to spend the next few minutes discussing the sort of things that one can do with storage rings in the strongly interacting particle field.
Solitary and shock waves in magnetized electron-positron plasma
Lu, Ding; Li, Zi-Liang; Abdukerim, Nuriman; Xie, Bai-Song
2014-02-15
An Ohm's law for electron-positron (EP) plasma is obtained. In the framework of EP magnetohydrodynamics, we investigate nonrelativistic nonlinear waves' solutions in a magnetized EP plasma. In the collisionless limit, quasistationary propagating solitary wave structures for the magnetic field and the plasma density are obtained. It is found that the wave amplitude increases with the Mach number and the Alfvén speed. However, the dependence on the plasma temperature is just the opposite. Moreover, for a cold EP plasma, the existence range of the solitary waves depends only on the Alfvén speed. For a hot EP plasma, the existence range depends on the Alfvén speed as well as the plasma temperature. In the presence of collision, the electromagnetic fields and the plasma density can appear as oscillatory shock structures because of the dissipation caused by the collisions. As the collision frequency increases, the oscillatory shock structure becomes more and more monotonic.
Future directions in high energy electron-positron experimentation
Trilling, G.H.
1988-09-01
In this report, the possibilities of studying particle physics at the TeV scale with high energy electron-positron linear colliders are discussed. A status report on the SLC and the MARK II program is given to provide some insights on the feasibility of experiments at linear colliders. The technical issues in going from SLC to the development of TeV colliders are briefly discussed. Some of the elements of the e/sup +/e/sup -/ experimental environment which differentiate it from that in hadron colliders and give examples of processes particularly well suited to attack by e/sup +/e/sup -/ annihilation are summarized. Finally, some concluding remarks are given. 8 refs., 10 figs., 2 tabs.
Electronics for the Donner 600-Crystal Positron Tomograph
Cahoon, J.L.; Huesman, R.H.; Derenzo, S.E.; Geyer, A.B.; Uber, D.C.; Turko, B.T.; Budinger, T.F.
1985-10-01
The data acquisition system, designed for the Donner 600-Crystal Positron Tomograph, is described. Coincidence timing resolution of less than five nanoseconds full width at half maximum and data rates in excess of one million events per second are achieved by using high-speed emitter coupled logic circuits, first-in first-out memory to derandomize data flow, and parallel architecture to increase throughput. These data rates allow the acquisition of adequate transmission data in a reasonable amount of time. Good timing resolution minimizes accidental coincidences and permits data rates greater than 100,000 image-forming events per second for high-speed dynamic emission tomography. Additional scatter and accidental rejection are accomplished for transmission data by using an orbiting source and a look-up table for valid events. Calibration of this complex electronic system is performed automatically under computer control. 4 refs., 5 figs.
NASA Astrophysics Data System (ADS)
Ali Shan, Shaukat; Imtiaz, Nadia
2017-10-01
The effect of electron trapping in an electron-positron-ion plasma is modeled with κ-distributed electrons. The trapped electron number density is truncated to some finite order of the electrostatic potential Φ. Small amplitude solitary structures with Sagdeev potential approach and reductive perturbation method (through Schamel equation) are found to be modified under the impact of superthermality index κ and trapping efficiency β. A modified Schamel equation which gives rise to the small amplitude double layers (SIADLs) is obtained. The role of various plasma parameters in particular, the superthermality index, the positron concentration, and the electron trapping efficiency on the small amplitude ion acoustic double layers (SIADLs) has been investigated. It can be inferred from this investigation that these parameters play modifying character in the formation of nonlinear structures like solitary waves and SIADLs in e-p-i plasma.
Radiation damping induced electron trapping and positron creation
NASA Astrophysics Data System (ADS)
Gu, Yanjun; Klimo, Ondrej; Weber, Stefan; Korn, Georg
2016-10-01
High power laser facilities with intensities up to 1022 W /cm2 have been realized and the forthcoming installations are expected to reach 10 22 - 24 W /cm2 or even higher. At these intensities, the radiation effects and quantum electrodynamics description come into play. The emitted photon momentum becomes comparable to the momentum of the emitting electrons. In this work, we propose a regime of electron self-injection and trapping in the ultra-high intensity laser-plasma interaction. The electrons accumulated at the head of the laser pulse are injected into the pulse centre due to the strong longitudinal electrostatic field created by the high density shell. These electrons, which experience a restoring force provided by the emitted photons, can be confined in the laser pulse for a long time. The corresponding photons are produced in the region where the laser field is strong. High energy and well collimated positron bunches are produced. This regime may be beneficial for the potential experiments to be carried out on large laser facilities such as ELI. This work was supported by the project ELI: Extreme Light Infrastructure (CZ.02.1.01/0.0/0.0/15_008/0000162) from European Regional Development.
Alinejad, H.; Mamun, A. A.
2011-11-15
A theoretical investigation is carried out to understand the basic features of linear and nonlinear propagation of ion-acoustic (IA) waves subjected to an external magnetic field in an electron-positron-ion plasma which consists of a cold magnetized ion fluid, Boltzmann distributed positrons, and superthermal electrons. In the linear regime, the propagation of two possible modes (fast and slow) and their evolution are investigated. It is shown that the electron superthermality and the relative fraction of positrons cause both modes to propagate with smaller phase velocities. Also, two special cases of dispersion relation are found, which are related to the direction of the wave propagation. In the nonlinear regime, the Korteweg-de Vries (KdV) equation describing the propagation of fast and slow IA waves is derived. The latter admits a solitary wave solution with only negative potential in the weak amplitude limit. It is found that the effects of external magnetic field (obliqueness), superthermal electrons, positron concentration, and temperature ratio significantly modify the basic features of solitary waves.
NASA Astrophysics Data System (ADS)
Lu, Ding; Li, Zi-Liang; Xie, Bai-Song
2013-09-01
The effects of ion mobility and positron fraction on the solitary waves of the laser field envelope and the potential of the electrostatic field in weak relativistic electron-positron-ion plasma are investigated. The parameter region for the existence of solitary waves is obtained analytically, and a reasonable choice of parameters is clarified. Both cases of mobile and immobile ions are considered. It is found that the amplitudes of solitary waves in the former case are larger compared to the latter case. For small plasma density, the localized solitary wave solutions in terms of the approximate perturbation analytical method are very consistent with those by exact numerical calculations. However, as the plasma density increases the analytical method loses its validity more and more. The influence of the positron fraction on the amplitudes of solitary waves shows a monotonous increasing relation. The implications of our results to particle acceleration are also discussed briefly.
The VEPP-2000 electron-positron collider: First experiments
Berkaev, D. E. Shwartz, D. B.; Shatunov, P. Yu.; Rogovskii, Yu. A.; Romanov, A. L.; Koop, I. A.; Shatunov, Yu. M.; Zemlyanskii, I. M.; Lysenko, A. P.; Perevedentsev, E. A.; Stankevich, A. S.; Senchenko, A. I.; Khazin, B. I.; Anisenkov, A. V.; Gayazov, S. E.; Kozyrev, A. N.; Ryzhenenkov, A. E.; Shemyakin, D. N.; Epshtein, L. B.; Serednyakov, S. I.; and others
2011-08-15
In 2007, at the Institute of Nuclear Physics (Novosibirsk), the construction of the VEPP-2000 electron-positron collider was completed. The first electron beam was injected into the accelerator structure with turned-off solenoids of the final focus. This mode was used to tune all subsystems of the facility and to train the vacuum chamber using synchrotron radiation at electron currents of up to 150 mA. The VEPP-2000 structure with small beta functions and partially turned-on solenoids was used for the first testing of the 'round beams' scheme at an energy of 508 MeV. Beam-beam effects were studied in strong-weak and strong-strong modes. Measurements of the beam sizes in both cases showed a dependence corresponding to model predictions for round colliding beams. Using a modernized SND (spherical neutral detector), the first energy calibration of the VEPP-2000 collider was performed by measuring the excitation curve of the phimeson resonance; the phi-meson mass is known with high accuracy from previous experiments at VEEP-2M. In October 2009, a KMD-3 (cryogenic magnetic detector) was installed at the VEPP-2000 facility, and the physics program with both the SND and LMD-3 particle detectors was started in the energy range of 1-1.9 GeV. This first experimental season was completed in summer 2010 with precision energy calibration by resonant depolarization.
Sadiq, Safeer; Mahmood, S.; Haque, Q.; Ali, Munazza Zulfiqar
2014-09-20
The propagation of electrostatic waves in a dense magnetized electron-positron-ion (EPI) plasma with nonrelativistic and ultrarelativistic degenerate electrons and positrons is investigated. The linear dispersion relation is obtained for slow and fast electrostatic waves in the EPI plasma. The limiting cases for ion acoustic wave (slow) and ion cyclotron wave (fast) are also discussed. Using the reductive perturbation method, two-dimensional propagation of ion acoustic solitons is found for both the nonrelativistic and ultrarelativistic degenerate electrons and positrons. The effects of positron concentration, magnetic field, and mass of ions on ion acoustic solitons are shown in numerical plots. The proper form of Fermi temperature for nonrelativistic and ultrarelativistic degenerate electrons and positrons is employed, which has not been used in earlier published work. The present investigation is useful for the understanding of linear and nonlinear electrostatic wave propagation in the dense magnetized EPI plasma of compact stars. For illustration purposes, we have applied our results to a pulsar magnetosphere.
Imprints of Electron-Positron Winds on the Multiwavelength Afterglows of Gamma-ray Bursts
NASA Astrophysics Data System (ADS)
Geng, J. J.; Wu, X. F.; Huang, Y. F.; Li, L.; Dai, Z. G.
2016-07-01
Optical rebrightenings in the afterglows of some gamma-ray bursts (GRBs) are unexpected within the framework of the simple external shock model. While it has been suggested that the central engines of some GRBs are newly born magnetars, we aim to relate the behaviors of magnetars to the optical rebrightenings. A newly born magnetar will lose its rotational energy in the form of Poynting-flux, which may be converted into a wind of electron-positron pairs through some magnetic dissipation processes. As proposed by Dai, this wind will catch up with the GRB outflow and a long-lasting reverse shock (RS) would form. By applying this scenario to GRB afterglows, we find that the RS propagating back into the electron-positron wind can lead to an observable optical rebrightening and a simultaneous X-ray plateau (or X-ray shallow decay). In our study, we select four GRBs (i.e., GRB 080413B, GRB 090426, GRB 091029, and GRB 100814A), of which the optical afterglows are well observed and show clear rebrightenings. We find that they can be well interpreted. In our scenario, the spin-down timescale of the magnetar should be slightly smaller than the peak time of the rebrightening, which can provide a clue to the characteristics of the magnetar.
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.
NASA Astrophysics Data System (ADS)
Koehn, Christoph; Ebert, Ute
2015-04-01
Thunderstorms can emit high-energy particles, photons with energies of up to at least 40 MeV, leptons (electrons, positrons) and hadrons (neutrons and protons) with energies of tens of MeV. Some of these events have been correlated with negative lightning leaders propagating upwards in the cloud. For particular lightning events we show that photons, leptons and hadrons can reach ground altitude as well as satellite altitude, and we present the number as well as the spatial and energy distribution of photons, leptons and hadrons. We have reviewed the latest literature on cross sections for collisions of photons, leptons and hadrons with air molecules and have implemented them in our Monte Carlo code. We initialize a photon beam with the characteristic energy distribution of a TGF at thunderstorm altitude and we use the Monte Carlo model to trace these photons; we include the production of secondary electrons through photoionization, Compton scattering and pair production, the production of positrons through pair production as well as the production of neutrons and protons through photonuclear processes. Subsequently we calculate the motion and energy dissipation of these leptons and hadrons with the feedback of electrons and positrons producing new photons through Bremsstrahlung and through positron annihilation at shell electrons. Additionally we provide analytic estimates for the energy losses of photons, leptons and hadrons in the energy range between 0.03 eV and 100 MeV based on the relevant cross sections. We provide the spectral analysis of how many photons, leptons and hadrons will reach ground or satellite altitude and what their energies are, depending on the initial photon energy. This is of particular interest because of campaigns measuring fluxes of all these species at 0 and 500 km altitude without knowing the actual energies of initial electrons converting into photons within a thundercloud.
NASA Astrophysics Data System (ADS)
Ahmad, Rashid; Gul, Nabi; Adnan, Muhammad; Tribeche, Mouloud; Khattak, Fida Younus
2017-04-01
A hydrodynamic model is employed to investigate the linear and non-linear propagation of electrostatic positron acoustic waves (EPAWs) in a 4-component relativistic-degenerate electron-positron-ion plasma. The plasma constituents are cold positrons, hot relativistic-degenerate electrons and positrons, and cold static ions in the background. The hot electrons and positrons are treated as inertialess, and the cold positrons provide the inertia while the restoring force comes from the hot species. A dispersion relation for low-frequency EPAWs is derived. It is observed that an increase in the relative density of hot positrons to cold positrons and relativistic effects tend to reduce the speed of the EPAWs. Employing the standard Reductive Perturbation Technique, a Korteweg de Vries (KdV)-type equation is derived, and the existence of KdV solitons is demonstrated. In this case, an increase in the relative density of hot to cold positrons and relativistic effects decreases both the amplitude and width of the solitons. Furthermore, a Non-Linear Schrödinger (NLS) equation is also derived. The variation in the group velocity shows less change with the wavenumber for the higher concentration of positrons and also with the stronger relativistic effects. The interchange in the behaviour of group velocity with the positron concentration is observed for values k > 1. The growth rate of modulation instability is derived, and its dependence on the positron concentration and relativistic effects are discussed. The relativistic effects reduce the stability region while the growth rate is enhanced while moving from weak-relativistic to ultra-relativistic cases. The hot positron concentration makes the wave modulationally stable for an extended region of the wavenumber k. The solution of the NLS equation admits the existence of both bright and dark envelope solitons. The profiles of the envelope solitons show inverse dependence on the positron concentration and on the relativistic
Detection of Ga vacancies in electron irradiated GaAs by positrons
Hautojaervi, P.; Moser, P.; Stucky, M.; Corbel, C.; Plazaola, F.
1986-03-24
Positron lifetime measurements have been used to study the recovery of electron irradiated GaAs between 77 and 800 K. Below room temperature positrons are trapped by vacancies in Ga sublattices. The Ga vacancies recover between 200 and 350 K.
Properties of the electron cloud in a high-energy positron and electron storage ring
Harkay, K. C.; Rosenberg, R. A.
2003-03-20
Low-energy, background electrons are ubiquitous in high-energy particle accelerators. Under certain conditions, interactions between this electron cloud and the high-energy beam can give rise to numerous effects that can seriously degrade the accelerator performance. These effects range from vacuum degradation to collective beam instabilities and emittance blowup. Although electron-cloud effects were first observed two decades ago in a few proton storage rings, they have in recent years been widely observed and intensely studied in positron and proton rings. Electron-cloud diagnostics developed at the Advanced Photon Source enabled for the first time detailed, direct characterization of the electron-cloud properties in a positron and electron storage ring. From in situ measurements of the electron flux and energy distribution at the vacuum chamber wall, electron-cloud production mechanisms and details of the beam-cloud interaction can be inferred. A significant longitudinal variation of the electron cloud is also observed, due primarily to geometrical details of the vacuum chamber. Furthermore, such experimental data can be used to provide realistic limits on key input parameters in modeling efforts, leading ultimately to greater confidence in predicting electron-cloud effects in future accelerators.
Properties of the electron cloud in a high-energy positron and electron storage ring
Harkay, K. C.; Rosenberg, R. A.
2003-03-20
Low-energy, background electrons are ubiquitous in high-energy particle accelerators. Under certain conditions, interactions between this electron cloud and the high-energy beam can give rise to numerous effects that can seriously degrade the accelerator performance. These effects range from vacuum degradation to collective beam instabilities and emittance blowup. Although electron-cloud effects were first observed two decades ago in a few proton storage rings, they have in recent years been widely observed and intensely studied in positron and proton rings. Electron-cloud diagnostics developed at the Advanced Photon Source enabled for the first time detailed, direct characterization of the electron-cloud properties in amore » positron and electron storage ring. From in situ measurements of the electron flux and energy distribution at the vacuum chamber wall, electron-cloud production mechanisms and details of the beam-cloud interaction can be inferred. A significant longitudinal variation of the electron cloud is also observed, due primarily to geometrical details of the vacuum chamber. Furthermore, such experimental data can be used to provide realistic limits on key input parameters in modeling efforts, leading ultimately to greater confidence in predicting electron-cloud effects in future accelerators.« less
Wakefields generated by collisional neutrinos in neutral-electron-positron-ion plasma
Tinakiche, Nouara
2015-12-15
A classical fluid description is adopted to investigate nonlinear interaction between an electron-type neutrino beam and a relativistic collisionless unmagnetized neutral-electron-positron-ion plasma. In this work, we consider the collisions of the neutrinos with neutrals in the plasma and study their effect on the generation of wakefields in presence of a fraction of ions in a neutral-electron-positron plasma. The results obtained in the present work are interpreted and compared with previous studies.
Javan, N. Sepehri Homami, S. H. H.
2015-02-15
Self-guided nonlinear propagation of intense circularly-polarized electromagnetic waves in a hot electron-positron-ion magnetoplasma is studied. Using a relativistic fluid model, a nonlinear equation is derived, which describes the interaction of the electromagnetic wave with the plasma in the quasi-neutral approximation. Transverse Eigen modes, the nonlinear dispersion relation and the group velocity are obtained. Results show that the transverse profile in the case of magnetized plasma with cylindrical symmetry has a radially damping oscillatory form. Effect of applying external magnetic fields, existence of the electron-positron pairs, changing the amplitude of the electromagnetic wave, and its polarization on the nonlinear dispersion relation and Eigen modes are studied.
EL-Labany, S. K.; Khedr, D. M.; El-Shamy, E. F.; Sabry, R.
2013-01-15
In the present research paper, the effect of bounded nonplanar (cylindrical and spherical) geometry on the interaction between two nonplanar electrostatic solitary waves (NESWs) in electron-positron-ion plasmas has been studied. The extended Poincare-Lighthill-Kuo method is used to obtain nonplanar phase shifts after the interaction of the two NESWs. This study is a first attempt to investigate nonplanar phase shifts and trajectories for NESWs in a two-fluid plasma (a pair-plasma) consisting of electrons and positrons, as well as immobile background positive ions in nonplanar geometry. The change of phase shifts and trajectories for NESWs due to the effect of cylindrical geometry, spherical geometry, the physical processes (either isothermal or adiabatic), and the positions of two NESWs are discussed. The present investigation may be beneficial to understand the interaction between two NESWs that may occur in active galactic nuclei.
Ridgers, C. P.; Bell, A. R.; Brady, C. S.; Bennett, K.; Arber, T. D.; Duclous, R.; Kirk, J. G.
2013-05-15
In simulations of a 12.5 PW laser (focussed intensity I=4×10{sup 23}Wcm{sup −2}) striking a solid aluminum target, 10% of the laser energy is converted to gamma-rays. A dense electron-positron plasma is generated with a maximum density of 10{sup 26}m{sup −3}, seven orders of magnitude denser than pure e{sup −} e{sup +} plasmas generated with 1PW lasers. When the laser power is increased to 320 PW (I=10{sup 25}Wcm{sup −2}), 40% of the laser energy is converted to gamma-ray photons and 10% to electron-positron pairs. In both cases, there is strong feedback between the QED emission processes and the plasma physics, the defining feature of the new “QED-plasma” regime reached in these interactions.
High Power Polarized Positron Source
NASA Astrophysics Data System (ADS)
Mikhailichenko, Alexander
2009-09-01
We discuss the basics of polarized positron production by low energy polarized electrons. Efficiency of conversion ˜0.1-1% might be interesting for the Continuous Electron Beam Accelerator Facility (CEBAF) and the International Linear Collider (ILC).
Studies of slow-positron production using low-energy primary electron beams.
Lessner, E.
1999-04-20
Slow-positron beams produced from negative-work-function solid-state moderators have found numerous applications in condensed matter physics. There are potential advantages in using low-energy primary electron beams for positron production, including reduced radiation damage to single-crystal moderators and reduced activation of nearby components. We present numerical calculations of positron yields and other beam parameters for various target-moderator configurations using the Argonne Wakefield Accelerator (AWA) [1] and Advanced Photon Source (APS) [2] electron linacs [3] as examples of sources for the primary electron beams. The status of experiments at these facilities is reviewed.
Scaling laws for positron production in laser-electron-beam collisions
NASA Astrophysics Data System (ADS)
Blackburn, T. G.; Ilderton, A.; Murphy, C. D.; Marklund, M.
2017-08-01
Showers of γ rays and positrons are produced when a high-energy electron beam collides with a superintense laser pulse. We present scaling laws for the electron-beam energy loss, the γ -ray spectrum, and the positron yield and energy that are valid in the nonlinear, radiation-reaction-dominated regime. As an application we demonstrate that by employing the collision of a >GeV electron beam with a laser pulse of intensity >5 ×1021W cm-2 , today's high-intensity laser facilities are capable of producing O (104) positrons per shot via light-by-light scattering.
Two dimensional electrostatic shock waves in relativistic electron positron ion plasmas
Masood, W.; Rizvi, H.
2010-05-15
Ion-acoustic shock waves (IASWs) are studied in an unmagnetized plasma consisting of electrons, positrons and hot ions. In this regard, Kadomtsev-Petviashvili-Burgers (KPB) equation is derived using the small amplitude perturbation expansion method. The dependence of the IASWs on various plasma parameters is numerically investigated. It is observed that ratio of ion to electron temperature, kinematic viscosity, positron concentration, and the relativistic ion streaming velocity affect the structure of the IASW. Limiting case of the KPB equation is also discussed. Stability of KPB equation is also presented. The present investigation may have relevance in the study of electrostatic shock waves in relativistic electron-positron-ion plasmas.
NASA Astrophysics Data System (ADS)
Vranic, Marija; Klimo, Ondrej; Korn, Georg; Weber, Stefan
2017-05-01
A new generation laser system at ELI beamlines will provide a 10 PW peak power in a 150 fs laser pulse. This opens new possibilities for experiments on laser-electron scattering at extreme intensities. High energy photons (x-rays or gamma-rays) are produced through nonlinear Compton scattering, and they subsequently decay into electron-positron pairs. The pair yield depends on several factors: the electron beam energy, the laser intensity and the duration of the interaction. Prevous studies focused mostly on the short lasers ( 30 fs). However, using a longer laser pulse ( 150 fs) can be an advantage, because it increases the effective interaction time and can deliver a higher number of pairs. A powerful tool that supports theoretical studies of laser-matter interactions and helps design of experiments are particle-in-cell (PIC) codes. PIC code OSIRIS has an additional Quantum electrodynamics (QED) module that includes discrete photon emission (non-linear Compton scattering) and Breit-Wheeler electron-positron pair production, as well as macroparticle merging that allows to control the total number of particles in the simulation. In this work, OSIRIS is deployed to model the interaction of short and long lasers of extreme intensities (I>10^22) with electron beams obtained from a laser wakefield accelerator. Measurable experimental signatures are discussed, the number of electron-positron pairs and the overall quality of the newly produced beam.
Stable confinement of electron plasma and initial results on positron injection in RT-1
NASA Astrophysics Data System (ADS)
Saitoh, H.; Yoshida, Z.; Morikawa, J.; Yano, Y.; Kasaoka, N.; Sakamoto, W.; Nogami, T.
2013-03-01
The Ring Trap 1 (RT-1) device is a dipole field configuration generated by a levitated superconducting magnet. It offers very interesting opportunities for research on the fundamental properties on non-neutral plasmas, such as self-organization of charged particles in the strongly positive and negative charged particles on magnetic surfaces. When strong positron sources will be available in the future, the dipole field configuration will be potentially applicable to the formation of an electron-positron plasma. We have realized stable, long trap of toroidal pure electron plasma in RT-1; Magnetic levitation of the superconducting magnet resulted in more than 300s of confinement for electron plasma of ˜ 1011 m-3. Aiming for the confinement of positrons as a next step, we started a positron injection experiment. For the formation of positron plasma in the closed magnetic surfaces, one of the key issues to be solved is the efficient injection method of positron across closed magnetic surfaces. In contrast to linear configurations, toroidal configurations have the advantage that they are capable of trapping high energy positrons in the dipole field configuration and consider the possibility of direct trapping of positrons emitted from a 22Na source.
Third order transport coefficients for electrons and positrons in gases
NASA Astrophysics Data System (ADS)
Dujko, Sasa; Simonovic, Ilija; White, Ronald; Petrovic, Zoran
2016-09-01
Third order transport coefficients (the skewness tensor) of the electron and positron swarms, in atomic and molecular gases, are investigated. The knowledge of the skewness tensor is necessary for the conversion of the hydrodynamic transport coefficients to the arrival time and steady-state Townsend transport data as well as for the determination of the deviations of the spatial density profiles from an ideal Gaussian. In this work, we investigate the structure and symmetries along individual elements of the skewness tensor by the group projector method. Individual components of the skewness tensor are calculated using a Monte Carlo simulation technique and multi term theory for solving the Boltzmann equation. Results obtained by these two methods are in excellent agreement. We extend previous studies by considering the sensitivity of the skewness components to explicit and implicit effects of non-conservative collisions, post-ionization energy partitioning, and inelastic collisions. The errors of the two term approximation for solving the Boltzmann equation are highlighted. We also investigate the influence of a magnetic field on the skewness tensor in varying configurations of electric and magnetic fields. Among many interesting points, we have observed a strong correlation between the skewness and diffusion.
Ultrashort megaelectronvolt positron beam generation based on laser-accelerated electrons
Xu, Tongjun; Shen, Baifei Xu, Jiancai Li, Shun; Yu, Yong; Li, Jinfeng; Lu, Xiaoming; Wang, Cheng; Wang, Xinliang; Liang, Xiaoyan; Leng, Yuxin; Li, Ruxin; Xu, Zhizhan
2016-03-15
Experimental generation of ultrashort MeV positron beams with high intensity and high density using a compact laser-driven setup is reported. A high-density gas jet is employed experimentally to generate MeV electrons with high charge; thus, a charge-neutralized MeV positron beam with high density is obtained during laser-accelerated electrons irradiating high-Z solid targets. It is a novel electron–positron source for the study of laboratory astrophysics. Meanwhile, the MeV positron beam is pulsed with an ultrashort duration of tens of femtoseconds and has a high peak intensity of 7.8 × 10{sup 21} s{sup −1}, thus allows specific studies of fast kinetics in millimeter-thick materials with a high time resolution and exhibits potential for applications in positron annihilation spectroscopy.
Neutrino emissivity from electron-positron annihilation in hot matter in a strong magnetic field
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.
Mukherjee, S.; Shastry, K.; Anto, C. V.; Joglekar, P. V.; Nadesalingam, M. P.; Xie, S.; Jiang, N.; Weiss, A. H.
2016-03-15
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.
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.
Shock waves and double layers in a quantum electron-positron-ion plasma
NASA Astrophysics Data System (ADS)
Dip, P. R.; Hossen, M. A.; Salahuddin, M.; Mamun, A. A.
2016-02-01
The ion-acoustic (IA) shock waves and double layers (DLs) in an unmagnetized, dissipative, quantum electron-positron-ion (EPI) plasma (composed of a viscous heavy ion fluid, Fermi electrons and positrons) have been theoretically investigated. The higher-order Burgers and Gardner equations are derived by employing the reductive perturbation method. The basic features of the IA shock waves and the DLs are identified by analyzing the solutions of both the higher-order Burgers and Gardner equations. The ratio of the Fermi temperature of the positron to that of the electron, the Fermi pressure of electrons and positrons, the viscous force, the plasma particle number densities, etc. are found to change remarkably the basic features (viz. amplitude, width, phase speed, etc.) of the IA waves. The results of our investigation may be helpful in understanding the nonlinear features of localized IA waves propagating in quantum EPI plasmas which are ubiquitous in astrophysical, as well as laboratory, environments.
Wave dispersion in a counterstreaming, relativistic thermal, magnetized, electron-positron plasma.
Verdon, M W; Melrose, D B
2011-05-01
The dispersion equation is analyzed for waves in a strongly magnetized, electron-positron plasma in which counterstreaming electrons and positrons have a relativistic thermal distribution in their respective rest frames, for propagation parallel to the magnetic field. We derive the response tensor for the medium, demonstrate the dispersion curves for different temperatures, and discuss the differences from the cold-plasma case. Application to the case of pulsar magnetospheres is discussed. © 2011 American Physical Society
Antiproton, positron, and electron imaging with a microchannel plate/phosphor detector
NASA Astrophysics Data System (ADS)
Andresen, G. B.; Bertsche, W.; Bowe, P. D.; Bray, C. C.; Butler, E.; Cesar, C. L.; Chapman, S.; Charlton, M.; El Nasr, S. Seif; Fajans, J.; Fujiwara, M. C.; Gill, D. R.; Hangst, J. S.; Hardy, W. N.; Hayano, R. S.; Hayden, M. E.; Humphries, A. J.; Hydomako, R.; Jørgensen, L. V.; Kerrigan, S. J.; Kurchaninov, L.; Lambo, R.; Madsen, N.; Nolan, P.; Olchanski, K.; Olin, A.; Povilus, A. P.; Pusa, P.; Sarid, E.; Silveira, D. M.; Storey, J. W.; Thompson, R. I.; van der Werf, D. P.; Yamazaki, Y.; Alpha Collaboration
2009-12-01
A microchannel plate (MCP)/phosphor screen assembly has been used to destructively measure the radial profile of cold, confined antiprotons, electrons, and positrons in the ALPHA experiment, with the goal of using these trapped particles for antihydrogen creation and confinement. The response of the MCP to low energy (10-200 eV, <1 eV spread) antiproton extractions is compared to that of electrons and positrons.
Antiproton, positron, and electron imaging with a microchannel plate/phosphor detector
Andresen, G. B.; Bowe, P. D.; Hangst, J. S.; Bertsche, W.; Butler, E.; Charlton, M.; Humphries, A. J.; Joergensen, L. V.; Kerrigan, S. J.; Madsen, N.; Werf, D. P. van der; Bray, C. C.; Chapman, S.; Fajans, J.; Povilus, A. P.; Cesar, C. L.; Lambo, R.; Fujiwara, M. C.; Gill, D. R.; Collaboration: ALPHA Collaboration; and others
2009-12-15
A microchannel plate (MCP)/phosphor screen assembly has been used to destructively measure the radial profile of cold, confined antiprotons, electrons, and positrons in the ALPHA experiment, with the goal of using these trapped particles for antihydrogen creation and confinement. The response of the MCP to low energy (10-200 eV, <1 eV spread) antiproton extractions is compared to that of electrons and positrons.
Positrons for linear colliders
Ecklund, S.
1987-11-01
The requirements of a positron source for a linear collider are briefly reviewed, followed by methods of positron production and production of photons by electromagnetic cascade showers. Cross sections for the electromagnetic cascade shower processes of positron-electron pair production and Compton scattering are compared. A program used for Monte Carlo analysis of electromagnetic cascades is briefly discussed, and positron distributions obtained from several runs of the program are discussed. Photons from synchrotron radiation and from channeling are also mentioned briefly, as well as positron collection, transverse focusing techniques, and longitudinal capture. Computer ray tracing is then briefly discussed, followed by space-charge effects and thermal heating and stress due to showers. (LEW)
Electronic correlations in vanadium revealed by electron-positron annihilation measurements
NASA Astrophysics Data System (ADS)
Weber, Josef Andreas; Benea, Diana; Appelt, Wilhelm H.; Ceeh, Hubert; Kreuzpaintner, Wolfgang; Leitner, Michael; Vollhardt, Dieter; Hugenschmidt, Christoph; Chioncel, Liviu
2017-02-01
The electronic structure of vanadium measured by angular correlation of electron-positron annihilation radiation (ACAR) is compared with the predictions of the combined density functional and dynamical mean-field theory (DMFT). Reconstructing the momentum density from five two-dimensional projections we were able to determine the full Fermi surface and found excellent agreement with the DMFT calculations. In particular, we show that the local, dynamic self-energy corrections contribute to the anisotropy of the momentum density and need to be included to explain the experimental results.
Small amplitude Kinetic Alfven waves in a superthermal electron-positron-ion plasma
NASA Astrophysics Data System (ADS)
Adnan, Muhammad; Mahmood, Sahahzad; Qamar, Anisa; Tribeche, Mouloud
2016-11-01
We are investigating the propagating properties of coupled Kinetic Alfven-acoustic waves in a low beta plasma having superthermal electrons and positrons. Using the standard reductive perturbation method, a nonlinear Korteweg-de Vries (KdV) type equation is derived which describes the evolution of Kinetic Alfven waves. It is found that nonlinearity and Larmor radius effects can compromise and give rise to solitary structures. The parametric role of superthermality and positron content on the characteristics of solitary wave structures is also investigated. It is found that only sub-Alfvenic and compressive solitons are supported in the present model. The present study may find applications in a low β electron-positron-ion plasma having superthermal electrons and positrons.
Measurement of internal pairs from {sup 206}Pb
Ahmad, I.; Back, B.B.; Betts, R.R.
1995-08-01
The failure to observe sharp sum-energy lines in measurements of {sup 238}U + {sup 181}Ta and {sup 238}U + {sup 232}Th raises the issue of the correct functioning of APEX under in-beam conditions. Extensive measurements with electron and pair emitting sources were used to demonstrate the resolution and acceptance of APEX, but the possibility remains that some unforeseen background or other effects might compromise the ability to see peaks in-beam. In order to test the functioning of APEX under the most stringent conditions, we also performed a measurement of internal pairs produced in the decay of the 2.648-MeV 3{sup -} state in {sup 206}Pb to the 2{sup +} state at 0.803 MeV. The 3{sup -} state was excited in the {sup 206}Pb + {sup 206}Pb reaction at 5.9 MeV/u with a cross section of roughly 40 mb, resulting in an expected pair cross section of approximately 16 {mu}b. It should be emphasized that this measurement represents a much stricter test of the functioning of the apparatus than the observation of sum-energy lines would represent, as the internal pair measurement requires a Doppler shift correction before the transition can be seen. These data were analyzed and clearly show the expected peak. A Doppler-corrected sum-energy spectrum showing the expected IPC line at 823 keV. At present we are evaluating the acceptance of APEX for events of this type but it is clear that the observed yield is close to expectations.
Secondary electron spectra of gold under bombardment by very low-energy positrons
NASA Astrophysics Data System (ADS)
Mukherjee, S.; Nadesalingam, M. P.; Guagliardo, Paul; Sergeant, A. D.; Williams, J. F.; Weiss, A. H.
2008-10-01
Measurements of the secondary electron energy spectra resulting from very low-energy positron bombardment of a polycrystalline Au surface are presented. The low-energy part of the secondary spectra contain significant contributions from two processes: (1) annihilation-induced Auger electrons that have lost energy before leaving the surface and (2) secondary electrons resulting from direct energy exchange with an incident positron. Our data indicate that the second process (direct energy exchange with the primary positron) is still important at and below 3 eV incident beam energy. Since energy conservation precludes secondary electron generation below an incident beam energy equal to the difference between the electron and positron work functions (˜3 eV), the fact that we still observe significant secondary electron emission at energies at or below this value provides strong evidence that the incident positrons are falling directly into the surface state and transferring all of the energy difference to an outgoing secondary electron. These measurements were also used to obtain the first experimentally determined upper limit on the intensity of the spectrum of Auger-induced secondary electrons.
QCD PHYSICS OPPORTUNITIES IN LOW-ENERGY ELECTRON-POSITRON ANNIHILATION
Brodsky, S
2003-11-21
I survey a number of interesting tests of quantum chromodynamics at the amplitude level which can be carried out in electron-positron annihilation and in photon-photon collisions at low energy. Some of the tests require e{sup +}e{sup -} center of mass energy as small as {radical}s = 2 GeV. Other tests which involve a spectrum of energies can be carried out advantageously at high energy facilities using the radiative return method. These include measurements of fundamental processes such as timelike form factors and transition amplitudes, timelike Compton scattering, timelike photon to meson transition amplitudes, and two-photon exclusive processes. Many of these reactions test basic principles of QCD such as hadronization at the amplitude level, factorization, and hadron helicity conservation, tools also used in the analysis of exclusive B and D decays. Measurements of the final-state polarization in hadron pair production determine the relative phase of the timelike form factors and thus strongly discriminate between analytic forms of models which fit the form factors in the spacelike region. The role of two-photon exchange amplitudes can be tested using the charge asymmetry of the e{sup +}e{sup -} {yields} B{bar B} processes. These tests can help resolve the discrepancy between the Jefferson laboratory measurements of the ratio of G{sub E} and G{sub M} proton form factors using the polarization transfer method versus measurements using the traditional Rosenbluth method. Precision measurements of the electron-positron annihilation cross section can test the generalized Crewther relation and determine whether the effective couplings defined from physical measurements show infrared fixed-point and near conformal behavior. I also discuss a number of tests of novel QCD phenomena accessible in e{sup +}e{sup -} annihilation, including near-threshold reactions, the production of baryonium, gluonium states, and pentaquarks.
Shahmansouri, M.; Misra, A. P. E-mail: apmisra@gmail.com
2016-07-15
The dispersion properties of elliptically polarized electromagnetic waves in a magnetized electron-positron-pair (EP-pair) plasma are studied with the effects of particle dispersion associated with the Bohm potential, the Fermi degenerate pressure, and the exchange-correlation force. Two possible modes of the extraordinary or X wave, modified by these quantum effects, are identified and their propagation characteristics are investigated numerically. It is shown that the upper-hybrid frequency and the cutoff and resonance frequencies are no longer constants but are dispersive due to these quantum effects. It is found that the particle dispersion and the exchange-correlation force can have different dominating roles on each other depending on whether the X waves are of short or long wavelengths (in comparison with the Fermi Debye length). The present investigation should be useful for understanding the collective behaviors of EP plasma oscillations and the propagation of extraordinary waves in magnetized dense EP-pair plasmas.
The scaling of electron and positron generation in intense laser-solid interactionsa)
NASA Astrophysics Data System (ADS)
Chen, Hui; Link, A.; Sentoku, Y.; Audebert, P.; Fiuza, F.; Hazi, A.; Heeter, R. F.; Hill, M.; Hobbs, L.; Kemp, A. J.; Kemp, G. E.; Kerr, S.; Meyerhofer, D. D.; Myatt, J.; Nagel, S. R.; Park, J.; Tommasini, R.; Williams, G. J.
2015-05-01
This paper presents experimental scalings of the electrons and positrons produced by intense laser-target interactions at relativistic laser intensities (1018-1020 W cm-2). The data were acquired from three short-pulse laser facilities with laser energies ranging from 80 to 1500 J. We found a non-linear (≈EL2) scaling of positron yield [Chen et al., Phys. Rev. Lett. 114, 215001 (2015)] and a linear scaling of electron yield with the laser energy. These scalings are explained by theoretical and numerical analyses. Positron acceleration by the target sheath field is confirmed by the positron energy spectrum, which has a pronounced peak at energies near the sheath potential, as determined by the observed maximum energies of accelerated protons. The parameters of laser-produced electron-positron jets are summarized together with the theoretical energy scaling. The measured energy-squared scaling of relativistic electron-positron jets indicates the possibility to create an astrophysically relevant experimental platform with such jets using multi-kilojoule high intensity lasers currently under construction.
The scaling of electron and positron generation in intense laser-solid interactions
Chen, Hui; Link, A.; Fiuza, F.; Hazi, A.; Heeter, R. F.; Kemp, A. J.; Kemp, G. E.; Nagel, S. R.; Park, J.; Tommasini, R.; Williams, G. J.; Sentoku, Y.; Audebert, P.; Hill, M.; Hobbs, L.; Kerr, S.; Meyerhofer, D. D.; Myatt, J.
2015-05-15
This paper presents experimental scalings of the electrons and positrons produced by intense laser-target interactions at relativistic laser intensities (10{sup 18}–10{sup 20} W cm{sup −2}). The data were acquired from three short-pulse laser facilities with laser energies ranging from 80 to 1500 J. We found a non-linear (≈E{sub L}{sup 2}) scaling of positron yield [Chen et al., Phys. Rev. Lett. 114, 215001 (2015)] and a linear scaling of electron yield with the laser energy. These scalings are explained by theoretical and numerical analyses. Positron acceleration by the target sheath field is confirmed by the positron energy spectrum, which has a pronounced peak at energies near the sheath potential, as determined by the observed maximum energies of accelerated protons. The parameters of laser-produced electron-positron jets are summarized together with the theoretical energy scaling. The measured energy-squared scaling of relativistic electron-positron jets indicates the possibility to create an astrophysically relevant experimental platform with such jets using multi-kilojoule high intensity lasers currently under construction.
INTEGRAL SPI Limits on Electron-Positron Annihilation Radiation from the Galactic Plane
NASA Astrophysics Data System (ADS)
Teegarden, B. J.; Watanabe, K.; Jean, P.; Knödlseder, J.; Lonjou, V.; Roques, J. P.; Skinner, G. K.; von Ballmoos, P.; Weidenspointner, G.; Bazzano, A.; Butt, Y. M.; Decourchelle, A.; Fabian, A. C.; Goldwurm, A.; Güdel, M.; Hannikainen, D. C.; Hartmann, D. H.; Hornstrup, A.; Lewin, W. H. G.; Makishima, K.; Malzac, A.; Miller, J.; Parmar, A. N.; Reynolds, S. P.; Rothschild, R. E.; Schönfelder, V.; Tomsick, J. A.; Vink, J.
2005-03-01
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 2002 October, 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|>40deg) of our Galaxy. In this paper we describe the observations and data analysis methods and give limits on the 511 keV flux.
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.
Design of An 18 MW Beam Dump for 500 GeV Electron/Positron Beams at An ILC
Amann, John; Arnold, Ray; Seryi, Andrei; Walz, Dieter; Kulkarni, Kiran; Rai, Pravin; Satyamurthy, Polepalle; Tiwari, Vikar; Vincke, Heinz; /CERN
2012-07-05
This article presents a report on the progress made in designing 18 MW water based Beam Dumps for electrons or positrons for an International Linear Collider (ILC). Multi-dimensional technology issues have to be addressed for the successful design of the Beam Dump. They include calculations of power deposition by the high energy electron/positron beam bunch trains, computational fluid dynamic analysis of turbulent water flow, mechanical design, process flow analysis, hydrogen/oxygen recombiners, handling of radioactive 7Be and 3H, design of auxiliary equipment, provisions for accident scenarios, remote window exchanger, radiation shielding, etc. The progress made to date is summarized, the current status, and also the issues still to be addressed.
Simultaneous confinement of low-energy electrons and positrons in a compact magnetic mirror trap
NASA Astrophysics Data System (ADS)
Higaki, H.; Kaga, C.; Fukushima, K.; Okamoto, H.; Nagata, Y.; Kanai, Y.; Yamazaki, Y.
2017-02-01
More than 107 electrons and 105 positrons with energy less than a few eV were confined simultaneously for the first time in a compact magnetic mirror trap with plugging potentials. The exponential decay time constant of the confined positrons exceeded 70 ms at the beginning of the simultaneous confinement. Particle simulations in the early stages of the mixing process were also conducted. The results obtained in the experiments and simulations suggested that an improved setup would make it possible to investigate the unexplored field of low-energy electron–positron plasmas experimentally.
Nonlinear waves in electron-positron-ion plasmas including charge separation
NASA Astrophysics Data System (ADS)
Mugemana, A.; Moolla, S.; Lazarus, I. J.
2017-02-01
Nonlinear low-frequency electrostatic waves in a magnetized, three-component plasma consisting of hot electrons, hot positrons and warm ions have been investigated. The electrons and positrons are assumed to have Boltzmann density distributions while the motion of the ions are governed by fluid equations. The system is closed with the Poisson equation. This set of equations is numerically solved for the electric field. The effects of the driving electric field, ion temperature, positron density, ion drift, Mach number and propagation angle are investigated. It is shown that depending on the driving electric field, ion temperature, positron density, ion drift, Mach number and propagation angle, the numerical solutions exhibit waveforms that are sinusoidal, sawtooth and spiky. The introduction of the Poisson equation increased the Mach number required to generate the waveforms but the driving electric field E 0 was reduced. The results are compared with satellite observations.
Pair production from vacuum at the focus of an X-ray free electron laser
NASA Astrophysics Data System (ADS)
Ringwald, A.
2001-06-01
There are definite plans for the construction of X-ray free electron lasers (FEL), both at DESY, where the so-called XFEL is part of the design of the electron-positron linear collider TESLA, as well as at SLAC, where the so-called Linac Coherent Light Source (LCLS) has been proposed. Such an X-ray laser would allow for high-field science applications: one could make use of not only the high energy and transverse coherence of the X-ray beam, but also of the possibility of focusing it to a spot with a small radius, hopefully in the range of the laser wavelength. Along this route one obtains very large electric fields, much larger than those obtainable with any optical laser of the same power. In this Letter we discuss the possibility of obtaining an electric field so high that electron-positron pairs are spontaneously produced in vacuum (Schwinger pair production). We find that if X-ray optics can be improved to approach the diffraction limit of focusing, and if the power of the planned X-ray FELs can be increased to the terawatt region, then there is ample room for an investigation of the Schwinger pair production mechanism.
Sirjoosingh, Andrew; Pak, Michael V; Swalina, Chet; Hammes-Schiffer, Sharon
2013-07-21
In the application of the nuclear-electronic orbital (NEO) method to positronic systems, all electrons and the positron are treated quantum mechanically on the same level. Explicit electron-positron correlation can be included using Gaussian-type geminal functions within the variational self-consistent-field procedure. In this paper, we apply the recently developed reduced explicitly correlated Hartree-Fock (RXCHF) approach to positronic molecular systems. In the application of RXCHF to positronic systems, only a single electronic orbital is explicitly correlated to the positronic orbital. We apply NEO-RXCHF to three systems: positron-lithium, lithium positride, and positron-lithium hydride. For all three of these systems, the RXCHF approach provides accurate two-photon annihilation rates, average contact densities, electronic and positronic single-particle densities, and electron-positron contact densities. Moreover, the RXCHF approach is significantly more accurate than the original XCHF approach, in which all electronic orbitals are explicitly correlated to the positronic orbital in the same manner, because the RXCHF wavefunction is optimized to produce a highly accurate description of the short-ranged electron-positron interaction that dictates the annihilation rates and other local properties. Furthermore, RXCHF methods that neglect or approximate the electronic exchange interactions between the geminal-coupled electronic orbital and the regular electronic orbitals lead to virtually identical annihilation rates and densities as the fully antisymmetric RXCHF method but offer substantial advantages in computational tractability. Thus, NEO-RXCHF is a promising, computationally practical approach for studying larger positron-containing systems.
Study on Momentum Density of Electrons and Fermi Surface in Niobium by Positron Annihilation
NASA Astrophysics Data System (ADS)
Kubota, Takeshi; Kondo, Hitoshi; Watanabe, Kazuhiro; Murakami, Yasukazu; Cho, Yang-Koo; Tanigawa, Shoichiro; Kawano, Takao; Bahng, Gun-Woong
1990-12-01
The three dimensional electron-positron momentum density in niobium has been reconstructed from measurements of two dimensional angular correlation of positron annihilation radiations (2D-ACAR) followed by the image reconstruction technique based on a direct Fourier transformation. We determined the position of the Fermi surface sheets; \\varGamma-centered hole octahedron, multiply connected jungle-gym arms and N-centered hole ellipsoids. The Fermi surface topology is in good agreement with the theory.
NASA Astrophysics Data System (ADS)
Kounine, A.; Weng, Z.; Xu, W.; Zhang, C.
2017-10-01
The Alpha Magnetic Spectrometer, AMS, is successfully collecting data on the International Space Station since its installation on May 19, 2011. One of the main objectives of AMS is the precision measurement of high energy cosmic ray electrons and positrons. The key detector for this measurement is the Electromagnetic Calorimeter. Reconstruction of electrons and positrons in the calorimeter uses a 3-dimensional shower parametrization, which accounts for the detector specifics: finite size of the calorimeter, non-uniform efficiency of the signal collection, and saturation effects due to the electronics and due to high energy density in the active calorimeter elements. This technique provides AMS with a precision energy measurement of electrons and positrons up to several TeV as well as an excellent rejection of the proton background.
Presenting International Literature through Author Studies and Author Pairings.
ERIC Educational Resources Information Center
Lynch-Brown, Carol; Tomlinson, Carl M.
1997-01-01
Discusses the value of international books as a source of literature for middle school students. Considers the benefits of international books, and instructional strategies including focusing on an international author and author pairings. Provides an annotated list of works by Robin Klein, John Marsden, Uri Orlev, Anthony Browne, and Jorg Muller.…
Scaling the Yield of Laser-Driven Electron-Positron Jets to Laboratory Astrophysical Applications
NASA Astrophysics Data System (ADS)
Chen, Hui; Fiuza, F.; Link, A.; Hazi, A.; Hill, M.; Hoarty, D.; James, S.; Kerr, S.; Meyerhofer, D. D.; Myatt, J.; Park, J.; Sentoku, Y.; Williams, G. J.
2015-05-01
We report new experimental results obtained on three different laser facilities that show directed laser-driven relativistic electron-positron jets with up to 30 times larger yields than previously obtained and a quadratic (˜EL2 ) dependence of the positron yield on the laser energy. This favorable scaling stems from a combination of higher energy electrons due to increased laser intensity and the recirculation of MeV electrons in the mm-thick target. Based on this scaling, first principles simulations predict the possibility of using such electron-positron jets, produced at upcoming high-energy laser facilities, to probe the physics of relativistic collisionless shocks in the laboratory.
Positron and electron scattering from alkane molecules. Normal- and cyclo-octane
NASA Astrophysics Data System (ADS)
Sueoka, O.; Makochekanwa, C.; Kimura, M.
2006-03-01
Total cross-sections (TCSs) for 0.2 1000 eV positrons and 0.4 1000 eV electrons colliding with normal-octane and cyclo-octane molecules have been studied using a relative measurement method. The TCS curves for positron and electron vary smoothly and compare well with other alkane molecules, in order of increasing carbon number. For positron scattering, weak humps at 1.5 2.5 eV for both normal- and cyclo-octane were observed. In the energy range lower than 2.2 eV, positron TCSs are roughly equal to or larger than electron TCSs. For electron scattering, a resonance peak at 8 eV and a shoulder at 25.0 eV were observed for both molecules. Over all the energy range, the TCS values for normal-octane are larger than those of cyclo-octane. The positron and electron TCS data for normal- and cyclo-octane molecules are briefly compared with those for normal- and cyclo-hexane.
Resonance method to produce a polarisation asymmetry in electron-positron storage rings
Toner, W.T.
1988-01-01
Pulsed solenoids of a few tens of ampere turns, operated in synchronism with the ..gamma..(g-2/2) 'th harmonic of the orbit period, can be used to prevent a stored electron beam from becoming polarised through the emission of synchrotron radiation. With such low fields it is easy to arrange that only some of the stored bunches are affected. This makes it possible to produce collisions between counter-rotating electrons and positrons stored in a single ring in which the electron and positron polarisations are not equal and opposite. 8 refs.
Environmental assessment for the proposed B-Factory (Asymmetric Electron Positron Collider)
Not Available
1993-11-01
This document presents the potential environmental consequences associated with the construction and operation of an Asymmetric Electron Positron Collider, also known as a B-Factory. DOE proposes to modify either the existing Positron-Electron Project at the Stanford Linear Accelerator Center (SLAC) or the Cornell Electron Storage Ring (CESR) at Cornell University. PEP and CESR provide the most technically promising and practical options for a B-Factory. A B-Factory can be constructed by modifying the existing facilities and with minor or no conventional construction. Details involved with the upgrade along with two alternatives to the proposed action are described.
Wave dispersion in a counterstreaming, cold, magnetized, electron-positron plasma.
Verdon, M W; Melrose, D B
2008-04-01
The dispersion equation is analyzed for waves in a strongly magnetized, electron-positron plasma in which counterstreaming electrons are cold in their respective rest frames. For propagation parallel to the magnetic field the dispersion equation factorizes into equations for two longitudinal modes and four transverse modes. Instabilities occur in both longitudinal and transverse modes, with the most notable being at low wave numbers where a longitudinal branch has purely imaginary frequency. For oblique propagation at small angles, the modes reconnect at points where the parallel modes intersect, either deviating away from each another, or being separated by a pair of complex modes. In addition, intrinsically oblique branches of the dispersion equation appear. The results are applied to an oscillating model for a pulsar magnetosphere, in which the oscillations are purely temporal with a frequency well below relevant wave frequencies, and in which the counterstreaming becomes highly relativistic. We assume that the medium may be treated as time stationary in treating the wave dispersion and wave growth. The wave properties, including the wave frequency, vary periodically with the phase of the oscillations. The fastest growing instability is when the counterstreaming is nonrelativistic or mildly relativistic. A given wave can experience bursts of growth over many oscillations. Mode coupling associated with the cyclotron resonance may be effective in generating the observed orthogonally polarized modes at phases of the oscillation where the (relativistic) cyclotron and wave frequencies are comparable.
Particle Acceleration and Magnetic Field Generation in Electron-Positron Relativistic Shocks
NASA Technical Reports Server (NTRS)
Nishikawa, K.-L.; Hardee, P.; Richardson, G.; Preece, R.; Sol, H.; Fishman, G. J.
2004-01-01
Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., Buneman, Weibel and other two-stream instabilities) created in collisionless shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic electron-positron jet front propagating into an ambient electron-positron plasma with and without initial magnetic fields. We find small differences in the results for no ambient and modest ambient magnetic fields. Simulations show that the Weibel instability created in the collisionless shock front accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction. The non-linear fluctuation amplitudes of densities, currents, electric, and magnetic fields in the electron-positron shock are larger than those found in the electron-ion shock studied in a previous paper at the comparable simulation time. This comes from the fact that both electrons and positrons contribute to generation of the Weibel instability. Additionally, we have performed simulations with different electron skin depths. We find that growth times scale inversely with the plasma frequency, and the sizes of structures created by the Weibel instability scale proportional to the electron skin depth. This is the expected result and indicates that the simulations have sufficient grid resolution. While some Fermi acceleration may occur at the jet front, the majority of electron and positron acceleration takes place behind the jet front and cannot be characterized as Fermi acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying nonuniform: small-scale magnetic fields which contribute to the electron's (positron's) transverse deflection behind the jet head. This small scale magnetic field structure
Particle Acceleration and Magnetic Field Generation in Electron-Positron Relativistic Shocks
NASA Technical Reports Server (NTRS)
Nishikawa, K.-I.; Hardee, P.; Richardson, G.; Preece, R.; Sol, H.; Fishman, G. J.
2004-01-01
Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., Buneman, Weibel and other two-stream instabilities) created in collisionless shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic electron-positron jet front propagating into an ambient electron-positron plasma with and without initial magnetic fields. We find small differences in the results for no ambient and modest ambient magnetic fields. Simulations show that the Weibel instability created in the collisionless shock front accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction. The non-linear fluctuation amplitudes of densities, currents, electric, and magnetic fields in the electron-positron shock are larger than those found in the electron-ion shock studied in a previous paper. This comes from the fact that both electrons and positrons contribute to generation of the Weibel instability. Additionally, we have performed simulations with different electron skin depths. We find that growth times scale inversely with the plasma frequency, and the sizes of structures created by the Weibel instability scale proportional to the electron skin depth. This is the expected result and indicates that the simulations have sufficient grid resolution. While some Fermi acceleration may occur at the jet front, the majority of electron and positron acceleration takes place behind the jet front and cannot be characterized as Fermi acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying nonuniform, small-scale magnetic fields which contribute to the electron's (positron's) transverse deflection behind the jet head. This small scale magnetic field structure is appropriate to the generation
Particle Acceleration and Magnetic Field Generation in Electron-Positron Relativistic Shocks
NASA Technical Reports Server (NTRS)
Nishikawa, K.-I.; Hardee, P.; Richardson, G.; Preece, R.; Sol, H.; Fishman, G. J.
2005-01-01
Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., Buneman, Weibel, and other two-stream instabilities) created in collisionless shocks are responsible for particle (electron, positron, and ion) acceleration. Using a three-dimensional relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic electron-positron jet front propagating into an ambient electron-positron plasma with and without initial magnetic fields. We find small differences in the results for no ambient and modest ambient magnetic fields. New simulations show that the Weibel instability created in the collisionless shock front accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction. Furthermore, the nonlinear fluctuation amplitudes of densities, currents, and electric and magnetic fields in the electron-positron shock are larger than those found in the electron-ion shock studied in a previous paper at a comparable simulation time. This comes from the fact that both electrons and positrons contribute to generation of the Weibel instability. In addition, we have performed simulations with different electron skin depths. We find that growth times scale inversely with the plasma frequency, and the sizes of structures created by tine Weibel instability scale proportionally to the electron skin depth. This is the expected result and indicates that the simulations have sufficient grid resolution. While some Fermi acceleration may occur at the jet front, the majority of electron and positron acceleration takes place behind the jet front and cannot be characterized as Fermi acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying nonuniform, small-scale magnetic fields, which contribute to the electron s (positron s) transverse deflection behind the jet head. This
Electromagnetic envelope solitons in ultrarelativistic inhomogeneous electron-positron-ion plasma
Du, Hong-E; Cheng, Li-Hong; Yu, Zi-Fa; Xue, Ju-Kui
2014-08-15
The nonlinear interaction of ultra-intense short laser beam and homogeneous/inhomogeneous electron-positron-ion (e-p-i) plasma is investigated. It is found that soliton solutions can exist in both homogeneous and inhomogeneous e-p-i plasma. The influence of the positron density, the phase velocity, the inhomogeneity nature, and the Hamiltonian of the system on the soliton structure is investigated. The evolution of envelope solitons in homogeneous e-p-i plasma is analyzed analytically by using a two-time-scale method and confirmed by numerical simulations. However, the soliton solutions can exist in inhomogeneous e-p-i plasma only when the positron density is high enough. Furthermore, the phase diagram for existing envelope soliton in positron density and phase velocity of the wave plane is obtained.
Wakefields generated by collisional neutrinos in neutral-electron-positron plasma
Tinakiche, Nouara
2013-02-15
A classical fluid description is adopted to investigate nonlinear interaction between an electron-type neutrino beam and a relativistic collisionless unmagnetized neutral-electron-positron plasma. In this work, we consider the collisions of the neutrinos with neutrals in the plasma and study their effect on the generation of wakefields in this plasma.
Arbitrary amplitude Langmuir solitons in a relativistic electron-positron plasma
NASA Astrophysics Data System (ADS)
Lazarus, I. J.; Bharuthram, R.; Singh, S. V.; Lakhina, G. S.
2012-04-01
The arbitrary amplitude Langmuir solitons are investigated in an unmagnetized, warm, relativistic plasma, consisting of electrons and positrons. Both the species are considered to have equal non-relativistic temperatures, but can have arbitrary relativistic drift speeds, and their dynamics are governed by fluid equations. Using the Sagdeev psuedo-potential approach, the effects of drift speed, Mach number, and thermal temperature on the amplitude and width of the Langmuir solitons are investigated. For the parameters considered, only rarefactive solitons are found. These solitons represent dip in electron density or electron holes in the configuration space. Existence domain of the Langmuir solitons is limited by the minimum and maximum Mach numbers for given parameters. An increase in the electron (positron) temperature leads to an increase in the Langmuir soliton amplitude and their half-widths. On the other hand, increasing the electron (positron) drift speeds results in decreasing soliton amplitudes and their half-widths. For some typical parameters corresponding to the pulsar magnetosphere, namely electron density ~106 cm-3 and electron thermal velocity of one-tenth of the velocity of light, the electric field of the Langmuir solitons can be of the order of (3-24)kV/m. The presence of such large amplitude electrostatic solitary structures may accelerate electrons and positrons and also produce fine structures of (1-5) microseconds in pulsar radio emissions.
Teaching Valence Shell Electron Pair Repulsion (VSEPR) Theory
ERIC Educational Resources Information Center
Talbot, Christopher; Neo, Choo Tong
2013-01-01
This "Science Note" looks at the way that the shapes of simple molecules can be explained in terms of the number of electron pairs in the valence shell of the central atom. This theory is formally known as valence shell electron pair repulsion (VSEPR) theory. The article explains the preferred shape of chlorine trifluoride (ClF3),…
Teaching Valence Shell Electron Pair Repulsion (VSEPR) Theory
ERIC Educational Resources Information Center
Talbot, Christopher; Neo, Choo Tong
2013-01-01
This "Science Note" looks at the way that the shapes of simple molecules can be explained in terms of the number of electron pairs in the valence shell of the central atom. This theory is formally known as valence shell electron pair repulsion (VSEPR) theory. The article explains the preferred shape of chlorine trifluoride (ClF3),…
Electron Pairing, Repulsion, and Correlation: A Simplistic Approach
ERIC Educational Resources Information Center
Olsson, Lars-Fride; Kloo, Lars
2004-01-01
The interplay between a nucleus and an electron pair is explained through a basic application of an electrostatic and balanced model to determine the correlated and repulsive movements of the electron pair. The stable correlation depends on the positive charge produced by the combined force, which in turn establishes a negative potential energy.
Electron Pairing, Repulsion, and Correlation: A Simplistic Approach
ERIC Educational Resources Information Center
Olsson, Lars-Fride; Kloo, Lars
2004-01-01
The interplay between a nucleus and an electron pair is explained through a basic application of an electrostatic and balanced model to determine the correlated and repulsive movements of the electron pair. The stable correlation depends on the positive charge produced by the combined force, which in turn establishes a negative potential energy.
Kinematic distributions for electron pair production by muons
NASA Technical Reports Server (NTRS)
Linsker, R.
1972-01-01
Cross sections and kinematic distributions for the trident production process plus or negative muon plus charge yields plus or minus muon plus electron plus positron plus charge (with charge = dipion moment and Fe) are given for beam energies of 100 to 300 GeV at fixed (electron positron) masses from 5 to 15 GeV. This process is interesting as a test of quantum electrodynamics at high energies, and in particular as a test of the form of the photon propagator at large timelike (four-momentum) squared. For this purpose, it is desirable to impose kinematic cuts that favor those Bethe-Heitler graphs which contain a timelike photon propagator. It is found that there are substantial differences between the kinematic distributions for the full Bethe-Heitler matrix element and the distributions for the two timelike-photon graphs alone; these differences can be exploited in the selection of appropriate kinematic cuts.
NASA Technical Reports Server (NTRS)
Gidley, D. W.; Rich, A.; Van House, J. C.; Zitzewitz, P. W.
1981-01-01
A positronium-formation experiment with a high sensitivity to a possible relation between the helicity of beta particles emitted in nuclear beta decay and the optical asymmetry of biological molecules is presented. The experiment is based on a mechanism in which the electrons in optically active molecules possess a helicity of less than 0.001, too weak to detect in radiolysis experiments, the sign of which depends on the chirality of the isomer. A helicity-dependent asymmetry is sought in the formation of the triplet ground state of positronium when a low-energy beam of polarized positrons of reversible helicity interacts with an optically active substance coating a channel electron multiplier. Asymmetries between positronium decays observed at positive and negative helicities for the same substance can thus be determined with a sensitivity of 0.0001, which represents a factor of 100 improvement over previous positronium experiments.
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
On a plasma having nonextensive electrons and positrons: Rogue and solitary wave propagation
El-Awady, E. I.; Moslem, W. M.
2011-08-15
Generation of nonlinear ion-acoustic waves in a plasma having nonextensive electrons and positrons has been studied. Two wave modes existing in such plasma are considered, namely solitary and rogue waves. The reductive perturbation method is used to obtain a Korteweg-de Vries equation describing the system. The latter admits solitary wave pulses, while the dynamics of the modulationally unstable wave packets described by the Korteweg-de Vries equation gives rise to the formation of rogue excitation that is described by a nonlinear Schroedinger equation. The dependence of both solitary and rogue waves profiles on the nonextensive parameter, positron-to-ion concentration ratio, electron-to-positron temperature ratio, and ion-to-electron temperature ratio are investigated numerically. The results from this work are expected to contribute to the in-depth understanding of the nonlinear excitations that may appear in nonextensive astrophysical plasma environments, such as galactic clusters, interstellar medium, etc.
Nonlinear ion-acoustic structures in dusty plasma with superthermal electrons and positrons
El-Tantawy, S. A.; El-Bedwehy, N. A.; Moslem, W. M.
2011-05-15
Nonlinear ion-acoustic structures are investigated in an unmagnetized, four-component plasma consisting of warm ions, superthermal electrons and positrons, as well as stationary charged dust impurities. The basic set of fluid equations is reduced to modified Korteweg-de Vries equation. The latter admits both solitary waves and double layers solutions. Numerical calculations indicate that these nonlinear structures cannot exist for all physical parameters. Therefore, the existence regions for both solitary and double layers excitations have been defined precisely. Furthermore, the effects of temperature ratios of ions-to-electrons and electrons-to-positrons, positrons and dust concentrations, as well as superthermal parameters on the profiles of the nonlinear structures are investigated. Also, the acceleration and deceleration of plasma species have been highlight. It is emphasized that the present investigation may be helpful in better understanding of nonlinear structures which propagate in astrophysical environments, such as in interstellar medium.
NASA Astrophysics Data System (ADS)
Iqbal, M. J.; Masood, W.; Shah, H. A.; Tsintsadze, N. L.
2017-01-01
In the present work, we have investigated the effect of trapping as a microscopic phenomenon on the formation of solitary structures in the presence of a quantizing magnetic field in an electron-positron-ion (e-p-i) plasma having degenerate electrons and positrons, whereas ions are taken to be classical and cold. We have found that positron concentration, quantizing magnetic field, and finite electron temperature effects not only affect the linear dispersion characteristics of the electrostatic waves under consideration but also have a significant bearing on the propagation of solitary structures in the nonlinear regime. Importantly, the system under consideration has been found to allow the formation of compressive solitary structures only. The work presented here may be beneficial to understand the propagation of nonlinear electrostatic structures in dense astrophysical environments and in intense-laser plasma interactions.
NASA Astrophysics Data System (ADS)
Hafez, M. G.; Talukder, M. R.; Hossain Ali, M.
2016-01-01
The Korteweg-de Vries Burgers (KdVB) -like equation is derived to study the characteristics of nonlinear propagation of ion acoustic solitions in a highly relativistic plasma containing relativistic ions and nonextensive distribution of electrons and positrons using the well known reductive perturbation technique. The KdVB-like equation is solved employing the Bernoulli's equation method taking unperturbed positron to electron concentration ratio, electron to positron temperature ratio, strength of nonextensivity, ion kinematic viscosity, and highly relativistic streaming factor. It is found that these parameters significantly modify the structures of the solitonic excitation. The ion acoustic shock profiles are observed due to the influence of ion kinematic viscosity. In the absence of dissipative term to the KdVB equation, compressive and rarefactive solitons are observed in case of superthermality, but only compressive solitons are found for the case of subthermality.
Photons, Electrons and Positrons Transport in 3D by Monte Carlo Techniques
2014-12-01
Version 04 FOTELP-2014 is a new compact general purpose version of the previous FOTELP-2K6 code designed to simulate the transport of photons, electrons and positrons through three-dimensional material and sources geometry by Monte Carlo techniques, using subroutine package PENGEOM from the PENELOPE code under Linux-based and Windows OS. This new version includes routine ELMAG for electron and positron transport simulation in electric and magnetic fields, RESUME option and routine TIMER for obtaining starting random number and for measuring the time of simulation.
Electron and positron scattering on rubidium at 200 eV
Chin, J. H.; Ratnavelu, K.; Zhou, Y.
2014-03-05
The recent implementation of the coupled-channels-optical method (CCOM) [1,2], in the study of the electron and positron-Rubidium(Rb) scattering at intermediate energies [3,4], shows that the continuum effect remains important as the energy increases, even to 100 eV. Here, we study the effect of the continuum in electron and positron scattering on Rb at an even higher energy namely 200 eV. The total, elastic and inelastic integral and differential cross sections are therefore calculated and compared to the available experimental [5] and theoretical data [6,7].
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.
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.
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.
Visible and dark matter genesis and cosmic positron and electron excesses
Gu Peihong; Sarkar, Utpal; Zhang Xinmin
2009-10-01
Dark and baryonic matter contribute comparable energy density to the present universe. The dark matter may also be responsible for the cosmic positron and electron excesses. We connect these phenomena with the Dirac seesaw for neutrino masses. In our model (i) the dark matter relic density is a dark matter asymmetry generated simultaneously with the baryon asymmetry so that we can naturally understand the coincidence between the dark and baryonic matter and (ii) the dark matter mostly decays into the leptons so that its decay can interpret the anomalous cosmic rays with positron and electron excesses.
PREFACE: 13th International Workshop on Slow Positron Beam Techniques and Applications (SLOPOS13)
NASA Astrophysics Data System (ADS)
2014-04-01
These proceedings originate from the 13th International Workshop on Slow Positron Beam Techniques and Applications SLOPOS13 which was held at the campus of the Technische Universität München in Garching between 15th-20th September, 2013. This event is part of a series of triennial SLOPOS conferences. In total 123 delegates from 21 countries participated in the SLOPOS13. The excellent scientific program comprised 50 talks and 58 posters presented during two poster sessions. It was very impressive to learn about novel technical developments on positron beam facilities and the wide range of their applications all over the world. The workshop reflected the large variety of positron beam experiments covering fundamental studies, e.g., for efficient production of anti-hydrogen as well as applied research on defects in bulk materials, thin films, surfaces, and interfaces. The topics comprised: . Positron transport and beam technology . Pulsed beams and positron traps . Defect profiling in bulk and layered structures . Nanostructures, porous materials, thin films . Surfaces and interfaces . Positronium formation and emission . Positron interactions with atoms and molecules . Many positrons and anti-hydrogen . Novel experimental techniques The international advisory committee of SLOPOS awarded student prizes for the best presented scientific contributions to a team of students from Finland, France, and the NEPOMUC team at TUM. The conference was overshadowed by the sudden death of Professor Klaus Schreckenbach immediately before the workshop. In commemoration of him as a spiritus rectus of the neutron induced positron source a minutes' silence was hold. We are most grateful for the hard work of the Local Organising Committee, the help of the International Advisory Committee, and all the students for their friendly and efficient support during the meeting. The workshop could not have occurred without the generous support of the Heinz Maier-Leibnitz Zentrum (MLZ), Deutsche
Semiclassical picture for electron-positron photoproduction in strong laser fields
NASA Astrophysics Data System (ADS)
Meuren, Sebastian; Keitel, Christoph H.; Di Piazza, Antonino
2016-04-01
The nonlinear Breit-Wheeler process is studied in the presence of strong and short laser pulses. We show that for a relativistically intense plane-wave laser field many features of the momentum distribution of the produced electron-positron pair like its extension, region of highest probability and carrier-envelope phase effects can be explained from the classical evolution of the created particles in the background field. To this end an intuitive semiclassical picture based on the local constant-crossed field approximation applied on the probability-amplitude level is established and compared with the standard approach used in QED-PIC codes. The main difference is the substructure of the spectrum, which results from interference effects between macroscopically separated formation regions. In order to compare the predictions of the semiclassical approach with exact calculations, a very fast numerical scheme is introduced. It renders the calculation of the fully differential spectrum on a grid which resolves all interference fringes feasible. Finally, the difference between classical and quantum absorption of laser four-momentum in the process is pointed out and the dominance of the former is proven. As a self-consistent treatment of the quantum absorption is not feasible within existing QED-PIC approaches, our results provide reliable error estimates relevant for regimes where the laser depletion due to a developing QED cascade becomes significant.
Modulation of a compressional electromagnetic wave in a magnetized electron-positron quantum plasma.
Amin, M R
2015-09-01
Amplitude modulation of a compressional electromagnetic wave in a strongly magnetized electron-positron pair plasma is considered in the quantum magnetohydrodynamic regime. The important ingredients of this study are the inclusion of the external strong magnetic field, Fermi quantum degeneracy pressure, particle exchange potential, quantum diffraction effects via the Bohm potential, and dissipative effect due to collision of the charged carriers. A modified-nonlinear Schödinger equation is developed for the compressional magnetic field of the electromagnetic wave by employing the standard reductive perturbation technique. The linear and nonlinear dispersions of the electromagnetic wave are discussed in detail. For some parameter ranges, relevant to dense astrophysical objects such as the outer layers of white dwarfs, neutron stars, and magnetars, etc., it is found that the compressional electromagnetic wave is modulationally unstable and propagates as a dissipated electromagnetic wave. It is also found that the quantum effects due to the particle exchange potential and the Bohm potential are negligibly small in comparison to the effects of the Fermi quantum degeneracy pressure. The numerical results on the growth rate of the modulation instability is also presented.
Overview of laser-driven generation of electron-positron beams
NASA Astrophysics Data System (ADS)
Sarri, G.; Dieckmann, M. E.; Kourakis, I.; di Piazza, A.; Reville, B.; Keitel, C. H.; Zepf, M.
2015-08-01
Electron-positron (e-p) plasmas are widely thought to be emitted, in the form of ultra-relativistic winds or collimated jets, by some of the most energetic or powerful objects in the Universe, such as black-holes, pulsars, and quasars. These phenomena represent an unmatched astrophysical laboratory to test physics at its limit and, given their immense distance from Earth (some even farther than several billion light years), they also provide a unique window on the very early stages of our Universe. However, due to such gigantic distances, their properties are only inferred from the indirect interpretation of their radiative signatures and from matching numerical models: their generation mechanism and dynamics still pose complicated enigmas to the scientific community. Small-scale reproductions in the laboratory would represent a fundamental step towards a deeper understanding of this exotic state of matter. Here we present recent experimental results concerning the laser-driven production of ultra-relativistic e-p beams. In particular, we focus on the possibility of generating beams that present charge neutrality and that allow for collective effects in their dynamics, necessary ingredients for the testing pair-plasma physics in the laboratory. A brief discussion of the analytical and numerical modelling of the dynamics of these plasmas is also presented in order to provide a summary of the novel plasma physics that can be accessed with these objects. Finally, general considerations on the scalability of laboratory plasmas up to astrophysical scenarios are given.
Modulation of a compressional electromagnetic wave in a magnetized electron-positron quantum plasma
NASA Astrophysics Data System (ADS)
Amin, M. R.
2015-09-01
Amplitude modulation of a compressional electromagnetic wave in a strongly magnetized electron-positron pair plasma is considered in the quantum magnetohydrodynamic regime. The important ingredients of this study are the inclusion of the external strong magnetic field, Fermi quantum degeneracy pressure, particle exchange potential, quantum diffraction effects via the Bohm potential, and dissipative effect due to collision of the charged carriers. A modified-nonlinear Schödinger equation is developed for the compressional magnetic field of the electromagnetic wave by employing the standard reductive perturbation technique. The linear and nonlinear dispersions of the electromagnetic wave are discussed in detail. For some parameter ranges, relevant to dense astrophysical objects such as the outer layers of white dwarfs, neutron stars, and magnetars, etc., it is found that the compressional electromagnetic wave is modulationally unstable and propagates as a dissipated electromagnetic wave. It is also found that the quantum effects due to the particle exchange potential and the Bohm potential are negligibly small in comparison to the effects of the Fermi quantum degeneracy pressure. The numerical results on the growth rate of the modulation instability is also presented.
NASA Astrophysics Data System (ADS)
Shaukat, Muzzamal Iqbal
2017-06-01
In the present work, we have investigated the effect of trapping as a microscopic phenomenon on the propagation of 1 and 2D linear and nonlinear quantum drift ion acoustic waves in a spatially inhomogeneous degenerate electron-positron-ion plasma in the presence of quantizing magnetic field having degenerate electrons and positrons. We derive the linear dispersion relation and nonlinear Korteweg-deVries and Kadomtsev Petviashvili equation for drift ion acoustic waves. It is observed that the characteristics of the dispersion relation and nonlinear drift ion solitary structures have been modified significantly by the positron concentration and quantizing magnetic field. The work presented here may be beneficial to understand the propagation of drift solitary structures in dense astrophysical environments and in intense-laser plasma interactions.
NASA Astrophysics Data System (ADS)
Ali Shan, S.; -Ur-Rehman, Aman; Mushtaq, A.
2017-03-01
Ion-acoustic solitary waves (IASWs) are investigated in a plasma having a cold positron beam fluid, electrons following a vortex-like distribution with entropic index q, and dynamic ions. Using a standard procedure, a pseudo-potential energy equation is derived. The presence of nonextensive q - distributed trapped electrons and cold positron beam has been shown to influence the small amplitude soliton structure quite significantly. From the analysis of our results, it is shown that compressive IASWs are supported in this plasma model. As the real plasma situations are observed with plasma species having a relative flow, our present analysis should be beneficial for comprehending the electrostatic solitary structures observed in fusion plasma devices and positron winds observed in astrophysical plasmas.
Measurement of Separate Cosmic-Ray Electron and Positron Spectra with the Fermi Large Area Telescope
NASA Technical Reports Server (NTRS)
Ferrara, E. C.; Harding, A. K.; McEnery, J. E.; Moiseev, A. A.; Ackemann, M.
2012-01-01
We measured separate cosmic-ray electron and positron spectra with the Fermi Large Area Telescope. Because the instrument does not have an onboard magnet, we distinguish the two species by exploiting Earth's shadow, which, is offset in opposite directions for opposite charges due to Earth's magnetic field. We estimate and subtract the cosmic-ray proton background using two different methods that produce consistent results. We report the electron-only spectrum, the positron-only spectrum, and the positron fraction between 20 and 200 Ge V. We confirm that the fraction rises with energy in the 20-100 Ge V range. The three new spectral points between 100 and 200 GeV are consistent with a fraction that is continuing to rise with energy.
Measurement of Separate Cosmic-Ray Electron and Positron Spectra with the Fermi Large Area Telescope
NASA Technical Reports Server (NTRS)
Ackermann, M.; Ajello, M.; Allafort, A.; Baldini, L.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Blandford, R. D.;
2011-01-01
We measured separate cosmic-ray electron and positron spectra with the Fermi Large Area Telescope. Because the instrument does not have an onboard magnet, we distinguish the two species by exploiting the Earth's shadow, which is offset in opposite directions for opposite charges due to the Earth's magnetic field. We estimate and subtract the cosmic-ray proton background using two different methods that produce consistent results. We report the electron-only spectrum, the positron-only spectrum, and the positron fraction between 20 GeV and 200 GeV, We confirm that the fraction rises with energy in the 20-100 GeV range and determine for the first time that it continues to rise between 100 and 200 GeV,
Positron Acceleration by Plasma Wakefields Driven by a Hollow Electron Beam
NASA Astrophysics Data System (ADS)
Jain, Neeraj; Antonsen, T. M.; Palastro, J. P.
2015-11-01
A scheme for positron plasma wakefield acceleration using hollow or donut-shaped electron driver beams is studied. An annular-shaped, electron-free region forms around the hollow driver beam, creating a favorable region (longitudinal field is accelerating and transverse field is focusing) for positron acceleration. For Facility for Advanced Accelerator Experimental Tests (FACET)-like parameters, the hollow beam driver produces accelerating gradients on the order of 10 GV /m . The accelerating gradient increases linearly with the total charge in the driver beam. Simulations show acceleration of a 23-GeV positron beam to 35.4 GeV with a maximum energy spread of 0.4% and very small emittance over a plasma length of 140 cm is possible.
Measurement of Separate Cosmic-Ray Electron and Positron Spectra with the Fermi Large Area Telescope
Ackermann, M.
2012-01-05
We measured separate cosmic-ray electron and positron spectra with the Fermi Large Area Telescope. Because the instrument does not have an onboard magnet, we distinguish the two species by exploiting the Earth’s shadow, which is offset in opposite directions for opposite charges due to the Earth’s magnetic field. We estimate and subtract the cosmic-ray proton background using two different methods that produce consistent results. We report the electron-only spectrum, the positron-only spectrum, and the positron fraction between 20 GeV and 200 GeV. We confirm that the fraction rises with energy in the 20–100 GeV range. The three new spectral pointsmore » between 100 and 200 GeV are consistent with a fraction that is continuing to rise with energy.« less
Measurement of Separate Cosmic-Ray Electron and Positron Spectra with the Fermi Large Area Telescope
Ackermann, M.
2012-01-05
We measured separate cosmic-ray electron and positron spectra with the Fermi Large Area Telescope. Because the instrument does not have an onboard magnet, we distinguish the two species by exploiting the Earth’s shadow, which is offset in opposite directions for opposite charges due to the Earth’s magnetic field. We estimate and subtract the cosmic-ray proton background using two different methods that produce consistent results. We report the electron-only spectrum, the positron-only spectrum, and the positron fraction between 20 GeV and 200 GeV. We confirm that the fraction rises with energy in the 20–100 GeV range. The three new spectral points between 100 and 200 GeV are consistent with a fraction that is continuing to rise with energy.
Positron Acceleration by Plasma Wakefields Driven by a Hollow Electron Beam.
Jain, Neeraj; Antonsen, T M; Palastro, J P
2015-11-06
A scheme for positron plasma wakefield acceleration using hollow or donut-shaped electron driver beams is studied. An annular-shaped, electron-free region forms around the hollow driver beam, creating a favorable region (longitudinal field is accelerating and transverse field is focusing) for positron acceleration. For Facility for Advanced Accelerator Experimental Tests (FACET)-like parameters, the hollow beam driver produces accelerating gradients on the order of 10 GV/m. The accelerating gradient increases linearly with the total charge in the driver beam. Simulations show acceleration of a 23-GeV positron beam to 35.4 GeV with a maximum energy spread of 0.4% and very small emittance over a plasma length of 140 cm is possible.
Ion acoustic shock waves in plasmas with warm ions and kappa distributed electrons and positrons
Hussain, S.; Mahmood, S.; Hafeez Ur-Rehman
2013-06-15
The monotonic and oscillatory ion acoustic shock waves are investigated in electron-positron-ion plasmas (e-p-i) with warm ions (adiabatically heated) and nonthermal kappa distributed electrons and positrons. The dissipation effects are included in the model due to kinematic viscosity of the ions. Using reductive perturbation technique, the Kadomtsev-Petviashvili-Burgers (KPB) equation is derived containing dispersion, dissipation, and diffraction effects (due to perturbation in the transverse direction) in e-p-i plasmas. The analytical solution of KPB equation is obtained by employing tangent hyperbolic (Tanh) method. The analytical condition for the propagation of oscillatory and monotonic shock structures are also discussed in detail. The numerical results of two dimensional monotonic shock structures are obtained for graphical representation. The dependence of shock structures on positron equilibrium density, ion temperature, nonthermal spectral index kappa, and the kinematic viscosity of ions are also discussed.
A new equation in two dimensional fast magnetoacoustic shock waves in electron-positron-ion plasmas
Masood, W.; Jehan, Nusrat; Mirza, Arshad M.
2010-03-15
Nonlinear properties of the two dimensional fast magnetoacoustic waves are studied in a three-component plasma comprising of electrons, positrons, and ions. In this regard, Kadomtsev-Petviashvili-Burger (KPB) equation is derived using the small amplitude perturbation expansion method. Under the condition that the electron and positron inertia are ignored, Burger-Kadomtsev-Petviashvili (Burger-KP) for a fast magnetoacoustic wave is derived for the first time, to the best of author's knowledge. The solutions of both KPB and Burger-KP equations are obtained using the tangent hyperbolic method. The effects of positron concentration, kinematic viscosity, and plasma beta are explored both for the KPB and the Burger-KP shock waves and the differences between the two are highlighted. The present investigation may have relevance in the study of nonlinear electromagnetic shock waves both in laboratory and astrophysical plasmas.
Kao, Y H; Tan, E H; Lim, K Y; Ng, C E; Goh, S W
2012-01-01
Yttrium-90 (90Y) internal pair production can be imaged by positron emission tomography (PET)/CT and is superior to bremsstrahlung single-photon emission CT/CT for evaluating hepatic 90Y microsphere biodistribution. We illustrate a case of 90Y imaging using first generation PET/CT technology, producing high-quality images for qualitative diagnostic purposes. PMID:21976634
Ion-acoustic cnoidal waves in plasmas with warm ions and kappa distributed electrons and positrons
NASA Astrophysics Data System (ADS)
Kaladze, T.; Mahmood, S.
2014-03-01
Electrostatic ion-acoustic periodic (cnoidal) waves and solitons in unmagnetized electron-positron-ion (EPI) plasmas with warm ions and kappa distributed electrons and positrons are investigated. Using the reductive perturbation method, the Korteweg-de Vries (KdV) equation is derived with appropriate boundary conditions for periodic waves. The corresponding analytical and various numerical solutions are presented with Sagdeev potential approach. Differences between the results caused by the kappa and Maxwell distributions are emphasized. It is revealed that only hump (compressive) structures of the cnoidal waves and solitons are formed. It is shown that amplitudes of the cnoidal waves and solitons are reduced in an EPI plasma case in comparison with the ordinary electron-ion plasmas. The effects caused by the temperature variations of the warm ions are also discussed. It is obtained that the amplitude of the cnoidal waves and solitons decreases for a kappa distributed (nonthermal) electrons and positrons plasma case in comparison with the Maxwellian distributed (thermal) electrons and positrons EPI plasmas. The existence of kappa distributed particles leads to decreasing of ion-acoustic frequency up to thermal ions frequency.
Ion-acoustic cnoidal waves in plasmas with warm ions and kappa distributed electrons and positrons
Kaladze, T.; Mahmood, S.
2014-03-15
Electrostatic ion-acoustic periodic (cnoidal) waves and solitons in unmagnetized electron-positron-ion (EPI) plasmas with warm ions and kappa distributed electrons and positrons are investigated. Using the reductive perturbation method, the Korteweg-de Vries (KdV) equation is derived with appropriate boundary conditions for periodic waves. The corresponding analytical and various numerical solutions are presented with Sagdeev potential approach. Differences between the results caused by the kappa and Maxwell distributions are emphasized. It is revealed that only hump (compressive) structures of the cnoidal waves and solitons are formed. It is shown that amplitudes of the cnoidal waves and solitons are reduced in an EPI plasma case in comparison with the ordinary electron-ion plasmas. The effects caused by the temperature variations of the warm ions are also discussed. It is obtained that the amplitude of the cnoidal waves and solitons decreases for a kappa distributed (nonthermal) electrons and positrons plasma case in comparison with the Maxwellian distributed (thermal) electrons and positrons EPI plasmas. The existence of kappa distributed particles leads to decreasing of ion-acoustic frequency up to thermal ions frequency.
Aguilar, M; Alberti, G; Alpat, B; Alvino, A; Ambrosi, G; Andeen, K; Anderhub, H; Arruda, L; Azzarello, P; Bachlechner, A; Barao, F; Baret, B; Barrau, A; Barrin, L; Bartoloni, A; Basara, L; Basili, A; Batalha, L; Bates, J; Battiston, R; Bazo, J; Becker, R; Becker, U; Behlmann, M; Beischer, B; Berdugo, J; Berges, P; Bertucci, B; Bigongiari, G; Biland, A; Bindi, V; Bizzaglia, S; Boella, G; de Boer, W; Bollweg, K; Bolmont, J; Borgia, B; Borsini, S; Boschini, M J; Boudoul, G; Bourquin, M; Brun, P; Buénerd, M; Burger, J; Burger, W; Cadoux, F; Cai, X D; Capell, M; Casadei, D; Casaus, J; Cascioli, V; Castellini, G; Cernuda, I; Cervelli, F; Chae, M J; Chang, Y H; Chen, A I; Chen, C R; Chen, H; Cheng, G M; Chen, H S; Cheng, L; Chernoplyiokov, N; Chikanian, A; Choumilov, E; Choutko, V; Chung, C H; Clark, C; Clavero, R; Coignet, G; Commichau, V; Consolandi, C; Contin, A; Corti, C; Costado Dios, M T; Coste, B; Crespo, D; Cui, Z; Dai, M; Delgado, C; Della Torre, S; Demirkoz, B; Dennett, P; Derome, L; Di Falco, S; Diao, X H; Diago, A; Djambazov, L; Díaz, C; von Doetinchem, P; Du, W J; Dubois, J M; Duperay, R; Duranti, M; D'Urso, D; Egorov, A; Eline, A; Eppling, F J; Eronen, T; van Es, J; Esser, H; Falvard, A; Fiandrini, E; Fiasson, A; Finch, E; Fisher, P; Flood, K; Foglio, R; Fohey, M; Fopp, S; Fouque, N; Galaktionov, Y; Gallilee, M; Gallin-Martel, L; Gallucci, G; García, B; García, J; García-López, R; García-Tabares, L; Gargiulo, C; Gast, H; Gebauer, I; Gentile, S; Gervasi, M; Gillard, W; Giovacchini, F; Girard, L; Goglov, P; Gong, J; Goy-Henningsen, C; Grandi, D; Graziani, M; Grechko, A; Gross, A; Guerri, I; de la Guía, C; Guo, K H; Habiby, M; Haino, S; Hauler, F; He, Z H; Heil, M; Heilig, J; Hermel, R; Hofer, H; Huang, Z C; Hungerford, W; Incagli, M; Ionica, M; Jacholkowska, A; Jang, W Y; Jinchi, H; Jongmanns, M; Journet, L; Jungermann, L; Karpinski, W; Kim, G N; Kim, K S; Kirn, Th; Kossakowski, R; Koulemzine, A; Kounina, O; Kounine, A; Koutsenko, V; Krafczyk, M S; Laudi, E; Laurenti, G; Lauritzen, C; Lebedev, A; Lee, M W; Lee, S C; Leluc, C; León Vargas, H; Lepareur, V; Li, J Q; Li, Q; Li, T X; Li, W; Li, Z H; Lipari, P; Lin, C H; Liu, D; Liu, H; Lomtadze, T; Lu, Y S; Lucidi, S; Lübelsmeyer, K; Luo, J Z; Lustermann, W; Lv, S; Madsen, J; Majka, R; Malinin, A; Mañá, C; Marín, J; Martin, T; Martínez, G; Masciocchi, F; Masi, N; Maurin, D; McInturff, A; McIntyre, P; Menchaca-Rocha, A; Meng, Q; Menichelli, M; Mereu, I; Millinger, M; Mo, D C; Molina, M; Mott, P; Mujunen, A; Natale, S; Nemeth, P; Ni, J Q; Nikonov, N; Nozzoli, F; Nunes, P; Obermeier, A; Oh, S; Oliva, A; Palmonari, F; Palomares, C; Paniccia, M; Papi, A; Park, W H; Pauluzzi, M; Pauss, F; Pauw, A; Pedreschi, E; Pensotti, S; Pereira, R; Perrin, E; Pessina, G; Pierschel, G; Pilo, F; Piluso, A; Pizzolotto, C; Plyaskin, V; Pochon, J; Pohl, M; Poireau, V; Porter, S; Pouxe, J; Putze, A; Quadrani, L; Qi, X N; Rancoita, P G; Rapin, D; Ren, Z L; Ricol, J S; Riihonen, E; Rodríguez, I; Roeser, U; Rosier-Lees, S; Rossi, L; Rozhkov, A; Rozza, D; Sabellek, A; Sagdeev, R; Sandweiss, J; Santos, B; Saouter, P; Sarchioni, M; Schael, S; Schinzel, D; Schmanau, M; Schwering, G; Schulz von Dratzig, A; Scolieri, G; Seo, E S; Shan, B S; Shi, J Y; Shi, Y M; Siedenburg, T; Siedling, R; Son, D; Spada, F; Spinella, F; Steuer, M; Stiff, K; Sun, W; Sun, W H; Sun, X H; Tacconi, M; Tang, C P; Tang, X W; Tang, Z C; Tao, L; Tassan-Viol, J; Ting, Samuel C C; Ting, S M; Titus, C; Tomassetti, N; Toral, F; Torsti, J; Tsai, J R; Tutt, J C; Ulbricht, J; Urban, T; Vagelli, V; Valente, E; Vannini, C; Valtonen, E; Vargas Trevino, M; Vaurynovich, S; Vecchi, M; Vergain, M; Verlaat, B; Vescovi, C; Vialle, J P; Viertel, G; Volpini, G; Wang, D; Wang, N H; Wang, Q L; Wang, R S; Wang, X; Wang, Z X; Wallraff, W; Weng, Z L; Willenbrock, M; Wlochal, M; Wu, H; Wu, K Y; Wu, Z S; Xiao, W J; Xie, S; Xiong, R Q; Xin, G M; Xu, N S; Xu, W; Yan, Q; Yang, J; Yang, M; Ye, Q H; Yi, H; Yu, Y J; Yu, Z Q; Zeissler, S; Zhang, J G; Zhang, Z; Zhang, M M; Zheng, Z M; Zhuang, H L; Zhukov, V; Zichichi, A; Zuccon, P; Zurbach, C
2013-04-05
A precision measurement by the Alpha Magnetic Spectrometer on the International Space Station of the positron fraction in primary cosmic rays in the energy range from 0.5 to 350 GeV based on 6.8 × 10(6) positron and electron events is presented. The very accurate data show that the positron fraction is steadily increasing from 10 to ∼ 250 GeV, but, from 20 to 250 GeV, the slope decreases by an order of magnitude. The positron fraction spectrum shows no fine structure, and the positron to electron ratio shows no observable anisotropy. Together, these features show the existence of new physical phenomena.
Marler, J. P.; Surko, C. M.
2005-12-15
Absolute measurements are presented for the positron-impact cross sections for positronium formation, direct ionization, and total ionization of the diatomic molecules N{sub 2}, CO, and O{sub 2}, in the range of energies from threshold to 90 eV. Cross sections for the electronic excitation of the a {sup 1}{pi} and a{sup '} {sup 1}{sigma} state in N{sub 2} and the A {sup 1}{pi} state in CO near threshold are also presented. The experiment uses a cold, trap-based positron beam and the technique of studying positron scattering in a strong magnetic field. In O{sub 2}, a feature previously seen in the total ionization cross section is observed in both the positronium formation and total ionization cross sections. The possible origin of this feature and its relationship to positron-induced dissociation is discussed. In N{sub 2}, the near-threshold electronic excitation cross section is larger than that for positronium formation. This likely explains the relatively high efficiency of this molecule when used for buffer-gas positron trapping.
Development of an Electron-Positron Source for Positron Annihilation Lifetime Spectroscopy
2009-12-19
coherent processes were sponsored by the NSF Quasi- monoenergetic MeV electron spectra emitted by an SiO2 plasma with (red) and without...adhering to the target surface. Aspects of this work that were directed toward neutron production were sponsored by the NRL. High-order
Hashemzadeh, M.
2015-11-15
The effect of q-nonextensive parameter and saturation time on the electron density steepening in electron-positron-ion plasmas is studied by particle in cell method. Phase space diagrams show that the size of the holes, and consequently, the number of trapped particles strongly depends on the q-parameter and saturation time. Furthermore, the mechanism of the instability and exchange of energy between electron-positron and electric field is explained by the profiles of the energy density. Moreover, it is found that the q-parameter, saturation time, and electron and positron velocities affect the nonlinear evolution of the electron density which leads to the steepening of its structure. The q-nonextensive parameter or degree of nonextensivity is the relation between temperature gradient and potential energy of the system. Therefore, the deviation of q-parameter from unity indicates the degree of inhomogeneity of temperature or deviation from equilibrium. Finally, using the kinetic theory, a generalized q-dispersion relation is presented for electron-positron-ion plasma systems. It is found that the simulation results in the linear regime are in good agreement with the growth rate results obtained by the kinetic theory.
NASA Astrophysics Data System (ADS)
Hashemzadeh, M.
2015-11-01
The effect of q-nonextensive parameter and saturation time on the electron density steepening in electron-positron-ion plasmas is studied by particle in cell method. Phase space diagrams show that the size of the holes, and consequently, the number of trapped particles strongly depends on the q-parameter and saturation time. Furthermore, the mechanism of the instability and exchange of energy between electron-positron and electric field is explained by the profiles of the energy density. Moreover, it is found that the q-parameter, saturation time, and electron and positron velocities affect the nonlinear evolution of the electron density which leads to the steepening of its structure. The q-nonextensive parameter or degree of nonextensivity is the relation between temperature gradient and potential energy of the system. Therefore, the deviation of q-parameter from unity indicates the degree of inhomogeneity of temperature or deviation from equilibrium. Finally, using the kinetic theory, a generalized q-dispersion relation is presented for electron-positron-ion plasma systems. It is found that the simulation results in the linear regime are in good agreement with the growth rate results obtained by the kinetic theory.
Linear electrostatic waves in two-temperature electron-positron plasmas
NASA Astrophysics Data System (ADS)
Lazarus, I. J.; Bharuthram, R.; Singh, S. V.; Pillay, S. R.; Lakhina, G. S.; Lakhina
2012-12-01
Linear electrostatic waves in a magnetized four-component, two-temperature electron-positron plasma are investigated, with the hot species having the Boltzmann density distribution and the dynamics of cooler species governed by fluid equations with finite temperatures. A linear dispersion relation for electrostatic waves is derived for the model and analyzed for different wave modes. Analysis of the dispersion relation for perpendicular wave propagation yields a cyclotron mode with contributions from both cooler and hot species, which in the absence of hot species goes over to the upper hybrid mode of cooler species. For parallel propagation, both electron-acoustic and electron plasma modes are obtained, whereas for a single-temperature electron-positron plasma, only electron plasma mode can exist. Dispersion characteristics of these modes at different propagation angles are studied numerically.
Ali, S.; Ata-ur-Rahman
2014-04-15
The linear and nonlinear properties of the ion-acoustic (IA) waves are investigated in a relativistically degenerate magnetoplasma, whose constituents are the electrons, positrons, and ions. The electrons and positrons are assumed to obey the Fermi-Dirac statistics, whereas the cold ions are taken to be inertial and magnetized. In linear analysis, various limiting cases are discussed both analytically and numerically. However, for nonlinear studies, the well-known reductive perturbation technique is employed to derive the Zakharov-Kuznetsov and Zakharov-Kuznetsov Burgers equations in the presence of relativistically degenerate electrons and positrons. Furthermore, with the use of hyperbolic tangent method, the equations are simplified to admit the soliton and shock wave solutions. Numerically, it is shown that the amplitude, width, and phase speed associated with the localized IA solitons and shocks are significantly influenced by the various intrinsic plasma parameters relevant to our model. The present analysis can be useful for understanding the collective processes in dense astrophysical environments like neutron stars, where the electrons and positrons are expected to be relativistic and degenerate.
Maroof, R.; Ali, S.; Mushtaq, A.; Qamar, A.
2015-11-15
Linear properties of high and low frequency waves are studied in an electron-positron-ion (e-p-i) dense plasma with spin and relativity effects. In a low frequency regime, the magnetohydrodynamic (MHD) waves, namely, the magnetoacoustic and Alfven waves are presented in a magnetized plasma, in which the inertial ions are taken as spinless and non-degenerate, whereas the electrons and positrons are treated quantum mechanically due to their smaller mass. Quantum corrections associated with the spin magnetization and density correlations for electrons and positrons are re-considered and a generalized dispersion relation for the low frequency MHD waves is derived to account for relativistic degeneracy effects. On the basis of angles of propagation, the dispersion relations of different modes are discussed analytically in a degenerate relativistic plasma. Numerical results reveal that electron and positron relativistic degeneracy effects significantly modify the dispersive properties of MHD waves. Our present analysis should be useful for understanding the collective interactions in dense astrophysical compact objects, like, the white dwarfs and in atmosphere of neutron stars.
Alam, M. S.; Uddin, M. J.; Mamun, A. A.; Masud, M. M.
2014-09-01
Positron-acoustic (PA) solitary waves (SWs) and double layers (DLs) in four-component plasmas consisting of immobile positive ions, mobile cold positrons, and superthermal (kappa distributed) hot positrons and electrons are investigated both numerically and analytically by deriving Korteweg–de Vries (K-dV), modified K-dV (mK-dV), and Gardner equations along with their DLs solutions using the reductive perturbation method. It is examined that depending on the plasma parameters, the K-dV SWs, Gardner SWs, and DLs support either compressive or rarefactive structures, whereas mK-dV SWs support only compressive structure. It is also found that the presence of superthermal (kappa distributed) hot positrons and hot electrons significantly modify the basic features of PA SWs as well as PA DLs. Besides, the critical number density ratio of hot positrons and cold positrons play an important role in the polarity of PA SWs and DLs. The implications of our results in different space as well as laboratory plasma environments are briefly discussed.
Sensitivity of Electron Transfer Mediated Decay to Ion Pairing.
Pohl, Marvin N; Richter, Clemens; Lugovoy, Evgeny; Seidel, Robert; Slavíček, Petr; Aziz, Emad F; Abel, Bernd; Winter, Bernd; Hergenhahn, Uwe
2017-08-17
Ion pairing in electrolyte solutions remains a topic of discussion despite a long history of research. Very recently, nearest-neighbor mediated electronic de-excitation processes of core hole vacancies (electron transfer mediated decay, ETMD) were proposed to carry a spectral fingerprint of local solvation structure and in particular of contact ion pairs. Here, for the first time, we apply electron-electron coincidence detection to a liquid microjet, and record ETMD spectra of Li 1s vacancies in aqueous solutions of lithium chloride (LiCl) in direct comparison to lithium acetate (LiOAc). A change in the ETMD spectrum dependent on the electrolyte anion identity is observed for 4.5 M salt concentration. We discuss these findings within the framework of the formation and presence of contact ion pairs and the unique sensitivity of ETMD spectroscopy to ion pairing.
Ali Shan, S.; El-Tantawy, S. A.; Moslem, W. M.
2013-08-15
Arbitrary amplitude ion-acoustic waves in an unmagnetized plasma consisting of cold positive ions, superthermal electrons, and positrons beam are reported. The basic set of fluid equations is reduced to an energy-balance like equation. The latter is numerically analyzed to examine the existence regions for solitary and shock waves. It is found that only solitary waves can propagate, however, the model cannot support shocks. The effects of superthermality and beam parameters (via, positrons concentration and streaming velocity) on the existence region, as well as solitary wave profile have been discussed.
NASA Astrophysics Data System (ADS)
Zammit, Mark; Fursa, Dmitry; Savage, Jeremy; Bray, Igor
2016-09-01
Vibrational excitation and vibrationally resolved electronic excitation cross sections of positron-H2 scattering have been calculated using the single-centre molecular convergent close-coupling (CCC) method. The adiabatic-nuclei approximation was utilized to model the above scattering processes and obtain the vibrationally resolved positron-H2 scattering length. As previously demonstrated, the CCC results are converged and accurately account for virtual and physical positronium formation by coupling basis functions with large orbital angular momentum. Here vibrationally resolved integrated and differential cross sections are presented over a wide energy range and compared with previous calculations and available experiments. Los Alamos National Laboratory and Curtin University.
J-PET detector system for studies of the electron-positron annihilations
NASA Astrophysics Data System (ADS)
Pawlik-Niedźwiecka, M.; Khreptak, O.; Gajos, A.; Wieczorek, A.; Alfs, D.; Bednarski, T.; Białas, P.; Curceanu, C.; Czerwiński, E.; Dulski, K.; Głowacz, B.; Gupta-Sharma, N.; Gorgol, M.; Hiesmayr, B. C.; Jasińska, B.; Kamińska, D.; Korcyl, G.; Kowalski, P.; Krzmień, W.; Krawczyk, N.; Kubicz, E.; Mohammed, M.; Niedźwiecki, Sz.; Raczyński, L.; Rudy, Z.; Silarski, M.; Wiślicki, W.; Zgardzińska, B.; Zieliński, M.; Moskal, P.
2016-11-01
Jagiellonian Positron Emission Tomograph (J-PET) has been recently constructed at the Jagiellonian University as a prototype of a cost-effective scanner for the metabolic imaging of the whole human body. J-PET detector is optimized for the measurement of momentum and polarization of photons from the electron-positron annihilations. It is built out of strips of plastic scintillators, forming three cylindrical layers. As detector of gamma quanta it will be used for studies of discrete symmetries and multiparticle entanglement of photons originating from the decays of ortho-positronium atoms.
International Competitiveness in Electronics.
ERIC Educational Resources Information Center
Congress of the U.S., Washington, DC. Office of Technology Assessment.
This assessment continues the Office of Technology Assessment's (OTA) exploration of the meaning of industrial policy in the United States context, while also examining the industrial policies of several U.S. economic rivals. The major focus is on electronics, an area which virtually defines "high technology" of the 1980's. The…
Novel time-of-flight spectrometer for the analysis of positron annihilation induced Auger electrons
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.
Heat Deposition in Positron Sources for ILC
Bharadwaj, V.; Pitthan, R.; Sheppard, J.; Vincke, H.; Wang, J.W.; /SLAC
2006-03-15
In the International Linear Collider (ILC) positron source, multi-GeV electrons or multi-MeV photons impinge on a metal target to produce the needed positrons in the resulting electromagnetic showers. The incoming beam power is hundreds of kilowatts. Various computer programs -- such as FLUKA or MARS -- can calculate how the incoming beam showers in the target and can track the particle showers through the positron source system. Most of the incoming energy ends up as heat in the various positron source elements. This paper presents results from such calculations and their impact on the design of a positron source for the ILC.
Intense source of slow positrons
NASA Astrophysics Data System (ADS)
Perez, P.; Rosowsky, A.
2004-10-01
We describe a novel design for an intense source of slow positrons based on pair production with a beam of electrons from a 10 MeV accelerator hitting a thin target at a low incidence angle. The positrons are collected with a set of coils adapted to the large production angle. The collection system is designed to inject the positrons into a Greaves-Surko trap (Phys. Rev. A 46 (1992) 5696). Such a source could be the basis for a series of experiments in fundamental and applied research and would also be a prototype source for industrial applications, which concern the field of defect characterization in the nanometer scale.
Second-order Born approximation for the ionization of molecules by electron and positron impact
Dal Cappello, C.; Rezkallah, Z.; Houamer, S.; Charpentier, I.; Hervieux, P. A.; Ruiz-Lopez, M. F.; Dey, R.; Roy, A. C.
2011-09-15
Second-order Born approximation is applied to study the ionization of molecules. The initial and final states are described by single-center wave functions. For the initial state a Gaussian wave function is used while for the ejected electron it is a distorted wave. Results of the present model are compared with recent (e,2e) experiments on the water molecule. Preliminary results are also presented for the ionization of the thymine molecule by electrons and positrons.
Observation of Magnetic Resonances in Electron Clouds in a Positron Storage Ring
Pivi, M.T.F.; Ng, J.S.T.; Cooper, F.; Kharakh, D.; King, F.; Kirby, R.E.; Kuekan, B.; Spencer, Cherrill M.; Raubenheimer, T.O.; Wang, L.F.; /SLAC
2011-08-24
The first experimental observation of magnetic resonances in electron clouds is reported. The resonance was observed as a modulation in cloud intensity for uncoated as well as TiN-coated aluminum surfaces in the positron storage ring of the PEP-II collider at SLAC. Electron clouds frequently arise in accelerators of positively charged particles, and severely impact the machines performance. The TiN coating was found to be an effective remedy, reducing the cloud intensity by three orders of magnitude.
Second-order Born approximation for the ionization of molecules by electron and positron impact
NASA Astrophysics Data System (ADS)
Dal Cappello, C.; Rezkallah, Z.; Houamer, S.; Charpentier, I.; Hervieux, P. A.; Ruiz-Lopez, M. F.; Dey, R.; Roy, A. C.
2011-09-01
Second-order Born approximation is applied to study the ionization of molecules. The initial and final states are described by single-center wave functions. For the initial state a Gaussian wave function is used while for the ejected electron it is a distorted wave. Results of the present model are compared with recent (e,2e) experiments on the water molecule. Preliminary results are also presented for the ionization of the thymine molecule by electrons and positrons.
NASA Astrophysics Data System (ADS)
Passoja, A.; Tikkanen, P.; Krasznahorkay, A.; Gácsi, Z.; Kibédi, T.; Fényes, T.
1984-06-01
The Debrecen superconducting magnetic spectrometer (SMS) has been adapted for in-beam internal-pair studies. Test measurements have been carried out using a 207Bi radioactive source and the 19F(p, αγ) 16O, 23Na(p, αγ) 20Ne, 27Al(p,p'γ) 27Al and 42Ca(p, p'γ) 42Ca reactions (at bombarding energies Ep = 3.5-4.0 MeV). Convenient spectrometer parameters, backscattering of electrons and positrons from one detector to the other, and methods for background reduction have been investigated. Experimental values of (14±3)%, (12±3)%, and (14±2)% for the one-detector pair-line efficiencies were determined for the 20Ne(E2; 1634 keV), 42Ca(E0; 1837 keV) and 27Al(M1 + E2; 2211 keV) transitions, respectively. The observed pair-line detection efficiencies for two detectors operated in sum-coincidence mode were (35 ± 7)% and (34 +-6)% for the 42Ca(E0; 1837 keV) and 27Al(M1 + E2; 2211 keV) transitions, respectively. The energy resolution of the spectrometer was ≈ 0.5% in singles and ≈ o.6% in sum-coincidence measurements for the 2211 keV M1 + E2 pair line of 27Al. Effective pair-formation coefficients for one-detector and opposite two-detector geometries have been calculated theoretically for various multipoles. Different methods for the determination of the multipolarity of internal-pair transitions have been investigated. Optimum multipole discrimination effects have been discussed. The experiments show that a good multipole discrimination power can be achieved with the SMS.
Paired and Interacting Galaxies: International Astronomical Union Colloquium No. 124
NASA Technical Reports Server (NTRS)
Sulentic, Jack W. (Editor); Keel, William C. (Editor); Telesco, C. M. (Editor)
1990-01-01
The proceedings of the International Astronomical Union Colloquium No. 124, held at the University of Alabama at Tuscaloosa, on December 4 to 7, are given. The purpose of the conference was to describe the current state of theoretical and observational knowledge of interacting galaxies, with particular emphasis on galaxies in pairs.
Interaction of two solitary waves in quantum electron-positron-ion plasma
Xu Yanxia; Lin Maimai; Shi Yuren; Duan Wenshan; Liu Zongming; Chen Jianmin
2011-05-15
The collision between two ion-acoustic solitary waves with arbitrary colliding angle {theta} in an unmagnetized, ultracold quantum three-component e-p-i plasma has been investigated. By using the extended Poincare-Lighthill-Kuo (PLK) perturbation method, we obtain the KdV equations and the analytical phase shifts after the collision of two solitary waves in this three-component plasma. The effects of the quantum parameter H, the ratio of Fermi positron temperature to Fermi electron temperature {sigma}, the ratio of Fermi positron number density to Fermi electron number density {mu}, and the ratio of Fermi ion temperature to Fermi electron temperature {rho} on the phase shifts are studied. It is found that these parameters can significantly influence the phase shifts of the solitons.
Jeans instability in a degenerate electron-positron-ion and classical dusty plasma
NASA Astrophysics Data System (ADS)
Rozina, Ch.; Tsintsadze, N. L.; Khadija, A.
2017-08-01
We follow the quantum hydrodynamic model to study the newly suggested problem of Jeans instability in collisionless self-gravitating multicomponent, dense, astrophysical quantum plasmas. Here, the quantum effects appear through the quantum diffraction and Fermi pressure, whereas the quantum statistical effects are important only for degenerate electron-positron- ion and dust being the heaviest is treated as classical. We have obtained dispersion relations for three particular plasmas; every time, Fermi pressure is found to be numerically larger than the quantum diffraction term which tends to stabilize Jeans instability even more than the Madelung term. The Jeans critical wave number and the corresponding critical mass are defined for particular plasmas. We have displayed our results numerically and have shown that the gravitational instability of quantum electron-ion-dust plasmas and electron-positron-dust plasmas is achieved by increasing both the number density and mass of the dust grains. Moreover, the degeneracy quantum corrections effectively stabilizing the Jeans instability was focused.
Ion-acoustic nonlinear periodic waves in electron-positron-ion plasma
Chawla, J. K.; Mishra, M. K.
2010-10-15
Ion-acoustic nonlinear periodic waves, namely, ion-acoustic cnoidal waves have been studied in electron-positron-ion plasma. Using reductive perturbation method and appropriate boundary condition for nonlinear periodic waves, the Korteweg-de Vries (KdV) equation is derived for the system. The cnoidal wave solution of the KdV equation is discussed in detail. It is found that the frequency of the cnoidal wave is a function of its amplitude. It is also found that the positron concentration modifies the properties of the ion-acoustic cnoidal waves. The existence regions for ion-acoustic cnoidal wave in the parameters space (p,{sigma}), where p and {sigma} are the positron concentration and temperature ratio of electron to positron, are discussed in detail. In the limiting case these ion-acoustic cnoidal waves reduce to the ion-acoustic soliton solutions. The effect of other parameters on the characteristics of the nonlinear periodic waves is also discussed.
Simulating Terrestrial Gamma Ray Flashes due to cosmic ray shower electrons and positrons
NASA Astrophysics Data System (ADS)
Connell, Paul
2017-04-01
The University of Valencia has developed a software simulator LEPTRACK to simulate the relativistic runaway electron avalanches, RREA, that are presumed to be the cause of Terrestrial Gamma Ray Flashes and their powerful accompanying Ionization/Excitation Flashes. We show here results of LEPTRACK simulations of RREA by the interaction of MeV energy electrons/positrons and photons in cosmic ray showers traversing plausible electric field geometries expected in storm clouds. The input beams of MeV shower products were created using the CORSIKA software package from the Karlsruhe Institute of Technology. We present images, videos and plots showing the different Ionization, Excitation and gamma-ray photon density fields produced, along with their time and spatial profile evolution, which depend critically on where the line of shower particles intercept the electric field geometry. We also show a new effect of incoming positrons in the shower, which make up a significant fraction of shower products, in particular their apparent "orbiting" within a high altitude negative induced shielding charge layer, which has been conjectured to produce a signature microwave emission, as well as a short range 511 keV annihilation line. The interesting question posed is if this conjectured positron emission can be observed and correlated with TGF orbital observations to show if a TGF originates in the macro E-fields of storm clouds or the micro E-fields of lightning leaders where this positron "orbiting" is not likely to occur.
Positron lifetime studies on 8 MeV electron-irradiated n-type 6H silicon carbide
NASA Astrophysics Data System (ADS)
Lam, C. H.; Lam, T. W.; Ling, C. C.; Fung, S.; Beling, C. D.; De-Sheng, Hang; Huimin, Weng
2004-11-01
The positron lifetime technique was employed to study vacancy-type defects in 8 MeV electron-irradiated n-type 6H silicon carbide. A long-lifetime component having a characteristic lifetime of 223-232 ps was observed in the irradiated sample and was attributed to the VCVSi divacancy. Other positron traps, which dominated at low temperatures, were observed to compete with the VCVSi for trapping positrons. A positron trapping model involving a positron shallow trap, a negatively charged monovacancy and the VCVSi divacancy was found to give a good description of the temperature-dependent positron lifetime data of the 1200 °C annealed sample. The identity of the monovacancy could not be unambiguously determined, but its lifetime was found to be in the range 160-172 ps.
Hunting for glueballs in electron-positron annihilation
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.
Hunting for Glueballs in Electron-Positron Annihilation
Brodsky, Stanley J.
2003-05-28
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 -} J/{psi} + h for h = {eta}{sub c} and {chi}{sub c0}, and is larger by a factor 2 than that for h = {eta}c(2S). As the subprocesses {gamma}* {yields} (c{bar c})(c{bar c}) and {gamma}* {yields} (c{bar c})(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{sup +}e{sup -} {yields} J/{psi}X may actually be due to the production of charmonium-glueball J/{psi}G{sub J} pairs.
Metabolic positron emission tomography imaging of cancer: Pairing lipid metabolism with glycolysis
Kwee, Sandi A; Lim, John
2016-01-01
The limitations of fluorine-18 fluorodeoxy-D-glucose (FDG) in detecting some cancers has prompted a longstanding search for other positron emission tomography (PET) tracers to complement the imaging of glycolysis in oncology, with much attention paid to lipogenesis based on observations that the production of various lipid and lipid-containing compounds is increased in most cancers. Radiolabeled analogs of choline and acetate have now been used as oncologic PET probes for over a decade, showing convincingly improved detection sensitivity over FDG for certain cancers. However, neither choline nor acetate have been thoroughly validated as lipogenic biomarkers, and while acetyl-CoA produced from acetate is used in de-novo lipogenesis to synthesize fatty acids, acetate is also consumed by various other synthetic and metabolic pathways, with recent experimental observations challenging the assumption that lipogenesis is its predominant role in all cancers. Since tumors detected by acetate PET are also frequently detected by choline PET, imaging of choline metabolism might serve as an alternative albeit indirect marker of lipogenesis, particularly if the fatty acids produced in cancer cells are mainly destined for membrane synthesis through incorporation into phosphatidylcholines. Aerobic glycolysis may or may not coincide with changes in lipid metabolism, resulting in combinatorial metabolic phenotypes that may have different prognostic or therapeutic implications. Consequently, PET imaging using dual metabolic tracers, in addition to being diagnostically superior to imaging with individual tracers, could eventually play a greater role in supporting precision medicine, as efforts to develop small-molecule metabolic pathway inhibitors are coming to fruition. To prepare for this advent, clinical and translational studies of metabolic PET tracers must go beyond simply estimating tracer diagnostic utility, and aim to uncover potential therapeutic avenues associated with
Alternate approaches to future electron-positron linear colliders
Loew, G.A.
1998-07-01
The purpose of this article is two-fold: to review the current international status of various design approaches to the next generation of e{sup +}e{sup {minus}} linear colliders, and on the occasion of his 80th birthday, to celebrate Richard B. Neal`s many contributions to the field of linear accelerators. As it turns out, combining these two tasks is a rather natural enterprise because of Neal`s long professional involvement and insight into many of the problems and options which the international e{sup +}e{sup {minus}} linear collider community is currently studying to achieve a practical design for a future machine.
NASA Astrophysics Data System (ADS)
Galper, A. M.; Aptekar, R. L.; Arkhangelskaya, I. V.; Boezio, M.; Bonvicini, V.; Dolgoshein, B. A.; Farber, M. O.; Fradkin, M. I.; Gecha, V. Ya.; Kachanov, V. A.; Kaplin, V. A.; Mazets, E. P.; Menshenin, A. L.; Picozza, P.; Prilutskii, O. F.; Rodin, V. G.; Runtso, M. F.; Spillantini, P.; Suchkov, S. I.; Topchiev, N. P.; Vacchi, A.; Yurkin, Yu. T.; Zampa, N.; Zverev, V. G.
2011-02-01
The GAMMA-400 space observatory will provide precise measurements of gamma rays, electrons, and positrons in the energy range 0.1-3000 GeV. The good angular and energy resolutions, as well as identification capabilities (angular resolution ~0.01°, energy resolution ~1%, and proton rejection factor ~106) will allow us to study the main galactic and extragalactic sources, diffuse gamma-ray background, gamma-ray bursts, and to measure electron and positron fluxes. The peculiar characteristics of the experiment is simultaneous detection of gamma rays and cosmic-ray electrons and positrons, which can be connected with annihilation or decay of dark matter particles.
Elemental composition, isotopes, electrons and positrons in cosmic rays
NASA Technical Reports Server (NTRS)
Balasubrahmanyan, V. K.
1979-01-01
Papers presented at the 16th International Cosmic Ray Conference, Kyoto, Japan, dealing with the composition of cosmic rays are reviewed. Particular interest is given to data having bearing on nucleosynthesis sites, supernovae, gamma-process, comparison with solar system composition, multiplicity of sources, and the energy dependence of composition.
Nonlinear dust-acoustic structures in space plasmas with superthermal electrons, positrons, and ions
NASA Astrophysics Data System (ADS)
Saberian, E.; Esfandyari-Kalejahi, A.; Afsari-Ghazi, M.
2017-01-01
Some features of nonlinear dust-acoustic (DA) structures are investigated in a space plasma consisting of superthermal electrons, positrons, and positive ions in the presence of negatively charged dust grains with finite-temperature by employing a pseudo-potential technique in a hydrodynamic model. For this purpose, it is assumed that the electrons, positrons, and ions obey a kappa-like (κ) distribution in the background of adiabatic dust population. In the linear analysis, it is found that the dispersion relation yield two positive DA branches, i.e., the slow and fast DA waves. The upper branch (fast DA waves) corresponds to the case in which both (negatively charged) dust particles and (positively charged) ion species oscillate in phase with electrons and positrons. On the other hand, the lower branch (slow DA waves) corresponds to the case in which only dust particles oscillate in phase with electrons and positrons, while ion species are in antiphase with them. On the other hand, the fully nonlinear analysis shows that the existence domain of solitons and their characteristics depend strongly on the dust charge, ion charge, dust temperature, and the spectral index κ. It is found that the minimum/maximum Mach number increases as the spectral index κ increases. Also, it is found that only solitons with negative polarity can propagate and that their amplitudes increase as the parameter κ increases. Furthermore, the domain of Mach number shifts to the lower values, when the value of the dust charge Z d increases. Moreover, it is found that the Mach number increases with an increase in the dust temperature. Our analysis confirms that, in space plasmas with highly charged dusts, the presence of superthermal particles (electrons, positrons, and ions) may facilitate the formation of DA solitary waves. Particularly, in two cases of hydrogen ions H+ ( Z i = 1) and doubly ionized Helium atoms He2+ ( Z i = 2), the mentioned results are the same. Additionally, the
NASA Astrophysics Data System (ADS)
Zammit, Mark C.; Fursa, Dmitry V.; Savage, Jeremy S.; Bray, Igor
2017-06-01
Starting from first principles, this tutorial describes the development of the adiabatic-nuclei convergent close-coupling (CCC) method and its application to electron and (single-centre) positron scattering from diatomic molecules. We give full details of the single-centre expansion CCC method, namely the formulation of the molecular target structure; solving the momentum-space coupled-channel Lippmann-Schwinger equation; deriving adiabatic-nuclei cross sections and calculating V-matrix elements. Selected results are presented for electron and positron scattering from molecular hydrogen H2 and electron scattering from the vibrationally excited molecular hydrogen ion {{{H}}}2+ and its isotopologues (D2 +, {{{T}}}2+, HD+, HT+ and TD+). Convergence in both the close-coupling (target state) and projectile partial-wave expansions of fixed-nuclei electron- and positron-molecule scattering calculations is demonstrated over a broad energy-range and discussed in detail. In general, the CCC results are in good agreement with experiments.
Heavy ion-acoustic rogue waves in electron-positron multi-ion plasmas
NASA Astrophysics Data System (ADS)
Chowdhury, N. A.; Mannan, A.; Hasan, M. M.; Mamun, A. A.
2017-09-01
The nonlinear propagation of heavy-ion-acoustic (HIA) waves (HIAWs) in a four-component multi-ion plasma (containing inertial heavy negative ions and light positive ions, as well as inertialess nonextensive electrons and positrons) has been theoretically investigated. The nonlinear Schrödinger (NLS) equation is derived by employing the reductive perturbation method. It is found that the NLS equation leads to the modulational instability (MI) of HIAWs, and to the formation of HIA rogue waves (HIARWs), which are due to the effects of nonlinearity and dispersion in the propagation of HIAWs. The conditions for the MI of HIAWs and the basic properties of the generated HIARWs are identified. It is observed that the striking features (viz., instability criteria, growth rate of MI, amplitude and width of HIARWs, etc.) of the HIAWs are significantly modified by the effects of nonextensivity of electrons and positrons, the ratio of light positive ion mass to heavy negative ion mass, the ratio of electron number density to light positive ion number density, the ratio of electron temperature to positron temperature, etc. The relevancy of our present investigation to the observations in space (viz., cometary comae and earth's ionosphere) and laboratory (viz., solid-high intense laser plasma interaction experiments) plasmas is pointed out.
Toward tests of QED and CPT with improved electron and positron g-factor measurements
NASA Astrophysics Data System (ADS)
Novitski, Elise; Dorr, Joshua; Fogwell Hoogerheide, Shannon; Gabrielse, Gerald
2013-05-01
We describe progress toward improved measurements of the electron and positron g-factors using quantum jump spectroscopy between the lowest quantum states of either particle trapped in a 100 mK cylindrical Penning trap. In a new apparatus--designed for improved stability and a better geometry for cavity-assisted sideband cooling--we have trapped a single electron, driven and observed single cyclotron transitions, and trapped positrons in a loading trap. This should enable measurements of both g-factors with better than the 0.28 ppt precision of the best electron value (the most precise measurement of a fundamental property of an elementary particle), thereby improving the positron value by a factor of more than 15., These measurements, in combination with QED theory relating the electron g-factor to α, will improve on the most precise determination of α, the fine structure constant. The comparison of this value with an independent measurement of α is the most precise test of QED. The comparison of the e- and e+ g-factors will improve upon the best test of CPT symmetry in a lepton system. This work is supported by the NSF
Electron pair escape from fullerene cage via collective modes
Schüler, Michael; Pavlyukh, Yaroslav; Bolognesi, Paolo; Avaldi, Lorenzo; Berakdar, Jamal
2016-01-01
Experiment and theory evidence a new pathway for correlated two-electron release from many-body compounds following collective excitation by a single photon. Using nonequilibrium Green’s function approach we trace plasmon oscillations as the key ingredient of the effective electron-electron interaction that governs the correlated pair emission in a dynamic many-body environment. Results from a full ab initio implementation for C60 fullerene are in line with experimental observations. The findings endorse the correlated two-electron photoemission as a powerful tool to access electronic correlation in complex systems. PMID:27086559
Multi-pair excitations in an electron liquid
NASA Astrophysics Data System (ADS)
Bachlechner, M. E.; Holas, A.; Böhm, H. M.; Schinner, A.
1996-07-01
Single (particle-hole)-pair excitations, as described in the well-known Lindhard function, are restricted to a strip in the ( q, ω) plane — the so-called particle-hole continuum. We present a perturbational analysis of the dynamic dielectric function allowing a generalization of this property for n-pair contributions. Consequences for the electron energy-loss function and related quantities are discussed.
Feasibility study of TPC at electron positron colliders at Z pole operation
NASA Astrophysics Data System (ADS)
Zhao, M.; Ruan, M.; Qi, H.; Gao, Y.
2017-07-01
TPC is a promising technology for the future electron positron colliders. However, its application might be limited at high event rate and high hit occupancies. In this paper, we study the feasibility of using TPC at the circular electron positron collider (CEPC) at Z pole using full simulated Z→ qbar q samples, by evaluating the local charge density and voxel occupancy at different TPC parameters. Our study shows that the TPC could be applied to the CEPC Z pole operation if back flow ion is controlled to per mille level. We also find that the distortion is considerable for the FCC-ee Z pole operation. And a few approaches are proposed to reduce the distortion.
NASA Astrophysics Data System (ADS)
Paul, Ashesh; Bandyopadhyay, Anup; Das, K. P.
2017-01-01
The purpose of this paper is to extend the recent work of Paul and Bandyopadhyay [Astrophys. Space Sci. 361, 172 (2016)] on the existence of different dust ion acoustic solitary structures in an unmagnetized collisionless dusty plasma consisting of negatively charged static dust grains, adiabatic warm ions, nonthermal electrons, and isothermal positrons in a more generalized form by considering nonthermal positrons instead of isothermal positrons. The present system supports both positive and negative potential double layers, coexistence of solitary waves of both polarities, and positive potential supersolitons. The qualitative and quantitative changes in existence domains of different solitary structures, which occur in the presence of nonthermal positrons, have been presented in comparison with the results of Paul and Bandyopadhyay [Astrophys. Space Sci. 361, 172 (2016)]. The formation of supersoliton structures and their limitations has been analyzed with the help of phase portraits of the dynamical system corresponding to the dust ion acoustic solitary structures. Phase portrait analysis clearly indicates a smooth transition between solitons and supersolitons.
RELATIVISTIC POSITRON-ELECTRON-ION SHEAR FLOWS AND APPLICATION TO GAMMA-RAY BURSTS
Liang, Edison; Fu, Wen; Smith, Ian; Roustazadeh, Parisa; Boettcher, Markus
2013-12-20
We present particle-in-cell simulation results of relativistic shear flows for hybrid positron-electron-ion plasmas and compare to those for pure e {sup +} e {sup –} and pure e {sup –} ion plasmas. Among the three types of relativistic shear flows, we find that only hybrid shear flow is able to energize the electrons to form a high-energy spectral peak plus a hard power law tail. Such electron spectra are needed to model the observational properties of gamma-ray bursts.
Production of intense positron beams at the VEPP-5 injection complex
Astrelina, K. V.; Blinov, M. F.; Vsevolozhskaya, T. A.; Dikanskii, N. S.; Emanov, F. A.; Lapik, R. M.; Logachev, P. V.; Martyshkin, P. V.; Petrenko, A. V.; Rybitskaya, T. V.; Skrinskii, A. N.; Shiyankov, S. V.; Yaskina, T. A.
2008-01-15
A source of positrons allowing 5 x 10{sup 8} positrons accelerated to the energy of 70 MeV to be produced per pulse has been developed. The process of electron-positron pair production in an electromagnetic shower is used for production of positrons. The electromagnetic shower is generated in a tantalum target by a beam of 2 x 10{sup 10} electrons with energy 270 MeV. A high efficiency of positron collection (positron yield Y {approx} 0.1 GeV{sup -1}) is ensured by a unique design of the matching device.
Production of intense positron beams at the VEPP-5 injection complex
Astrelina, K. V.; Blinov, M. F.; Vsevolozhskaya, T. A.; Dikanskii, N. S.; Emanov, F. A.; Lapik, R. M.; Logachev, P. V.; Martyshkin, P. V.; Petrenko, A. V.; Rybitskaya, T. V.; Skrinskii, A. N.; Shiyankov, S. V.; Yaskina, T. A.
2008-01-15
A source of positrons allowing 5 Multiplication-Sign 10{sup 8} positrons accelerated to the energy of 70 MeV to be produced per pulse has been developed. The process of electron-positron pair production in an electromagnetic shower is used for production of positrons. The electromagnetic shower is generated in a tantalum target by a beam of 2 Multiplication-Sign 10{sup 10} electrons with energy 270 MeV. A high efficiency of positron collection (positron yield Y Almost-Equal-To 0.1 GeV{sup -1}) is ensured by a unique design of the matching device.
Electron Positron Proton Spectrometer for use at Laboratory for Laser Energetics
Ayers, S L
2010-04-07
The Electron Positron Proton Spectrometer (EPPS) is mounted in a TIM (Ten-Inch Manipulator) system on the Omega-60 or Omega-EP laser facilities at the University of Rochester, Laboratory for Laser Energetics (LLE), when in use, see Fig. 1. The Spectrometer assembly, shown in Fig. 2, is constructed of a steel box containing magnets, surrounded by Lead 6% Antimony shielding with SS threaded insert, sitting on an Aluminum 6061-T6 plate.
NASA Astrophysics Data System (ADS)
Onodera, K.; Oka, T.; Kino, Y.; Sekine, T.
2017-01-01
Degradation of electron beam irradiated high-density polyethylene was studied by positron annihilation lifetime spectroscopy (PALS), micro-FT-IR, and gel fraction measurements. The obtained results indicated that ortho-positronium intensity is influenced not only by the irradiation but also the post oxidation, which illustrates that PALS may be a promising tool to monitor/evaluate the degradation of polyethylene induced by irradiation and long-term storage.
Theories of statistical equilibrium in electron-positron colliding-beam storage rings
Schonfeld, J.F.
1985-01-01
In this lecture I introduce you to some recent theoretical work that represents a significant and long overdue departure from the mainstream of ideas on the physics of colliding- beam storage rings. The goal of the work in question is to understand analytically - without recourse to computer simulation - the role that dissipation and noise play in the observed colliding-beam behavior of electron-positron storage rings.
On thermalization of electron-positron-photon plasma
Siutsou, I. A.; Aksenov, A. G.
2015-12-17
Recently a progress has been made in understanding thermalization mechanism of relativistic plasma starting from a non-equilibrium state. Relativistic Boltzmann equations were solved numerically for homogeneous isotropic plasma with collision integrals for two- and three-particle interactions calculated from the first principles by means of QED matrix elements. All particles were assumed to fulfill Boltzmann statistics. In this work we follow plasma thermalization by accounting for Bose enhancement and Pauli blocking in particle interactions. Our results show that particle in equilibrium reach Bose-Einstein distribution for photons, and Fermi-Dirac one for electrons, respectively.
Oblique propagation of ion-acoustic solitary waves in a magnetized electron-positron-ion plasma
Ferdousi, M.; Sultana, S.; Mamun, A. A.
2015-03-15
The properties of obliquely propagating ion-acoustic solitary waves in the presence of ambient magnetic field have been investigated theoretically in an electron-positron-ion nonthermal plasma. The plasma nonthermality is introduced via the q-nonextensive distribution of electrons and positrons. The Korteweg-de Vries (K-dV) and modified K-dV (mK-dV) equations are derived by adopting reductive perturbation method. The solution of K-dV and modified K-dV equation, which describes the solitary wave characteristics in the long wavelength limit, is obtained by steady state approach. It is seen that the electron and positron nonextensivity and external magnetic field (obliqueness) have significant effects on the characteristics of solitary waves. A critical value of nonextensivity is found for which solitary structures transit from positive to negative potential. The findings of this investigation may be used in understanding the wave propagation in laboratory and space plasmas where static external magnetic field is present.
Saeed, R.; Shah, Asif; Noaman-ul-Haq, Muhammad
2010-10-15
The nonlinear propagation of ion-acoustic solitons in relativistic electron-positron-ion plasma comprising of Boltzmannian electrons, positrons, and relativistic thermal ions has been examined. The Korteweg-de Vries equation has been derived by reductive perturbation technique. The effect of various plasma parameters on amplitude and structure of solitary wave is investigated. The pert graphical view of the results has been presented for illustration. It is observed that increase in the relativistic streaming factor causes the soliton amplitude to thrive and its width shrinks. The soliton amplitude and width decline as the ion to electron temperature ratio is increased. The increase in positron concentration results in reduction of soliton amplitude. The soliton amplitude enhances as the electron to positron temperature ratio is increased. Our results may have relevance in the understanding of astrophysical plasmas.
NASA Astrophysics Data System (ADS)
Saeed, R.; Shah, Asif; Noaman-Ul-Haq, Muhammad
2010-10-01
The nonlinear propagation of ion-acoustic solitons in relativistic electron-positron-ion plasma comprising of Boltzmannian electrons, positrons, and relativistic thermal ions has been examined. The Korteweg-de Vries equation has been derived by reductive perturbation technique. The effect of various plasma parameters on amplitude and structure of solitary wave is investigated. The pert graphical view of the results has been presented for illustration. It is observed that increase in the relativistic streaming factor causes the soliton amplitude to thrive and its width shrinks. The soliton amplitude and width decline as the ion to electron temperature ratio is increased. The increase in positron concentration results in reduction of soliton amplitude. The soliton amplitude enhances as the electron to positron temperature ratio is increased. Our results may have relevance in the understanding of astrophysical plasmas.
EL-Shamy, E. F.
2014-08-15
The solitary structures of multi–dimensional ion-acoustic solitary waves (IASWs) have been considered in magnetoplasmas consisting of electron-positron-ion with high-energy (superthermal) electrons and positrons are investigated. Using a reductive perturbation method, a nonlinear Zakharov-Kuznetsov equation is derived. The multi-dimensional instability of obliquely propagating (with respect to the external magnetic field) IASWs has been studied by the small-k (long wavelength plane wave) expansion perturbation method. The instability condition and the growth rate of the instability have been derived. It is shown that the instability criterion and their growth rate depend on the parameter measuring the superthermality, the ion gyrofrequency, the unperturbed positrons-to-ions density ratio, the direction cosine, and the ion-to-electron temperature ratio. Clearly, the study of our model under consideration is helpful for explaining the propagation and the instability of IASWs in space observations of magnetoplasmas with superthermal electrons and positrons.
NASA Astrophysics Data System (ADS)
Vyacheslavov, L. N.; Ivantsivskii, M. V.; Meshkov, O. I.; Popov, S. S.; Smaluk, V. V.
2012-03-01
Optical diagnostics is widely used, both in plasma-physics experiments and in measuring parameters of electron and positron beams in accelerators. In doing so, the approaches with the same methodological base are often applied, which is explained by similarity of certain properties of objects under study despite the fact that these fields of physics are absolutely specific and require using the specialized techniques. The possibility of close contacts and cooperation among scientists concerned with similar problems in different fields of physics contributes to the fruitful exchange of ideas and helps to overcome these problems. It is especially characteristic of the Budker Institute of Nuclear Physics, Siberian Branch of Russian Academy of Sciences, which is famous for pioneering works in the field of electron-positron colliders and controlled thermonuclear fusion. The first part of this paper presents a review of optical diagnostics of the stationary beam parameters in cyclic accelerators of electrons and positrons. The only techniques considered are those that became the recognized tools at colliders and storage rings of the latest generation, without which the routine operation of the facility is difficult to imagine. The second part of the paper describes optical diagnostics used in experiments of heating the plasma by a high-current electron beam.
Magnetosonic wave in pair-ion electron collisional plasmas
NASA Astrophysics Data System (ADS)
Hussain, S.; Hasnain, H.
2017-03-01
Low frequency magnetosonic waves in positive and negative ions of equal mass and opposite charges in the presence of electrons in collisional plasmas are studied. The collisions of ions and electrons with neutrals are taken into account. The nonlinearities in the plasma system arise due to ion and electrons flux, Lorentz forces, and plasma current densities. The reductive perturbation method is applied to derive the Damped Korteweg de Vries (DKdV) equation. The time dependent solution of DKdV is presented. The effects of variations of different plasma parameters on propagation characteristics of magnetosonic waves in pair-ion electron plasma in the context of laboratory plasmas are discussed.
NASA Astrophysics Data System (ADS)
Banerjee, Gadadhar; Maitra, Sarit
2016-12-01
Existence of arbitrary amplitude solitons and double layers have been studied in collisionless unmagnetized multicomponent dusty plasmas with nonthermally distributed positrons and electrons by using Sagdeev's pseudopotential method. The linear dispersion relation is obtained for dust ion acoustic wave mode. The present model supports the coexistence of positive potential solitary waves and negative potential solitary waves and double layers. The criterion for the existence of solitary waves and double layers is derived in terms of Mach number limit. The effects of ion temperature and nonthermality of electrons and positrons are studied. Also the effects of positron and dust concentration on the wave propagation are observed.
Evidence of Positron Annihilation at Electronic Excitation Threshold for N2 ^*
NASA Astrophysics Data System (ADS)
Miller, E. G.; Edwards, J. J.; Kauppila, W. E.; Stein, T. S.; Surdutovich, E.
2006-05-01
We are investigating Positronium (Ps) formation for < 20 eV positrons interacting with N2 in a gas scattering cell. The technique [1] of Ps annihilation ratio spectroscopy (PsARS) is used to obtain the ratios of coincidence signals for two of the three gamma rays (S3γ) in the photon energy window 300 to 460 keV resulting from ortho-Ps decay to that for two 511 keV gamma rays (S2γ) arising from para-Ps decay and other processes. By comparing these ratios of S3 γ/S2γ for N2 to those for Ar it is found that N2 exhibits strikingly anomalous behavior near and below the Ps formation threshold. Typically, this ratio remains constant within 2 eV above the Ps threshold. For N2, this ratio decreases to zero at the threshold and an S2 γ signal remains for an energy of ˜0.3 eV below. Since N2 has an electronic excitation threshold for positron impact that opens up at ˜0.3 eV below the Ps threshold, the present results strongly suggest that the incident positron is electronically exciting N2 and then binding to the excited N2 in a temporary resonance-like state from which the bound positron annihilates with a molecular electron. ^*Research supported by NSF Grant PHY 99-88093.[1] W.E. Kauppila, E.G. Miller, H. F.M. Mohamed, K. Pipinos, T. S. Stein, and E. Surdutovich, Phys. Rev. Lett. 93, 113401 (2004).
NASA Astrophysics Data System (ADS)
Neese, Frank; Wennmohs, Frank; Hansen, Andreas
2009-03-01
Coupled-electron pair approximations (CEPAs) and coupled-pair functionals (CPFs) have been popular in the 1970s and 1980s and have yielded excellent results for small molecules. Recently, interest in CEPA and CPF methods has been renewed. It has been shown that these methods lead to competitive thermochemical, kinetic, and structural predictions. They greatly surpass second order Møller-Plesset and popular density functional theory based approaches in accuracy and are intermediate in quality between CCSD and CCSD(T) in extended benchmark studies. In this work an efficient production level implementation of the closed shell CEPA and CPF methods is reported that can be applied to medium sized molecules in the range of 50-100 atoms and up to about 2000 basis functions. The internal space is spanned by localized internal orbitals. The external space is greatly compressed through the method of pair natural orbitals (PNOs) that was also introduced by the pioneers of the CEPA approaches. Our implementation also makes extended use of density fitting (or resolution of the identity) techniques in order to speed up the laborious integral transformations. The method is called local pair natural orbital CEPA (LPNO-CEPA) (LPNO-CPF). The implementation is centered around the concepts of electron pairs and matrix operations. Altogether three cutoff parameters are introduced that control the size of the significant pair list, the average number of PNOs per electron pair, and the number of contributing basis functions per PNO. With the conservatively chosen default values of these thresholds, the method recovers about 99.8% of the canonical correlation energy. This translates to absolute deviations from the canonical result of only a few kcal mol-1. Extended numerical test calculations demonstrate that LPNO-CEPA (LPNO-CPF) has essentially the same accuracy as parent CEPA (CPF) methods for thermochemistry, kinetics, weak interactions, and potential energy surfaces but is up to 500
Pair 2-electron reduced density matrix theory using localized orbitals
NASA Astrophysics Data System (ADS)
Head-Marsden, Kade; Mazziotti, David A.
2017-08-01
Full configuration interaction (FCI) restricted to a pairing space yields size-extensive correlation energies but its cost scales exponentially with molecular size. Restricting the variational two-electron reduced-density-matrix (2-RDM) method to represent the same pairing space yields an accurate lower bound to the pair FCI energy at a mean-field-like computational scaling of O (r3) where r is the number of orbitals. In this paper, we show that localized molecular orbitals can be employed to generate an efficient, approximately size-extensive pair 2-RDM method. The use of localized orbitals eliminates the substantial cost of optimizing iteratively the orbitals defining the pairing space without compromising accuracy. In contrast to the localized orbitals, the use of canonical Hartree-Fock molecular orbitals is shown to be both inaccurate and non-size-extensive. The pair 2-RDM has the flexibility to describe the spectra of one-electron RDM occupation numbers from all quantum states that are invariant to time-reversal symmetry. Applications are made to hydrogen chains and their dissociation, n-acene from naphthalene through octacene, and cadmium telluride 2-, 3-, and 4-unit polymers. For the hydrogen chains, the pair 2-RDM method recovers the majority of the energy obtained from similar calculations that iteratively optimize the orbitals. The localized-orbital pair 2-RDM method with its mean-field-like computational scaling and its ability to describe multi-reference correlation has important applications to a range of strongly correlated phenomena in chemistry and physics.
The Electron-Pair Repulsion Model for Molecular Geometry
ERIC Educational Resources Information Center
Gillespie, R. J.
1970-01-01
Describes how the electron-pair repulsion model qualitatively explains the size and shape of molecular orbitals. Briefly discusses trigonal bipyramidal molecules, three-center bonds, and transition elements. Describes cluster compounds and finishes with a discussion of the exceptions to the model and effects of ligand-ligand repulsions. (RR)
The Electron-Pair Repulsion Model for Molecular Geometry
ERIC Educational Resources Information Center
Gillespie, R. J.
1970-01-01
Describes how the electron-pair repulsion model qualitatively explains the size and shape of molecular orbitals. Briefly discusses trigonal bipyramidal molecules, three-center bonds, and transition elements. Describes cluster compounds and finishes with a discussion of the exceptions to the model and effects of ligand-ligand repulsions. (RR)
NASA Astrophysics Data System (ADS)
Holtzapple, R. L.; Billing, M. G.; Campbell, R. C.; Dugan, G. F.; Flanagan, J.; McArdle, K. E.; Miller, M. I.; Palmer, M. A.; Ramirez, G. A.; Sonnad, K. G.; Totten, M. M.; Tucker, S. L.; Williams, H. A.
2016-04-01
Electron cloud related emittance dilution and instabilities of bunch trains limit the performance of high intensity circular colliders. One of the key goals of the Cornell electron-positron storage ring Test Accelerator (CesrTA) research program is to improve our understanding of how the electron cloud alters the dynamics of bunches within the train. Single bunch beam diagnotics have been developed to measure the beam spectra, vertical beam size, two important dynamical effects of beams interacting with the electron cloud, for bunch trains on a turn-by-turn basis. Experiments have been performed at CesrTA to probe the interaction of the electron cloud with stored positron bunch trains. The purpose of these experiments was to characterize the dependence of beam-electron cloud interactions on the machine parameters such as bunch spacing, vertical chromaticity, and bunch current. The beam dynamics of the stored beam, in the presence of the electron cloud, was quantified using: 1) a gated beam position monitor (BPM) and spectrum analyzer to measure the bunch-by-bunch frequency spectrum of the bunch trains; 2) an x-ray beam size monitor to record the bunch-by-bunch, turn-by-turn vertical size of each bunch within the trains. In this paper we report on the observations from these experiments and analyze the effects of the electron cloud on the stability of bunches in a train under many different operational conditions.
Holtzapple, R. L.; Billing, M. G.; Campbell, R. C.; ...
2016-04-11
Electron cloud related emittance dilution and instabilities of bunch trains limit the performance of high intensity circular colliders. One of the key goals of the Cornell electron-positron storage ring Test Accelerator (CesrTA) research program is to improve our understanding of how the electron cloud alters the dynamics of bunches within the train. Single bunch beam diagnostics have been developed to measure the beam spectra, vertical beam size, two important dynamical effects of beams interacting with the electron cloud, for bunch trains on a turn-by-turn basis. Experiments have been performed at CesrTA to probe the interaction of the electron cloud withmore » stored positron bunch trains. The purpose of these experiments was to characterize the dependence of beam-electron cloud interactions on the machine parameters such as bunch spacing, vertical chromaticity, and bunch current. The beam dynamics of the stored beam, in the presence of the electron cloud, was quantified using: 1) a gated beam position monitor (BPM) and spectrum analyzer to measure the bunch-by-bunch frequency spectrum of the bunch trains, 2) an x-ray beam size monitor to record the bunch-by-bunch, turn-by-turn vertical size of each bunch within the trains. In this study we report on the observations from these experiments and analyze the effects of the electron cloud on the stability of bunches in a train under many different operational conditions.« less
Holtzapple, R. L.; Billing, M. G.; Campbell, R. C.; Dugan, G. F.; Flanagan, J.; McArdle, K. E.; Miller, M. I.; Palmer, M. A.; Ramirez, G. A.; Sonnad, K. G.; Totten, M. M.; Tucker, S. L.; Williams, H. A.
2016-04-11
Electron cloud related emittance dilution and instabilities of bunch trains limit the performance of high intensity circular colliders. One of the key goals of the Cornell electron-positron storage ring Test Accelerator (CesrTA) research program is to improve our understanding of how the electron cloud alters the dynamics of bunches within the train. Single bunch beam diagnostics have been developed to measure the beam spectra, vertical beam size, two important dynamical effects of beams interacting with the electron cloud, for bunch trains on a turn-by-turn basis. Experiments have been performed at CesrTA to probe the interaction of the electron cloud with stored positron bunch trains. The purpose of these experiments was to characterize the dependence of beam-electron cloud interactions on the machine parameters such as bunch spacing, vertical chromaticity, and bunch current. The beam dynamics of the stored beam, in the presence of the electron cloud, was quantified using: 1) a gated beam position monitor (BPM) and spectrum analyzer to measure the bunch-by-bunch frequency spectrum of the bunch trains, 2) an x-ray beam size monitor to record the bunch-by-bunch, turn-by-turn vertical size of each bunch within the trains. In this study we report on the observations from these experiments and analyze the effects of the electron cloud on the stability of bunches in a train under many different operational conditions.
Ion-acoustic rogue waves and breathers in relativistically degenerate electron-positron plasmas
NASA Astrophysics Data System (ADS)
Abdikian, A.; Ismaeel, S.
2017-08-01
In this paper, we employ a weakly relativistic fluid model to study the nonlinear amplitude modulation of electrostatic waves in an unmagnetized electron-positron-ion plasma. It is assumed that the degeneracy pressure law for electrons and positrons follows the Chandrasekhar limit of state whereas ions are warm and classical. The hydrodynamic approach along with the perturbation method have been applied to obtain the corresponding nonlinear Schrödinger equation (NLSE) in which nonlinearity is in balance with the dispersive terms. Using the NLSE, we could evaluate the modulational instability to show that various types of localized ion acoustic excitations exist in the form of either bright-type envelope solitons or dark-type envelope solitons. The regions of the stable and unstable envelope wave have been confined punctually for various regimes. Furthermore, it is proposed that the exact solutions of the NLSE for breather waves are the rogue waves (RWs), Akhmediev breather (AB), and Kuznetsov-Ma breather (KM) soliton. In order to show that the characteristics of breather structures is influenced by the plasma parameters (namely, relativistic parameter, positron concentration, and ionic temperature), the relevant numerical analysis of the NLSE is examined. In particular, it is observed that by increasing the values of the mentioned plasma parameters, the amplitude of the RWs will be decreased. Our results help researchers to explain the formation and dynamics of nonlinear electrostatic excitations in super dense astrophysical regimes.
Experiment with a crystal-assisted positron source using 6 and 10 GeV electrons
NASA Astrophysics Data System (ADS)
Artru, X.; Baier, V.; Beloborodov, K.; Bochek, G.; Bogdanov, A.; Bozhenok, A.; Bukin, A.; Burdin, S.; Chehab, R.; Chevallier, M.; Cizeron, R.; Dauvergne, D.; Dimova, T.; Drozdetsky, A.; Druzhinin, V.; Dubrovin, M.; Gatignon, L.; Golubev, V.; Jejcic, A.; Keppler, P.; Kirsch, R.; Kulibaba, V.; Lautesse, Ph.; Major, J.; Maslov, N.; Poizat, J.-C.; Potylitsin, A.; Remillieux, J.; Serednyakov, S.; Shary, V.; Strakhovenko, V.; Sylvia, C.; Vnukov, I.
2003-01-01
Axially oriented crystals, penetrated by high-energy electrons, are powerful photon sources and, hence, intense positron sources. Such kinds of positron sources have been studied experimentally at CERN, with the tertiary electron beam of the SPS having an energy of 6 and 10 GeV. Four and eight millimeters thick tungsten crystals and a compound target made of a 4 mm crystal followed by a 4 mm amorphous disk were used with an orientation along the <1 1 1> axis. The positrons were detected by a drift chamber, partially immersed in a magnetic field. The reconstructed trajectories allowed the determination of their energy and angular spectra. Significant enhancements were observed for the crystal source when compared to the amorphous one. The gain was about 3 for the 4 mm target and about 2 for the 8 mm and the compound targets. These preliminary results are described after short presentations of the experimental set-up and of the method of track reconstruction.
Two dimensional planar and nonplanar ion acoustic shock waves in electron-positron-ion plasmas
Masood, W.; Rizvi, H.
2009-09-15
Two dimensional ion acoustic shock waves (IASWs) are studied in an unmagnetized plasma consisting of electrons, positrons, and adiabatically hot positive ions. This is done by deriving the nonplanar Kadomstev-Petviashvili-Burgers (KPB) equation under the small amplitude perturbation expansion method. The dissipation is introduced by taking into account the kinematic viscosity among the plasma constituents. The limiting cases of the nonplanar KPB equation are also discussed. The analytical solution of the planar KPB equation is obtained using the tangent hyperbolic method that is used as the initial profile to numerically solve the nonplanar KPB equation. It is found that the strength of IASW is maximum for spherical, intermediate for cylindrical, and minimum for planar geometry. It is observed that the positron concentration and the plasma kinematic viscosity significantly modify the shock structure. Finally, the temporal evolution of the nonplanar IASW is investigated and the results are discussed from the numerical stand point. The results of the present study may be applicable in the study of small amplitude localized electrostatic shock structures in electron-positron-ion plasmas.
Measurement of electron-positron spectrum in high-energy cosmic rays in the PAMELA experiment
NASA Astrophysics Data System (ADS)
Karelin, A. V.; Adriani, O.; Barbarino, G. C.; Bazilevskaya, G. A.; Bellotti, R.; Boezio, M.; Bogomolov, E. A.; Bongi, M.; Bonvicini, V.; Bottai, S.; Bruno, A.; Cafagna, F.; Campana, D.; Carbone, R.; Carlson, P.; Casolino, M.; Castellini, G.; De Donato, C.; De Santis, C.; De Simone, N.; Di Felice, V.; Formato, V.; Galper, A. M.; Koldashov, S. V.; Koldobskiy, S. A.; Krutkov, S. Y.; Kvashnin, A. N.; Leonov, A. A.; Mayorov, A. G.; Malakhov, V. V.; Marcelli, L.; Martucci, M.; Menn, W.; Merge, M.; Mikhailov, V. V.; Mocchiutti, E.; Monaco, A.; Mori, N.; Munini, R.; Osteria, G.; Palma, F.; Panico, B.; Papini, P.; Pearce, M.; Picozza, P.; Ricci, M.; Ricciarini, S. B.; Sarkar, R.; Scotti, V.; Rossetto, L.; Simon, M.; Sparvoli, R.; Spillantini, P.; Vacchi, A.; Vannuccini, E.; Vasilyev, G. I.; Voronov, S. A.; Yurkin, Y. T.; Zampa, G.; Zampa, N.
2015-08-01
At present the existing data on the cosmic ray electron energy spectra in the high energy range are fragmented, and the situation is exacerbated by their small number. In the satellite PAMELA experiment measurements at high energies are carried out by the calorimeter. The experimental data accumulated for more than 8 years of measurements, with the information of the calorimeter, the neutron detector and the scintillation counters made it possible to obtain the total spectrum of high-energy electrons and positrons in energy range 0.3-3 TeV.
Monte Carlo Simulation of Pileup Effects in the Electron-Positron Annihilation Peak
NASA Astrophysics Data System (ADS)
do Nascimento, Eduardo; Fernández-Varea, José M.; Vanin, Vito R.; Maidana, Nora L.
2011-08-01
The Monte Carlo code PENELOPE is employed to simulate a typical experimental Doppler broadening coincidence spectrum (DBCS) where the energy spectrum of the photons emitted by the positrons interacting in the sample is recorded with two HPGe detectors in coincidence. The simulated spectrum reproduces well some of the structures observed in the measured DBCS, but not the prominent tails on the low- and high-energy sides of the electron-positron annihilation peak seen in the latter. Ad hoc variations of the cross sections implemented in PENELOPE did not improve the situation. A simple parameterization of the background noise in the DBCS is proposed, and the simulated spectrum is modified to account for pileup effects using this model of the background. The resulting spectrum is in good agreement with the experiment on the high-energy side of the annihilation peak.
Cosmic ray electrons and positrons from supernova explosions of massive stars.
Biermann, P L; Becker, J K; Meli, A; Rhode, W; Seo, E S; Stanev, T
2009-08-07
We attribute the recently discovered cosmic ray electron and cosmic ray positron excess components and their cutoffs to the acceleration in the supernova shock in the polar cap of exploding Wolf-Rayet and red supergiant stars. Considering a spherical surface at some radius around such a star, the magnetic field is radial in the polar cap as opposed to most of 4pi (the full solid angle), where the magnetic field is nearly tangential. This difference yields a flatter spectrum, and also an enhanced positron injection for the cosmic rays accelerated in the polar cap. This reasoning naturally explains the observations. Precise spectral measurements will be the test, as this predicts a simple E;{-2} spectrum for the new components in the source, steepened to E;{-3} in observations with an E;{-4} cutoff.
Ata-ur-Rahman,; Qamar, A.; Ali, S.; Mirza, Arshad M.
2013-04-15
We have studied the propagation of ion acoustic shock waves involving planar and non-planar geometries in an unmagnetized plasma, whose constituents are non-degenerate ultra-cold ions, relativistically degenerate electrons, and positrons. By using the reductive perturbation technique, Korteweg-deVries Burger and modified Korteweg-deVries Burger equations are derived. It is shown that only compressive shock waves can propagate in such a plasma system. The effects of geometry, the ion kinematic viscosity, and the positron concentration are examined on the ion acoustic shock potential and electric field profiles. It is found that the properties of ion acoustic shock waves in a non-planar geometry significantly differ from those in planar geometry. The present study has relevance to the dense plasmas, produced in laboratory (e.g., super-intense laser-dense matter experiments) and in dense astrophysical objects.
NASA Astrophysics Data System (ADS)
Gorlova, D. A.; Nedorezov, V. G.; Ivanov, K. A.; Savel'ev, A. B.; Turinge, A. A.; Tsymbalov, I. N.
2017-06-01
Based on the numerical simulations, we estimate the possibility of generating positrons by low-energy electrons (below 10 MeV) produced by electron accelerators and femtosecond lasers. A review of experimental work reported in the literature is presented. The simulation is carried out using the GEANT-4 software package for the particular conditions of a possible experiment at the terawatt femtosecond laser facility of the International Laser Centre at the Moscow State University and the LUE-8 MeV linear electron accelerator at the Institute for Nuclear Research, Russian Academy of Sciences.
8 Be Anomalous Internal Pair Production: Possible E2 Transitions
NASA Astrophysics Data System (ADS)
Ward, Thomas; Koltick, David; Wang, Haoyu
2017-01-01
Significant enhancement of 8 Be internal pair production at 16.7 MeV with large angle correlations from the 18.150 MeV (Jπ =1+) level have been interpreted as a possible dark matter candidate, a light (Jπ =1+) neutral boson or a fifth-force vector gauge boson. We present a conventional alternative interpretation, unseen E2 transitions from the Jπ =2+ levels at 16.626 MeV and 16.922 MeV populated in the decay of the 18.150 MeV (Jπ =1+) level. The calculated E2 transition probabilities agree well with the measured pair production intensity in the back angle correlation where one expects the E2 gamma-ray correlation to peak. Work partially funded under auspices of USDOE-NE Contract DE-DT0004091.
Prototyping of the ILC Baseline Positron Target
Gronberg, J; Brooksby, C; Piggott, T; Abbott, R; Javedani, J; Cook, E
2012-02-29
The ILC positron system uses novel helical undulators to create a powerful photon beam from the main electron beam. This beam is passed through a titanium target to convert it into electron-positron pairs. The target is constructed as a 1 m diameter wheel spinning at 2000 RPM to smear the 1 ms ILC pulse train over 10 cm. A pulsed flux concentrating magnet is used to increase the positron capture efficiency. It is cooled to liquid nitrogen temperatures to maximize the flatness of the magnetic field over the 1 ms ILC pulse train. We report on prototyping effort on this system.
PREFACE: 11th International Workshop on Positron and Positronium Chemistry (PPC-11)
NASA Astrophysics Data System (ADS)
Pujari, P. K.; Sudarshan, K.; Dutta, D.
2015-06-01
The International Workshop on Positron and Positronium Chemistry (PPC) is a prestigious triennial conference series with a rich history. The 11th meeting in the series (PPC-11) was held at Cidade de Goa, Goa, India during 9-14, November, 2014. It was organized by Bhabha Atomic Research Centre (BARC), Mumbai. The co-organizers were Saha Institute of Nuclear Physics (SINP), Kolkata, Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam and Indian Association of Nuclear Chemists and Allied Scientists (IANCAS), Mumbai. PPC-11 attracted participants both from academic institutions and industries. About 120 participants from 20 countries representing all continents participated in the conference. The conference continued the tradition of excellence in terms of quality of presentations and discussions. There were 33 plenary and invited talks, 39 oral presentations and 40 posters. The conference stood true to its multidisciplinary tag with papers presented in the fields of fundamentals of positron and positronium chemistry, applications in polymers, porous materials, metals/alloys, studies in liquids, biological applications as well as developments in theory and experimental techniques. The enthusiastic participation of senior researchers and young students made the scientific program a grand success. In order to encourage the student participants (twenty) and promote excellence, a committee of senior members evaluated their presentations and the top three contributions were awarded. The positron and positronium community paid homage to the memory of late Profs. J. Kristiak and A.T. Stewart. A brief sketch of their life and work was presented by Profs. Jan Kuriplach and Toshio Hyodo, respectively. All the papers published in these proceedings have been peer reviewed by the participants of PPC-11. Editors thank all the reviewers for sparing their valuable time and helping us in bringing out the proceedings with 43 contributed articles in the scheduled time. We are
NASA Astrophysics Data System (ADS)
Hafez, M. G.; Roy, N. C.; Talukder, M. R.; Hossain Ali, M.
2016-08-01
The characteristics of the nonlinear oblique propagation of ion acoustic solitary waves in unmagnetized plasmas consisting of Boltzmann positrons, trapped electrons and ions are investigated. The modified Kadomtsev-Petviashivili ( m K P ) equation is derived employing the reductive perturbation technique. The parametric effects on phase velocity, Sagdeev potential, amplitude and width of solitons, and electrostatic ion acoustic solitary structures are graphically presented with the relevant physical explanations. This study may be useful for the better understanding of physical phenomena concerned in plasmas in which the effects of trapped electrons control the dynamics of wave.
On-ground detection of an electron-positron annihilation line from thunderclouds
NASA Astrophysics Data System (ADS)
Umemoto, D.; Tsuchiya, H.; Enoto, T.; Yamada, S.; Yuasa, T.; Kawaharada, M.; Kitaguchi, T.; Nakazawa, K.; Kokubun, M.; Kato, H.; Okano, M.; Tamagawa, T.; Makishima, K.
2016-02-01
Thunderclouds can produce bremsstrahlung gamma-ray emission, and sometimes even positrons. At 00:27:00 (UT) on 13 January 2012, an intense burst of gamma rays from a thundercloud was detected by the GROWTH experiment, located in Japan, facing the Sea of Japan. The event started with a sharp gamma-ray flash with a duration of <300 ms coincident with an intracloud discharge, followed by a decaying longer gamma-ray emission lasting for ˜60 s. The spectrum of this prolonged emission reached ˜10 MeV, and contained a distinct line emission at 508 ±3 (stat .)±5 (sys .) keV, to be identified with an electron-positron annihilation line. The line was narrow within the instrumental energy resolution (˜80 keV) , and contained 520 ±50 photons which amounted to ˜10 % of the total signal photons of 5340 ±190 detected over 0.1-10 MeV. As a result, the line equivalent width reached 280 ±40 keV, which implies a nontrivial result. The result suggests that a downward positron beam produced both the continuum and the line photons.
Magnetorotational instability of weakly ionized and magnetized electron-positron-ion plasma
NASA Astrophysics Data System (ADS)
Mehdian, H.; Hajisharifi, K.; Azadnia, F.; Tajik-Nezhad, S.
2016-10-01
The magnetorotational instability in a differential rotating weakly ionized and magnetized plasma consisting of electron, positron, ion, and neutral particles has been investigated by using the multi-fluid model. Satisfying the current neutrality and homogeneity of the system in the equilibrium state by assuming the same unperturbed angular velocity for charge species and neutrals, the general local dispersion relation (DR) has been derived by taking into account the collision effects. By analytical examination of the obtained DR in the arbitrary and high frequency regimes, the instability conditions have been found in which the presence of light positive species (positrons) plays an important role in the instability criteria. Moreover, numerical investigation shows the broadening of instability range as well as increasing the maximum growth rate of instability (especially for the small number density ratio of light to heavy positive species) in the presence of positrons. The obtained results of the present investigation will greatly contribute to the understanding of the particles' dynamics as well as dissipation mechanism in some astrophysical environments, such as the region of accretion disks surrounding the central of black holes and protoplanetary disks.
On-ground detection of an electron-positron annihilation line from thunderclouds.
Umemoto, D; Tsuchiya, H; Enoto, T; Yamada, S; Yuasa, T; Kawaharada, M; Kitaguchi, T; Nakazawa, K; Kokubun, M; Kato, H; Okano, M; Tamagawa, T; Makishima, K
2016-02-01
Thunderclouds can produce bremsstrahlung gamma-ray emission, and sometimes even positrons. At 00:27:00 (UT) on 13 January 2012, an intense burst of gamma rays from a thundercloud was detected by the GROWTH experiment, located in Japan, facing the Sea of Japan. The event started with a sharp gamma-ray flash with a duration of <300 ms coincident with an intracloud discharge, followed by a decaying longer gamma-ray emission lasting for ∼60 s. The spectrum of this prolonged emission reached ∼10 MeV, and contained a distinct line emission at 508±3(stat.)±5(sys.) keV, to be identified with an electron-positron annihilation line. The line was narrow within the instrumental energy resolution (∼80keV), and contained 520±50 photons which amounted to ∼10% of the total signal photons of 5340±190 detected over 0.1-10 MeV. As a result, the line equivalent width reached 280±40 keV, which implies a nontrivial result. The result suggests that a downward positron beam produced both the continuum and the line photons.
Positron and electron scattering by glycine and alanine: Shape resonances and methylation effect
NASA Astrophysics Data System (ADS)
Nunes, Fernanda B.; Bettega, Márcio H. F.; Sanchez, Sergio d'Almeida
2016-12-01
We report integral cross sections (ICSs) for both positron and electron scattering by glycine and alanine amino acids. These molecules differ only by a methyl group. We computed the scattering cross sections using the Schwinger multichannel method for both glycine and alanine in different levels of approximation for both projectiles. The alanine ICSs are greater in magnitude than the glycine ICSs for both positron and electron scattering, probably due to the larger size of the molecule. In electron scattering calculations, we found two resonances for each molecule. Glycine presents one at 1.8 eV, and another centered at around 8.5 eV, in the static-exchange plus polarization (SEP) approximation. The ICS for alanine shows one resonance at 2.5 eV and another at around 9.5 eV, also in SEP approximation. The results are in good agreement with most of the data present in the literature. The comparison of the electron scattering ICSs for both molecules indicates that the methylation of glycine destabilizes the resonances, shifting them to higher energies.
Towards a Resolution of the Proton Form Factor Problem: New Electron and Positron Scattering Data
Adikaram, D.; Rimal, D.; Weinstein, L. B.; ...
2015-02-10
There is a significant discrepancy between the values of the proton electric form factor, GpE, extracted using unpolarized and polarized electron scattering. Calculations predict that small two-photon exchange (TPE) contributions can significantly affect the extraction of GpE from the unpolarized electron-proton cross sections. We determined the TPE contribution by measuring the ratio of positron-proton to electron-proton elastic scattering cross sections using a simultaneous, tertiary electron-positron beam incident on a liquid hydrogen target and detecting the scattered particles in the Jefferson Lab CLAS detector. This novel technique allowed us to cover a wide range in virtual photon polarization (epsilon) and momentummore » transfer (Q2) simultaneously, as well as to cancel luminosity-related systematic errors. The cross section ratio increases with decreasing ε at Q2=1.45 GeV2. This measurement is consistent with the size of the form factor discrepancy at Q2≈1.75 GeV2 and with hadronic calculations including nucleon and Delta intermediate states, which have been shown to resolve the discrepancy up to 2-3 GeV2.« less
Towards a Resolution of the Proton Form Factor Problem: New Electron and Positron Scattering Data
Adikaram, D.; Rimal, D.; Weinstein, L. B.; Raue, B.; Khetarpal, P.; Bennett, R.; Arrington, J.; Brooks, W.; Adhikari, K.; Afanasev, A.; Amaryan, M.; Anderson, M.; Anefalos Pereira, S.; Avakian, H.; Ball, J.; Battaglieri, M.; Bedlinskiy, I.; Biselli, A.; Bono, J.; Boiarinov, S.; Briscoe, W.; Burkert, V.; Carman, D.; Careccia, S.; Celentano, A.; Chandavar, S.; Charles, G.; Colaneri, L.; Cole, P.; Contalbrigo, M.; Crede, V.; D'Angelo, A.; Dashyan, N.; De Vita, R.; De Sanctis, E.; Deur, A.; Djalali, C.; Dodge, G.; Dupre, R.; Egiyan, H.; El Alaoui, A.; El Fassi, L.; Elouadrhiri, L.; Eugenio, P.; Fedotov, G.; Fegan, S.; Filippi, A.; Fleming, J.; Fradi, A.; Garillon, B.; Gilfoyle, G.; Giovanetti, K.; Girod, F.; Goetz, J.; Gohn, W.; Golovatch, E.; Gothe, R.; Griffioen, K.; Guegan, B.; Guidal, M.; Guo, L.; Hafidi, K.; Hakobyan, H.; Hanretty, C.; Harrison, N.; Hattawy, M.; Hicks, K.; Holtrop, M.; Hughes, S.; Hyde, C. E.; Ilieva, Y.; Ireland, D.; Ishkhanov, B.; Jenkins, D.; Jiang, H.; Jo, H.; Joo, K.; Joosten, S.; Kalantarians, N.; Keller, D.; Khandaker, M.; Kim, A.; Kim, W.; Klein, A.; Klein, F.; Koirala, S.; Kubarovsky, V.; Kuhn, S.; Livingston, K.; Lu, H.; MacGregor, I.; Markov, N.; Mattione, P.; Mayer, M.; McKinnon, B.; Mestayer, M.; Meyer, C.; Mirazita, M.; Mokeev, V.; Montgomery, R.; Moody, C.; Moutarde, H.; Movsisyan, A.; Camacho, C. Munoz; Nadel-Turonski, P.; Niccolai, S.; Niculescu, G.; Osipenko, M.; Ostrovidov, A.; Park, K.; Pasyuk, E.; Pisano, S.; Pogorelko, O.; Price, J.; Procureur, S.; Prok, Y.; Protopopescu, D.; Puckett, A.; Ripani, M.; Rizzo, A.; Rosner, G.; Rossi, P.; Roy, P.; Sabati, F.; Salgado, C.; Schott, D.; Schumacher, R.; Seder, E.; Sharabian, Y.; Simonyan, A.; Skorodumina, I.; Smith, E.; Smith, G.; Sober, D.; Sokhan, D.; Sparveris, N.; Stepanyan, S.; Stoler, P.; Strauch, S.; Sytnik, V.; Taiuti, M.; Tian, Ye; Trivedi, A.; Ungaro, M.; Voskanyan, H.; Voutier, E.; Walford, N.; Watts, D.; Wei, X.; Wood, M.; Zachariou, N.; Zana, L.; Zhang, J.; Zhao, Z.; Zonta, I.
2015-02-10
There is a significant discrepancy between the values of the proton electric form factor, GpE, extracted using unpolarized and polarized electron scattering. Calculations predict that small two-photon exchange (TPE) contributions can significantly affect the extraction of GpE from the unpolarized electron-proton cross sections. We determined the TPE contribution by measuring the ratio of positron-proton to electron-proton elastic scattering cross sections using a simultaneous, tertiary electron-positron beam incident on a liquid hydrogen target and detecting the scattered particles in the Jefferson Lab CLAS detector. This novel technique allowed us to cover a wide range in virtual photon polarization (epsilon) and momentum transfer (Q2) simultaneously, as well as to cancel luminosity-related systematic errors. The cross section ratio increases with decreasing ε at Q2=1.45 GeV2. This measurement is consistent with the size of the form factor discrepancy at Q2≈1.75 GeV2 and with hadronic calculations including nucleon and Delta intermediate states, which have been shown to resolve the discrepancy up to 2-3 GeV2.
Towards a resolution of the proton form factor problem: new electron and positron scattering data.
Adikaram, D; Rimal, D; Weinstein, L B; Raue, B; Khetarpal, P; Bennett, R P; Arrington, J; Brooks, W K; Adhikari, K P; Afanasev, A V; Amaryan, M J; Anderson, M D; Anefalos Pereira, S; Avakian, H; Ball, J; Battaglieri, M; Bedlinskiy, I; Biselli, A S; Bono, J; Boiarinov, S; Briscoe, W J; Burkert, V D; Carman, D S; Careccia, S; Celentano, A; Chandavar, S; Charles, G; Colaneri, L; Cole, P L; Contalbrigo, M; Crede, V; D'Angelo, A; Dashyan, N; De Vita, R; De Sanctis, E; Deur, A; Djalali, C; Dodge, G E; Dupre, R; Egiyan, H; El Alaoui, A; El Fassi, L; Elouadrhiri, L; Eugenio, P; Fedotov, G; Fegan, S; Filippi, A; Fleming, J A; Fradi, A; Garillon, B; Gilfoyle, G P; Giovanetti, K L; Girod, F X; Goetz, J T; Gohn, W; Golovatch, E; Gothe, R W; Griffioen, K A; Guegan, B; Guidal, M; Guo, L; Hafidi, K; Hakobyan, H; Hanretty, C; Harrison, N; Hattawy, M; Hicks, K; Holtrop, M; Hughes, S M; Hyde, C E; Ilieva, Y; Ireland, D G; Ishkhanov, B S; Jenkins, D; Jiang, H; Jo, H S; Joo, K; Joosten, S; Kalantarians, N; Keller, D; Khandaker, M; Kim, A; Kim, W; Klein, A; Klein, F J; Koirala, S; Kubarovsky, V; Kuhn, S E; Livingston, K; Lu, H Y; MacGregor, I J D; Markov, N; Mattione, P; Mayer, M; McKinnon, B; Mestayer, M D; Meyer, C A; Mirazita, M; Mokeev, V; Montgomery, R A; Moody, C I; Moutarde, H; Movsisyan, A; Camacho, C Munoz; Nadel-Turonski, P; Niccolai, S; Niculescu, G; Osipenko, M; Ostrovidov, A I; Park, K; Pasyuk, E; Peña, C; Pisano, S; Pogorelko, O; Price, J W; Procureur, S; Prok, Y; Protopopescu, D; Puckett, A J R; Ripani, M; Rizzo, A; Rosner, G; Rossi, P; Roy, P; Sabatié, F; Salgado, C; Schott, D; Schumacher, R A; Seder, E; Sharabian, Y G; Simonyan, A; Skorodumina, I; Smith, E S; Smith, G D; Sober, D I; Sokhan, D; Sparveris, N; Stepanyan, S; Stoler, P; Strauch, S; Sytnik, V; Taiuti, M; Tian, Ye; Trivedi, A; Ungaro, M; Voskanyan, H; Voutier, E; Walford, N K; Watts, D P; Wei, X; Wood, M H; Zachariou, N; Zana, L; Zhang, J; Zhao, Z W; Zonta, I
2015-02-13
There is a significant discrepancy between the values of the proton electric form factor, G(E)(p), extracted using unpolarized and polarized electron scattering. Calculations predict that small two-photon exchange (TPE) contributions can significantly affect the extraction of G(E)(p) from the unpolarized electron-proton cross sections. We determined the TPE contribution by measuring the ratio of positron-proton to electron-proton elastic scattering cross sections using a simultaneous, tertiary electron-positron beam incident on a liquid hydrogen target and detecting the scattered particles in the Jefferson Lab CLAS detector. This novel technique allowed us to cover a wide range in virtual photon polarization (ϵ) and momentum transfer (Q(2)) simultaneously, as well as to cancel luminosity-related systematic errors. The cross section ratio increases with decreasing ϵ at Q(2)=1.45 GeV(2). This measurement is consistent with the size of the form factor discrepancy at Q(2)≈1.75 GeV(2) and with hadronic calculations including nucleon and Δ intermediate states, which have been shown to resolve the discrepancy up to 2-3 GeV(2).
Towards a Resolution of the Proton Form Factor Problem: New Electron and Positron Scattering Data
NASA Astrophysics Data System (ADS)
Adikaram, D.; Rimal, D.; Weinstein, L. B.; Raue, B.; Khetarpal, P.; Bennett, R. P.; Arrington, J.; Brooks, W. K.; Adhikari, K. P.; Afanasev, A. V.; Amaryan, M. J.; Anderson, M. D.; Anefalos Pereira, S.; Avakian, H.; Ball, J.; Battaglieri, M.; Bedlinskiy, I.; Biselli, A. S.; Bono, J.; Boiarinov, S.; Briscoe, W. J.; Burkert, V. D.; Carman, D. S.; Careccia, S.; Celentano, A.; Chandavar, S.; Charles, G.; Colaneri, L.; Cole, P. L.; Contalbrigo, M.; Crede, V.; D'Angelo, A.; Dashyan, N.; De Vita, R.; De Sanctis, E.; Deur, A.; Djalali, C.; Dodge, G. E.; Dupre, R.; Egiyan, H.; El Alaoui, A.; El Fassi, L.; Elouadrhiri, L.; Eugenio, P.; Fedotov, G.; Fegan, S.; Filippi, A.; Fleming, J. A.; Fradi, A.; Garillon, B.; Gilfoyle, G. P.; Giovanetti, K. L.; Girod, F. X.; Goetz, J. T.; Gohn, W.; Golovatch, E.; Gothe, R. W.; Griffioen, K. A.; Guegan, B.; Guidal, M.; Guo, L.; Hafidi, K.; Hakobyan, H.; Hanretty, C.; Harrison, N.; Hattawy, M.; Hicks, K.; Holtrop, M.; Hughes, S. M.; Hyde, C. E.; Ilieva, Y.; Ireland, D. G.; Ishkhanov, B. S.; Jenkins, D.; Jiang, H.; Jo, H. S.; Joo, K.; Joosten, S.; Kalantarians, N.; Keller, D.; Khandaker, M.; Kim, A.; Kim, W.; Klein, A.; Klein, F. J.; Koirala, S.; Kubarovsky, V.; Kuhn, S. E.; Livingston, K.; Lu, H. Y.; MacGregor, I. J. D.; Markov, N.; Mattione, P.; Mayer, M.; McKinnon, B.; Mestayer, M. D.; Meyer, C. A.; Mirazita, M.; Mokeev, V.; Montgomery, R. A.; Moody, C. I.; Moutarde, H.; Movsisyan, A.; Camacho, C. Munoz; Nadel-Turonski, P.; Niccolai, S.; Niculescu, G.; Osipenko, M.; Ostrovidov, A. I.; Park, K.; Pasyuk, E.; Peña, C.; Pisano, S.; Pogorelko, O.; Price, J. W.; Procureur, S.; Prok, Y.; Protopopescu, D.; Puckett, A. J. R.; Ripani, M.; Rizzo, A.; Rosner, G.; Rossi, P.; Roy, P.; Sabatié, F.; Salgado, C.; Schott, D.; Schumacher, R. A.; Seder, E.; Sharabian, Y. G.; Simonyan, A.; Skorodumina, I.; Smith, E. S.; Smith, G. D.; Sober, D. I.; Sokhan, D.; Sparveris, N.; Stepanyan, S.; Stoler, P.; Strauch, S.; Sytnik, V.; Taiuti, M.; Tian, Ye; Trivedi, A.; Ungaro, M.; Voskanyan, H.; Voutier, E.; Walford, N. K.; Watts, D. P.; Wei, X.; Wood, M. H.; Zachariou, N.; Zana, L.; Zhang, J.; Zhao, Z. W.; Zonta, I.; CLAS Collaboration
2015-02-01
There is a significant discrepancy between the values of the proton electric form factor, GEp, extracted using unpolarized and polarized electron scattering. Calculations predict that small two-photon exchange (TPE) contributions can significantly affect the extraction of GEp from the unpolarized electron-proton cross sections. We determined the TPE contribution by measuring the ratio of positron-proton to electron-proton elastic scattering cross sections using a simultaneous, tertiary electron-positron beam incident on a liquid hydrogen target and detecting the scattered particles in the Jefferson Lab CLAS detector. This novel technique allowed us to cover a wide range in virtual photon polarization (ɛ ) and momentum transfer (Q2) simultaneously, as well as to cancel luminosity-related systematic errors. The cross section ratio increases with decreasing ɛ at Q2=1.45 GeV2 . This measurement is consistent with the size of the form factor discrepancy at Q2≈1.75 GeV2 and with hadronic calculations including nucleon and Δ intermediate states, which have been shown to resolve the discrepancy up to 2 - 3 GeV2 .
Positron 2D-ACAR experiments and electron-positron momentum density in YBa{sub 2}Cu{sub 3}O{sub 7-x}
Smedskjaer, L.C.; Welp, U.; Fang, Y.; Bailey, K.G.; Bansil, A.
1991-12-01
We discuss positron annihilation (2D-ACAR) measurements in the C- projection on an untwinned metallic single crystal of YBa{sub 2}Cu{sub 3}O{sub 7-x} as a function of temperature, for five temperatures ranging from 30K to 300K. The measured 2D-ACAR intensities are interpreted in terms of the electron-positron momentum density obtained within the KKR-band theory framework. The temperature dependence of the 2D-ACAR spectra is used to extract a ``background corrected`` experimental spectrum which is in remarkable accord with the corresponding band theory predictions, and displays in particular clear signatures of the electron ridge Fermi surface.
Positron 2D-ACAR experiments and electron-positron momentum density in YBa sub 2 Cu sub 3 O sub 7-x
Smedskjaer, L.C.; Welp, U.; Fang, Y.; Bailey, K.G. ); Bansil, A. . Dept. of Physics)
1991-12-01
We discuss positron annihilation (2D-ACAR) measurements in the C- projection on an untwinned metallic single crystal of YBa{sub 2}Cu{sub 3}O{sub 7-x} as a function of temperature, for five temperatures ranging from 30K to 300K. The measured 2D-ACAR intensities are interpreted in terms of the electron-positron momentum density obtained within the KKR-band theory framework. The temperature dependence of the 2D-ACAR spectra is used to extract a background corrected'' experimental spectrum which is in remarkable accord with the corresponding band theory predictions, and displays in particular clear signatures of the electron ridge Fermi surface.
An 8×8 Row-Column Summing Readout Electronics for Preclinical Positron Emission Tomography Scanners
Shih, Y. C.; Sun, F. W.; MacDonald, L. R.; Otis, B. P.; Miyaoka, R. S.; McDougald, W.; Lewellen, T. K.
2010-01-01
This work presents a row/column summing readout electronics for an 8×8 silicon photomultiplier array. The summation circuit greatly reduces the number of electronic channels, which is desirable for pursuing higher resolution positron emission tomography scanners. By using a degenerated common source topology in the summation circuit, more fan-in is possible and therefore a greater reduction in the number of electronic channels can be achieved. The timing signal is retrieved from a common anode, which allows the use of a single fast-sampling analog to digital converter (ADC) for the timing channel and slower, lower power ADCs for the 64 spatial channels. Preliminary results of one row summation of the 8×8 readout electronics exhibited FWHM energy resolution of 17.8% and 18.3% with and without multiplexing, respectively. The measured timing resolution is 2.9ns FWHM. PMID:20729983
NASA Astrophysics Data System (ADS)
Ma, S. K.; Lui, M. K.; Ling, C. C.; Fung, S.; Beling, C. D.; Li, K. F.; Cheah, K. W.; Gong, M.; Hang, H. S.; Weng, H. M.
2004-09-01
Electron irradiated undoped liquid encapsulated Czochralski (LEC) grown GaSb samples were studied by positron lifetime spectroscopy (PLS) and photoluminescence (PL). In addition to the 315 ps component reported in the previous studies, another defect with a lifetime of 280 ps was also identified in the present electron irradiated samples. The bulk lifetime of the GaSb material was found to be 258 ps. The VGa,280 ps and the VGa,315 ps defects were associated with two independent Ga vacancy related defects having different microstructures. The well known 777 meV PL signal (usually band A) was also observed in the electron irradiated undoped GaSb samples. The band A intensity decreases with increasing electron irradiation dosage and it disappears after the 300 °C annealing regardless of the irradiation dosage. The origin of the band A signal is also discussed.
Pair-production in inhomogeneous electric fields
NASA Astrophysics Data System (ADS)
Xue, She-Sheng
2008-01-01
This is a preliminary study on the rate of electron-positron pair production in spatially inhomogeneous electric fields. We study the rate in the Sauter field and compare it to the rate in the homogeneous field.
Fazleev, N. G.; Nadesalingam, M. P.; Maddox, W.; Weiss, A. H.
2011-06-01
Positron annihilation induced Auger electron spectroscopy (PAES) measurements from the surface of an oxidized Cu(100) single crystal show a large increase in the intensity of the annihilation induced Cu M2,3VV Auger peak as the sample is subjected to a series of isochronal anneals in vacuum up to annealing temperature 300 deg. C. The PAES intensity then decreases monotonically as the annealing temperature is increased to {approx}550 deg. C. Experimental positron annihilation probabilities with Cu 3p and O 1s core electrons are estimated from the measured intensities of the positron annihilation induced Cu M{sub 2,3}VV and O KLL Auger transitions. PAES results are analyzed by performing calculations of positron surface states and annihilation probabilities of the surface-trapped positrons with relevant core electrons taking into account the charge redistribution at the surface and various surface structures associated with low and high oxygen coverages. The variations in atomic structure and chemical composition of the topmost layers of the oxidized Cu(100) surface are found to affect localization and spatial extent of the positron surface state wave function. The computed positron binding energy and annihilation characteristics reveal their sensitivity to charge transfer effects, atomic structure and chemical composition of the topmost layers of the oxidized Cu(100) surface. Theoretical positron annihilation probabilities with Cu 3p and O 1s core electrons computed for the oxidized Cu(100) surface are compared with experimental ones. The obtained results provide a demonstration of thermal reduction of the copper oxide surface after annealing at 300 deg. C followed by re-oxidation of the Cu(100) surface at higher annealing temperatures presumably due to diffusion of subsurface oxygen to the surface.
Photon-pair shot noise in electron shot noise
NASA Astrophysics Data System (ADS)
Simoneau, Jean Olivier; Virally, Stéphane; Lupien, Christian; Reulet, Bertrand
2017-02-01
We report the measurement of the statistics of photons in the nonclassical radiation emitted by a tunnel junction. This is obtained by measuring up to the fourth cumulant of the voltage fluctuations generated by the sample. When the electron shot noise generates a squeezed electromagnetic field, the measurement provides a strong signature of the presence of photon pairs, characterized by a Fano factor of the photon flux above unity.
Beam-Beam Study on the Upgrade of Beijing Electron Positron Collider
Wang, S.; Cai, Y.; /SLAC
2006-02-10
It is an important issue to study the beam-beam interaction in the design and performance of such a high luminosity collider as BEPCII, the upgrade of Beijing Electron Positron Collider. The weak-strong simulation is generally used during the design of a collider. For performance a large scale tune scan, the weak-strong simulation studies on beam-beam interaction were done, and the geometry effects were taken into account. The strong-strong simulation studies were done for investigating the luminosity goal and the dependence of the luminosity on the beam parameters.
Liang, Edison; Smith, Ian; Boettcher, Markus E-mail: iansmith@rice.edu
2013-04-01
Using particle-in-cell simulations, we study the kinetic physics of relativistic shear flow in collisionless electron-positron (e+e-) plasmas. We find efficient magnetic field generation and particle energization at the shear boundary, driven by streaming instabilities across the shear interface and sustained by the shear flow. Nonthermal, anisotropic high-energy particles are accelerated across field lines to produce a power-law tail turning over just below the shear Lorentz factor. These results have important implications for the dissipation and radiation of jets in blazars and gamma-ray bursts.
Comoving acceleration of overdense electron-positron plasma by colliding ultra-intense laser pulses
Liang, Edison
2006-06-15
Particle-in-cell (PIC) simulation results of sustained acceleration of electron-positron (e+e-) plasmas by comoving electromagnetic (EM) pulses are presented. When a thin slab of overdense e+e- plasma is irradiated with linear-polarized ultra-intense short laser pulses from both sides, the pulses are transmitted when the plasma is compressed to thinner than {approx}2 relativistic skin depths. A fraction of the plasma is then captured and efficiently accelerated by self-induced JxB forces. For 1 {mu}m laser and 10{sup 21} W cm{sup -2} intensity, the maximum energy exceeds GeV in a picosecond.
NASA Astrophysics Data System (ADS)
Akhtar, N.; El-Taibany, W. F.; Mahmood, S.; Behery, E. E.; Khan, S. A.; Ali, S.; Hussain, S.
2015-10-01
> . The magnetic field has no effect on the amplitude of the IASW, whereas the obliqueness angle of the wave propagation, the ion-to-electron temperature ratio and positron-to-ion density concentration ratio affect both the amplitude and the width of the solitary wave structures. The transverse instability analysis illustrates that the one soliton solution has a constant growth rate, and it suffers from instability in the transverse direction. The relevance of the present study to astrophysical space plasmas is also discussed.
Reestimation of the production spectra of cosmic ray secondary positrons and electrons in the ISM
NASA Technical Reports Server (NTRS)
Wong, C. M.; Ng, L. K.
1985-01-01
A detailed calculation of the production spectra of charged hadrons produced by interactions of cosmic rays in the interstellar medium is presented along with a thorough treatment of pion and muon decays. Newly parameterized inclusive cross sections of hadrons were used and exact kinematic limitations were taken into account. Single parametrized expressions for the production spectra of both secondary positrons and electrons in the energy range .1 to 100 GeV are presented. The results are compared with other authors' predictions. Equilibrium spectra using various models are also presented.
Online beam energy measurement of Beijing electron positron collider II linear accelerator
NASA Astrophysics Data System (ADS)
Wang, S.; Iqbal, M.; Liu, R.; Chi, Y.
2016-02-01
This paper describes online beam energy measurement of Beijing Electron Positron Collider upgraded version II linear accelerator (linac) adequately. It presents the calculation formula, gives the error analysis in detail, discusses the realization in practice, and makes some verification. The method mentioned here measures the beam energy by acquiring the horizontal beam position with three beam position monitors (BPMs), which eliminates the effect of orbit fluctuation, and is much better than the one using the single BPM. The error analysis indicates that this online measurement has further potential usage such as a part of beam energy feedback system. The reliability of this method is also discussed and demonstrated in this paper.
Phase-mixing of electrostatic modes in a cold magnetized electron-positron plasma
Maity, Chandan; Chakrabarti, Nikhil
2013-08-15
In a fluid description, we study space-time evolution of electrostatic oscillations in a cold magnetized electron-positron plasma. Nonlinear results up to third order, obtained by employing a simple perturbation technique, indicate phase-mixing and thus breaking of excited oscillations, and provide an expression for the phase-mixing time. It is shown that an increase in the strength of ambient magnetic field results in an increase in the phase-mixing time. The results of our investigation will be of relevance to astrophysical environments as well as laboratory experiments.
Science and Technology of the TESLA Electron-Positron Linear Collider
NASA Astrophysics Data System (ADS)
Wagner, Albrecht
2002-07-01
Recent analyses of the long term future of particles physics in Asia, Europe, and the U.S.A. have led to the consensus that the next major facility to be built to unravel the secrets of the micro-cosmos is an electron-positron linear collider in the energy range of 500 to 1000 GeV. This collider should be constructed in an as timely fashion as possible to overlap with the Large Hadron Collider, under construction at CERN. Here, the scientific potential and the technological aspects of the TESLA projects, a superconducting collider with an integrated X-ray laser laboratory, are summarised.
Dynamical Cooper pairing in nonequilibrium electron-phonon systems
NASA Astrophysics Data System (ADS)
Knap, Michael; Babadi, Mehrtash; Refael, Gil; Martin, Ivar; Demler, Eugene
2016-12-01
We analyze Cooper pairing instabilities in strongly driven electron-phonon systems. The light-induced nonequilibrium state of phonons results in a simultaneous increase of the superconducting coupling constant and the electron scattering. We demonstrate that the competition between these effects leads to an enhanced superconducting transition temperature in a broad range of parameters. Our results may explain the observed transient enhancement of superconductivity in several classes of materials upon irradiation with high intensity pulses of terahertz light, and may pave new ways for engineering high-temperature light-induced superconducting states.
Dynamical Cooper pairing in nonequilibrium electron-phonon systems
Knap, Michael; Babadi, Mehrtash; Refael, Gil; Martin, Ivar; Demler, Eugene
2016-12-08
In this paper, we analyze Cooper pairing instabilities in strongly driven electron-phonon systems. The light-induced nonequilibrium state of phonons results in a simultaneous increase of the superconducting coupling constant and the electron scattering. We demonstrate that the competition between these effects leads to an enhanced superconducting transition temperature in a broad range of parameters. Finally, our results may explain the observed transient enhancement of superconductivity in several classes of materials upon irradiation with high intensity pulses of terahertz light, and may pave new ways for engineering high-temperature light-induced superconducting states.
NASA Astrophysics Data System (ADS)
Xie, Shuping; Jiang, Neng; Weiss, A. H.
2003-03-01
Positron annihilation induced Auger electron spectroscopy (PAES) has been shown to have unique advantages over conventional electron collision induced Auger techniques, including the ability to eliminate the secondary electron background and selectively probe the top-most atomic layer on the sample surface. Here we report on the development of a new time-of-flight (TOF) spectrometer which combines features high efficiency magnetic transport and parrallel energy measurment with high resolution by using an innovative timing method. The new TOF-PAES system, was used to make the first quantitative comparative measurements of the Auger intensities associated with the annihilation of positrons with the deep core levels (1s) of S KLL (180eV), C KLL (270eV), N KLL (360eV), and O KLL (510eV). Experimental results of Auger probabilities at outer core level (3s, 3P) of Cu M2,3VV (60eV), M1VV (105eV) are compared with the theoretical value of Jensen and Weiss. Quantitatively study the surface adsorbate process on Cu is performed and concentration changes of surface components are obtained. These results demonstrate that TOF-PAES can be used to obtain quantitative,top-layer specific, information from chemically important elements including those with relatively deep core levels (e.g. C and O).
Theoretical calculation of electron-positron momentum density in YBa 2Cu 3O 7-δ
NASA Astrophysics Data System (ADS)
Massidda, S.
1990-07-01
We present calculations of the electron-positron momentum density for the high- Tc superconductor YBa 2Cu 3O 7-δ for δ=0 and for the insulating parent compound YBa 2Cu 3O 6, based on first-principle electronic structure calculations performed within the local density approximation (LDA) using the full potential linearized augmented plane wave (FLAPW) method. Our results indicate a small overlap of the positron wave function with the CuO 2 plane electrons and, as a consequence, relatively small signals due to the related Fermi surfaces. By contrast, the present calculations show, after the folding of Umklapp terms according to Lock, Crisp and West, clear Fermi surface breaks arising from the Cu-O chain bands. No general agreement with existing experiments allows a clear definition of Fermi surface structures in the latter. A comparison of the calculated momentum with the experimental two-dimensional angular correlation of annihilation radiation (2D-ACAR) recently measured in Geneva shows an overall agreement for the insulating compound, despite the spurious LDA metallic state, and possibly suggests the importance of O vacancies in experiments performed on non-stoichiometric YBa 2Cu 3O 7-δ samples.
Oscillating two-stream instability in a magnetized electron-positron-ion plasma
Tinakiche, Nouara; Annou, R.
2015-04-15
Oscillating two-stream instability (OTSI) in a magnetized electron-ion plasma has been thoroughly studied, e.g., in ionospheric heating experiments [C. S. Liu and V. K. Tripathi, Interaction of Electromagnetic Waves With Electron Beams and Plasmas (World Scientific, 1994); V. K. Tripathi and P. V. Siva Rama Prasad, J. Plasma Phys. 41, 13 (1989); K. Ramachandran and V. K. Tripathi, IEEE Trans. Plasma Sci. 25, 423 (1997)]. In this paper, OTSI is investigated in a magnetized electron-positron-ion plasma. The dispersion relation of the process is established. The pump field threshold, along with the maximum growth rate of the instability is assessed using the Arecibo and HAARP parameters.
Oscillating two-stream instability in a magnetized electron-positron-ion plasma
NASA Astrophysics Data System (ADS)
Tinakiche, Nouara; Annou, R.
2015-04-01
Oscillating two-stream instability (OTSI) in a magnetized electron-ion plasma has been thoroughly studied, e.g., in ionospheric heating experiments [C. S. Liu and V. K. Tripathi, Interaction of Electromagnetic Waves With Electron Beams and Plasmas (World Scientific, 1994); V. K. Tripathi and P. V. Siva Rama Prasad, J. Plasma Phys. 41, 13 (1989); K. Ramachandran and V. K. Tripathi, IEEE Trans. Plasma Sci. 25, 423 (1997)]. In this paper, OTSI is investigated in a magnetized electron-positron-ion plasma. The dispersion relation of the process is established. The pump field threshold, along with the maximum growth rate of the instability is assessed using the Arecibo and HAARP parameters.
Positron-proton to electron-proton elastic cross section ratios from CLAS
NASA Astrophysics Data System (ADS)
Adikaram, Dasuni; Rimal, Dipak; Weinstein, Larry; Raue, Brian
2014-03-01
There is a significant discrepancy between the ratio of the electromagnetic form factors of the proton measured by the Rosenbluth and the polarization transfer technique. The most likely explanation of this discrepancy is the inclusion of two-photon exchange (TPE) amplitude contributions to the elastic electron-proton cross section. The CLAS TPE experiment measured the TPE contribution in the wide range of Q2 and ɛ range using a comparison of positron-proton to electron-proton elastic cross sections (R = σ (e+ p) / σ (e- p)). Preliminary results will be presented, along with the estimations of systematic uncertainties. A detailed comparison of new results with previous R measurements and theoretical calculations will be presented. Implications of the CLAS TPE measurements on the elastic electron-proton cross section will be also discussed.
NASA Astrophysics Data System (ADS)
Rehman, Momin A.; Mishra, M. K.
2016-01-01
The ion-acoustic solitons in collisionless plasma consisting of warm adiabatic ions, isothermal positrons, and two temperature distribution of electrons have been studied. Using reductive perturbation method, Korteweg-de Vries (K-dV), the modified K-dV (m-KdV), and Gardner equations are derived for the system. The soliton solution of the Gardner equation is discussed in detail. It is found that for a given set of parameter values, there exists a critical value of β=Tc/Th, (ratio of cold to hot electron temperature) below which only rarefactive KdV solitons exist and above it compressive KdV solitons exist. At the critical value of β, both compressive and rarefactive m-KdV solitons co-exist. We have also investigated the soliton in the parametric regime where the KdV equation is not valid to study soliton solution. In this region, it is found that below the critical concentration the system supports rarefactive Gardner solitons and above it compressive Gardner solitons are found. The effects of temperature ratio of two-electron species, cold electron concentration, positron concentration on the characteristics of solitons are also discussed.
NASA Astrophysics Data System (ADS)
Franz, Jan
2017-02-01
We present correlation-polarization potentials for the calculation of scattering cross sections of positrons with atoms and molecules. The potentials are constructed from a short-range correlation term and a long-range polarization term. For the short-range correlation term we present four different potentials that are derived from multi-component density functionals. For the long-range polarization term we employ a multi-term expansion. Quantum scattering calculations are presented for low energy collisions of positrons with two atomic targets (argon and krypton) and two molecular targets (nitrogen and methane). For collision energies below the threshold for Positronium formation our calculations of scattering cross sections are in good agreement with recent data sets from experiments and theory. Contribution to the Topical Issue "Low-Energy Interactions related to Atmospheric and Extreme Conditions", edited by S. Ptasinska, M. Smialek-Telega, A. Milosavljevic and B. Sivaraman.
Triply differential measurements of single ionization of argon by 1-keV positron and electron impact
NASA Astrophysics Data System (ADS)
Gavin, J.; de Lucio, O. G.; DuBois, R. D.
2017-06-01
By establishing coincidences between target ions and scattered projectiles, and coincidences between target ions, scattered projectiles, and ejected electrons, triply differential cross-section (TDCS) information was generated in terms of projectile energy loss and scattering angles for interactions between 1-keV positrons and electrons and Ar atoms. The conversion of the raw experimental information to the TDCS is discussed. The single-ionization TDCS exhibits two distinguishable regions (lobes) where binary and recoil interactions can be described by two peaks. A comparison of the positron and electron impact data shows that the relative intensity of both binary and recoil interactions decreases exponentially as a function of the momentum transfer and is larger when ionization is induced by positron impact, when compared with electron impact.
NASA Astrophysics Data System (ADS)
Hafez, M. G.; Roy, N. C.; Talukder, M. R.; Hossain Ali, M.
2016-09-01
This work investigates the oblique nonlinear propagation of ion acoustic (IA) shock waves for both weakly and highly relativistic plasmas composed of nonthermal electrons and positrons with relativistic thermal ions. The KdVB-like equation, involving dispersive, weakly transverse dispersive, nonlinearity and dissipative coefficients, is derived employing the well known reductive perturbation method. The integration of this equation is carried out by the {tanh} method taking the stable shock formation condition into account. The effects of nonthermal electrons and positrons, nonthermal electrons with isothermal positrons, isothermal electrons with nonthermal positrons, and isothermal electrons and positrons on oblique propagation of IA shock waves in weakly relativistic regime are described. Furthermore, the effects of plasma parameters on oblique propagation of IA shock waves in highly relativistic regime are discussed and compared with weakly relativistic case. It is seen that the plasma parameters within certain limits significantly modify the structures of the IA shock waves in both cases. The results may be useful for better understanding of the interactions of charged particles with extra-galactic jets as well as astrophysical compact objects.
A coincidence study of electron and positron impact ionization of Ar (3p) at 1 keV
NASA Astrophysics Data System (ADS)
Campeanu, Radu I.; Walters, James H. R.; Whelan, Colm T.
2015-10-01
Distorted-wave calculations of the triple differential cross section (TDCS) are presented for electron and positron impact ionization of Ar(3p) in coplanar asymmetric geometry at an impact energy of 1 keV and are compared with a recent experiment. The experiment indicates that the positron TDCS is generally larger than the equivalent electron TDCS. It is shown that the magnitude of the TDCS is extremely sensitive to the energy of the ejected electron and that only when the cross section is averaged over energy do we get a reasonable agreement with experiment.
A coincidence study of electron and positron impact ionization of Ar (3p) at 1 keV
NASA Astrophysics Data System (ADS)
Campeanu, Radu I.; Walters, James H. R.; Whelan, Colm T.
2015-10-01
Distorted-wave calculations of the triple differential cross section (TDCS) are presented for electron and positron impact ionization of Ar(3 p) in coplanar asymmetric geometry at an impact energy of 1 keV and are compared with a recent experiment. The experiment indicates that the positron TDCS is generally larger than the equivalent electron TDCS. It is shown that the magnitude of the TDCS is extremely sensitive to the energy of the ejected electron and that only when the cross section is averaged over energy do we get a reasonable agreement with experiment.
PREFACE: The 16th International Conference on Positron Annihilation (ICPA-16)
NASA Astrophysics Data System (ADS)
Alam, Ashraf; Coleman, Paul; Dugdale, Stephen; Roussenova, Mina
2013-06-01
The 16th International Conference on Positron Annihilation (ICPA-16) was held at the University of Bristol, United Kingdom during 19-24 August, 2012. This triennial conference is the foremost gathering of the Positron Annihilation Physics community and it was hosted in the UK for the first time since the series of meetings first started back in 1965. The University of Bristol, the Alma Mater of Paul Dirac, is situated at the heart of the city, and it has established a worldwide reputation in research and teaching. Many of the topics which were discussed during ICPA-16 form an integral part of the research themes in the schools of Physics, Chemistry and Engineering of this University. ICPA-16 attracted a diverse audience, both from academic and industrial institutions, with over 200 participants from 29 countries. It continued the long held tradition of showcasing novel research in the field of positron annihilation and a total of 170 papers were presented as talks and posters. The papers reported studies of metallic and semi-conducting solids, polymers and soft matter, porous materials, surfaces and interfaces, as well as advances in experimental, analytical and biomedical applications. The high quality of the presented work, coupled with the enthusiastic exchange of ideas, provided an invaluable forum, especially for younger researchers and postgraduate students. The excellence of student presentations was acknowledged by the award of prizes for the best student posters, which were received by David Billington (University of Bristol, UK), Moussa Sidibe (CEMHTI, France) and Hongxia Xu (Tohoku University, Japan). All papers published in the Conference Proceedings were reviewed by ICPA-16 participants. We are indebted to all reviewers who contributed their time and intellectual resources, allowing the refereeing and editing process to move smoothly toward the compilation of the Proceedings. Our sincere thanks and gratitude go to everyone who contributed to the
The electronics system for the LBNL positron emission mammography (PEM) camera
NASA Astrophysics Data System (ADS)
Moses, W. W.; Young, J. W.; Baker, K.; Jones, W.; Lenox, M.; Ho, M. H.; Weng, M.
2001-06-01
Describes the electronics for a high-performance positron emission mammography (PEM) camera. It is based on the electronics for a human brain positron emission tomography (PET) camera (the Siemens/CTI HRRT), modified to use a detector module that incorporates a photodiode (PD) array. An application-specified integrated circuit (ASIC) services the photodetector (PD) array, amplifying its signal and identifying the crystal of interaction. Another ASIC services the photomultiplier tube (PMT), measuring its output and providing a timing signal. Field-programmable gate arrays (FPGAs) and lookup RAMs are used to apply crystal-by-crystal correction factors and measure the energy deposit and the interaction depth (based on the PD/PMT ratio). Additional FPGAs provide event multiplexing, derandomization, coincidence detection, and real-time rebinning. Embedded PC/104 microprocessors provide communication, real-time control, and configure the system. Extensive use of FPGAs make the overall design extremely flexible, allowing many different functions (or design modifications) to be realized without hardware changes. Incorporation of extensive onboard diagnostics, implemented in the FPGAs, is required by the very high level of integration and density achieved by this system.
Bernardo, Giuseppe Di; Evoli, Carmelo; Gaggero, Daniele; Grasso, Dario; Maccione, Luca E-mail: carmelo.evoli@desy.de E-mail: dario.grasso@pi.infn.it
2013-03-01
A multichannel analysis of cosmic ray electron and positron spectra and of the diffuse synchrotron emission of the Galaxy is performed by using the DRAGON code. This study is aimed at probing the interstellar electron source spectrum down to E ∼< 1GeV and at constraining several propagation parameters. We find that above 4GeV the e{sup −} source spectrum is compatible with a power-law of index ∼ 2.5. Below 4GeV instead it must be significantly suppressed and the total lepton spectrum is dominated by secondary particles. The positron spectrum and fraction measured below a few GeV are consistently reproduced only within low reacceleration models. We also constrain the scale-height z{sub t} of the cosmic-ray distribution using three independent (and, in two cases, original) arguments, showing that values of z{sub t} ∼< 2kpc are excluded. This result may have strong implications for particle dark matter searches.
Dipole anisotropy in cosmic electrons and positrons: inspection on local sources
NASA Astrophysics Data System (ADS)
Manconi, S.; Di Mauro, M.; Donato, F.
2017-01-01
The cosmic electrons and positrons have been measured with unprecedented statistics up to several hundreds GeV, thus permitting to explore the role that close single sources can have in shaping the flux at different energies. In the present analysis, we consider electrons and positrons in cosmic rays to be produced by spallations of hadron fluxes with the interstellar medium, by a smooth Supernova Remnant (SNR) population, by all the ATNF catalog pulsars, and by few discrete, local SNRs. We test several source models on the e++e‑ and e+ AMS-02 flux data. For the configurations compatible with the data, we compute the dipole anisotropy in e++e‑, e+, e+/e‑ from single sources. Our study includes a dedicated analysis to the Vela SNR. We show that Fermi-LAT present data on dipole anisotropy of e++e‑ start to explore some of the models for the Vela SNR selected by AMS-02 flux data. We also investigate how the observed anisotropy could result from a combination of local sources. Our analysis shows that the search of anisotropy in the lepton fluxes up to TeV energies can be an interesting tool for the inspection of properties of close SNRs, complementary to the high precision flux data.
Cosmic ray electron and positron excesses from a fourth generation heavy Majorana neutrino
Masina, Isabella; Sannino, Francesco E-mail: sannino@cp3-origins.net
2011-08-01
Unexpected features in the energy spectra of cosmic rays electrons and positrons have been recently observed by PAMELA and Fermi-LAT satellite experiments, opening to the exciting possibility of an indirect manifestation of new physics. A TeV-scale fourth lepton family is a natural extension of the Standard Model leptonic sector (also linked to the hierarchy problem in Minimal Walking Technicolor models). The heavy Majorana neutrino of this setup mixes with Standard Model charged leptons through a weak charged current interaction. Here, we first study analytically the energy spectrum of the electrons and positrons originated in the heavy Majorana neutrino decay modes, also including polarization effects. We then compare the prediction of this model with the experimental data, exploiting both the standard direct method and our recently proposed Sum Rules method. We find that the decay modes involving the tau and/or the muon charged leptons as primary decay products fit well the PAMELA and Fermi-LAT lepton excesses while there is tension with respect to the antiproton to proton fraction constrained by PAMELA.
NASA Astrophysics Data System (ADS)
Hafez, M. G.; Talukder, M. R.; Sakthivel, R.
2016-05-01
The theoretical and numerical studies have been investigated on nonlinear propagation of weakly relativistic ion acoustic solitary waves in an unmagnetized plasma system consisting of nonextensive electrons, positrons and relativistic thermal ions. To study the characteristics of nonlinear propagation of the three-component plasma system, the reductive perturbation technique has been applied to derive the Korteweg-de Vries equation, which divulges the soliton-like solitary wave solution. The ansatz method is employed to carry out the integration of this equation. The effects of nonextensive electrons, positrons and relativistic thermal ions on phase velocity, amplitude and width of soliton and electrostatic nonlinear propagation of weakly relativistic ion acoustic solitary waves have been discussed taking different plasma parameters into consideration. The obtained results can be useful in understanding the features of small amplitude localized relativistic ion acoustic solitary waves in an unmagnetized three-component plasma system for hard thermal photon production with relativistic heavy ions collision in quark-gluon plasma as well as for astrophysical plasmas.
Schultz, D.R. )
1989-09-01
We present and compare total cross sections for single-electron removal in collisions of electrons, positrons, protons, and antiprotons with atomic hydrogen and helium. These cross sections have been calculated using the classical trajectory Monte Carlo technique in the velocity range of 0.5--7.0 a.u. (6.25--1224 keV/u). The cross sections are compared at equal collision velocities and exhibit differences arising from variations in mass and sign of charge of the projectile. At low and intermediate velocities these differences are large in both the ionization and charge transfer channels. At high velocities the single-ionization cross section for each of these singly charged particles becomes equal. However, the differences in the single-charge-transfer cross sections for positron and proton impact persist to very large velocities. We extend our previous work (Phys. Rev. A 38, 1866 (1988)) to explain these mass and sign of the charge effects in single-electron removal collisions.
NASA Astrophysics Data System (ADS)
Azadegan, B.; Wagner, W.
2015-01-01
We present a Mathematica package for simulation of spectral-angular distributions and energy spectra of planar channeling radiation of relativistic electrons and positrons channeled along major crystallographic planes of a diamond-structure or tungsten single crystal. The program is based on the classical theory of channeling radiation which has been successfully applied to study planar channeling of light charged particles at energies higher than 100 MeV. Continuous potentials for different planes of diamond, Si, Ge and W single crystals are calculated using the Doyle-Turner approximation to the atomic scattering factor and taking thermal vibrations of the crystal atoms into account. Numerical methods are applied to solve the classical one-dimensional equation of motion. The code is designed to calculate the trajectories, velocities and accelerations of electrons (positrons) channeled by the planar continuous potential. In the framework of classical electrodynamics, these data allow realistic simulations of spectral-angular distributions and energy spectra of planar channeling radiation. Since the generated output is quantitative, the results of calculation may be useful, e.g., for setup configuration and crystal alignment in channeling experiments, for the study of the dependence of channeling radiation on the input parameters of particle beams with respect to the crystal orientation, but also for the simulation of positron production by means of pair creation what is mandatory for the design of efficient positron sources necessary in high-energy and collider physics. Although the classical theory of channeling is well established for long time, there is no adequate library program for simulation of channeling radiation up to now, which is commonly available, sufficiently simple and effective to employ and, therefore, of benefit as for special investigations as for a quick overview of basic features of this type of radiation.
NASA Astrophysics Data System (ADS)
Pramanik, Sourav; Maity, Chandan
2017-08-01
Spatiotemporal evolution of nonlinear electron-positron oscillations around a homogeneous background of massive ions has been analyzed in cold electron-positron-ion (EPI) plasmas by employing a simple perturbation method, demonstrating phase-mixing and thus wave-breaking of excited oscillations at arbitrarily low amplitudes [C. Maity, Phys. Plasmas 21, 072317 (2014)]. In this work, we investigate effects of the magnetic field on the phase-mixing phenomena of electron-positron oscillations in cold EPI plasmas. A perturbative analysis of governing fluid-Maxwell's equations has been carried out up to third order to obtain a rough estimate of the phase-mixing time. It has been shown that the presence of an external ambient magnetic field may induce a delay in the process of phase-mixing of such oscillations.
Scattering of Low Energy Electrons and Positrons from Hydrogenic Systems and Applications
NASA Technical Reports Server (NTRS)
Bhatia, Anand K.
2007-01-01
While the electron scatters from the target, the target no longer stays in its original form. One of the first methods to take into account the distortion of the target at low incident energies is the method of polarized orbitals. In this method the wave function for the process is written using the first-order perturbation theory and the equation for the scattering function is derived from the Schradinger equation. This method has been very successful in calculating the phase shifts and therefore the cross sections at various energies. The total wave function can be used to calculate photoionization cross sections. The disadvantage of this approach is that the method is not variational and therefore does not provide bounds on the phase shifts. These difficulties can be overcome by using the Feshbach projection operator formalism. This approach has been employed for the scattering of electrons and positrons from targets. Results of various calculations will be discussed.
NASA Astrophysics Data System (ADS)
Pommé, S.
2009-06-01
An analytical model is presented to calculate the total detection efficiency of a well-type radiation detector for photons, electrons and positrons emitted from a radioactive source at an arbitrary position inside the well. The model is well suited to treat a typical set-up with a point source or cylindrical source and vial inside a NaI well detector, with or without lead shield surrounding it. It allows for fast absolute or relative total efficiency calibrations for a wide variety of geometrical configurations and also provides accurate input for the calculation of coincidence summing effects. Depending on its accuracy, it may even be applied in 4π-γ counting, a primary standardisation method for activity. Besides an accurate account of photon interactions, precautions are taken to simulate the special case of 511 keV annihilation quanta and to include realistic approximations for the range of (conversion) electrons and β -- and β +-particles.
Ion-acoustic shocks in quantum electron-positron-ion plasmas
Roy, K.; Misra, A. P.; Chatterjee, P.
2008-03-15
Nonlinear propagation of quantum ion-acoustic waves (QIAWs) in a dense quantum plasma whose constituents are electrons, positrons, and positive ions is investigated using a quantum hydrodynamic model. The standard reductive perturbation technique is used to derive the Korteweg-de Vries-Burger (KdVB) equation for QIAWs. It is shown by numerical simulation that the KdVB equation has either oscillatory or monotonic shock wave solutions depending on the system parameters H proportional to quantum diffraction, {mu}{sub i} the effect of ion kinematic viscosity, and {mu} the equilibrium electron to ion density ratio. The results may have relevance in dense astrophysical plasmas (such as neutron stars) as well as in intense laser solid density plasma experiments where the particle density is about 10{sup 25}-10{sup 28} m{sup -3}.
Electron correlation within the relativistic no-pair approximation
NASA Astrophysics Data System (ADS)
Almoukhalalati, Adel; Knecht, Stefan; Jensen, Hans Jørgen Aa.; Dyall, Kenneth G.; Saue, Trond
2016-08-01
This paper addresses the definition of correlation energy within 4-component relativistic atomic and molecular calculations. In the nonrelativistic domain the correlation energy is defined as the difference between the exact eigenvalue of the electronic Hamiltonian and the Hartree-Fock energy. In practice, what is reported is the basis set correlation energy, where the "exact" value is provided by a full Configuration Interaction (CI) calculation with some specified one-particle basis. The extension of this definition to the relativistic domain is not straightforward since the corresponding electronic Hamiltonian, the Dirac-Coulomb Hamiltonian, has no bound solutions. Present-day relativistic calculations are carried out within the no-pair approximation, where the Dirac-Coulomb Hamiltonian is embedded by projectors eliminating the troublesome negative-energy solutions. Hartree-Fock calculations are carried out with the implicit use of such projectors and only positive-energy orbitals are retained at the correlated level, meaning that the Hartree-Fock projectors are frozen at the correlated level. We argue that the projection operators should be optimized also at the correlated level and that this is possible by full Multiconfigurational Self-Consistent Field (MCSCF) calculations, that is, MCSCF calculations using a no-pair full CI expansion, but including orbital relaxation from the negative-energy orbitals. We show by variational perturbation theory that the MCSCF correlation energy is a pure MP2-like correlation expression, whereas the corresponding CI correlation energy contains an additional relaxation term. We explore numerically our theoretical analysis by carrying out variational and perturbative calculations on the two-electron rare gas atoms with specially tailored basis sets. In particular, we show that the correlation energy obtained by the suggested MCSCF procedure is smaller than the no-pair full CI correlation energy, in accordance with the underlying
Electron correlation within the relativistic no-pair approximation.
Almoukhalalati, Adel; Knecht, Stefan; Jensen, Hans Jørgen Aa; Dyall, Kenneth G; Saue, Trond
2016-08-21
This paper addresses the definition of correlation energy within 4-component relativistic atomic and molecular calculations. In the nonrelativistic domain the correlation energy is defined as the difference between the exact eigenvalue of the electronic Hamiltonian and the Hartree-Fock energy. In practice, what is reported is the basis set correlation energy, where the "exact" value is provided by a full Configuration Interaction (CI) calculation with some specified one-particle basis. The extension of this definition to the relativistic domain is not straightforward since the corresponding electronic Hamiltonian, the Dirac-Coulomb Hamiltonian, has no bound solutions. Present-day relativistic calculations are carried out within the no-pair approximation, where the Dirac-Coulomb Hamiltonian is embedded by projectors eliminating the troublesome negative-energy solutions. Hartree-Fock calculations are carried out with the implicit use of such projectors and only positive-energy orbitals are retained at the correlated level, meaning that the Hartree-Fock projectors are frozen at the correlated level. We argue that the projection operators should be optimized also at the correlated level and that this is possible by full Multiconfigurational Self-Consistent Field (MCSCF) calculations, that is, MCSCF calculations using a no-pair full CI expansion, but including orbital relaxation from the negative-energy orbitals. We show by variational perturbation theory that the MCSCF correlation energy is a pure MP2-like correlation expression, whereas the corresponding CI correlation energy contains an additional relaxation term. We explore numerically our theoretical analysis by carrying out variational and perturbative calculations on the two-electron rare gas atoms with specially tailored basis sets. In particular, we show that the correlation energy obtained by the suggested MCSCF procedure is smaller than the no-pair full CI correlation energy, in accordance with the underlying
NASA Astrophysics Data System (ADS)
Nahid, F.; Zhang, J. D.; Yu, T. F.; Ling, C. C.; Fung, S.; Beling, C. D.
2011-04-01
Positronium (Ps) formation in high-density polyethylene (HDPE) has been studied below the glass transition temperature. The formation probability increases with positron irradiation time due to an increasing number of inter-track trapped electrons becoming available for positron capture. The temperature variation of the saturated Ps level is discussed in different models. The quenching of trapped electrons by light has been studied and the optical de-trapping cross-section for different photon energies has been estimated over the visible region.
NASA Astrophysics Data System (ADS)
Keeble, D. J.; Wicklein, S.; Jin, L.; Jia, C. L.; Egger, W.; Dittmann, R.
2013-05-01
Accommodation of nonstoichiometry in SrTiO3 pulsed laser deposited (PLD) films was investigated using positron annihilation lifetime spectroscopy and (scanning) transmission electron microscopy. Increasing PLD laser fluence changed the stoichiometry from Ti to Sr deficient. Cation vacancy defects were detected, and the concentration ratio of Sr to Ti vacancies, [VSr]/[VTi], was observed to increase systematically in the Sr-deficient region, although no change in the electron microscopy lattice images was detected. Increasing Ti deficiency resulted in the accommodation of SrO layers in planar defects, and in the formation of vacancy cluster defects. A change from VTi to VSr defect positron trapping was also detected.
Impact of Lone-Pair Electrons on Thermal Conductivity in CuSbS2 Compound
NASA Astrophysics Data System (ADS)
Du, Baoli; Zhang, Ruizhi; Chen, Kan; Reece, Michael; Material research institute Team
Compounds with intrinsically low lattice thermal conductivity are of practical importance for thermoelectric energy conversion. Recent studies suggest that s2 lone pair orbital electrons are a key contributing factor to the anomalously low lattice thermal conductivity of chalcogenide compounds that contain a nominally trivalent group VA element. CuSbS2 has an orthorhombic structure with space group Pnma. The pyramidal SbS5 units are separated by CuS4 tetrahedron so that the base of the square pyramidal units are aligned to face one another, thus directing the Sb lone pair electron density into the void separating the SbS5 units. Different from tetrahedrite, all the Cu atoms are bonded in the CuS4 tetrahedron. So, it has a perfect structure to study the influence of electron lone pair on thermal conductivity without the impact from trigonal coordinated Cu. In this work, the trivalent transition metal atom Fe and IIIA atom Ga without lone-pair electrons were chosen to substitute Sb in CuSbS2. The changes in the bonding environment by foreign atoms and their influences on the thermal properties have been studied and correlated. Marie Curie International Incoming Fellowship of the European Community Human Potential Program under Contract No. PIIF-GA-2013-622847.
Pair tunneling resonance in the single-electron transport regime.
Leijnse, M; Wegewijs, M R; Hettler, M H
2009-10-09
We predict a new electron pair tunneling (PT) resonance in nonlinear transport through quantum dots with positive charging energies exceeding the broadening due to thermal and quantum fluctuations. The PT resonance shows up in the single-electron transport (SET) regime as a peak in the derivative of the nonlinear conductance, d(2)I/dV(2), when the electrochemical potential of one electrode matches the average of two subsequent charge addition energies. For a single level quantum dot (Anderson model) we find the analytic peak shape and the dependence on temperature, magnetic field, and junction asymmetry and compare with the inelastic cotunneling peak which is of the same order of magnitude. In experimental transport spectroscopy the PT resonance may be mistaken for a weak SET resonance judging only by the voltage dependence of its position. Our results provide essential clues to avoid such erroneous interpretation.
Standing electromagnetic solitons in hot ultra-relativistic electron-positron plasmas
Heidari, E.; Aslaninejad, M.; Eshraghi, H.; Rajaee, L.
2014-03-15
Using a one-dimensional self-consistent fluid model, we investigate standing relativistic bright solitons in hot electron-positron plasmas. The positron dynamics is taken into account. A set of nonlinear coupled differential equations describing the evolution of electromagnetic waves in fully relativistic two-fluid plasma is derived analytically and solved numerically. As a necessary condition for the existence of standing solitons the system should be relativistic. For the case of ultra-relativistic plasma, we investigate non-drifting bright solitary waves. Detailed discussions of the acceptable solutions are presented. New single hump non-trivial symmetric solutions for the scalar potential were found, and single and multi-nodal symmetric and anti-symmetric solutions for the vector potential are presented. It is shown that for a fixed value of the fluid velocity excited modes with more zeros in the profile of the vector potential show a higher magnitude for the scalar potential. An increase in the plasma fluid velocity also increases the magnitude of the scalar potential. Furthermore, the Hamiltonian and the first integral of the system are given.
First year of Mark-J: physics with high energy electron-positron colliding beams. Report No. 107
Aachen DESY M.I.T. NIKHEF Peking Collaboration
1980-04-01
This report reviews the experimental investigation of high energy e/sup +/e/sup -/ interactions by the MARK J collaboration at PETRA, the electron-positron colliding beam accelerator at DESY in Hamburg, West Germany. The physics objectives include studies of several purely electromagnetic processes and hadronic final states, which further our knowledge of the nature of the fundamental constituents and of their strong, electromagnetic and weak interactions. Before discussing the physics results, the main features and the principal components of the MARK J detector are discussed in terms of design, function, and performance. Several aspects of the online data collection and the offline analysis are also outlined. Results are presented on tests of quantum electrodynamics using e/sup +/e/sup -/ ..-->.. e/sup +/e/sup -/, ..mu../sup +/..mu../sup -/ and tau/sup +/tau/sup -/, on the measurement of R, the ratio of the hadronic to the point-like muon pair cross section, on the search for new quark flavors, on the discovery of three jet events arising from the radiation of hard noncollinear gluons as predicted by quantum chromodynamics, and on the determination of the strong coupling constant ..cap alpha../sub s/.
Two state electron model for geminate recombination of electron-ion pairs in liquid isooctane
NASA Astrophysics Data System (ADS)
Lukin, L. V.; Yakovlev, B. S.
2011-04-01
Recombination kinetics of geminate electron-ion pairs is considered in the framework of the two state model for electron transport in liquid hydrocarbons. It is shown that the model well reproduces recent experimental data on the subpicosecond geminate recombination obtained in liquid isooctane. The life time of electrons in a localized state in isooctane is estimated to lie in the range between 0.14 ps and 0.57 ps at room temperature.
NASA Astrophysics Data System (ADS)
Fernández-Varea, José M.
1998-09-01
The algorithms implemented in the Monte Carlo codes LEEPS and PENELOPE for the simulation of the inelastic scattering of electrons and positrons are described. Both algorithms are based on the first Born approximation, in which the inelastic cross section is proportional to the generalized oscillator strength. This quantity is obtained by extrapolating the optical oscillator strength into the non-zero momentum transfer region using suitable extension algorithms. The calculated inelastic mean free paths and stopping powers are compared to other theoretical and experimental data available from the literature. The stability of PENELOPE's mixed simulation procedure under variations of the cutoff energy, which separates hard from soft collisions, is also analyzed. Finally, angular deflections of the projectile in inelastic collisions are considered.
INTEGRAL/SPI Observations of Electron-Positron Annihilation Radiation from our Galaxy
NASA Astrophysics Data System (ADS)
Teegarden, B. J.; Watanabe, K.; Knoedlseder, J.; Jean, P.; Lonjou, V.; Weidenspointner, G.; Skinner, G.; von Ballmoos, P.; Vedrenne, G.; Roques, J.-P.; Schanne, S.; Schoenfelder, V.
2004-12-01
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. INTEGRAL is a project of ESA. This work was supported by NASA and CNES.
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.;
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.
Observation of exclusive electron-positron production in hadron-hadron collisions.
Abulencia, A; Adelman, J; Affolder, T; Akimoto, T; Albrow, M G; Ambrose, D; Amerio, S; Amidei, D; Anastassov, A; Anikeev, K; Annovi, A; Antos, J; Aoki, M; Apollinari, G; Arguin, J-F; Arisawa, T; Artikov, A; Ashmanskas, W; Attal, A; Azfar, F; Azzi-Bacchetta, P; Azzurri, P; Bacchetta, N; Badgett, W; Barbaro-Galtieri, A; Barnes, V E; Barnett, B A; Baroiant, S; Bartsch, V; Bauer, G; Bedeschi, F; Behari, S; Belforte, S; Bellettini, G; Bellinger, J; Belloni, A; Benjamin, D; Beretvas, A; Beringer, J; Berry, T; Bhatti, A; Binkley, M; Bisello, D; Blair, R E; Blocker, C; Blumenfeld, B; Bocci, A; Bodek, A; Boisvert, V; Bolla, G; Bolshov, A; Bortoletto, D; Boudreau, J; Boveia, A; Brau, B; Brigliadori, L; Bromberg, C; Brubaker, E; Budagov, J; Budd, H S; Budd, S; Budroni, S; Burkett, K; Busetto, G; Bussey, P; Byrum, K L; Cabrera, S; Campanelli, M; Campbell, M; Canelli, F; Canepa, A; Carillo, S; Carlsmith, D; Caron, B; Carosi, R; Casarsa, M; Castro, A; Catastini, P; Cauz, D; Cavalli-Sforza, M; Cerri, A; Cerrito, L; Chang, S H; Chen, Y C; Chertok, M; Chiarelli, G; Chlachidze, G; Chlebana, F; Cho, I; Cho, K; Chokheli, D; Chou, J P; Choudalakis, G; Chuang, S H; Chung, K; Chung, W H; Chung, Y S; Ciljak, M; Ciobanu, C I; Ciocci, M A; Clark, A; Clark, D; Coca, M; Compostella, G; Convery, M E; Conway, J; Cooper, B; Copic, K; Cordelli, M; Cortiana, G; Crescioli, F; Almenar, C Cuenca; Cuevas, J; Culbertson, R; Cully, J C; Cyr, D; Daronco, S; D'Auria, S; Davies, T; D'Onofrio, M; Dagenhart, D; de Barbaro, P; Cecco, S De; Deisher, A; Lentdecker, G De; Dell'orso, M; Paoli, F Delli; Demortier, L; Deng, J; Deninno, M; Pedis, D De; Derwent, P F; Giovanni, G P Di; Dionisi, C; Ruzza, B Di; Dittmann, J R; Dituro, P; Dörr, C; Donati, S; Donega, M; Dong, P; Donini, J; Dorigo, T; Dube, S; Efron, J; Erbacher, R; Errede, D; Errede, S; Eusebi, R; Fang, H C; Farrington, S; Fedorko, I; Fedorko, W T; Feild, R G; Feindt, M; Fernandez, J P; Field, R; Flanagan, G; Foland, A; Forrester, S; Foster, G W; Franklin, M; Freeman, J C; Furic, I; Gallinaro, M; Galyardt, J; Garcia, J E; Garberson, F; Garfinkel, A F; Gay, C; Gerberich, H; Gerdes, D; Giagu, S; Giannetti, P; Gibson, A; Gibson, K; Gimmell, J L; Ginsburg, C; Giokaris, N; Giordani, M; Giromini, P; Giunta, M; Giurgiu, G; Glagolev, V; Glenzinski, D; Gold, M; Goldschmidt, N; Goldstein, J; Gomez, G; Gomez-Ceballos, G; Goncharov, M; González, O; Gorelov, I; Goshaw, A T; Goulianos, K; Gresele, A; Griffiths, M; Grinstein, S; Grosso-Pilcher, C; Grundler, U; da Costa, J Guimaraes; Gunay-Unalan, Z; Haber, C; Hahn, K; Hahn, S R; Halkiadakis, E; Hamilton, A; Han, B-Y; Han, J Y; Handler, R; Happacher, F; Hara, K; Hare, M; Harper, S; Harr, R F; Harris, R M; Hartz, M; Hatakeyama, K; Hauser, J; Heijboer, A; Heinemann, B; Heinrich, J; Henderson, C; Herndon, M; Heuser, J; Hidas, D; Hill, C S; Hirschbuehl, D; Hocker, A; Holloway, A; Hou, S; Houlden, M; Hsu, S-C; Huffman, B T; Hughes, R E; Husemann, U; Huston, J; Incandela, J; Introzzi, G; Iori, M; Ishizawa, Y; Ivanov, A; Iyutin, B; James, E; Jang, D; Jayatilaka, B; Jeans, D; Jensen, H; Jeon, E J; Jindariani, S; Jones, M; Joo, K K; Jun, S Y; Jung, J E; Junk, T R; Kamon, T; Karchin, P E; Kato, Y; Kemp, Y; Kephart, R; Kerzel, U; Khotilovich, V; Kilminster, B; Kim, D H; Kim, H S; Kim, J E; Kim, M J; Kim, S B; Kim, S H; Kim, Y K; Kimura, N; Kirsch, L; Klimenko, S; Klute, M; Knuteson, B; Ko, B R; Kondo, K; Kong, D J; Konigsberg, J; Korytov, A; Kotwal, A V; Kovalev, A; Kraan, A C; Kraus, J; Kravchenko, I; Kreps, M; Kroll, J; Krumnack, N; Kruse, M; Krutelyov, V; Kubo, T; Kuhlmann, S E; Kuhr, T; Kusakabe, Y; Kwang, S; Laasanen, A T; Lai, S; Lami, S; Lammel, S; Lancaster, M; Lander, R L; Lannon, K; Lath, A; Latino, G; Lazzizzera, I; Lecompte, T; Lee, J; Lee, J; Lee, Y J; Lee, S W; Lefèvre, R; Leonardo, N; Leone, S; Levy, S; Lewis, J D; Lin, C; Lin, C S; Lindgren, M; Lipeles, E; Lister, A; Litvintsev, D O; Liu, T; Lockyer, N S; Loginov, A; Loreti, M; Loverre, P; Lu, R-S; Lucchesi, D; Lujan, P; Lukens, P; Lungu, G; Lyons, L; Lys, J; Lysak, R; Lytken, E; Mack, P; Macqueen, D; Madrak, R; Maeshima, K; Makhoul, K; Maki, T; Maksimovic, P; Malde, S; Manca, G; Margaroli, F; Marginean, R; Marino, C; Marino, C P; Martin, A; Martin, M; Martin, V; Martínez, M; Maruyama, T; Mastrandrea, P; Masubuchi, T; Matsunaga, H; Mattson, M E; Mazini, R; Mazzanti, P; McFarland, K S; McIntyre, P; McNulty, R; Mehta, A; Mehtala, P; Menzemer, S; Menzione, A; Merkel, P; Mesropian, C; Messina, A; Miao, T; Miladinovic, N; Miles, J; Miller, R; Mills, C; Milnik, M; Mitra, A; Mitselmakher, G; Miyamoto, A; Moed, S; Moggi, N; Mohr, B; Moore, R; Morello, M; Fernandez, P Movilla; Mülmenstädt, J; Mukherjee, A; Muller, Th; Mumford, R; Murat, P; Nachtman, J; Nagano, A; Naganoma, J; Nakano, I; Napier, A; Necula, V; Neu, C; Neubauer, M S; Nielsen, J; Nigmanov, T; Nodulman, L; Norniella, O; Nurse, E; Oh, S H; Oh, Y D; Oksuzian, I; Okusawa, T; Oldeman, R; Orava, R; Osterberg, K; Pagliarone, C; Palencia, E; Papadimitriou, V; Paramonov, A A; Parks, B; Pashapour, S; Patrick, J; Pauletta, G; Paulini, M; Paus, C; Pellett, D E; Penzo, A; Phillips, T J; Piacentino, G; Piedra, J; Pinera, L; Pinfold, J; Pitts, K; Plager, C; Pondrom, L; Portell, X; Poukhov, O; Pounder, N; Prakoshyn, F; Pronko, A; Proudfoot, J; Ptohos, F; Punzi, G; Pursley, J; Rademacker, J; Rahaman, A; Ranjan, N; Rappoccio, S; Reisert, B; Rekovic, V; Renton, P; Rescigno, M; Richter, S; Rimondi, F; Ristori, L; Robson, A; Rodrigo, T; Rogers, E; Rolli, S; Roser, R; Rossi, M; Rossin, R; Ruiz, A; Russ, J; Rusu, V; Saarikko, H; Sabik, S; Safonov, A; Sakumoto, W K; Salamanna, G; Saltó, O; Saltzberg, D; Sánchez, C; Santi, L; Sarkar, S; Sartori, L; Sato, K; Savard, P; Savoy-Navarro, A; Scheidle, T; Schlabach, P; Schmidt, E E; Schmidt, M P; Schmitt, M; Schwarz, T; Scodellaro, L; Scott, A L; Scribano, A; Scuri, F; Sedov, A; Seidel, S; Seiya, Y; Semenov, A; Sexton-Kennedy, L; Sfyrla, A; Shapiro, M D; Shears, T; Shepard, P F; Sherman, D; Shimojima, M; Shochet, M; Shon, Y; Shreyber, I; Sidoti, A; Sinervo, P; Sisakyan, A; Sjolin, J; Slaughter, A J; Slaunwhite, J; Sliwa, K; Smith, J R; Snider, F D; Snihur, R; Soderberg, M; Soha, A; Somalwar, S; Sorin, V; Spalding, J; Spinella, F; Spreitzer, T; Squillacioti, P; Stanitzki, M; Staveris-Polykalas, A; Denis, R St; Stelzer, B; Stelzer-Chilton, O; Stentz, D; Strologas, J; Stuart, D; Suh, J S; Sukhanov, A; Sun, H; Suzuki, T; Taffard, A; Takashima, R; Takeuchi, Y; Takikawa, K; Tanaka, M; Tanaka, R; Tecchio, M; Teng, P K; Terashi, K; Thom, J; Thompson, A S; Thomson, E; Tipton, P; Tiwari, V; Tkaczyk, S; Toback, D; Tokar, S; Tollefson, K; Tomura, T; Tonelli, D; Torre, S; Torretta, D; Tourneur, S; Trischuk, W; Tsuchiya, R; Tsuno, S; Turini, N; Ukegawa, F; Unverhau, T; Uozumi, S; Usynin, D; Vallecorsa, S; van Remortel, N; Varganov, A; Vataga, E; Vázquez, F; Velev, G; Veramendi, G; Veszpremi, V; Vidal, R; Vila, I; Vilar, R; Vine, T; Vollrath, I; Volobouev, I; Volpi, G; Würthwein, F; Wagner, P; Wagner, R G; Wagner, R L; Wagner, J; Wagner, W; Wallny, R; Wang, S M; Warburton, A; Waschke, S; Waters, D; Wester, W C; Whitehouse, B; Whiteson, D; Wicklund, A B; Wicklund, E; Williams, G; Williams, H H; Wilson, P; Winer, B L; Wittich, P; Wolbers, S; Wolfe, C; Wright, T; Wu, X; Wynne, S M; Yagil, A; Yamamoto, K; Yamaoka, J; Yamashita, T; Yang, C; Yang, U K; Yang, Y C; Yao, W M; Yeh, G P; Yoh, J; Yorita, K; Yoshida, T; Yu, G B; Yu, I; Yu, S S; Yun, J C; Zanello, L; Zanetti, A; Zaw, I; Zhang, X; Zhou, J; Zucchelli, S
2007-03-16
We present the first observation of exclusive e(+)e(-) production in hadron-hadron collisions, using pp[over] collision data at (square root) s = 1.96 TeV taken by the run II Collider Detector at Fermilab, and corresponding to an integrated luminosity of 532 pb(-1). We require the absence of any particle signatures in the detector except for an electron and a positron candidate, each with transverse energy E(T) > 5 GeV and pseudorapidity |eta| < 2. With these criteria, 16 events are observed compared to a background expectation of 1.9+/-0.3 events. These events are consistent in cross section and properties with the QED process pp[over] --> p + e(+)e(-) + p[over] through two-photon exchange. The measured cross section is 1.6(-0.3)(+0.5)(stat) +/- 0.3(syst) pb. This agrees with the theoretical prediction of 1.71+/-0.01 pb.
Enhanced Dark Matter Annihilation Rate for Positron and Electron Excesses from Q-Ball Decay
McDonald, John
2009-10-09
We show that Q-ball decay in Affleck-Dine baryogenesis models can account for dark matter when the annihilation cross section is sufficiently enhanced to explain the positron and electron excesses observed by PAMELA, ATIC, and PPB-BETS. For Affleck-Dine baryogenesis along a d=6 flat direction, the reheating temperature is approximately 30 GeV and the Q-ball decay temperature is in the range of 10-100 MeV. The lightest supersymmetric particles produced by Q-ball decay annihilate down to the observed dark matter density if the cross section is enhanced by a factor approx10{sup 3} relative to the thermal relic cross section.
NASA Astrophysics Data System (ADS)
Hafez, M. G.; Talukder, M. R.
2015-09-01
This work investigates the theoretical and numerical studies on nonlinear propagation of ion acoustic solitary waves (IASWs) in an unmagnetized plasma consisting of nonextensive electrons, Boltzmann positrons and relativistic thermal ions. The Korteweg-de Vries (KdV) equation is derived by using the well known reductive perturbation method. This equation admits the soliton like solitary wave solution. The effects of phase velocity, amplitude of soliton, width of soliton and electrostatic nonlinear propagation of weakly relativistic ion-acoustic solitary waves have been discussed with graphical representation found in the variation of the plasma parameters. The obtained results can be helpful in understanding the features of small but finite amplitude localized relativistic ion-acoustic waves for an unmagnetized three component plasma system in astrophysical compact objects.
Noorian, Zainab; Eslami, Parvin; Javidan, Kurosh
2013-11-15
Interaction of a muon beam with hot dense QED plasma is investigated. Plasma system contains electrons and positrons with Fermi-Dirac distribution and Bose-Einstein distributed photons while the beam particles have nonthermal distribution. The energy loss of the beam particles during the interaction with plasma is calculated to complete leading order of interaction in terms of the QED coupling constant using thermal field theory approach. The screening effects of the plasma are computed consistently using resummation of perturbation theory with hard thermal loop approximation according to the Braaten-Pisarski method. Time evolution of the plasma characteristics and also plasma identifications during the interaction are investigated. Effects of the nonthermal parameter of the beam distribution on the energy exchange and the evolution of plasma-beam system are also explained.
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.
Luo, Wen; Zhu, Yi-Bo; Song, Ying-Ming; Zhu, Zhi-Chao; Wang, Xiao-Dong; Zhuo, Hong-Bin; Ma, Yan-Yun; Li, Xing-Huo; Turcu, I. C. E.; Chen, Min
2015-06-15
We use quantum electrodynamics (QED) particle-in-cell simulations to investigate and compare the generation of dense electron-positron plasmas and intense γ-ray bursts in the case of counter-propagating laser solid interaction (two-side irradiation) and single laser solid interaction (one-side irradiation). In the case of counter-propagating linearly polarized laser pulses irradiating a thin aluminum foil with each pulse peak power of 12.5 PW (I = 4 × 10{sup 23 }W/cm{sup 2}), we calculate that about 20% of the laser energy is converted into a burst of γ-rays with flux exceeding 10{sup 14 }s.{sup −1} This would be one of the most intense γ-ray sources among those currently available in laboratories. The γ-ray conversion efficiency in the case of two-side irradiation is three times higher than in the case of one-side irradiation using a single 12.5 PW laser. Dense electron-positron plasma with a maximum density of 6 × 10{sup 27 }m{sup −3} are generated simultaneously during the two-side irradiation which is eightfold denser compared to the one-side irradiation. The enhancement of the effects in the case of counter-propagating lasers are the results of the symmetrical compression of the foil target and the formation of electric potential and standing wave around the target. Realizing experimentally the proposed counter-propagating QED-strong laser-solid interaction to produce dense electron-positron pairs and prolific γ-rays will be made possible by the Extreme Light Infrastructure-Nuclear Physics facility under construction.
NASA Astrophysics Data System (ADS)
Luo, Wen; Zhu, Yi-Bo; Zhuo, Hong-Bin; Ma, Yan-Yun; Song, Ying-Ming; Zhu, Zhi-Chao; Wang, Xiao-Dong; Li, Xing-Huo; Turcu, I. C. E.; Chen, Min
2015-06-01
We use quantum electrodynamics (QED) particle-in-cell simulations to investigate and compare the generation of dense electron-positron plasmas and intense γ-ray bursts in the case of counter-propagating laser solid interaction (two-side irradiation) and single laser solid interaction (one-side irradiation). In the case of counter-propagating linearly polarized laser pulses irradiating a thin aluminum foil with each pulse peak power of 12.5 PW (I = 4 × 1023 W/cm2), we calculate that about 20% of the laser energy is converted into a burst of γ-rays with flux exceeding 1014 s.-1 This would be one of the most intense γ-ray sources among those currently available in laboratories. The γ-ray conversion efficiency in the case of two-side irradiation is three times higher than in the case of one-side irradiation using a single 12.5 PW laser. Dense electron-positron plasma with a maximum density of 6 × 1027 m-3 are generated simultaneously during the two-side irradiation which is eightfold denser compared to the one-side irradiation. The enhancement of the effects in the case of counter-propagating lasers are the results of the symmetrical compression of the foil target and the formation of electric potential and standing wave around the target. Realizing experimentally the proposed counter-propagating QED-strong laser-solid interaction to produce dense electron-positron pairs and prolific γ-rays will be made possible by the Extreme Light Infrastructure-Nuclear Physics facility under construction.
Space-Qualified Nanosatellite Electronics Platform for Photon Pair Experiments
NASA Astrophysics Data System (ADS)
Cheng, Cliff; Chandrasekara, Rakhitha; Tan, Yue Chuan; Ling, Alexander
2015-12-01
We report the design and implementation of a complete electronics platform for conducting a quantum optics experiment that will be operated on board a 1U CubeSat (a 10 x 10 x 10 cm satellite). The quantum optics experiment is designed to produce polarization-entangled photon pairs using non-linear optical crystals and requires opto-electronic components such as a pump laser, single photon detectors and liquid crystal based polarization rotators in addition to passive optical elements. The platform provides mechanical support for the optical assembly. It also communicates autonomously with the host satellite to provide experiment data for transmission to a ground station. A limited number of commands can be transmitted from ground to the platform enabling it to switch experimental modes. This platform requires less than 1.5W for all operations, and is space qualified. The implementation of this electronics platform is a major step on the road to operating quantum communication experiments using nanosatellites.
Rashba spin-splitting of single electrons and Cooper pairs
NASA Astrophysics Data System (ADS)
Shekhter, R. I.; Entin-Wohlman, O.; Jonson, M.; Aharony, A.
2017-02-01
Electric weak links, the term used for those parts of an electrical circuit that provide most of the resistance against the flow of an electrical current, are important elements of many nanodevices. Quantum dots, nanowires and nano-constrictions that bridge two bulk conductors (or superconductors) are examples of such weak links. Here we consider nanostructures where the electronic spin-orbit interaction is strong in the weak link but is un-important in the bulk conductors, and explore theoretically the role of the spin-orbit active weak link (which we call a "Rashba spin splitter") as a source of new spin-based functionality in both normal and superconducting devices. Some recently predicted phenomena, including mechanically-controlled spin- and charge currents as well as the effect of spin polarization of superconducting Cooper pairs, are reviewed.
Banerjee, Gadadhar Maitra, Sarit
2016-06-21
Sagdeev pseudopotential method is employed to study the arbitrary amplitude quantum ion-acoustic solitary waves in an unmagnetized electron-positron-ion plasma by using one dimensional quantum hydrodynamic model together with the Poisson equation. Sagdeev potential function is obtained in terms of electrostatic potential and analyzed with and without the effect of quantum diffraction parameter H. Effects of the parameter H on both the amplitude and width of the solitary waves have been observed. It is also observed that the positron density can affect the wave propagation.
Recent Developments in the Design of the NLC Positron Source
Kotseroglou, T.; Bharadwaj, V.; Clendenin, J.E.; Ecklund, S,; Frisch, J.; Krejcik, P,; Kukikov, A.V.; Liu, J.; Maruyama, T.; Millage, K.K.; Mulhollan, G.; Nelson, W.R.; Schultz, D.C.; Sheppard, J.C.; Turner, J.; Van Bibber, K.; Flottmann, K.; Namito, Y.
1999-11-05
Recent developments in the design of the Next Linear Collider (NLC) positron source based on updated beam parameters are described. The unpolarized NLC positron source [1,2] consists of a dedicated 6.2 GeV S-band electron accelerator, a high-Z positron production target, a capture system and an L-band positron linac. The 1998 failure of the SLC target, which is currently under investigation, may lead to a variation of the target design. Progress towards a polarized positron source is also presented. A moderately polarized positron beam colliding with a highly polarized electron beam results in an effective polarization large enough to explore new physics at NLC. One of the schemes towards a polarized positron source incorporates a polarized electron source, a 50 MeV electron accelerator, a thin target for positron production and a new capture system optimized for high-energy, small angular-divergence positrons. The yield for such a process, checked using the EGS4 code, is of the order of 10{sup -3}. The EGS4 code has being enhanced to include the effect of polarization in bremsstrahlung and pair-production process.
Phase-mixing of Langmuir oscillations in cold electron-positron-ion plasmas
Maity, Chandan
2014-07-15
Space-time evolution of Langmuir oscillations in a cold homogeneous electron-positron-ion plasma has been analyzed by employing a straightforward perturbation expansion method, showing phase-mixing and, thus, wave-breaking of excited oscillations at arbitrary amplitudes. Within an assumption of infinitely massive ions, an approximate phase-mixing time is found to scale as ω{sub pe}t{sub mix}∼[(6/δ{sup 2})((2−α){sup 5/2}/(1−α))]{sup 1/3}, where “δ” and “α” (= n{sub 0i}/n{sub 0e}) are the amplitude of perturbation and the ratio of equilibrium ion density to equilibrium electron density, respectively, and ω{sub pe}∼√(4πn{sub 0e}e{sup 2}/m) is the electron plasma frequency. The results presented on phase-mixing of Langmuir modes in multispecies plasmas are expected to be relevant to laboratory and astrophysical environments.
Positron Annihilation in the Bipositronium Ps2
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.
Excitation of Electronic States of Ar, H{sub 2}, and N{sub 2} by Positron Impact
Sullivan, J. P.; Marler, J. P.; Gilbert, S. J.; Buckman, S. J.; Surko, C. M.
2001-08-13
We have measured the first state-resolved, absolute cross sections for positron excitation of electronic states of an atom or molecule using a high resolution ({Delta}E{approx}25 meV FWHM) beam of positrons from a Penning-Malmberg trap. We present cross sections for the excitation of the low-lying levels of Ar, H{sub 2}, and N{sub 2} for incident positron energies between threshold and 30eV. For Ar and H{sub 2}, comparison can be made with theoretical calculations, and, in the case of H{sub 2}, the results resolve a significant discrepancy between the only two available calculations.
Head on collision of multi-solitons in an electron-positron-ion plasma having superthermal electrons
Roy, Kaushik; Chatterjee, Prasanta Roychoudhury, Rajkumar
2014-10-15
The head-on collision and overtaking collision of four solitons in a plasma comprising superthermal electrons, cold ions, and Boltzmann distributed positrons are investigated using the extended Poincare-Lighthill-Kuo (PLK) together with Hirota's method. PLK method yields two separate Korteweg-de Vries (KdV) equations where solitons obtained from any KdV equation move along a direction opposite to that of solitons obtained from the other KdV equation, While Hirota's method gives multi-soliton solution for each KdV equation all of which move along the same direction where the fastest moving soliton eventually overtakes the other ones. We have considered here two soliton solutions obtained from Hirota's method. Phase shifts acquired by each soliton due to both head-on collision and overtaking collision are calculated analytically.
Conceptual design of an intense positron source based on an LIA
NASA Astrophysics Data System (ADS)
Long, Ji-Dong; Yang, Zhen; Dong, Pan; Shi, Jin-Shui
2012-04-01
Accelerator based positron sources are widely used due to their high intensity. Most of these accelerators are RF accelerators. An LIA (linear induction accelerator) is a kind of high current pulsed accelerator used for radiography. A conceptual design of an intense pulsed positron source based on an LIA is presented in the paper. One advantage of an LIA is its pulsed power being higher than conventional accelerators, which means a higher amount of primary electrons for positron generations per pulse. Another advantage of an LIA is that it is very suitable to decelerate the positron bunch generated by bremsstrahlung pair process due to its ability to adjustably shape the voltage pulse. By implementing LIA cavities to decelerate the positron bunch before it is moderated, the positron yield could be greatly increased. These features may make the LIA based positron source become a high intensity pulsed positron source.
Design Issues for the ILC Positron Source
Bharadwaj, V.; Batygin, Yu.K.; Pitthan, R.; Schultz, D.C.; Sheppard, J.; Vincke, H.; Wang, J.W.; Gronberg, J.; Stein, W.; /LLNL, Livermore
2006-02-15
A positron source for the International Linear Collider (ILC) can be designed using either a multi-GeV electron beam or a multi-MeV photon beam impinging on a metal target. The major design issues are: choice of drive beam and its generation, choice of target material, the target station, positron capture section, target vault and beam transport to the ILC positron damping ring complex. This paper lists the ILC positron source requirements and their implications for the design of the positron source. A conceptual design for the ILC is expected to be finished in the next two years. With emphasis on this timescale, source design issues and possible solutions are discussed.
A search for supersymmetric electrons with the Mark II detector at PEP (Positron Electron Project)
LeClaire, B.W.
1987-10-01
An experimental search for selectrons, the supersymmetric partner of the electron, has been performed at the PEP storage ring at SLAC using the Mark II detector. The experimental search done was based upon hypothetical reaction in e/sup +/e/sup -/ interactions at PEP center of mass energies of 29 GeV. In this reaction the selectrons, e-tilde, are assumed produced by the interaction of one of initial state electrons with a photon radiated from the other initial state electron. This latter electron is assumed to continue down the beam pipe undetected. The photon and electron then produce a selectron and a photino, ..gamma..-tilde, in the supersymmetric analog of Compton scattering. The photino is assumed to be the lightest supersymmetric particle, and as such, does not interact in the detector, thereby escaping detection very much like a neutrino. The selectron is assumed to immediately decay into an electron and photino. This electron is produced with large p perpendicular with respect to the beam pipe, since it must balance the transverse momentum carried off by the photinos. Thus, the experimental signature of the process is a single electron in the detector with a large unbalanced tranverse momentum. No events of this type were observed in the original search of 123 pb/sup -1/ of data, resulting in a cross section limit of less than 2.4 x 10/sup -2/ pb (at the 95% CL) within the detector acceptance. This cross section upper limit applies to any process which produces anomalous single electron events with missing transverse momentum. When interpreted as a supersymmetry search it results in a lower selectron mass limit of 22.2 GeV/c/sup 2/ for the case of massless photinos. Limits for non-zero mass photinos have been calculated. 87 refs., 67 figs., 17 tabs.
Electron-Hole Pairs Created by Photons and Intrinsic Properties in Detector Materials
Gao, Fei; Campbell, Luke W.; Xie, YuLong; Devanathan, Ram; Peurrung, Anthony J.; Weber, William J.
2008-06-26
A Monte Carlo (MC) code has been developed to simulate the interaction of gamma-rays with semiconductors and scintillators, and the subsequent energy partitioning of fast electrons. The results provide insights on the processes involved in the electron-hole pair yield and intrinsic variance through simulations of full electron energy cascades. The MC code has been applied to simulate the production of electron-hole pairs and to evaluate intrinsic resolution in a number of semiconductors. In addition, the MC code is also able to consider the spatial distribution of electron-hole pairs induced by photons and electrons in detector materials, and has been employed to obtain details of the spatial distribution of electron-hole pairs in Ge, as a benchmark case. The preliminary results show that the distribution of electron-hole pairs exhibit some important features; (a) the density of electron-hole pairs along the main electron track is very high and (b) most electron-hole pairs produced by interband transitions are distributed at the periphery of the cascade volume. The spatial distribution and density of thermalized electron-hole pairs along the primary and secondary tracks are important for large scale simulations of electron-hole pair transport.
The electron-cloud instability in the arcs of the PEP-II positron ring
Furman, Miguel A.; Lambertson, Glen R.
1998-03-01
We have applied our simulation code ''POSINST'' to evaluate, in linear approximation, the contribution to the growth rate of the electron-cloud instability (ECI) from the pumping sections and the dipole bending magnets in the arcs of the PEP-II positron ring. A key ingredient in our model is a detailed description of the secondary emission process off the TiN-coated chambers. Another important element is the analytic computation of the electric field produced by the beam, including the effects from surface charges. Space-charge forces of the electron cloud upon itself are also included, although these forces are negligible under nominal conditions. Bunch-length effects are optionally included by slicing the bunch into several kicks. We conclude that the growth rate is dominated by the pumping sections and scales linearly with the photoelectric yield Y'. For Y' = 1, our present estimate is in the range {approx} 1000-1300 s{sup -1}, depending upon the value of the photon reflectivity R. This is in the range controllable by the transverse feedback system. The contributions to the growth rate from other magnets and from other sections of the ring remain to be evaluated.
FPGA-Based Front-End Electronics for Positron Emission Tomography.
Haselman, Michael; Dewitt, Don; McDougald, Wendy; Lewellen, Thomas K; Miyaoka, Robert; Hauck, Scott
2009-02-22
Modern Field Programmable Gate Arrays (FPGAs) are capable of performing complex discrete signal processing algorithms with clock rates above 100MHz. This combined with FPGA's low expense, ease of use, and selected dedicated hardware make them an ideal technology for a data acquisition system for positron emission tomography (PET) scanners. Our laboratory is producing a high-resolution, small-animal PET scanner that utilizes FPGAs as the core of the front-end electronics. For this next generation scanner, functions that are typically performed in dedicated circuits, or offline, are being migrated to the FPGA. This will not only simplify the electronics, but the features of modern FPGAs can be utilizes to add significant signal processing power to produce higher resolution images. In this paper two such processes, sub-clock rate pulse timing and event localization, will be discussed in detail. We show that timing performed in the FPGA can achieve a resolution that is suitable for small-animal scanners, and will outperform the analog version given a low enough sampling period for the ADC. We will also show that the position of events in the scanner can be determined in real time using a statistical positioning based algorithm.
PIC simulations of the MagnetoRotational instability in electron-positron plasmas
NASA Astrophysics Data System (ADS)
Inchingolo, Giannandrea; Grismayer, Thomas; Loureiro, Nuno F.; Fonseca, Ricardo A.; Silva, Luis O.
2016-10-01
The magnetorotational instability (MRI) is a crucial mechanism of angular momentum transport in a variety of astrophysical scenarios, as e-e+ plasmas accretion disks nearness neutron stars and black holes. The MRI has been widely studied using MHD models and simulations, in order to understand the behavior of astrophysical fluids in a state of differential rotation. When the timescale for electron and ion collisions is longer than the inflow time in the disk, the plasma is macroscopically collisionless and MHD breaks down. This is the case of the limit of weak magnetic field, i.e., as the ratio of the ion cyclotron frequency to orbital frequency becomes small. Leveraging on the recent addition of the shearing co-rotating frames equations of motion and Maxwell's equations modules in our PIC code OSIRIS 3.0, we intend to present our recent results of the analysis of MRI in electron-positron plasma in the limit of weak magnetic field. We will recall the theoretical 1D linear model of Krolik et Zweibel that describes the behavior of MRI in the limit of weak magnetic field and use it to support our results. Moving to 2D simulations, the analysis of MRI via PIC code permits to investigate also how MRI will act in comparison with other Kinetic instabilities, like mirror instability.
Justifying the Vacuum as an Electron-Positron Aggregation and Experimental Falsification
NASA Astrophysics Data System (ADS)
Guy Grantham, R.; Montgomery, Ian G.
2013-09-01
Historical aether models are placed in context with the electron-positron lattice (epola) model of space due to M. Simhony. A brief outline of the model as an aggregation state of matter, intermediate to the nuclear state and the atomic aggregation state, includes reference to its derivation of physical laws and fundamental constants. The broad application of the epola model is appraised for its validation against a range of physical laws, experiments and constants. Simhony declared a specific dependence for the stability of atomic matter upon speed through the epola, suggesting a test for falsification. This theme is further developed by the same logic to suggest practical experimental and theoretical tests of the epola model. A formula for the inverse fine structure constant of space, providing the accepted CODATA value, is derived from Simhony's explanation of the Bohr - de Broglie model of the ground state electron orbital of the hydrogen atom by including a term for speed through the Cosmos. A theoretical solution of the Michelson-Morley experiment is applied as evidence for the concept. The mechanism of motion through the epola is considered further for possible implications of speed including dependency of decay rates by radio nuclides and the results of former and ongoing experiments are considered.
A new measurement of cosmic-ray electrons and positrons with the Large Area Telescope
NASA Astrophysics Data System (ADS)
Manfreda, Alberto; Fermi-LAT Collaboration
2017-01-01
We present an updated measurement of the cosmic-ray electron and positron spectrum between 7 GeV and 2 TeV, based on 7 years of data collected with the Fermi Large Area Telescope (LAT). The LAT is the first space-based instrument to directly explore the region above 1 TeV. At such high energies, the shape of the spectrum can provide useful information about the origin and propagation of cosmic-ray electrons in the nearby Galactic space. The best fit to the spectrum that we measure is given by a broken power-law, with the break located at 53 +/-8 GeV. Such break, however, is not significant when all the systematic uncertainties are taken into account. Above 50 GeV our data are well described by a single power law with a spectral index of 3.07 +/- 0.02 (stat + syst) +/- 0.06 (energy scale). An exponential cut-off lower than 1.7 TeV is excluded at 95% CL.
Study of secondary electrons and positrons produced by Terrestrial Gamma-ray Flashes
NASA Astrophysics Data System (ADS)
Sarria, D.; Blelly, P.-L.; Forme, F.
2015-12-01
Terrestrial Gamma ray Flahes are emissions of X and gamma rays, correlated to thunderstorms. By interacting with the atmosphere, the photons produce a large number of electrons and positrons. Some of these reach altitudes above ˜ 100 km that their interactions with the atmosphere become negligible, and they are then guided by Earth's magnetic field lines, forming the so called Terrestrial Electron Beams. The GBM instrument of the Fermi Space Telescope made a particularly interesting measurement of such an event that happened the 12/09/2009. We perform Monte-Carlo simulations to study this event in detail and we focus on the resulting time histograms. In agreement with previous works, we show that the histogram measured by Fermi GBM can be reproduced from simulations. We then show that the time histogram can be decomposed into three populations of leptons, coming from the hemisphere opposite from the TGF, and mirroring back to the satellite with interactions with the atmosphere or not, and that these we can be clearly distinguished both with their pitch angles.
NASA Astrophysics Data System (ADS)
Rafat, A.; Rahman, M. M.; Alam, M. S.; Mamun, A. A.
2015-07-01
A precise theoretical investigation has been made on electron-acoustic (EA) Gardner solitons (GSs) and double layers (DLs) in a four-component plasma system consisting of nonextensive hot electrons and positrons, inertial cold electrons, and immobile positive ions. The well-known reductive perturbation method has been used to derive the Korteweg-de Vries (K-dV), modified K-dV (mK-dV), and Gardner equations along with their solitary wave as well as double layer solutions. It has been found that depending on the plasma parameters, the K-dV solitons and GSs are either compressive or rarefactive, whereas the mK-dV solitons are only compressive, and Gardner DLs are only rarefactive. The analytical comparison among the K-dV solitons, mK-dV solitons, and GSs are also investigated. It has been identified that the basic properties of such EA solitons and EA DLs are significantly modified due to the effects of nonextensivity and other plasma parameters related to plasma particle number densities and to temperature of different plasma species. The results of our present investigation can be helpful for understanding the nonlinear electrostatic structures associated with EA waves in various interstellar space plasma environments and cosmological scenarios (viz. quark-gluon plasma, protoneutron stars, stellar polytropes, hadronic matter, dark-matter halos, etc.)
Operating instructions for ORELA (Oak Ridge Electron Linear Accelerator) positron beam line
Donohue, D.L.; Hulett, L.D. Jr.; Lewis, T.A.
1990-11-01
This report will contain details of the construction and operation of the positron beam line. Special procedures which are performed on a less frequent basis will also be described. Appendices will contain operating instructions for experiments which make use of the positron beam and are connected to the beam line. Finally, a review of safety-related considerations will be presented.
Undulator-based production of polarized positrons
NASA Astrophysics Data System (ADS)
Alexander, G.; Barley, J.; Batygin, Y.; Berridge, S.; Bharadwaj, V.; Bower, G.; Bugg, W.; Decker, F.-J.; Dollan, R.; Efremenko, Y.; Flöttmann, K.; Gharibyan, V.; Hast, C.; Iverson, R.; Kolanoski, H.; Kovermann, J. W.; Laihem, K.; Lohse, T.; McDonald, K. T.; Mikhailichenko, A. A.; Moortgat-Pick, G. A.; Pahl, P.; Pitthan, R.; Pöschl, R.; Reinherz-Aronis, E.; Riemann, S.; Schälicke, A.; Schüler, K. P.; Schweizer, T.; Scott, D.; Sheppard, J. C.; Stahl, A.; Szalata, Z.; Walz, D. R.; Weidemann, A.
2009-11-01
Full exploitation of the physics potential of a future International Linear Collider will require the use of polarized electron and positron beams. Experiment E166 at the Stanford Linear Accelerator Center (SLAC) has demonstrated a scheme in which an electron beam passes through a helical undulator to generate photons (whose first-harmonic spectrum extended to 7.9 MeV) with circular polarization, which are then converted in a thin target to generate longitudinally polarized positrons and electrons. The experiment was carried out with a 1-m-long, 400-period, pulsed helical undulator in the Final Focus Test Beam (FFTB) operated at 46.6 GeV. Measurements of the positron polarization have been performed at five positron energies from 4.5 to 7.5 MeV. In addition, the electron polarization has been determined at 6.7 MeV, and the effect of operating the undulator with a ferrofluid was also investigated. To compare the measurements with expectations, detailed simulations were made with an upgraded version of G EANT4 that includes the dominant polarization-dependent interactions of electrons, positrons, and photons with matter. The measurements agree with calculations, corresponding to 80% polarization for positrons near 6 MeV and 90% for electrons near 7 MeV.
The effect of direct positron production on relativistic feedback rates
NASA Astrophysics Data System (ADS)
Vodopiyanov, I. B.; Dwyer, J. R.; Lucia, R. J.; Cramer, E. S.; Arabshahi, S.; Rassoul, H.
2013-12-01
Relativistic feedback produces a self-sustaining runaway electron discharge via the production of backward propagating positrons and back-scattered x-rays. To date, only positrons created from pair-production by gamma-rays interacting with the air have been considered. In contrast, direct pair-production involves the creation of electron-positron pairs directly from the interaction of energetic runaway electrons with nuclei, and so it does not require the generation of bremsstrahlung gamma-rays. For high electric fields, where the runaway electron avalanche length scales are short, pair-production involving bremsstrahlung gamma-rays makes a smaller contribution to the total relativistic feedback rates than at lower fields, since both the bremsstrahlung interaction and the pair-production need to occur over a short length. On the other hand, for high fields, because direct positron production only involves one interaction, it may make a significant contribution to relativistic feedback rates in some cases. In this poster, we shall present the direct positron production cross-sections and calculate the effects on the relativistic feedback rates due to this process.
Characterization of paired helical filaments by scanning transmission electron microscopy.
Ksiezak-Reding, Hanna; Wall, Joseph S
2005-07-01
Paired helical filaments (PHFs) are abnormal twisted filaments composed of hyperphosphorylated tau protein. They are found in Alzheimer's disease and other neurodegenerative disorders designated as tauopathies. They are a major component of intracellular inclusions known as neurofibrillary tangles (NFTs). The objective of this review is to summarize various structural studies of PHFs in which using scanning transmission electron microscopy (STEM) has been particularly informative. STEM provides shape and mass per unit length measurements important for studying ultrastructural aspects of filaments. These include quantitative comparisons between dispersed and aggregated populations of PHFs as well as comparative studies of PHFs in Alzheimer's disease and other neurodegenerative disorders. Other approaches are also discussed if relevant or complementary to studies using STEM, e.g., application of a novel staining reagent, Nanovan. Our understanding of the PHF structure and the development of PHFs into NFTs is presented from a historical perspective. Others goals are to describe the biochemical and ultrastructural complexity of authentic PHFs, to assess similarities between authentic and synthetic PHFs, and to discuss recent advances in PHF modeling.
Akbari-Moghanjoughi, M.
2010-08-15
Large-amplitude ion-acoustic solitary wave (IASW) propagation and matching criteria of existence of such waves are investigated in a degenerate dense electron-positron-ion plasma considering the ion-temperature as well as electron/positron degeneracy effects. It is shown that the ion-temperature effects play an important role in the existence criteria and allowed Mach-number range in such plasmas. Furthermore, a fundamental difference is remarked in the existence of supersonic IASW propagations between degenerate plasmas with nonrelativistic and ultrarelativistic electrons and positrons. Current study may be helpful in astrophysical as well as the laboratory inertial confinement fusion-research.
A search for single electron production in electron positron annihilation at E = 29 GeV
Steele, T.R.
1989-09-01
This thesis presents experimental results from the ASP detector which took data on e{sup +}e{sup -} interactions in the PEP storage ring at SLAC. Its design was particularly suitable for searching for production of supersymmetric particles. The motivations for and phenomenology of Supersymmetry are discussed. In particular, the production of a single supersymmetric electron ( selectron'', {tilde e}) in combination with a supersymmetric photon ( photino'', {tilde {gamma}}) would result in events in which a single electron and no other particles are observed in the detector at an e{sup +}e{sup -} collider such as PEP, provided the masses of these particles are not too large. Such events would also result from the production of a single supersymmetric W-boson ( wino'', {tilde W}) in combination with a supersymmetric neutrino ( sneutrino'', {tilde {nu}}). These processes make it possible to search for electrons and winos with masses greater than the beam energy. Observation of these unusual events would distinctly indicate the production of new particles. The ASP detector was designed to be hermetic and to provide efficient event reconstruction for low multiplicity events. The detector is described and its performance is evaluated; it is found to be well-suited to this study. The data sample collected with the detector was thoroughly analyzed for evidence of single-electron events. The various possible background processes are considered and Monte Carlo calculations of the distributions from single selectron and single wino production are presented. Using this information an efficient off-line event selection process was developed, and it is described in detail. 82 refs., 41 figs., 4 tabs.
Observation of Exclusive Electron-Positron Production in Hadron-Hadron Collisions
Abulencia, A.; Adelman, J.; Affolder, T.; Akimoto, T.; Albrow, M.G.; Ambrose, D.; Amerio, S.; Amidei, D.; Anastassov, A.; Anikeev, K.; Annovi, A.
2006-11-01
We present the first observation of exclusive e{sup +}e{sup -} production in hadron-hadron collisions, using p{bar p} collision data at {radical}s = 1.96 TeV taken by the Run II Collider Detector at Fermilab, and corresponding to an integrated luminosity of 532 pb{sup -1}. We require the absence of any particle signatures in the detector except for an electron and a positron candidate, each with transverse energy E{sub T} > 5 GeV and pseudorapidity |{eta}| < 2. With these criteria, 16 events are observed compared to a background expectation of 1.9 {+-} 0.3 events. These events are consistent in cross section and properties with the QED process p{bar p} {yields} p + e{sup +}e{sup -} + {bar p} through two-photon exchange. The measured cross section is 1.6{sub -0.3}{sup +0.5}(stat) {+-} 0.3(syst) pb. This agrees with the theoretical prediction of 1.71 {+-} 0.01 pb.
The beam energy feedback system for Beijing electron positron collider II linac.
Wang, S; Iqbal, M; Chi, Y; Liu, R; Huang, X
2017-03-01
A beam-energy feedback system has been developed for the injection linac to meet the beam quality needed for the Beijing electron positron collider II storage ring. This paper describes the implementation and commissioning of this system in detail. The system consists of an energy measurement unit, application software, and an actuator unit. A non-intersecting beam energy monitor was developed to allow real-time online energy adjustment. The beam energy adjustment is achieved by adjusting the output microwave phase of the RF power source station. The phase control mechanism has also been modified, and a new control method taking the return difference of the phase shifter into account is used to improve the system's performance. This system achieves the design aim and can adjust the beam center energy with a rate of 2 Hz. With the energy feedback system, the stability of the injection rate is better; the fluctuation range is reduced from 20 mA/min to 10 mA/min, while the stability of the beam center energy is maintained within ±0.1%.
Fast magnetic reconnection in low-density electron-positron plasmas
Bessho, Naoki; Bhattacharjee, A.
2010-10-15
Two-dimensional particle-in-cell simulations have been performed to study magnetic reconnection in low-density electron-positron plasmas without a guide magnetic field. Impulsive reconnection rates become of the order of unity when the background density is much smaller than 10% of the density in the initial current layer. It is demonstrated that the outflow speed is less than the upstream Alfven speed, and that the time derivative of the density must be taken into account in the definition of the reconnection rate. The reconnection electric fields in the low-density regime become much larger than the ones in the high-density regime, and it is possible to accelerate the particles to high energies more efficiently. The inertial term in the generalized Ohm's law is the most dominant term that supports a large reconnection electric field. An effective collisionless resistivity is produced and tracks the extension of the diffusion region in the late stage of the reconnection dynamics, and significant broadening of the diffusion region is observed. Because of the broadening of the diffusion region, no secondary islands, which have been considered to play a role to limit the diffusion region, are generated during the extension of the diffusion region in the outflow direction.
Simulation of ultra-relativistic electrons and positrons channeling in crystals with MBN EXPLORER
Sushko, Gennady B.; Bezchastnov, Victor G.; Solov'yov, Ilia A.; Korol, Andrei V.; Greiner, Walter; Solov'yov, Andrey V.
2013-11-01
A newly developed code, implemented as a part of the MBN EXPLORER package (Solov'yov et al., 2012; (http://www.mbnexplorer.com/), 2012) [1,2] to simulate trajectories of an ultra-relativistic projectile in a crystalline medium, is presented. The motion of a projectile is treated classically by integrating the relativistic equations of motion with account for the interaction between the projectile and crystal atoms. The probabilistic element is introduced by a random choice of transverse coordinates and velocities of the projectile at the crystal entrance as well as by accounting for the random positions of the atoms due to thermal vibrations. The simulated trajectories are used for numerical analysis of the emitted radiation. Initial approbation and verification of the code have been carried out by simulating the trajectories and calculating the radiation emitted by ε=6.7 GeV and ε=855 MeV electrons and positrons in oriented Si(110) crystal and in amorphous silicon. The calculated spectra are compared with the experimental data and with predictions of the Bethe–Heitler theory for the amorphous environment.
Simulation of ultra-relativistic electrons and positrons channeling in crystals with MBN EXPLORER
NASA Astrophysics Data System (ADS)
Sushko, Gennady B.; Bezchastnov, Victor G.; Solov'yov, Ilia A.; Korol, Andrei V.; Greiner, Walter; Solov'yov, Andrey V.
2013-11-01
A newly developed code, implemented as a part of the MBN EXPLORER package (Solov'yov et al., 2012; http://www.mbnexplorer.com/, 2012) [1,2] to simulate trajectories of an ultra-relativistic projectile in a crystalline medium, is presented. The motion of a projectile is treated classically by integrating the relativistic equations of motion with account for the interaction between the projectile and crystal atoms. The probabilistic element is introduced by a random choice of transverse coordinates and velocities of the projectile at the crystal entrance as well as by accounting for the random positions of the atoms due to thermal vibrations. The simulated trajectories are used for numerical analysis of the emitted radiation. Initial approbation and verification of the code have been carried out by simulating the trajectories and calculating the radiation emitted by ε=6.7 GeV and ε=855 MeV electrons and positrons in oriented Si(110) crystal and in amorphous silicon. The calculated spectra are compared with the experimental data and with predictions of the Bethe-Heitler theory for the amorphous environment.
Denison, A B; Meulenberg, R; Eijt, S W H; Van Veen, A; Mijnarends, P E; Barbiellini, B; Bansil, A; Fischer, C; Weber, M H; Lynn, K G
2003-07-31
We present depth-resolved positron 2D angular correlation of annihilation radiation (2DACAR) experiments on CdSe quantum dots in the diameter range from 2.5 to 6 nm, deposited as micrometer thin layers. The average radial distribution of the valence electron momentum density (EMD) of CdSe quantum dots has been extracted, which reveals a systematic dependence upon particle size. The quantum confinement related changes and their size scaling observable at the Jones zone momentum of {approx}0.8 a.u. seem to agree with the previous coincidence Doppler study. In addition, the average radial EMD shows an increase in the low-momentum range (<0.6 a.u.) and a reduction in the high-momentum range (>1.6 a.u.) with respect to that measured on a bulk CdSe single crystal. Possible origins of these are described. First-principles calculations based on the Korringa-Kohn-Rostoker (KKR) method were performed to gain a better insight.
Propagation of ultra-intense electromagnetic waves through electron-positron-ion plasma
NASA Astrophysics Data System (ADS)
Rozina, Ch.; Tsintsadze, N. L.; Jamil, M.
2016-07-01
A kinetic approach is used to study the propagation of ultrarelativistic (amplitude) electromagnetic waves through electron-positron-ion plasma. For our purposes, we formulate a new plasma particle distribution function in the presence of ultrarelativistically intense circularly polarized electromagnetic (EM) waves. An effective dispersion relation of constant amplitude ultrarelativistic EM wave is derived, skin depth is calculated in particular, frequency regimes and has shown numerically that the penetration depth increases with the amplitude of ultra-intense electromagnetic waves, λ s k ˜ a /1 2 , i.e., plasma will be heated more in the region of skin depth. Next, we have found that the nonlinear interaction of ultrarelativistically intense EM waves of time and space varying amplitude leads to construct kinetic nonlinear Schrödinger equation (KNSE), containing both local and non-local nonlinear terms, where nonlocal nonlinear term appears due to density perturbations of plasma species. Taking the effects of the latter into consideration, nonlinear Landau damping is discussed for KNSE, damping rate is computed, and numerically ultrarelativistic EM waves are shown to decay exponentially. The present results should be helpful to understand the specific properties of the ultrarelativistic EM waves in astrophysical plasmas, e.g., pulsars, black holes, and neutron stars.
Rouhani, M. R.; Akbarian, A.; Mohammadi, Z.
2013-08-15
The behavior of quantum dust ion acoustic soliton and shocks in a plasma including inertialess quantum electrons and positrons, classical cold ions, and stationary negative dust grains are studied, using arbitrary amplitude approach. The effect of dissipation due to viscosity of ions is taken into account. The numerical analysis of Sagdeev potential for small value of quantum diffraction parameter (H) shows that for chosen plasma, only compressive solitons can exist and the existence domain of this type of solitons is decreased by increasing dust density (d). Additionally, the possibility of propagation of both subsonic and supersonic compressive solitons is investigated. It is shown that there is a critical dust density above which only supersonic solitons are observed. Moreover, increasing d leads to a reduction in the existence domain of compressive solitons and the possibility of propagation of rarefactive soliton is provided. So, rarefactive solitons are observed only due to the presence of dust particles in this model quantum plasma. Furthermore, numerical solution of governed equations for arbitrary amplitude shock waves has been investigated. It is shown that only compressive large amplitude shocks can propagate. Finally, the effects of plasma parameters on these structures are investigated. This research will be helpful in understanding the properties of dense astrophysical (i.e., white dwarfs and neutron stars) and laboratory dusty plasmas.
Dynamics of laser beams in inhomogeneous electron-positron-ion plasmas
NASA Astrophysics Data System (ADS)
Cheng, Li-Hong; Tang, Rong-An; Du, Hong-E.; Xue, Ju-Kui
2015-07-01
Nonlinear interaction of laser and electron-positron-ion plasmas is investigated by invoking the variational principle and numerical simulation, in terms of a nonlinear Schrödinger equation with inhomogeneities effect. It is shown that the plasma inhomogeneity has great influence on the laser beam dynamics. The laser beam can be self-trapped, focused, or defocused depending on the inhomogeneity character. The linearly decreasing axial plasma density makes the laser beam defocus, while the linearly increasing axial plasma density results in self-trapping of the beam. The self-focusing of the trapped beam is found in a high-density region. For the Gaussian types of density distribution, the beam field submits nonlinearly oscillating regime. The results provide an efficient way to manipulate the dynamics of laser beam propagating in plasma. Project supported by the National Natural Science Foundation of China (Grant Nos. 11274255 and 11305132), the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20136203110001), the Natural Science Foundation of Gansu Province, China (Grant No. 2011GS04358), and the Creation of Science and Technology of Northwest Normal University, China (Grant Nos. NWNU-KJCXGC-03-48 and NWNU-LKQN-12-12).
Positron annihilation study of defects in electron-irradiated single crystal zinc oxide
NASA Astrophysics Data System (ADS)
To, C. K.; Yang, B.; Beling, C. D.; Fung, S.; Ling, C. C.; Gong, M.
2011-01-01
Pressurized melt grown zinc oxide (ZnO) single crystals purchased from Cermet Inc. were irradiated by 2MeV electrons with fluence of 6x1017cm-2. Isochronal annealing from 100°C-800°C was performed on the crystals under argon and air ambience. Variable Energy Doppler Broadening Spectroscopy (VEDBS) was carried out on both the as-grown and the irradiated samples at each annealing step. The migration, agglomeration and annealing of grown-in and irradiated-introduced defects were studied. It was observed that the grown-in vacancy-type defects concentration decreased at 300°C and 600 °C. For the irradiated sample annealed in argon, the positron trapping vacancy-type defect concentration decreased at 300°C and 600°C. Further annealing the as-grown and irradiated samples in argon increased the S parameter further. For the irradiated sample annealed in air, the vacancy-type defect concentration decreases at 300°C and 700°C.
NASA Astrophysics Data System (ADS)
Rozina, Ch.; Tsintsade, N. L.; Maryam, N.; Komal, S.
2016-11-01
In this study, we have analytically investigated the effects of nonlinear Landau damping on the temporal growth rate of modulation and filamentation instabilities. Here, the nonlocal nonlinear Landau damping phenomena is appearing due to the nonlinear interaction between ultrarelativistic electromagnetic (UREM) wave (having wave vector normal to the beam) and electron-positron-ion plasma. We found that the ultrarelativistic ponderomotive force is linear, while usually it is nonlinear in relativistic case. We construct three dimensional kinetic nonlinear Schrödinger equation for a slowly varying spatio and temporal amplitude of UREM waves. The equations are then Fourier analyzed to obtain dispersion relation, which admit both modulation and filamentation instabilities. It is shown that nonlinear Landau damping is the main source of modulation instability, for a particular condition taking into account later one the maximum growth rate of modulation instability obtained as a function of amplitude of UREM waves and is displayed graphically. Further, it is shown that for an oscillating density profile, plane wave of uniform intensity becomes unstable and gets filamented. Growth rate of stationary state filament is found to be a function of amplitude of UREM waves and is emphasized that the maximum value of growth rate of filamentation instability is further increased in the presence of nonlinear Landau damping term. Finally, the growth rate of non stationary state filamentation instability is calculated and is shown that the characteristic growth length increases both with perpendicular wave vector and the amplitude of UREM waves.
Pumped helium system for cooling positron and electron traps to 1.2 K
NASA Astrophysics Data System (ADS)
Wrubel, J.; Gabrielse, G.; Kolthammer, W. S.; Larochelle, P.; McConnell, R.; Richerme, P.; Grzonka, D.; Oelert, W.; Sefzick, T.; Zielinski, M.; Borbely, J. S.; George, M. C.; Hessels, E. A.; Storry, C. H.; Weel, M.; Müllers, A.; Walz, J.; Speck, A.
2011-06-01
Extremely precise tests of fundamental particle symmetries should be possible via laser spectroscopy of trapped antihydrogen ( H¯) atoms. H¯ atoms that can be trapped must have an energy in temperature units that is below 0.5 K—the energy depth of the deepest magnetic traps that can currently be constructed with high currents and superconducting technology. The number of atoms in a Boltzmann distribution with energies lower than this trap depth depends sharply upon the temperature of the thermal distribution. For example, ten times more atoms with energies low enough to be trapped are in a thermal distribution at a temperature of 1.2 K than for a temperature of 4.2 K. To date, H¯ atoms have only been produced within traps whose electrode temperature is 4.2 K or higher. A lower temperature apparatus is desirable if usable numbers of atoms that can be trapped are to eventually be produced. This report is about the pumped helium apparatus that cooled the trap electrodes of an H¯ apparatus to 1.2 K for the first time. Significant apparatus challenges include the need to cool a 0.8 m stack of 37 trap electrodes separated by only a mm from the substantial mass of a 4.2 K Ioffe trap and the substantial mass of a 4.2 K solenoid. Access to the interior of the cold electrodes must be maintained for antiprotons, positrons, electrons and lasers.
Lopez, Rodrigo A.; Munoz, Victor; Asenjo, Felipe A.; Alejandro Valdivia, J.
2012-08-15
The nonlinear evolution of a circularly polarized electromagnetic wave in an electron-positron plasma propagating along a constant background magnetic field is considered, by studying its parametric decays. Relativistic effects, of the particle motion in the wave field and of the plasma temperature, are included to obtain the dispersion relation of the decays. The exact dispersion relation of the pump wave has been previously calculated within the context of a relativistic fluid theory and presents two branches: an electromagnetic and an Alfven one. We investigate the parametric decays for the pump wave in these two branches, including the anomalous dispersion zone of the Alfven branch where the group velocity is negative. We solve the nonlinear dispersion relation for different pump wave amplitudes and plasma temperatures, finding various resonant and nonresonant wave couplings. We are able to identify these couplings and study their behavior as we modify the plasma parameters. Some of these couplings are suppressed for larger amplitudes or temperatures. We also find two kinds of modulational instabilities, one involving two sideband daughter waves and another involving a forward-propagating electroacoustic mode and a sideband daughter wave.
Ion acoustic shock waves in electron-positron-ion quantum plasma
Masood, W.; Mirza, Arshad M.; Hanif, M.
2008-07-15
Ion acoustic shock waves (IASWs) are studied in an unmagnetized quantum plasma consisting of electrons, positrons, and ions employing the quantum hydrodynamic (QHD) model. Nonlinear quantum IASWs are investigated by deriving the Korteweg-deVries-Burger equation under the small amplitude perturbation expansion method. The dissipation is introduced by taking into account the kinematic viscosity among the plasma constituents. It is found that the strength of the ion acoustic shock wave is maximum for spherical, intermediate for cylindrical, and minimum for planar geometry. The temporal evolution of the shock for a quantum e-p-i plasma in a spherical geometry is also investigated. It is found that the strength and the steepness of the quantum ion acoustic shock wave increases with decreasing stretched time coordinate (representing slow time scale) |{tau}|. It is also found that an increase in the quantum Bohm potential decreases the strength as well as the steepness of the shock. The temporal evolution of the quantum ion acoustic solitons in an e-p-i plasma for cylindrical and spherical geometries is also explored by substituting the dissipative coefficient C equal to zero. The relevance of the present study with regard to the dense astrophysical environments is also pointed out.
Strongly separated pairs of core electrons in computed ground states of small molecules.
Gottlieb, Alex D; Weishäupl, Rada M
2013-03-01
We have performed full configuration interaction computations of the ground states of the molecules Be, BeH2, Li, LiH, B, and BH and verified that the core electrons constitute "separated electron pairs." These separated pairs of core electrons have nontrivial structure; the core pair does not simply occupy a single spatial orbital. Our method of establishing the presence of separated electron pairs is direct and conclusive. We do not fit a separated pair model; we work with the wavefunctions of interest directly. To establish that a given group of spin-orbitals contains a quasi-separated pair, we verify by direct computation that the quantum state of the electrons that occupy those spin-orbitals is nearly a pure 2-electron state.
Search for Heavy Particles Decaying into Electron-Positron Pairs in ppbar Collisions
NASA Astrophysics Data System (ADS)
Abazov, V. M.; Abbott, B.; Abdesselam, A.; Abolins, M.; Abramov, V.; Acharya, B. S.; Adams, D. L.; Adams, M.; Ahmed, S. N.; Alexeev, G. D.; Alves, G. A.; Amos, N.; Anderson, E. W.; Baarmand, M. M.; Babintsev, V. V.; Babukhadia, L.; Bacon, T. C.; Baden, A.; Baldin, B.; Balm, P. W.; Banerjee, S.; Barberis, E.; Baringer, P.; Barreto, J.; Bartlett, J. F.; Bassler, U.; Bauer, D.; Bean, A.; Begel, M.; Belyaev, A.; Beri, S. B.; Bernardi, G.; Bertram, I.; Besson, A.; Beuselinck, R.; Bezzubov, V. A.; Bhat, P. C.; Bhatnagar, V.; Bhattacharjee, M.; Blazey, G.; Blessing, S.; Boehnlein, A.; Bojko, N. I.; Borcherding, F.; Bos, K.; Brandt, A.; Breedon, R.; Briskin, G.; Brock, R.; Brooijmans, G.; Bross, A.; Buchholz, D.; Buehler, M.; Buescher, V.; Burtovoi, V. S.; Butler, J. M.; Canelli, F.; Carvalho, W.; Casey, D.; Casilum, Z.; Castilla-Valdez, H.; Chakraborty, D.; Chan, K. M.; Chekulaev, S. V.; Cho, D. K.; Choi, S.; Chopra, S.; Christenson, J. H.; Chung, M.; Claes, D.; Clark, A. R.; Cochran, J.; Coney, L.; Connolly, B.; Cooper, W. E.; Coppage, D.; Cummings, M. A.; Cutts, D.; Davis, G. A.; Davis, K.; de, K.; de Jong, S. J.; del Signore, K.; Demarteau, M.; Demina, R.; Demine, P.; Denisov, D.; Denisov, S. P.; Desai, S.; Diehl, H. T.; Diesburg, M.; di Loreto, G.; Doulas, S.; Draper, P.; Ducros, Y.; Dudko, L. V.; Duensing, S.; Duflot, L.; Dugad, S. R.; Dyshkant, A.; Edmunds, D.; Ellison, J.; Elvira, V. D.; Engelmann, R.; Eno, S.; Eppley, G.; Ermolov, P.; Eroshin, O. V.; Estrada, J.; Evans, H.; Evdokimov, V. N.; Fahland, T.; Feher, S.; Fein, D.; Ferbel, T.; Filthaut, F.; Fisk, H. E.; Fisyak, Y.; Flattum, E.; Fleuret, F.; Fortner, M.; Frame, K. C.; Fuess, S.; Gallas, E.; Galyaev, A. N.; Gao, M.; Gavrilov, V.; Genik, R. J.; Genser, K.; Gerber, C. E.; Gershtein, Y.; Gilmartin, R.; Ginther, G.; Gómez, B.; Gómez, G.; Goncharov, P. I.; González Solís, J. L.; Gordon, H.; Goss, L. T.; Gounder, K.; Goussiou, A.; Graf, N.; Graham, G.; Grannis, P. D.; Green, J. A.; Greenlee, H.; Grinstein, S.; Groer, L.; Grünendahl, S.; Gupta, A.; Gurzhiev, S. N.; Gutierrez, G.; Gutierrez, P.; Hadley, N. J.; Haggerty, H.; Hagopian, S.; Hagopian, V.; Hall, R. E.; Hanlet, P.; Hansen, S.; Hauptman, J. M.; Hays, C.; Hebert, C.; Hedin, D.; Heinson, A. P.; Heintz, U.; Heuring, T.; Hildreth, M. D.; Hirosky, R.; Hobbs, J. D.; Hoeneisen, B.; Huang, Y.; Illingworth, R.; Ito, A. S.; Jaffré, M.; Jain, S.; Jesik, R.; Johns, K.; Johnson, M.; Jonckheere, A.; Jones, M.; Jöstlein, H.; Juste, A.; Kahn, S.; Kajfasz, E.; Kalinin, A. M.; Karmanov, D.; Karmgard, D.; Kehoe, R.; Kharchilava, A.; Kim, S. K.; Klima, B.; Knuteson, B.; Ko, W.; Kohli, J. M.; Kostritskiy, A. V.; Kotcher, J.; Kotwal, A. V.; Kozelov, A. V.; Kozlovsky, E. A.; Krane, J.; Krishnaswamy, M. R.; Krivkova, P.; Krzywdzinski, S.; Kubantsev, M.; Kuleshov, S.; Kulik, Y.; Kunori, S.; Kupco, A.; Kuznetsov, V. E.; Landsberg, G.; Leflat, A.; Leggett, C.; Lehner, F.; Li, J.; Li, Q. Z.; Lima, J. G.; Lincoln, D.; Linn, S. L.; Linnemann, J.; Lipton, R.; Lucotte, A.; Lueking, L.; Lundstedt, C.; Luo, C.; Maciel, A. K.; Madaras, R. J.; Malyshev, V. L.; Manankov, V.; Mao, H. S.; Marshall, T.; Martin, M. I.; Martin, R. D.; Mauritz, K. M.; May, B.; Mayorov, A. A.; McCarthy, R.; McDonald, J.; McMahon, T.; Melanson, H. L.; Merkin, M.; Merritt, K. W.; Miao, C.; Miettinen, H.; Mihalcea, D.; Mishra, C. S.; Mokhov, N.; Mondal, N. K.; Montgomery, H. E.; Moore, R. W.; Mostafa, M.; da Motta, H.; Nagy, E.; Nang, F.; Narain, M.; Narasimham, V. S.; Neal, H. A.; Negret, J. P.; Negroni, S.; Nunnemann, T.; O'Neil, D.; Oguri, V.; Olivier, B.; Oshima, N.; Padley, P.; Pan, L. J.; Papageorgiou, K.; Para, A.; Parashar, N.; Partridge, R.; Parua, N.; Paterno, M.; Patwa, A.; Pawlik, B.; Perkins, J.; Peters, M.; Peters, O.; Pétroff, P.; Piegaia, R.; Piekarz, H.; Pope, B. G.; Popkov, E.; Prosper, H. B.; Protopopescu, S.; Qian, J.; Raja, R.; Rajagopalan, S.; Ramberg, E.; Rapidis, P. A.; Reay, N. W.; Reucroft, S.; Rha, J.; Ridel, M.; Rijssenbeek, M.; Rockwell, T.; Roco, M.; Rubinov, P.; Ruchti, R.; Rutherfoord, J.; Sabirov, B. M.; Santoro, A.; Sawyer, L.; Schamberger, R. D.; Schellman, H.; Schwartzman, A.; Sen, N.; Shabalina, E.; Shivpuri, R. K.; Shpakov, D.; Shupe, M.; Sidwell, R. A.; Simak, V.; Singh, H.; Singh, J. B.; Sirotenko, V.; Slattery, P.; Smith, E.; Smith, R. P.; Snihur, R.; Snow, G. R.; Snow, J.; Snyder, S.; Solomon, J.; Sorín, V.; Sosebee, M.; Sotnikova, N.; Soustruznik, K.; Souza, M.; Stanton, N. R.; Steinbrück, G.; Stephens, R. W.; Stichelbaut, F.; Stoker, D.; Stolin, V.; Stoyanova, D. A.; Strauss, M.; Strovink, M.; Stutte, L.; Sznajder, A.; Taylor, W.; Tentindo-Repond, S.; Tripathi, S. M.; Trippe, T. G.; Turcot, A. S.; Tuts, P. M.; van Gemmeren, P.; Vaniev, V.; van Kooten, R.; Varelas, N.; Vertogradov, L. S.; Volkov, A. A.; Vorobiev, A. P.; Wahl, H. D.; Wang, H.; Wang, Z.-M.; Warchol, J.; Watts, G.; Wayne, M.; Weerts, H.; White, A.; White, J. T.; Whiteson, D.; Wightman, J. A.; Wijngaarden, D. A.; Willis, S.; Wimpenny, S. J.; Womersley, J.; Wood, D. R.; Yamada, R.; Yamin, P.; Yasuda, T.; Yatsunenko, Y. A.; Yip, K.; Youssef, S.; Yu, J.; Yu, Z.; Zanabria, M.; Zheng, H.; Zhou, Z.; Zielinski, M.; Zieminska, D.; Zieminski, A.; Zutshi, V.; Zverev, E. G.; Zylberstejn, A.
2001-08-01
We present results of searches for technirho (ρT), techniomega (ωT), and Z' particles, using the decay channels ρT,ωT,Z'-->e+e-. The search is based on 124.8 pb-1 of data collected by the D0 detector at the Fermilab Tevatron during 1992-1996. In the absence of a signal, we set 95% C.L. upper limits on the cross sections for the processes ppbar-->ρT,ωT,Z'-->e+e- as a function of the mass of the decaying particle. For certain model parameters, we exclude the existence of degenerate ρT and ωT states with masses below about 200 GeV. We exclude a Z' with mass below 670 GeV, assuming that it has the same couplings to fermions as the Z boson.
The all-sky distribution of 511 keV electron-positron annihilation emission
NASA Astrophysics Data System (ADS)
Knödlseder, J.; Jean, P.; Lonjou, V.; Weidenspointner, G.; Guessoum, N.; Gillard, W.; Skinner, G.; von Ballmoos, P.; Vedrenne, G.; Roques, J.-P.; Schanne, S.; Teegarden, B.; Schönfelder, V.; Winkler, C.
2005-10-01
We present a map of 511 keV electron-positron annihilation emission, based on data accumulated with the SPI spectrometer aboard ESA's INTEGRAL gamma-ray observatory, that covers approximately ~95% of the celestial sphere. Within the exposed sky area, 511 keV line emission is significantly detected towards the galactic bulge region and, at a very low level, from the galactic disk. The bulge emission is highly symmetric and is centred on the galactic centre with an extension of ~ 8° (FWHM). The emission is equally well described by models that represent the stellar bulge or halo populations. The detection significance of the bulge emission is ~ 50σ, that of the galactic disk is ~ 4σ. The disk morphology is only weakly constrained by the present data, being compatible with both the distribution of young and old stellar populations. The 511 keV line flux from the bulge and disk components is (1.05 ± 0.06) × 10-3 ph cm-2 s-1 and (0.7 ± 0.4) × 10-3 ph cm-2 s-1 respectively, corresponding to a bulge-to-disk flux ratio in the range 1-3. Assuming a positronium fraction of f_p=0.93 this translates into annihilation rates of (1.5 ± 0.1) × 1043 s-1and (0.3 ± 0.2) × 1043 s-1, respectively. The ratio of the bulge luminosity to that of the disk is in the range 3-9. We find no evidence for a point-like source in addition to the diffuse emission, down to a typical flux limit of ~10-4 ph cm-2 s-1. We also find no evidence for the positive latitude enhancement that has been reported from OSSE measurements; our 3σ upper flux limit for this feature is 1.5 × 10-4 ph cm-2 s-1. The disk emission can be attributed to the β^+-decay of the radioactive species 26 Al and 44Ti. The bulge emission arises from a different source which has only a weak or no disk component. We suggest that Type Ia supernovae and/or low-mass X-ray binaries are the prime candidates for the source of the galactic bulge positrons. Light dark matter annihilation could also explain the observed 511 ke
NASA Astrophysics Data System (ADS)
Kokrashvili, G. Z.; Pataraia, A. D.
1983-07-01
Reference is made to the studies by Melikidze et al. (1981) and Sakai and Kowata (1980), which dealt with a nonlinear transverse wave propagating in the direction of the magnetic field. It is noted that far from the surface of the pulsars, the lines of force of the magnetic field bend. For this reason, magnetoacoustic waves propagating at an angle to the magnetic field are investigated, and nonlinear equations are derived which describe the behavior of the amplitudes. The nonlinear waves in an electron-positron plasma in a magnetic field directed along the x axis are investigated with the aid of collisionless kinetic equations and the Maxwell equations. It is assumed that the nonperturbed distribution function is identical for the electrons and positrons and that it depends only on the x component of the momentum.
NASA Astrophysics Data System (ADS)
Petrović, Zoran Lj; Marjanović, Srdan; Dujko, Saša; Banković, Ana; Šašić, Olivera; Bošnjaković, Danko; Stojanović, Vladimir; Malović, Gordana; Buckman, Stephen; Garcia, Gustavo; White, Ron; Sullivan, James; Brunger, Michael
2014-04-01
Collisions of electrons, atoms, molecules, photons and ions are the basic processes in plasmas and ionized gases in general. This is especially valid for low temperature collisional plasmas. Kinetic phenomena in transport are very sensitivitive to the shape of the cross sections and may at the same time affect the macroscopic applications. We will show how transport theory or simulation codes, phenomenology, kinetic phenomena and transport data may be used to improve our knowledge of the cross sections, our understanding of the plasma models, application of the swarm physics in ionized gases and similar applications to model and improve gas filled traps of positrons. Swarm techniques could also be a starting point in applying atomic and molecular data in models of electron or positron therapy/diagnostics in radiation related medicine.
NASA Astrophysics Data System (ADS)
Bolorizadeh, M. A.; Brunger, M. J.; Maddern, T.; Ghanbari Adivi, E.
2007-03-01
We derive the exact analytic form for the second-order positron-electron interaction term in the Faddeev three-body approach which is applicable in the nonrelativistic high energy region. Although there is no nonintegrable singularity in the six-dimensional integral form of this amplitude, here the basic difficulty arises from the presence of complex nonintegral exponents in the components included in the integrand. Consequently, three brunch cuts must be handled simultaneously. However, by using an integral representation of the gamma function, these brunch cuts are removed from the integrand. Expanding the radial parts of the initial and final wave functions further reduces the second-order positron-electron interaction term to a one-variable integral in terms of Bessel functions of the third kind. The different final closed expressions are ultimately derived in terms of the generalized hypergeometric functions for different regions of the scattering angle.
Gevorgyan, N. E.; Dashyan, N. B.; Paremuzyan, R. G.; Stepanyan, S. G.
2010-01-01
We study the dependence of the sensitivity of response of the electromagnetic calorimeter of CLAS plant on the momenta of electrons and positrons. We made calculation of this dependence and elaborated a method for its employment in identification of e- and e+. We have shown that the new method of selection of e- and e+ improves the quality of identification by about 10%. We used the experimental data obtained with the plant CLAS of linear accelerator at Jefferson laboratory (USA).
Zhang Jiefang; Wang Yueyue; Wu Lei
2009-06-15
The propagation of ion acoustic waves in plasmas composed of ions, positrons, and nonthermally distributed electrons is investigated. By means of the reduction perturbation technique, a nonlinear Schroedinger equation is derived and the modulation instability of ion acoustic wave is analyzed, where the nonthermal parameter is found to be of significant importance. Furthermore, analytical expressions for the bright and dark solitons are obtained, and the interaction of multiple solitons is discussed.
Ritchie, B.G.; Avignone, F.T. III; Carter, H.K.; Mlekodaj, R.L.; Spejewski, E.H.
1981-04-01
The isotopes /sup 206/Fr and /sup 208/Fr were produced by the reactions Ir(/sup 20/Ne,xn)/sup 206,208/Fr and mass separated on-line. The electron-capture and positron decays to /sup 206/Rn and /sup 208/Rn were studied by collecting ..gamma.. ray and internal conversion electron singles spectra as a function of decay time as well as ..gamma..-..gamma.., ..gamma..-e/sup -/, and ..gamma..-x ray coincidence spectra. The energies and many of the spins were determined for 18 excited, even parity states in /sup 208/Rn and for 10 excited, even parity states in /sup 206/Rn. These nuclei appear to be excellent candidates for interpretation in terms of a weak coupling shell model. The energy levels were also compared to the predictions of the interacting boson approximation model.
Evaluation of an International Roommate-Pairing Program
ERIC Educational Resources Information Center
Tolman, Steven
2016-01-01
There are over 700,000 international students currently studying in the U.S. (McMurtrie, 2011) contributing close to $12 billion yearly to the U.S. economy (Altbach, 2004). Universities cannot take for granted that international students will choose U.S. institutions. While great attention and research efforts have been given to support programs…
Evaluation of an International Roommate-Pairing Program
ERIC Educational Resources Information Center
Tolman, Steven
2016-01-01
There are over 700,000 international students currently studying in the U.S. (McMurtrie, 2011) contributing close to $12 billion yearly to the U.S. economy (Altbach, 2004). Universities cannot take for granted that international students will choose U.S. institutions. While great attention and research efforts have been given to support programs…
Fine-grid calculations for stellar electron and positron capture rates on Fe isotopes
Nabi, Jameel-Un; Tawfik, Abdel Nasser
2013-03-15
The acquisition of precise and reliable nuclear data is a prerequisite to success for stellar evolution and nucleosynthesis studies. Core-collapse simulators find it challenging to generate an explosion from the collapse of the core of massive stars. It is believed that a better understanding of the microphysics of core-collapse can lead to successful results. The weak interaction processes are able to trigger the collapse and control the lepton-to-baryon ratio (Y{sub e}) of the corematerial. It is suggested that the temporal variation of Y{sub e} within the core of a massive star has a pivotal role to play in the stellar evolution and a fine-tuning of this parameter at various stages of presupernova evolution is the key to generate an explosion. During the presupernova evolution of massive stars, isotopes of iron, mainly {sup 54-56}Fe, are considered to be key players in controlling Y{sub e} ratio via electron capture on these nuclides. Recently an improved microscopic calculation of weak-interaction-mediated rates for iron isotopes was introduced using the proton-neutron quasiparticle random-phase-approximation (pn-QRPA) theory. The pn-QRPA theory allows a microscopic state-by-state calculation of stellar capture rates which greatly increases the reliability of calculated rates. The results were suggestive of some fine-tuning of the Y{sub e} ratio during various phases of stellar evolution. Here we present for the first time the fine-grid calculation of the electron and positron capture rates on {sup 54-56}Fe. The sensitivity of the pn-QRPA calculated capture rates to the deformation parameter is also studied in this work. Core-collapse simulators may find this calculation suitable for interpolation purposes and for necessary incorporation in the stellar evolution codes.
NASA Astrophysics Data System (ADS)
Folegati, P.; Makkonen, I.; Ferragut, R.; Puska, M. J.
2007-02-01
Electron-positron momentum distributions measured by the coincidence Doppler broadening method can be used in the chemical analysis of the annihilation environment, typically a vacancy-impurity complex in a solid. In the present work, we study possibilities for a quantitative analysis, i.e., for distinguishing the average numbers of different atomic species around the defect. First-principles electronic structure calculations self-consistently determining electron and positron densities and ion positions are performed for vacancy-solute complexes in Al-Cu , Al-Mg-Cu , and Al-Mg-Cu-Ag alloys. The ensuing simulated coincidence Doppler broadening spectra are compared with measured ones for defect identification. A linear fitting procedure, which uses the spectra for positrons trapped at vacancies in pure constituent metals as components, has previously been employed to find the relative percentages of different atomic species around the vacancy [A. Somoza Phys. Rev. B 65, 094107 (2002)]. We test the reliability of the procedure by the help of first-principles results for vacancy-solute complexes and vacancies in constituent metals.
Abdollahi, S; Ackermann, M; Ajello, M; Albert, A; Atwood, W B; Baldini, L; Barbiellini, G; Bellazzini, R; Bissaldi, E; Bloom, E D; Bonino, R; Bottacini, E; Brandt, T J; Bruel, P; Buson, S; Caragiulo, M; Cavazzuti, E; Chekhtman, A; Ciprini, S; Costanza, F; Cuoco, A; Cutini, S; D'Ammando, F; de Palma, F; Desiante, R; Digel, S W; Di Lalla, N; Di Mauro, M; Di Venere, L; Donaggio, B; Drell, P S; Favuzzi, C; Focke, W B; Fukazawa, Y; Funk, S; Fusco, P; Gargano, F; Gasparrini, D; Giglietto, N; Giordano, F; Giroletti, M; Green, D; Guiriec, S; Harding, A K; Jogler, T; Jóhannesson, G; Kamae, T; Kuss, M; Larsson, S; Latronico, L; Li, J; Longo, F; Loparco, F; Lubrano, P; Magill, J D; Malyshev, D; Manfreda, A; Mazziotta, M N; Meehan, M; Michelson, P F; Mitthumsiri, W; Mizuno, T; Moiseev, A A; Monzani, M E; Morselli, A; Negro, M; Nuss, E; Ohsugi, T; Omodei, N; Paneque, D; Perkins, J S; Pesce-Rollins, M; Piron, F; Pivato, G; Principe, G; Rainò, S; Rando, R; Razzano, M; Reimer, A; Reimer, O; Sgrò, C; Simone, D; Siskind, E J; Spada, F; Spandre, G; Spinelli, P; Strong, A W; Tajima, H; Thayer, J B; Torres, D F; Troja, E; Vandenbroucke, J; Zaharijas, G; Zimmer, S
2017-03-03
The Large Area Telescope on board the Fermi Gamma-ray Space Telescope has collected the largest ever sample of high-energy cosmic-ray electron and positron events since the beginning of its operation. Potential anisotropies in the arrival directions of cosmic-ray electrons or positrons could be a signature of the presence of nearby sources. We use almost seven years of data with energies above 42 GeV processed with the Pass 8 reconstruction. The present data sample can probe dipole anisotropies down to a level of 10^{-3}. We take into account systematic effects that could mimic true anisotropies at this level. We present a detailed study of the event selection optimization of the cosmic-ray electrons and positrons to be used for anisotropy searches. Since no significant anisotropies have been detected on any angular scale, we present upper limits on the dipole anisotropy. The present constraints are among the strongest to date probing the presence of nearby young and middle-aged sources.
Abdollahi, S.; Ackermann, M.; Ajello, M.; ...
2017-03-01
We present the Large Area Telescope on board the Fermi Gamma-ray Space Telescope that has collected the largest ever sample of high-energy cosmic-ray electron and positron events since the beginning of its operation. Potential anisotropies in the arrival directions of cosmic-ray electrons or positrons could be a signature of the presence of nearby sources. We use almost seven years of data with energies above 42 GeV processed with the Pass 8 reconstruction. The present data sample can probe dipole anisotropies down to a level of 10-3. We take into account systematic effects that could mimic true anisotropies at this level.more » We present a detailed study of the event selection optimization of the cosmic-ray electrons and positrons to be used for anisotropy searches. Since no significant anisotropies have been detected on any angular scale, we present upper limits on the dipole anisotropy. Lastly, the present constraints are among the strongest to date probing the presence of nearby young and middle-aged sources.« less
NASA Astrophysics Data System (ADS)
Saha, Asit; Chatterjee, Prasanta; Chatterjee
2014-08-01
Ion acoustic solitary waves and periodic waves in an unmagnetized plasma with superthermal (kappa-distributed) electrons and positrons are investigated through a non-perturbative approach. Model equations are transformed to a planar dynamical system. Then by using the bifurcations of phase portraits of this planar dynamical system, we have established that our model has solitary wave and periodic wave solutions. We have obtained two analytical solutions for these solitary and periodic waves depending on the parameters. From these solitary wave and periodic wave solutions, we have shown the combined effects of temperature ratio (σ) of electrons and positrons, spectral index (κ), speed of the traveling wave (v), and density ratio (p) of positrons and electrons on the characteristics of ion acoustic solitary and periodic waves. The spectral index, density ratio, speed of the traveling wave, and temperature ratio significantly affect the characteristics of ion acoustic solitary and periodic structures. The present study might be helpful to understand the salient features of nonlinear ion acoustic solitary and periodic structures in the interstellar medium.
NASA Astrophysics Data System (ADS)
Abdollahi, S.; Ackermann, M.; Ajello, M.; Albert, A.; Atwood, W. B.; Baldini, L.; Barbiellini, G.; Bellazzini, R.; Bissaldi, E.; Bloom, E. D.; Bonino, R.; Bottacini, E.; Brandt, T. J.; Bruel, P.; Buson, S.; Caragiulo, M.; Cavazzuti, E.; Chekhtman, A.; Ciprini, S.; Costanza, F.; Cuoco, A.; Cutini, S.; D'Ammando, F.; de Palma, F.; Desiante, R.; Digel, S. W.; Di Lalla, N.; Di Mauro, M.; Di Venere, L.; Donaggio, B.; Drell, P. S.; Favuzzi, C.; Focke, W. B.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Giglietto, N.; Giordano, F.; Giroletti, M.; Green, D.; Guiriec, S.; Harding, A. K.; Jogler, T.; Jóhannesson, G.; Kamae, T.; Kuss, M.; Larsson, S.; Latronico, L.; Li, J.; Longo, F.; Loparco, F.; Lubrano, P.; Magill, J. D.; Malyshev, D.; Manfreda, A.; Mazziotta, M. N.; Meehan, M.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Moiseev, A. A.; Monzani, M. E.; Morselli, A.; Negro, M.; Nuss, E.; Ohsugi, T.; Omodei, N.; Paneque, D.; Perkins, J. S.; Pesce-Rollins, M.; Piron, F.; Pivato, G.; Principe, G.; Rainò, S.; Rando, R.; Razzano, M.; Reimer, A.; Reimer, O.; Sgrò, C.; Simone, D.; Siskind, E. J.; Spada, F.; Spandre, G.; Spinelli, P.; Strong, A. W.; Tajima, H.; Thayer, J. B.; Torres, D. F.; Troja, E.; Vandenbroucke, J.; Zaharijas, G.; Zimmer, S.; Fermi-LAT Collaboration
2017-03-01
The Large Area Telescope on board the Fermi Gamma-ray Space Telescope has collected the largest ever sample of high-energy cosmic-ray electron and positron events since the beginning of its operation. Potential anisotropies in the arrival directions of cosmic-ray electrons or positrons could be a signature of the presence of nearby sources. We use almost seven years of data with energies above 42 GeV processed with the Pass 8 reconstruction. The present data sample can probe dipole anisotropies down to a level of 10-3 . We take into account systematic effects that could mimic true anisotropies at this level. We present a detailed study of the event selection optimization of the cosmic-ray electrons and positrons to be used for anisotropy searches. Since no significant anisotropies have been detected on any angular scale, we present upper limits on the dipole anisotropy. The present constraints are among the strongest to date probing the presence of nearby young and middle-aged sources.