NLO QCD corrections to graviton induced deep inelastic scattering
NASA Astrophysics Data System (ADS)
Stirling, W. J.; Vryonidou, E.
2011-06-01
We consider Next-to-Leading-Order QCD corrections to ADD graviton exchange relevant for Deep Inelastic Scattering experiments. We calculate the relevant NLO structure functions by calculating the virtual and real corrections for a set of graviton interaction diagrams, demonstrating the expected cancellation of the UV and IR divergences. We compare the NLO and LO results at the centre-of-mass energy relevant to HERA experiments as well as for the proposed higher energy lepton-proton collider, LHeC, which has a higher fundamental scale reach.
NLO QCD + NLO EW corrections to WZZ productions with leptonic decays at the LHC
NASA Astrophysics Data System (ADS)
Yong-Bai, Shen; Ren-You, Zhang; Wen-Gan, Ma; Xiao-Zhou, Li; Yu, Zhang; Lei, Guo
2015-10-01
Precision tests of the Standard Model (SM) require not only accurate experiments, but also precise and reliable theoretical predictions. Triple vector boson production provides a unique opportunity to investigate the quartic gauge couplings and check the validity of the gauge principle in the SM. Since the tree-level predictions alone are inadequate to meet this demand, the next-to-leading order (NLO) calculation becomes compulsory. In this paper, we calculate the NLO QCD + NLO electroweak (EW) corrections to the W ± ZZ productions with subsequent leptonic decays at the 14 TeV LHC by adopting an improved narrow width approximation which takes into account the off-shell contributions and spin correlations from the W ±- and Z-boson leptonic decays. The NLO QCD+EW corrected integrated cross sections for the W ± ZZ productions and some kinematic distributions of final products are provided. The results show that both the NLO QCD and NLO EW corrections are significant. In the jet-veto event selection scheme with p T,jet cut = 50 GeV, the NLO QCD+EW relative corrections to the integrated cross section are 20 .5% and 31 .1%, while the genuine NLO EW relative corrections are -5 .42% and -4 .58%, for the W + ZZ and W - ZZ productions, respectively. We also investigate the theoretical dependence of the integrated cross section on the factorization/renormalization scale, and find that the scale uncertainty is underestimated at the LO due to the fact that the strong coupling α s is not involved in the LO matrix elements.
NLO QCD corrections to tri-boson production
NASA Astrophysics Data System (ADS)
Binoth, T.; Ossola, G.; Papadopoulos, C. G.; Pittau, R.
2008-06-01
We present a calculation of the NLO QCD corrections for the production of three vector bosons at the LHC, namely ZZZ, W+W-Z, W+ZZ, and W+W-W+ production. The virtual corrections are computed using the recently proposed method of reduction at the integrand level (OPP reduction). Concerning the contributions coming from real emission we used the dipole subtraction to treat the soft and collinear divergences. We find that the QCD corrections for these electroweak processes are in the range between 70 and 100 percent. As such they have to be considered in experimental studies of triple vector boson production at the LHC.
NLO QCD corrections to ZZ jet production at hadron colliders
Binoth, T.; Gleisberg, T.; Karg, S.; Kauer, N.; Sanguinetti, G.; /Annecy, LAPTH
2010-05-26
A fully differential calculation of the next-to-leading order QCD corrections to the production of Z-boson pairs in association with a hard jet at the Tevatron and LHC is presented. This process is an important background for Higgs particle and new physics searches at hadron colliders. We find sizable corrections for cross sections and differential distributions, particularly at the LHC. Residual scale uncertainties are typically at the 10% level and can be further reduced by applying a veto against the emission of a second hard jet. Our results confirm that NLO corrections do not simply rescale LO predictions.
The NLO QCD corrections to B c meson production in Z 0 decays
NASA Astrophysics Data System (ADS)
Qiao, Cong-Feng; Sun, Li-Ping; Zhu, Rui-Lin
2011-08-01
The decay width of Z 0 to B c meson is evaluated at the next-to-leading order (NLO) accuracy in strong interaction. Numerical calculation shows that the NLO correction to this process is remarkable. The quantum chromodynamics (QCD) renormalization scale dependence of the results is obviously depressed, and hence the uncertainties lying in the leading order calculation are reduced.
The NLO QCD corrections to associate production of squarks and charginos at LHC
Xiao Zhenjun; Jin Ligang; Yu Huan; Cheng Hongmei
2010-02-10
In this talk, we present our calculations for the next-to-leading order(NLO) QCD corrections to the cross sections (CS) of the associate production processes pp->gq->q-tilde{sub i}chi-tilde{sub j}{sup +}-+X with q = (u,d) in the constrained minimal supersymmetric standard model in the CERN LHC experiments. The NLO QCD corrections can in general provide a 30-40% enhancement to the corresponding cross sections, and significantly reduce the dependence of the total cross section on the renormalization and factorization scales.
NLO QCD CORRECTIONS TO HADRONIC HIGGS PRODUCTION WITH HEAVY QUARKS.
DAWSON,S.; JACKSON,C.; ORR,L.; REINA,L.; WACHEROTH,D.
2003-07-02
The production of a Higgs boson in association with a pair of t{bar t} or b{bar b} quarks plays a very important role at both the Tevatron and the Large Hadron Collider. The theoretical prediction of the corresponding cross sections has been improved by including the complete next-to-leading order QCD corrections. After a brief description of the most relevant technical aspects of the calculation, we review the results obtained for both the Tevatron and the Large Hadron Collider.
NLO QCD corrections to Zbb production with massive bottom quarks at the Fermilab Tevatron
Febres Cordero, F.; Reina, L.; Wackeroth, D.
2008-10-01
We calculate the next-to-leading order (NLO) QCD corrections to Zbb production in hadronic collisions including full bottom-quark mass effects. We present results for the total cross section and the invariant mass distribution of the bottom-quark jet pair at the Fermilab Tevatron pp collider. We perform a detailed comparison with a calculation that considers massless bottom quarks, as implemented in the Monte Carlo program MCFM. We find that neglecting bottom-quark mass effects overestimates the total NLO QCD cross section for Zbb production at the Tevatron by about 7%, independent of the choice of the renormalization and factorization scales. Moreover, bottom-quark mass effects can impact the shape of the bottom-quark pair invariant mass distribution, in particular, in the low invariant mass region.
Electroweakino pair production at the LHC: NLO SUSY-QCD corrections and parton-shower effects
NASA Astrophysics Data System (ADS)
Baglio, Julien; Jäger, Barbara; Kesenheimer, Matthias
2016-07-01
We present a set of NLO SUSY-QCD calculations for the pair production of neutralinos and charginos at the LHC, and their matching to parton-shower programs in the framework of the POWHEG-BOX program package. The code we have developed provides a SUSY Les Houches Accord interface for setting supersymmetric input parameters. Decays of the neutralinos and charginos and parton-shower effects can be simulated with PYTHIA. To illustrate the capabilities of our program, we present phenomenological results for a representative SUSY parameter point. We find that NLO-QCD corrections increase the production rates for neutralinos and charginos significantly. The impact of parton-shower effects on distributions of the weakinos is small, but non-negligible for jet distributions.
NLO QCD corrections to Drell-Yan processes in the SANC framework
Andonov, A.; Arbuzov, A. B. Bondarenko, S. G.; Christova, P.; Kolesnikov, V. A.; Nanava, G.; Sadykov, R. R.
2010-10-15
NLO QCD corrections to charged and neutral current Drell-Yan processes are computed with help of the computer system SANC. At the partonic level both quark-antiquark and quark-gluon scattering channels are taken into account. Subtraction of collinear singularities in the massive quark scheme is compared with the one in the MS-bar scheme. Numerical results at the hadronic level are received for the LHC conditions with help of Monte-Carlo integrators and event generator programs based on the standard SANC modules. Comparison with analogous results of the MCFM package is shown.
NLO-QCD corrections to Higgs pair production in the MSSM
NASA Astrophysics Data System (ADS)
Agostini, A.; Degrassi, G.; Gröber, R.; Slavich, P.
2016-04-01
We take a step towards a complete NLO-QCD determination of the production of a pair of Higgs scalars in the MSSM. Exploiting a low-energy theorem that connects the Higgs-gluon interactions to the derivatives of the gluon self-energy, we obtain analytic results for the one- and two-loop squark contributions to Higgs pair production in the limit of vanishing external momenta. We find that the two-loop squark contributions can have non-negligible effects in MSSM scenarios with stop masses below the TeV scale. We also show how our results can be adapted to the case of Higgs pair production in the NMSSM.
NLO QCD and electroweak corrections to W + γ production with leptonic W-boson decays
NASA Astrophysics Data System (ADS)
Denner, Ansgar; Dittmaier, Stefan; Hecht, Markus; Pasold, Christian
2015-04-01
We present a calculation of the next-to-leading-order electroweak corrections to W+γ production, including the leptonic decay of the W boson and taking into account all off-shell effects of the W boson, where the finite width of the W boson is implemented using the complex-mass scheme. Corrections induced by incoming photons are fully included and find particular emphasis in the discussion of phenomenological predictions for the LHC. The corresponding next-to-leading-order QCD corrections are reproduced as well. In order to separate hard photons from jets, a quark-to-photon fragmentation function á la Glover and Morgan is employed. Our results are implemented into Monte Carlo programs allowing for the evaluation of arbitrary differential cross sections. We present integrated cross sections for the LHC at 7 TeV, 8 TeV, and 14 TeV as well as differential distributions at 14 TeV for bare muons and dressed leptons. Finally, we discuss the impact of anomalous W W γ couplings.
NLO QCD and electroweak corrections to Z + γ production with leptonic Z-boson decays
NASA Astrophysics Data System (ADS)
Denner, Ansgar; Dittmaier, Stefan; Hecht, Markus; Pasold, Christian
2016-02-01
The next-to-leading-order electroweak corrections to ppto {l}+{l}-/overline{ν}ν +\\upgamma +X production, including all off-shell effects of intermediate Z bosons in the complex-mass scheme, are calculated for LHC energies, revealing the typically expected large corrections of tens of percent in the TeV range. Contributions from quark-photon and photon-photon initial states are taken into account as well, but their impact is found to be moderate or small. Moreover, the known next-to-leading-order QCD corrections are reproduced. In order to separate hard photons from jets, both a quark-to-photon fragmentation function á la Glover/Morgan and Frixione's cone isolation are employed. The calculation is available in the form of Monte Carlo programs allowing for the evaluation of arbitrary differential cross sections. Predictions for integrated cross sections are presented for the LHC at 7 TeV, 8 TeV, and 14 TeV, and differential distributions are discussed at 14 TeV for bare muons and dressed leptons. Finally, we consider the impact of anomalous ZZγ and Zγγ couplings.
NASA Astrophysics Data System (ADS)
Xiong, Shou-Jian; Ma, Wen-Gan; Guo, Lei; Chen, Chong; Zhang, Ren-You
2014-06-01
We present the calculations for the same-sign T-odd mirror quark pair production of the first two generations in the littlest Higgs model with T parity (LHT) at the √s =14 TeV LHC up to the QCD next-to-leading order (NLO) including the subsequent decays of the T-odd mirror quarks. The uncertainties from the factorization/renormalization scale and parton distribution functions are discussed. Our numerical results show that the parton distribution function uncertainty of the NLO QCD corrected cross section for the same-sign T-odd mirror quark pair production of the first two generations is comparable with the scale uncertainty, and the combined uncertainty at the QCD NLO is much smaller than that at the LO with the factorization/renormalization scale μ in the range of [μ0/4,4μ0]. We also study the dependence of the total cross section on the LHT parameters, and provide the transverse momentum, rapidity, invariant mass and HT distributions of final products.
QCD corrections to triboson production
NASA Astrophysics Data System (ADS)
Lazopoulos, Achilleas; Melnikov, Kirill; Petriello, Frank
2007-07-01
We present a computation of the next-to-leading order QCD corrections to the production of three Z bosons at the Large Hadron Collider. We calculate these corrections using a completely numerical method that combines sector decomposition to extract infrared singularities with contour deformation of the Feynman parameter integrals to avoid internal loop thresholds. The NLO QCD corrections to pp→ZZZ are approximately 50% and are badly underestimated by the leading order scale dependence. However, the kinematic dependence of the corrections is minimal in phase space regions accessible at leading order.
Diphoton signals in theories with large extra dimensions to NLO QCD at hadron colliders
NASA Astrophysics Data System (ADS)
Kumar, M. C.; Mathews, Prakash; Ravindran, V.; Tripathi, Anurag
2009-02-01
We present a full next-to-leading order (NLO) QCD corrections to diphoton production at the hadron colliders in both standard model and ADD model. The invariant mass and rapidity distributions of the diphotons are obtained using a semi-analytical two cut-off phase space slicing method which allows for a successful numerical implementation of various kinematical cuts used in the experiments. The fragmentation photons are systematically removed using smooth-cone-isolation cuts on the photons. The NLO QCD corrections not only stabilise the perturbative predictions but also enhance the production cross section significantly.
Vector boson production in association with KK modes of the ADD model to NLO in QCD at the LHC
NASA Astrophysics Data System (ADS)
Kumar, M. C.; Mathews, Prakash; Ravindran, V.; Seth, Satyajit
2011-05-01
Next-to-leading order (NLO) QCD corrections to the associated production of the vector boson (Z/W±) with the Kaluza-Klein (KK) modes of the graviton in large extra-dimensional model at the Large Hadron Collider (LHC) are presented. We have obtained various kinematic distributions using a Monte Carlo code which is based on the two-cutoff phase space slicing method that handles soft and collinear singularities appearing at the NLO level. We estimate the impact of the QCD corrections on various observables and find that they are significant. We also show the reduction in factorization scale uncertainty when QCD corrections are included.
NLO QCD+EW predictions for V + jets including off-shell vector-boson decays and multijet merging
NASA Astrophysics Data System (ADS)
Kallweit, S.; Lindert, J. M.; Maierhöfer, P.; Pozzorini, S.; Schönherr, M.
2016-04-01
We present next-to-leading order (NLO) predictions including QCD and electroweak (EW) corrections for the production and decay of off-shell electroweak vector bosons in association with up to two jets at the 13 TeV LHC. All possible dilepton final states with zero, one or two charged leptons that can arise from off-shell W and Z bosons or photons are considered. All predictions are obtained using the automated implementation of NLO QCD+EW corrections in the O penLoops matrix-element generator combined with the Munich and Sherpa Monte Carlo frameworks. Electroweak corrections play an especially important role in the context of BSM searches, due to the presence of large EW Sudakov logarithms at the TeV scale. In this kinematic regime, important observables such as the jet transverse momentum or the total transverse energy are strongly sensitive to multijet emissions. As a result, fixed-order NLO QCD+EW predictions are plagued by huge QCD corrections and poor theoretical precision. To remedy this problem we present an approximate method that allows for a simple and reliable implementation of NLO EW corrections in the MePs@Nlo multijet merging framework. Using this general approach we present an inclusive simulation of vector-boson production in association with jets that guarantees NLO QCD+EW accuracy in all phase-space regions involving up to two resolved jets.
QCD corrections to associated production of tt{gamma} at hadron colliders
Duan Pengfei; Ma Wengan; Zhang Renyou; Han Liang; Guo Lei; Wang Shaoming
2009-07-01
We report on the next-to-leading order (NLO) QCD computation of top-quark pair production in association with a photon at the Fermilab Tevatron RUN II and CERN Large Hadron Collider. We describe the impact of the complete NLO QCD radiative corrections to this process, and provide the predictions of the leading order (LO) and NLO integrated cross sections, distributions of the transverse momenta of the top quark and photon for the LHC and Tevatron, and the LO and NLO forward-backward top-quark charge asymmetries for the Tevatron. We investigate the dependence of the LO and NLO cross sections on the renormalization/factorization scale, and find the scale dependence of the LO cross section is obviously improved by the NLO QCD corrections. The K-factor of the NLO QCD correction is 0.977(1.524) for the Tevatron (LHC)
NLO QCD Predictions for W+3 jets
Maitre, Daniel; Berger, Carola F.; Bern, Zvi; Febres Cordero, Fernando; Ita, Harald; Dixon, Lance J.; Forde, Darren; Gleisberg, Tanju; Kosower, David; /Saclay, SPhT
2009-12-09
In this contribution we present results from the NLO computation of the production of a W boson in association with three jets in hadronic collisions. The results are obtained by combining two programs: BlackHat for the virtual one-loop matrix elements and Sherpa for the real-emission contributions. We present results for the Tevatron and the LHC, and address the issue of the choice of a common factorization and renormalization scale for this process.
NLO QCD method of the polarized semiinclusive DIS data analysis
Sissakian, A.N.; Shevchenko, O.Yu.; Ivanov, O.N.
2006-05-01
Method of polarized semi-inclusive deep inelastic scattering (SIDIS) data analysis in the next to leading order (NLO) QCD is developed. Within the method one first directly extracts in NLO few first truncated (available to measurement) Mellin moments of the quark helicity distributions. Second, using these moments as an input to the proposed modification of the Jacobi polynomial expansion method (MJEM), one eventually reconstructs the local quark helicity distributions themselves. All numerical tests demonstrate that MJEM allows us to reproduce with the high precision the input local distributions even inside the narrow Bjorken x region accessible for experiment. It is of importance that only four first input moments are sufficient to achieve a good quality of reconstruction. The application of the method to the simulated SIDIS data on the pion production is considered. The obtained results encourage one that the proposed NLO method can be successfully applied to the SIDIS data analysis. The analysis of HERMES data on pion production is performed. To this end the pion difference asymmetries are constructed from the measured by HERMES standard semi-inclusive spin asymmetries. The LO results of the valence distribution reconstruction are in a good accordance with the respective leading order SMC and HERMES results, while the NLO results are in agreement with the existing NLO parametrizations on these quantities.
NASA Astrophysics Data System (ADS)
Cascioli, F.; Höche, S.; Krauss, F.; Maierhöfer, P.; Pozzorini, S.; Siegert, F.
2014-01-01
We present precise predictions for four-lepton plus jets production at the LHC obtained within the fully automated S herpa + O penL oops framework. Off-shell intermediate vector bosons and related interferences are consistently included using the complex-mass scheme. Four-lepton plus 0- and 1-jet final states are described at NLO accuracy, and the precision of the simulation is further increased by squared quark-loop NNLO contributions in the gg → 4 ℓ, gg → 4 ℓ + g, g q → 4 ℓ + q, and → 4 ℓ + g channels. These NLO and NNLO contributions are matched to the S herpa parton shower, and the 0- and 1-jet final states are consistently merged using the M eps@N lo technique. Thanks to Sudakov resummation, the parton shower provides improved predictions and uncertainty estimates for exclusive observables. This is important when jet vetoes or jet bins are used to separate four-lepton final states arising from Higgs decays, diboson production, and top-pair production. Detailed predictions are presented for the Atlas and C ms H → WW* analyses at 8 TeV in the 0- and 1-jet bins. Assessing renormalisation-, factorisation- and resummationscale uncertainties, which reflect also unknown subleading Sudakov logarithms in jet bins, we find that residual perturbative uncertainties are as small as a few percent.
Prompt atmospheric neutrinos and muons: NLO versus LO QCD predictions
Gelmini, Graciela; Gondolo, Paolo; Varieschi, Gabriele
2000-02-01
We compare the leading and next-to-leading order QCD predictions for the flux of atmospheric muons and neutrinos from decays of charmed particles. We find that the full NLO lepton fluxes can be approximated to within {approx}10% by the Born-level fluxes multiplied by an overall factor of 2.2-2.4, which depends slightly on the PDF. This supports the approach of Thunman, Ingelman and Gondolo. We also find that their very low lepton fluxes are due to the mild slope they used for the gluon distribution function at small momentum fractions, and that substantially larger lepton fluxes result when the slope of the gluon distribution function at small momentum fractions is larger. (c) 2000 The American Physical Society.
Next-to-leading order perturbative QCD corrections to baryon correlators in matter
Groote, S.; Koerner, J. G.; Pivovarov, A. A.
2008-08-01
We compute the next-to-leading order (NLO) perturbative QCD corrections to the correlators of nucleon interpolating currents in relativistic nuclear matter. The main new result is the calculation of the O({alpha}{sub s}) perturbative corrections to the coefficient functions of the vector quark condensate in matter. This condensate appears in matter due to the violation of Lorentz invariance. The NLO perturbative QCD corrections turn out to be large which implies that the NLO corrections must be included in a sum rule analysis of the properties of both bound nucleons and relativistic nuclear matter.
QCD corrections to W+W- production through gluon fusion
NASA Astrophysics Data System (ADS)
Caola, Fabrizio; Melnikov, Kirill; Röntsch, Raoul; Tancredi, Lorenzo
2016-03-01
We compute the next-to-leading order (NLO) QCD corrections to the gg →W+W- → l1+ ν1 l2- νbar2 process, mediated by a massless quark loop, at the LHC. This process first contributes to the hadroproduction of W+W- at O (αs2), but, nevertheless, has a sizable impact on the total production rate. We find that the NLO QCD corrections to the gg →W+W- process amount to O (50)%, and increase the NNLO QCD cross sections of pp →W+W- by approximately two percent, at both the 8 TeV and 13 TeV LHC. We also compute the NLO corrections to gluonic W+W- production within a fiducial volume used by the ATLAS Collaboration in their 8 TeV measurement of the W+W- production rate and find that the QCD corrections are significantly smaller than in the inclusive case. While the current experimental uncertainties are still too large to make these differences relevant, the observed strong dependence of perturbative corrections on kinematic cuts underscores that extrapolation from a fiducial measurement to the total cross section is an extremely delicate matter, and calls for the direct comparison of fiducial volume measurements with corresponding theoretical computations.
Penguin-dominated B{yields}PV decays in NLO perturbative QCD
Li Hsiangnan; Mishima, Satoshi
2006-11-01
We study the penguin-dominated B{yields}PV decays, with P (V) representing a pseudoscalar (vector) meson, in the next-to-leading-order (NLO) perturbative QCD (PQCD) formalism, concentrating on the B{yields}K{phi}, {pi}K*, {rho}K, and {omega}K modes. It is found that the NLO corrections dramatically enhance the B{yields}{rho}K, {omega}K branching ratios, which were estimated to be small under the naive factorization assumption. The patterns of the direct CP asymmetries A{sub CP}(B{sup 0}{yields}{rho}{sup {+-}}K{sup {+-}}){approx_equal}A{sub CP}(B{sup {+-}}{yields}{rho}{sup 0}K{sup {+-}}) and A{sub CP}(B{sup 0}{yields}{pi}{sup {+-}}K*{sup {+-}})>A{sub CP}(B{sup {+-}}{yields}{pi}{sup 0}K*{sup {+-}}) are predicted, differing from A{sub CP}(B{sup 0}{yields}{pi}{sup {+-}}K{sup {+-}})>>A{sub CP}(B{sup {+-}}{yields}{pi}{sup 0}K{sup {+-}}). The above patterns, if confirmed by data, will support the source of strong phases from the scalar penguin annihilation in PQCD. The results for the mixing-induced CP asymmetries S{sub f} are consistent with those obtained in the literature, except that our S{sub {rho}{sup 0}}{sub K{sub S}} is as low as 0.5.
QCD corrections to stoponium production at hadron colliders
Younkin, James E.; Martin, Stephen P.
2010-03-01
If the lighter top squark has no kinematically allowed two-body decays that conserve flavor, then it will live long enough to form hadronic bound states. The observation of the diphoton decays of stoponium could then provide a uniquely precise measurement of the top squark mass. In this paper, we calculate the cross section for the production of stoponium in a hadron collider at next-to-leading order (NLO) in QCD. We present numerical results for the cross section for production of stoponium at the LHC and study the dependence on beam energy, stoponium mass, and the renormalization and factorization scale. The cross-section is substantially increased by the NLO corrections, counteracting a corresponding decrease found earlier in the NLO diphoton branching ratio.
ZZ jet and Graviton jet at NLO QCD: recent applications using GOLEM methods
Karg, Stefan; Binoth, Thomas; Gleisberg, Tanju; Kauer, Nikolas; Sanguinetti, Gregory; Kramer, Michael; Li, Qiang; Zeppenfeld, Dieter; /Karlsruhe U., ITP
2010-05-26
In this talk we discuss recent progress concerning precise predictions for hadron colliders. We show results of two applications of tensor reduction using GOLEM methods: the next-to-leading order (NLO) corrections to pp {yields} ZZ + jet as an important background for Higgs particle and new physics searches at hadron colliders, and the NLO corrections to graviton plus jet hadroproduction, which is an important channel for graviton searches at the Tevatron and the LHC.
Gao Jun; Li Chongsheng; Zhang Jiajun; Zhu Huaxing
2009-12-01
We present the calculations of the complete next-to-leading order (NLO) QCD effects on the single top productions induced by model-independent tqg flavor-changing neutral-current couplings at hadron colliders. Our results show that, for the tcg coupling, the NLO QCD corrections can enhance the total cross sections by about 60% and 30%, and for the tug coupling by about 50% and 20% at the Tevatron and LHC, respectively, which means that the NLO corrections can increase the experimental sensitivity to the flavor-changing neutral-current couplings by about 10%-30%. Moreover, the NLO corrections reduce the dependence of the total cross sections on the renormalization or factorization scale significantly, which lead to increased confidence on the theoretical predictions. Besides, we also evaluate the NLO corrections to several important kinematic distributions, and find that for most of them the NLO corrections are almost the same and do not change the shape of the distributions.
Electroweak top-quark pair production at the LHC with Z ' bosons to NLO QCD in POWHEG
NASA Astrophysics Data System (ADS)
Bonciani, Roberto; Ježo, Tomáš; Klasen, Michael; Lyonnet, Florian; Schienbein, Ingo
2016-02-01
We present the calculation of the NLO QCD corrections to the electroweak production of top-antitop pairs at the CERN LHC in the presence of a new neutral gauge boson. The corrections are implemented in the parton shower Monte Carlo program POWHEG. Standard Model (SM) and new physics interference effects are properly taken into account. QED singularities, first appearing at this order, are consistently subtracted. Numerical results are presented for SM and Z ' total cross sections and distributions in invariant mass, transverse momentum, azimuthal angle and rapidity of the top-quark pair. The remaining theoretical uncertainty from scale and PDF variations is estimated, and the potential of the charge asymmetry to distinguish between new physics models is investigated for the Sequential SM and a leptophobic topcolor model.
Probing top quark neutral couplings in the Standard Model Effective Field Theory at NLO in QCD
NASA Astrophysics Data System (ADS)
Bylund, Olga Bessidskaia; Maltoni, Fabio; Tsinikos, Ioannis; Vryonidou, Eleni; Zhang, Cen
2016-05-01
Top quark pair production in association with a Z-boson or a photon at the LHC directly probes neutral top-quark couplings. We present predictions for these two processes in the Standard Model (SM) Effective Field Theory (EFT) at next-to-leading order (NLO) in QCD. We include the full set of CP-even dimension-six operators that enter the top-quark interactions with the SM gauge bosons. For comparison, we also present predictions in the SMEFT for top loop-induced HZ production at the LHC and for toverline{t} production at the ILC at NLO in QCD. Results for total cross sections and differential distributions are obtained and uncertainties coming from missing higher orders in the strong coupling and in the EFT expansions are discussed. NLO results matched to the parton shower are available, allowing for event generation to be directly employed in an experimental analyses. Our framework provides a solid basis for the interpretation of current and future measurements in the SMEFT, with improved accuracy and precision.
Gao Jun; Li Chongsheng; Li Bohua; Zhu Huaxing; Yuan, C.-P.
2010-07-01
We present a complete next-to-leading order (NLO) QCD calculation to a heavy resonance production and decay into a top quark pair at the LHC, where the resonance could be either a Randall-Sundrum Kaluza-Klein graviton G or an extra gauge boson Z{sup '}. The complete NLO QCD corrections can enhance the total cross sections by about 80%-100% and 20%-40% for the G and the Z{sup '}, respectively, depending on the resonance mass. We also explore in detail the NLO corrections to the polar angle distributions of the top quark, and our results show that the shapes of the NLO distributions can be different from the leading order ones for the Kaluza-Klein graviton. Moreover, we study the NLO corrections to the spin correlations of the top quark pair production via the above process, and find that the corrections are small.
Next-to-leading-order QCD corrections to Higgs boson production plus three jets in gluon fusion.
Cullen, G; van Deurzen, H; Greiner, N; Luisoni, G; Mastrolia, P; Mirabella, E; Ossola, G; Peraro, T; Tramontano, F
2013-09-27
We report on the calculation of the cross section for Higgs boson production in association with three jets via gluon fusion, at next-to-leading-order (NLO) accuracy in QCD, in the infinite top-mass approximation. After including the complete NLO QCD corrections, we observe a strong reduction in the scale dependence of the result, and an increased steepness in the transverse momentum distributions of both the Higgs boson and the leading jets. The results are obtained with the combined use of GOSAM, SHERPA, and the MADDIPOLE-MADEVENT framework. PMID:24116766
Nonperturbative QCD corrections to electroweak observables
Dru B Renner, Xu Feng, Karl Jansen, Marcus Petschlies
2011-12-01
Nonperturbative QCD corrections are important to many low-energy electroweak observables, for example the muon magnetic moment. However, hadronic corrections also play a significant role at much higher energies due to their impact on the running of standard model parameters, such as the electromagnetic coupling. Currently, these hadronic contributions are accounted for by a combination of experimental measurements and phenomenological modeling but ideally should be calculated from first principles. Recent developments indicate that many of the most important hadronic corrections may be feasibly calculated using lattice QCD methods. To illustrate this, we will examine the lattice computation of the leading-order QCD corrections to the muon magnetic moment, paying particular attention to a recently developed method but also reviewing the results from other calculations. We will then continue with several examples that demonstrate the potential impact of the new approach: the leading-order corrections to the electron and tau magnetic moments, the running of the electromagnetic coupling, and a class of the next-to-leading-order corrections for the muon magnetic moment. Along the way, we will mention applications to the Adler function, the determination of the strong coupling constant and QCD corrections to muonic-hydrogen.
QCD corrections to polarization of J/{psi} and {upsilon} at Fermilab Tevatron and CERN LHC
Gong Bin; Wang Jianxiong
2008-10-01
In this work, we present more details of the calculation on the next-to-leading-order (NLO) QCD corrections to polarization of direct J/{psi} production via color singlet at the Tevatron and LHC, together with the results for {upsilon} for the first time. Our results show that the J/{psi} polarization status drastically changes from transverse polarization dominant at leading order into longitudinal polarization dominant in the whole range of the transverse momentum p{sub t} of J/{psi} when the NLO corrections are counted. For {upsilon} production, the p{sub t} distribution of the polarization status behaves almost the same as that for J/{psi} except that the NLO result is transverse polarization at small p{sub t} range. Although the theoretical evaluation predicts a larger longitudinal polarization than the measured value at the Tevatron, it may provide a solution towards the previous large discrepancy for J/{psi} and {upsilon} polarization between theoretical prediction and experimental measurement, and suggests that the next important step is to calculate the NLO corrections to hadronproduction of color-octet state J/{psi}{sup (8)} and {upsilon}{sup (8)}. Our calculations are performed in two ways: namely, we do and do not analytically sum over the polarizations, and then check them with each other.
Next-to-Leading-Order QCD Corrections to W{sup +}W{sup -}bb Production at Hadron Colliders
Denner, A.; Dittmaier, S.; Kallweit, S.; Pozzorini, S.
2011-02-04
Top-antitop quark pairs belong to the most abundantly produced and precisely measurable heavy-particle signatures at hadron colliders and allow for crucial tests of the standard model and new physics searches. Here we report on the calculation of the next-to-leading order (NLO) QCD corrections to hadronic W{sup +}W{sup -}bb production, which provides a complete NLO description of the production of top-antitop pairs and their subsequent decay into W bosons and bottom quarks, including interferences, off-shell effects, and nonresonant backgrounds. Numerical predictions for the Tevatron and the LHC are presented.
QCD and electroweak corrections to Z Z +jet production with Z -boson leptonic decays at the LHC
NASA Astrophysics Data System (ADS)
Wang, Yong; Zhang, Ren-You; Ma, Wen-Gan; Li, Xiao-Zhou; Guo, Lei
2016-07-01
In this paper we present the full next-to-leading-order (NLO) QCD +NLO electroweak (EW) corrections to the Z -boson pair production in association with a hard jet at the LHC. The subsequent Z -boson leptonic decays are included by adopting both the naive narrow-width approximation and madspin methods for comparison. Since the Z Z +jet production is an important background for single Higgs boson production and new physics searches at hadron colliders, the theoretical predictions with high accuracy for the hadronic production of Z Z +jet are necessary. We present the numerical results of the integrated cross section and various kinematic distributions of final particles, and conclude that it is necessary to take into account the spin correlation and finite-width effects from the Z -boson leptonic decays. We also find that the NLO EW correction is quantitatively non-negligible in matching the experimental accuracy at the LHC, particularly in the high-transverse-momentum region.
QCD radiative correction to color-octet J/{psi} inclusive production at B factories
Zhang Yujie; Ma Yanqing; Wang Kai; Chao Kuangta
2010-02-01
In nonrelativistic quantum chromodynamics (NRQCD), we study the next-to-leading order (NLO) QCD radiative correction to the color-octet J/{psi} inclusive production at B factories. Compared with the leading-order (LO) result, the NLO QCD corrections are found to enhance the short-distance coefficients in the color-octet J/{psi} production e{sup +}e{sup -{yields}}cc({sup 1}S{sub 0}{sup (8)} or {sup 3}P{sub J}{sup (8)})g (with J=0, 1, 2) by a factor of about 1.9. Moreover, the peak at the end point in the J/{psi} energy distribution predicted at LO can be smeared by the NLO corrections, but the major color-octet contribution still comes from the large energy region of J/{psi}. By fitting the latest data of {sigma}(e{sup +}e{sup -{yields}}J/{psi}+X{sub non-cc}) observed by Belle, we find that the values of color-octet matrix elements are much smaller than expected earlier by using the naive velocity scaling rules or extracted from fitting experimental data with LO calculations. As the most stringent constraint by setting the color-singlet contribution to be zero in e{sup +}e{sup -{yields}}J/{psi}+X{sub non-cc}, we get an upper limit of the color-octet matrix element, <0|O{sup J/{psi}[1S{sub 0}{sup (8)}]}|0>+4.0<0|O{sup J/{psi}[3P{sub 0}{sup (8)}]}|0>/m{sub c}{sup 2}<(2.0{+-}0.6)x10{sup -2} GeV{sup 3} at NLO in {alpha}{sub s}.
NASA Astrophysics Data System (ADS)
Leader, Elliot; Sidorov, Alexander V.; Stamenov, Dimiter B.
2016-04-01
An NLO QCD analysis of the final HERMES data on pion multiplicities is presented and a new set of pion fragmentation functions is extracted from the best fit to the data. We have studied the so-called [x ,z ] and [Q2,z ] presentations of their data, as given by HERMES, which, in principle, should simply be two different ways of presenting the experimental data. We have based our extraction on an excellent fit to the [Q2,z ] presentation of the data.
Dominant mixed QCD-electroweak O (αs α) corrections to Drell-Yan processes in the resonance region
NASA Astrophysics Data System (ADS)
Dittmaier, Stefan; Huss, Alexander; Schwinn, Christian
2016-03-01
A precise theoretical description of W- and Z-boson production in the resonance region is essential for the correct interpretation of high-precision measurements of the W-boson mass and the effective weak mixing angle. Currently, the largest unknown fixed-order contribution is given by the mixed QCD-electroweak corrections of O (αs α) . We argue, using the framework of the pole expansion for the NNLO QCD-electroweak corrections established in a previous paper, that the numerically dominant corrections arise from the combination of large QCD corrections to the production with the large electroweak corrections to the decay of the W / Z boson. We calculate these so-called factorizable corrections of "initial-final" type and estimate the impact on the W-boson mass extraction. We compare our results to simpler approximate combinations of electroweak and QCD corrections in terms of naive products of NLO QCD and electroweak correction factors and using leading-logarithmic approximations for QED final-state radiation as provided by the structure-function approach or QED parton-shower programs. We also compute corrections of "final-final" type, which are given by finite counterterms to the leptonic vector-boson decays and are found to be numerically negligible.
Higher derivative corrections in holographic QCD
Basu, Anirban
2007-12-15
We consider the effect of the R{sup 4} term in type IIA string theory on the supergravity background dual to N{sub c} D4-branes compactified on a circle with supersymmetry breaking boundary conditions. We study the dynamics of D8-branes in this perturbed geometry in the probe approximation. This leads to an analysis of higher derivative corrections in holographic QCD beyond the supergravity approximation. We make a rough estimate of the corrections to the masses of some of the lightest (axial) vector mesons. The corrections are suppressed by a factor of (g{sub YM}{sup 2}N{sub c}){sup -3} compared to their supergravity values. We find that the masses of these mesons increase from their supergravity values.
Measurement of the strange - antistrange asymmetry at NLO in QCD from NuTeV dimuon data
Mason, David Alexander
2006-03-01
A measurement of the asymmetry between the strange and antistrange quark distributions, from a next to leading order QCD analysis of dimuon events measured by the NuTeV experiment at Fermilab is presented. Neutrino charged current events with two muons in the final state provide a direct means for studying charm production and measuring the strange sea. NuTeV's sign selected beam allows independent measurement of the strange and antistrange seas. An improved measurement of the neutrino and antineutrino forward dimuon cross section tables, using the complete charged current event sample for normalization is performed. These tables are then analyzed at NLO to measure the strange and antistrange seas. Detector acceptance is modeled using an NLO charm cross section differential in all variables required. The strange quark distribution is found to have an integrated momentum weighted asymmetry of +0.00196 {+-} 0.00046(stat) {+-} 0.00045(syst) {+-} 0.00182(external). The charm mass is found to be 1.41 {+-} 0.10(stat) {+-} 0.08(syst) {+-} 0.12(external) GeV.
Ian Balitsky
2011-04-01
Deep inelastic scattering in the saturation region (for small $x$ and/or large nucleus) is described by the evolution of color dipoles. In the leading order this evolution is governed by the non-linear BK equation. To see if this equation is relevant for existing or future DIS accelerators (like EIC or LHeC) one needs to know how big are the next-to-leading order (NLO) corrections. I review the calculation of the NLO corrections to high-energy amplitudes in QCD.
QCD Corrections to e{sup +}e{sup -}{yields}J/{psi}+gg at B Factories
Ma Yanqing; Zhang Yujie; Chao Kuangta
2009-04-24
In heavy quarkonium production, the measured ratio R{sub cc}={sigma}[J/{psi}+cc+X]/{sigma}[J/{psi}+X] at B factories is much larger than existing theoretical predictions. To clarify this discrepancy, in nonrelativistic QCD we find the next-to-leading-order (NLO) QCD correction to e{sup +}e{sup -}{yields}J/{psi}+gg can enhance the cross section by about 20%. Together with the calculated NLO result for e{sup +}e{sup -}{yields}J/{psi}+cc, we show that the NLO corrections can significantly improve the fit to the ratio R{sub cc}. The effects of leading logarithm resummation near the end point on the J/{psi} momentum distribution and total cross section are also considered. Comparison of the calculated cross section for e{sup +}e{sup -}{yields}J/{psi}+gg with the observed cross section for e{sup +}e{sup -}{yields}J/{psi}+non-(cc) is expected to provide unique information on the issue of color-octet contributions.
Reduction of One-Loop Amplitudes at the Integrand Level -- NLO QCD Calculations
NASA Astrophysics Data System (ADS)
Ossola, G.; Papadopoulos, C. G.; Pittau, R.
2008-07-01
The recently proposed method (OPP) to extract the coefficients of the scalar one-loop integrals to any multi-particle (sub)-amplitude is described. Within this method no analytical information on the structure of the amplitude is needed, allowing for a purely numerical, but still algebraic, implementation of the algorithm. The algorithm can be used to automatically perform one-loop calculation both in QCD and in the EW Theory. As an application, we give QCD one-loop results for the process p p to ZZZ at the LHC.
NASA Astrophysics Data System (ADS)
Caola, Fabrizio; Dowling, Matthew; Melnikov, Kirill; Röntsch, Raoul; Tancredi, Lorenzo
2016-07-01
We compute next-to-leading order (NLO) QCD corrections to the production of two massive electroweak bosons in gluon fusion. We consider both the prompt production process gg → V V and the production mediated by an exchange of an s-channel Higgs boson, gg → H ∗ → V V . We include final states with both on- and off-shell vector bosons with leptonic decays. The gluonic production of vector bosons is a loop-induced process, including both massless and massive quarks in the loop. For gg → ZZ production, we obtain the NLO QCD corrections to the massive loops through an expansion around the heavy top limit. This approximation is valid below the top production threshold, giving a broad range of invariant masses between the Higgs production and the top production thresholds in which our results are valid. We explore the NLO QCD effects in gg → ZZ focusing, in particular, on the interference between prompt and Higgs-mediated processes. We find that the QCD corrections to the interference are large and similar in size to the corrections to both the signal and the background processes. At the same time, we observe that corrections to the interference change rapidly with the four-lepton invariant mass in the region around the ZZ production threshold. We also study the interference effects in gg → W + W - production where, due to technical limitations, we only consider contributions of massless loops. We find that the QCD corrections to the interference in this case are somewhat larger than those for either the signal or the background.
NASA Astrophysics Data System (ADS)
Bevilacqua, G.; Czakon, M.; Garzelli, M. V.; van Hameren, A.; Kardos, A.; Papadopoulos, C. G.; Pittau, R.; Worek, M.
2013-03-01
Based on the OPP technique and the HELAC framework, HELAC-1LOOP is a program that is capable of numerically evaluating QCD virtual corrections to scattering amplitudes. A detailed presentation of the algorithm is given, along with instructions to run the code and benchmark results. The program is part of the HELAC-NLO framework that allows for a complete evaluation of QCD NLO corrections. Catalogue identifier: AEOC_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEOC_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 290945 No. of bytes in distributed program, including test data, etc.: 3013326 Distribution format: tar.gz Programming language: Fortran (gfortran(http://gcc.gnu.org/fortran/), lahey95 (http://www.lahey.com), ifort3(http://software.intel.com)). Computer: Any. Operating system: Linux, Unix, Mac OS. Classification: 11.1. Nature of problem: The evaluation of virtual one-loop amplitudes for multi-particle scattering is a long-standing problem [1]. In recent years the OPP reduction technique [2] opened the road for a fully numerical approach based on the evaluation of the one-loop amplitude for well-defined values of the loop momentum. Solution method: By using HELAC [3-5] and CutTools [6], HELAC-1LOOP is capable of evaluating QCD virtual corrections [7]. The one-loop n-particle amplitudes are constructed as part of the n+2 tree-order ones, by using the basic recursive algorithm used in HELAC. A Les Houches Event (LHE) file is produced, combining the complete information from tree-order and virtual one-loop contributions. In conjunction with real corrections, obtained with the use of HELAC-DIPOLES [8], the full NLO corrections can be computed. The program has been successfully used in many applications.
W+n-Jet Predictions With MC@NLO in Sherpa
Hoeche, Stefan; Krauss, Frank; Schonherr, Marek; Siegert, Frank; /Freiburg U.
2012-03-20
Results for the production of W-bosons in conjunction with up to three jets including parton shower corrections are presented and compared to recent LHC data. These results consistently incorporate the full next-to leading order QCD corrections through the MC{at}NLO method, as implemented in the SHERPA event generator, with the virtual corrections obtained from the BLACKHAT library.
Duality between QCD perturbative series and power corrections
NASA Astrophysics Data System (ADS)
Narison, S.; Zakharov, V. I.
2009-08-01
We elaborate on the relation between perturbative and power-like corrections to short-distance sensitive QCD observables. We confront theoretical expectations with explicit perturbative calculations existing in literature. As is expected, the quadratic correction is dual to a long perturbative series and one should use one of them but not both. However, this might be true only for very long perturbative series, with number of terms needed in most cases exceeding the number of terms available. What has not been foreseen, the quartic corrections might also be dual to the perturbative series. If confirmed, this would imply a crucial modification of the dogma. We confront this quadratic correction against existing phenomenology (QCD (spectral) sum rules scales, determinations of light quark masses and of αs from τ-decay). We find no contradiction and (to some extent) better agreement with the data and with recent lattice calculations.
QCD Corrections to Heavy Quarkonium Production
Artoisenet, P.
2008-08-29
I discuss J/{psi} and {upsilon} production at the Tevatron. Working in the framework of NRQCD, I review the current theoretical status. Motivated by the polarization puzzle at the Tevatron, I present the brand-new computation of higher-order {alpha}{sub s} corrections to the color-singlet production and discuss the impact of these corrections both on the differential cross section and on the polarization of the quarkonium state. I finally comment on the relative importance of the various transitions that feed quarkonium hadroproduction.
QCD Corrections to Heavy Quarkonium Production
NASA Astrophysics Data System (ADS)
Artoisenet, P.
2008-08-01
I discuss J/ψ and Υ production at the Tevatron. Working in the framework of NRQCD, I review the current theoretical status. Motivated by the polarization puzzle at the Tevatron, I present the brand-new computation of higher-order αs corrections to the color-singlet production and discuss the impact of these corrections both on the differential cross section and on the polarization of the quarkonium state. I finally comment on the relative importance of the various transitions that feed quarkonium hadroproduction.
QCD Corrections and New Physics - Proceedings of the International Symposium
NASA Astrophysics Data System (ADS)
Kodaira, Jiro; Onogi, Tetsuya; Sasaki, Ken
1998-09-01
The Table of Contents for the full book PDF is as follows: * Preface * Opening Address * Top Quark Physics * Threshold Resummation of Soft Gluons in Hadronic Reactions - An Introduction * Recent Results from CDF * Top Quark Physics: Overview * Complete Description of Polarization Effects in Top Quark Decays Including Higher Order QCD Corrections * Top Pair Production in e+e- and γγ Processes * Structure Functions I * Highlights of Physics at HERA * Some Aspects of the BFKL Evolution * Structure Functions II * New Result from SMC on g_{1}^ρ * Studies of the Nucleon Spin Structure by HERMES * Recent Developments in Perturbative QCD: Q2 Evolution of Chiral-Odd Distributions h1(x,Q2) and hL(x,Q2) * The Small x Behavior of g1 in the Resummed Approach * Jet Physics * QCD Results from LEP1 and LEP2 * Twenty Years of Jet Physics : Old and New * Multi-Parton Loop Amplitudes and Next-to-Leading Order Jet Cross-Sections * Heavy Meson * PQCD Analysis of Inclusive Heavy Hadrons Decays * Strong Coupling Constant from Lattice QCD * Heavy-Light Decay Constant from Lattice NRQCD * Concluding Remarks * Program * Organizing Committee * List of Participants
Zhang Yujie; Gao Yingjia; Chao, K.-T.
2006-03-10
One of the most challenging open problems in heavy quarkonium physics is the double charm production in e{sup +}e{sup -} annihilation at B factories. The measured cross section of e{sup +}e{sup -}{yields}J/{psi}+{eta}{sub c} is much larger than leading order (LO) theoretical predictions. With the nonrelativistic QCD factorization formalism, we calculate the next-to-leading order (NLO) QCD correction to this process. Taking all one-loop self-energy, triangle, box, and pentagon diagrams into account, and factoring the Coulomb-singular term into the cc bound state wave function, we get an ultraviolet and infrared finite correction to the cross section of e{sup +}e{sup -}{yields}J/{psi}+{eta}{sub c} at {radical}(s)=10.6 GeV. We find that the NLO QCD correction can substantially enhance the cross section with a K factor (the ratio of NLO to LO) of about 1.8-2.1; hence, it greatly reduces the large discrepancy between theory and experiment.
Next-to-Leading QCD Effect on the Quark Compositeness Search at the LHC
Gao Jun; Li Chongsheng; Wang Jian; Zhu Huaxing; Yuan, C.-P.
2011-04-08
We present the exact next-to-leading order (NLO) QCD corrections to the dijet production induced by the quark contact interactions at the CERN Large Hadron Collider. We show that, as compared to the exact calculation, the scaled NLO QCD prediction adopted by the ATLAS Collaboration has overestimated the new physics effect on some direct observables by more than 30% and renders a higher limit on the quark compositeness scale. The destructive contribution from the exact NLO correction will also lower the compositeness scale limit set by the CMS Collaboration.
Dai Liang; Shao Dingyu; Gao Jun; Zhang Hao; Li Chongsheng
2011-03-01
We calculate the complete next-to-leading order (NLO) QCD corrections (including SUSY QCD corrections) to the inclusive total cross sections of the associated production processes pp{yields}A{sup 0}{gamma}+X in the minimal supersymmetric standard model (MSSM) at the CERN Large Hadron Collider (LHC). Our results show that the enhancement of the total cross sections from the NLO QCD corrections can reach 25%{approx}15% for 200 GeV
NASA Astrophysics Data System (ADS)
Baglio, Julien
2016-03-01
After the discovery of a Higgs boson in 2012 at the CERN Large Hadron Collider (LHC) the detailed study of its properties, and most importantly its couplings to other particles, has started. This is a very important task to be completed, in particular to test whether it is indeed the Higgs boson predicted by the Standard Model (SM). The precise study of the Higgs couplings to gauge bosons is of particular importance and requires as much information as possible. In this view this paper provides the next-to-leading order (NLO) QCD corrections to the production cross sections and differential distributions of a SM Higgs boson in association with a pair of weak bosons W+W- , W±Z and Z Z , matched with parton shower (PS) in the POWHEG-BOX framework. The NLO QCD corrections are found to be significant and PS effects are sizable at low pT in the jet differential distributions, as expected, while these effects are negligible in other distributions. We will also provide a detailed study of the theoretical uncertainties affecting the total production rates at the LHC and at the Future Circular Collider in hadron-hadron mode, the potential 100 TeV follow-up of the LHC machine: the scale uncertainty calculated by the variation of the renormalization and factorization scales, the parton distribution function and related αs errors as well as the parametric uncertainties on the input weak boson masses.
Gao Jun; Li Chongsheng; Li Zhao
2008-01-01
We present the calculations of the next-to-leading order (NLO) QCD corrections to the inclusive total cross sections for the associated production of the W{sup {+-}}H{sup {+-}} through bb annihilation in the minimal supersymmetric standard model at the CERN Large Hadron Collider. The NLO QCD corrections can either enhance or reduce the total cross sections, but they generally efficiently reduce the dependence of the total cross sections on the renormalization/factorization scale. The magnitude of the NLO QCD corrections is about 10% in most of the parameter space and can reach 15% in some parameter regions. We also show the Monte Carlo simulation results for the 2j+{tau}{sub jet}+pe{sub T} signature from the W{sup {+-}} and the H{sup {+-}} decays including the NLO QCD effects, and find an observable signal at a 5{sigma} level in some parameter region of the minimal supergravity model.
Huston, Joey [Co-Spokesperson; Ownes, Joseph [Co-Spokesperson
The Coordinated Theoretical-Experimental Project on QCD is a multi-institutional collaboration devoted to a broad program of research projects and cooperative enterprises in high-energy physics centered on Quantum Chromodynamics (QCD) and its implications in all areas of the Standard Model and beyond. The Collaboration consists of theorists and experimentalists at 18 universities and 5 national laboratories. More than 65 sets of Parton Distribution Functions are available for public access. Links to many online software tools, information about Parton Distribution Functions, papers, and other resources are also available.
Next-to-leading-order QCD correction to inclusive J/{psi}({Upsilon}) production in Z{sup 0} decay
Li, Rong; Wang, Jian-Xiong
2010-09-01
In this paper, we study the J/{psi}({Upsilon}) production in Z boson decay in a color-singlet model (CSM). We calculate the next-to-leading-order (NLO) QCD correction to Z{yields}quarkonium+QQ, the dominant contribution in the CSM, with the vector and axial-vector parts in the ZQQ vertex being treated separately. The results show that the vector and axial-vector parts have the same K factor (the ratio of the NLO result to the leading-order result) 1.13 with the renormalization scale {mu}=2m{sub c} and m{sub c}=1.5 GeV, and the K factor falls to 0.918 when applying the Brodsky, Lepage, and Mackenzie (BLM) renormalization scale scheme with obtained {mu}{sub BLM}=2.28 GeV and m{sub c}=1.5 GeV. By including the contributions from the next-dominant ones, the photon and gluon fragmentation processes, the branching ratio for Z{yields}J/{psi}{sub prompt}+X is (7.3-10.0)x10{sup -5} with the uncertainty consideration for the renormalization scale and charm quark mass. The results are about one-half of the central value of the experimental measurement 2.1x10{sup -4}. Furthermore, the J/{psi} energy distribution in our calculation cannot describe the experimental data. Therefore, even at QCD NLO, the contribution to Z{yields}J/{psi}{sub prompt}+X from the CSM cannot fully account for the experimental measurement. And there should be contributions from other mechanisms, such as the color-octet (COM) contributions. We define R{sub cc}=({Gamma}(Z{yields}J/{psi}ccX)/{Gamma}(Z{yields}J/{psi}X)) and obtain R{sub cc}=0.84 for only the CSM contribution and R{sub cc}=0.49 for COM and CSM contributions together. Then the R{sub cc} measurement could be used to clarify the COM contributions.
NASA Astrophysics Data System (ADS)
Gong, Bin; Lansberg, Jean-Philippe; Lorcé, Cédric; Wang, Jian-Xiong
2013-03-01
We update the study of the production of direct J/ψ in association with a Z boson at the Next-to-Leading Order (NLO) in α s by evaluating both the yield differential in P T and the J/ψ polarisation in the QCD-based Colour-Singlet Model (CSM). Contrary to an earlier claim, QCD corrections at small and mid P T are small if one assumes that the factorisation and the renormalisation scales are commensurate with the Z boson mass. As it can be anticipated, the t-channel gluon-exchange ( t-CGE) topologies start to be dominant only for P T ≳ m Z /2. The polarisation pattern is not altered by the QCD corrections. This is thus far the first quarkonium-production process where this is observed in the CSM. Along the same lines, our predictions for direct Y+Z are also given.
Next-to-Leading-Order QCD Corrections to e{sup +}e{sup -}{yields}J/{psi}gg at the B Factories
Gong Bin; Wang Jianxiong
2009-04-24
We calculate the next-to-leading-order (NLO) QCD corrections to e{sup +}e{sup -}{yields}J/{psi}gg via color singlet J/{psi}({sup 3}S{sub 1}) at the B factories. The result shows that the cross section is enhanced to 0.373 pb by a K factor (NLO/LO) of about 1.21. By considering its dependence on the charm quark mass and renormalization scale, the NLO cross section can range from 0.294 to 0.409 pb. Further including the {psi}{sup '} feed-down, {sigma}[e{sup +}e{sup -}{yields}J/{psi}X(non-cc)] is enhanced by another factor of about 1.29 and reach 0.482 pb. In addition, the momentum distributions of J/{psi} production and polarization are presented. Recent measurements from Belle agree well with our prediction for the cross section and momentum distribution. It is expected that this process can serve as a very good channel to clarify the J/{psi} polarization puzzle by performing further experimental measurements.
Next-to-leading order QCD corrections to electroweak Zjj production in the POWHEG BOX
NASA Astrophysics Data System (ADS)
Jäger, Barbara; Schneider, Steven; Zanderighi, Giulia
2012-09-01
We present an implementation of electroweak Z-boson production in association with two jets at hadron colliders in the POWHEG framework, a method that allows the interfacing of NLO-QCD calculations with parton-shower Monte Carlo programs. We focus on the leptonic decays of the weak gauge boson, and take photonic and non-resonant contributions to the matrix elements fully into account. We provide results for observables of particular importance for the suppression of QCD backgrounds to vector-boson fusion processes by means of central-jet-veto techniques. While parton-shower effects are small for most observables associated with the two hardest jets, they can be more pronounced for distributions that are employed in central-jet-veto studies.
Second-order QCD corrections to jet production at hadron colliders: the all-gluon contribution.
Gehrmann-De Ridder, A; Gehrmann, T; Glover, E W N; Pires, J
2013-04-19
We report the calculation of next-to-next-to-leading order QCD corrections in the purely gluonic channel to dijet production and related observables at hadron colliders. Our result represents the first next-to-next-to-leading order calculation of a massless jet observable at hadron colliders, and opens the path towards precision QCD phenomenology with the LHC. PMID:23679596
The NNLO QCD corrections to Z boson production at large transverse momentum
NASA Astrophysics Data System (ADS)
Ridder, A. Gehrmann-De; Gehrmann, T.; Glover, E. W. N.; Huss, A.; Morgan, T. A.
2016-07-01
The transverse momentum distribution of massive neutral vector bosons can be measured to high accuracy at hadron colliders. The transverse momentum is caused by a partonic recoil, and is determined by QCD dynamics. We compute the single and double-differential transverse momentum distributions for fully inclusive Z/γ ∗ production including leptonic decay to next-to-next-to-leading order (NNLO) in perturbative QCD. We also compute the same distributions normalised to the cross sections for inclusive Z/γ ∗ production, i.e. integrated over the transverse momentum of the lepton pair. We compare our predictions for the fiducial cross sections to the 8 TeV data set from the ATLAS and CMS collaborations, which both observed a tension between data and NLO theory predictions, using the experimental cuts and binning. We find that the inclusion of the NNLO QCD effects does not fully resolve the tension with the data for the unnormalised p T Z distribution. However, we observe that normalising the NNLO Z-boson transverse momentum distribution by the NNLO Drell-Yan cross section substantially improves the agreement between experimental data and theory, and opens the way for precision QCD studies of this observable.
Electroweak W+W- jj prodution at NLO in QCD matched with parton shower in the POWHEG-BOX
NASA Astrophysics Data System (ADS)
Jäger, Barbara; Zanderighi, Giulia
2013-04-01
We present an implementation of electroweak W + W - jj production at hadron colliders in the POWHEG framework, a method that allows the interfacing of a next-to-leading order QCD calculation with parton shower Monte Carlo programs. We provide results for both, fully and semi-leptonic decay modes of the weak bosons, taking resonant and non-resonant contributions and spin correlations of the final-state particles into account. To illustrate the versatility of our implementation, we provide phenomenological results for two representative scenarios with a light and with a heavy Higgs boson, respectively, and in a kinematic regime of highly boosted gauge bosons. The impact of the parton shower is found to depend on the setup and the observable under investigation. In particular, distributions related to a central-jet veto are more sensitive to these effects. Therefore the impact of radiation by the parton shower on next-to-leading order predictions should be assessed carefully on a case-by-case basis.
QCD CORRECTIONS TO DILEPTON PRODUCTION NEAR PARTONIC THRESHOLD IN PP SCATTERING.
SHIMIZU, H.; STERMAN, G.; VOGELSANG, W.; YOKOYA, H.
2005-10-02
We present a recent study of the QCD corrections to dilepton production near partonic threshold in transversely polarized {bar p}p scattering, We analyze the role of the higher-order perturbative QCD corrections in terms of the available fixed-order contributions as well as of all-order soft-gluon resummations for the kinematical regime of proposed experiments at GSI-FAIR. We find that perturbative corrections are large for both unpolarized and polarized cross sections, but that the spin asymmetries are stable. The role of the far infrared region of the momentum integral in the resummed exponent and the effect of the NNLL resummation are briefly discussed.
QCD corrections in two-Higgs-doublet extensions of the standard model with minimal flavor violation
NASA Astrophysics Data System (ADS)
Degrassi, G.; Slavich, P.
2010-04-01
We present the QCD corrections to Rb and to the ΔB=1 effective Hamiltonian in models with a second Higgs field that couples to the quarks respecting the criterion of minimal flavor violation, thus belonging either to the (1,2)1/2 or to the (8,2)1/2 representation of SU(3)×SU(2)×U(1). After the inclusion of the QCD corrections, the prediction for Rb becomes practically insensitive to the choice of renormalization scheme for the top mass, which for the type-I and type-II models translates in a more robust lower bound on tanβ. The QCD-corrected determinations of Rb and BR(B→Xsγ) are used to discuss the constraints on the couplings of a (colored) charged Higgs boson to top and bottom quarks.
QCD corrections to pair production of Type III Seesaw leptons at hadron colliders
NASA Astrophysics Data System (ADS)
Ruiz, Richard
2015-12-01
If kinematically accessible, hadron collider experiments provide an ideal laboratory for the direct production of heavy lepton partners in Seesaw models. In the context of the Type III Seesaw Mechanism, the O({α}_s) rate and shape corrections are presented for the pair production of hypothetical, heavy SU(2) L triplet leptons in pp collisions at √{s} = 13, 14 and 100TeV. The next-to-leading order (NLO) K-factors span, approximately, K NLO = 1 .1 - 1 .4 for both charged current and neutral current processes over a triplet mass range m T = 100 GeV - 2 TeV. Total production cross sections exhibit a - 6 % + 5 % scale dependence at 14 TeV and ±1% at 100 TeV. The NLO differential K-factors for heavy lepton kinematics are largely flat, suggesting that na¨ıve scaling by the total K NLO is reasonably justified. The resummed transverse momentum distribution of the dilepton system is presented at leading logarithmic (LL) accuracy. The effects of resummation are large in TeV-scale dilepton systems. Discovery potential to heavy lepton pairs at 14 and 100 TeV is briefly explored: at the High-Luminosity LHC, we estimate a 4 .8 - 6 .3 σ discovery potential maximally for m T = 1 .5 - 1 .6 TeV after 3000 fb-1. With 300 (3000) fb-1, there is 2σ sensitivity up to m T = 1 .3 - 1 .4 TeV (1 .7 - 1 .8 TeV) in the individual channels. At 100 TeV and with 10 fb-1, a 5 σ discovery can be achieved for m T = 1 .4 - 1 .6 TeV. Due to the factorization properties of Drell-Yan-type systems, the fixed order and resummed calculations reduce to convolutions over tree-level quantities.
Next-to-Leading-Order QCD Corrections to tt+jet Production at Hadron Colliders
Dittmaier, S.; Uwer, P.; Weinzierl, S.
2007-06-29
We report on the calculation of the next-to-leading-order QCD corrections to the production of top-quark-top-antiquark pairs in association with a hard jet at the Fermilab Tevatron and the CERN Large Hadron Collider. We present results for the tt+jet cross section and the forward-backward charge asymmetry. The corrections stabilize the leading-order prediction for the cross section. The charge asymmetry receives large corrections.
Large corrections to high-pT hadron-hadron scattering in QCD
Ellis, R. K.; Furman, M. A.; Haber, H. E.; Hinchliffe, I.
1980-10-01
We have eomputed the first non-trivial QCD corrections to the quark-quark scattering process which contributes to the production of hadrons at large p{sub T} in hadron-hadron collisions. Using quark distribution functions defined in deep inelastic scattering and fragmentation functions defined in one particle inclusive e{sup +}e{sup -} annihilation, we find that the corrections are large. This implies that QCD perturbation theory may not be reliable for large p{sub T} hadron physics.
Gao Xiangdong; Li Chongsheng; Gao Jun; Wang Jian; Oakes, Robert J.
2010-02-01
We present the calculations of the complete next-to-leading order (NLO) QCD corrections to the inclusive total cross sections for the Kaluza-Klein (KK) graviton and photon associated production process pp{yields}{gamma}G{sub KK}+X in the large extra dimensions model at the LHC. We show that the NLO QCD corrections in general enhance the total cross sections and reduce the dependence of the total cross sections on the factorization and renormalization scales. When jet veto is considered, the NLO corrections reduce the total cross sections. We also calculate some important differential cross sections for this process at NLO: the missing transverse momentum distribution, the transverse momentum distribution, and the pseudorapidity distribution of photon.
Radescu, Voica A.
2009-03-23
A new averaging method is used to combine previously published HERA-I data by the H1 and ZEUS Collaborations of neutral and charged current inclusive cross sections for e{sup {+-}}p scattering. The combination procedure takes into account the systematic error correlations in a coherent approach, leading to a significantly reduced overall cross section uncertainty. This precise combined HERA-I data set is then used as the sole input for a next-to-leading order (NLO) QCD parton distribution function (PDF) fit. The consistent treatment of systematic uncertainties in the combined data results in PDFs with greatly reduced experimental uncertainties compared to the separate analyses of the H1 and ZEUS experiments. Model uncertainties, including those arising from parametrisation dependence, are also carefully considered. The resulting HERAPDFs have impressive precision compared to the global fits.
Next-to-Leading-Order QCD Corrections to WW+Jet Production at Hadron Colliders
Dittmaier, S.; Kallweit, S.; Uwer, P.
2008-02-15
We report on the calculation of the next-to-leading-order QCD corrections to the production of W-boson pairs in association with a hard jet at the Fermilab Tevatron and CERN Large Hadron Collider, which is an important source of background for Higgs boson and new-physics searches. The corrections stabilize the leading-order prediction for the cross section considerably, in particular, if a veto against the emission of a second hard jet is applied.
Charged-Higgs-boson production at the LHC: Next-to-leading-order supersymmetric QCD corrections
Dittmaier, Stefan; Kraemer, Michael; Spira, Michael; Walser, Manuel
2011-03-01
The dominant production process for heavy charged-Higgs bosons at the LHC is the associated production with heavy quarks. We have calculated the next-to-leading-order supersymmetric QCD corrections to charged-Higgs production through the parton processes qq,gg{yields}tbH{sup {+-}} and present results for total cross sections and differential distributions. The QCD corrections reduce the renormalization and factorization scale dependence and thus stabilize the theoretical predictions. We present a comparison of the next-to-leading-order results for the inclusive cross section with a calculation based on bottom-gluon fusion gb{yields}tH{sup {+-}} and discuss the impact of the next-to-leading-order corrections on charged-Higgs searches at the LHC.
A critical appraisal of NLO+PS matching methods
NASA Astrophysics Data System (ADS)
Höche, Stefan; Krauss, Frank; Schönherr, Marek; Siegert, Frank
2012-09-01
In this publication, uncertainties in and differences between the M C@NLO and P OWHEG methods for matching next-to-leading order QCD calculations with parton showers are discussed. Implementations of both algorithms within the event generator S HERPA and based on Catani-Seymour subtraction are employed to assess the impact on a representative selection of observables. In the case of M C@NLO a substantial simplification is achieved by using dipole subtraction terms to generate the first emission. A phase space restriction is employed, which allows to vary in a transparent way the amount of non-singular radiative corrections that are exponentiated. Effects on various observables are investigated, using the production of a Higgs boson in gluon fusion, with or without an associated jet, as a benchmark process. The case of H+jet production is presented for the first time in an NLO+PS matched simulation. Uncertainties due to scale choices and non-perturbative effects are explored in the production of W ± and Z bosons in association with a jet. Corresponding results are compared to data from the Tevatron and LHC experiments.
A Critical Appraisal of NLO+PS Matching Methods
Hoeche, Stefan; Krauss, Frank; Schonherr, Marek; Siegert, Frank; /Freiburg U.
2012-03-19
In this publication, uncertainties in and differences between the MC{at}NLO and POWHEG methods for matching next-to-leading order QCD calculations with parton showers are discussed. Implementations of both algorithms within the event generator SHERPA are employed to assess the impact on a representative selection of observables. In the MC{at}NLO approach a phase space restriction has been added to subtraction and parton shower, which allows to vary in a transparent way the amount of non-singular radiative corrections that are exponentiated. Effects on various observables are investigated, using the production of a Higgs boson in gluon fusion, with or without an associated jet, as a benchmark process. The case of H+jet production is presented for the first time in an NLO+PS matched simulation. Uncertainties due to scale choices and non-perturbative effects are explored in the production of W{sup {+-}} and Z bosons in association with a jet. Corresponding results are compared to data from the Tevatron and LHC experiments.
Electroweak and QCD corrections to Higgs production via vector-boson fusion at the CERN LHC
Ciccolini, M.; Denner, A.; Dittmaier, S.
2008-01-01
The radiative corrections of the strong and electroweak interactions are calculated at next-to-leading order for Higgs-boson production in the weak-boson-fusion channel at hadron colliders. Specifically, the calculation includes all weak-boson fusion and quark-antiquark annihilation diagrams to Higgs-boson production in association with two hard jets, including all corresponding interferences. The results on the QCD corrections confirm that previously made approximations of neglecting s-channel diagrams and interferences are well suited for predictions of Higgs production with dedicated vector-boson fusion cuts at the LHC. The electroweak corrections, which also include real corrections from incoming photons and leading heavy Higgs-boson effects at two-loop order, are of the same size as the QCD corrections, viz. typically at the level of 5%-10% for a Higgs-boson mass up to {approx}700 GeV. In general, both types of corrections do not simply rescale differential distributions, but induce distortions at the level of 10%. The discussed corrections have been implemented in a flexible Monte Carlo event generator.
Two-Loop QCD correction to massive spin-2 resonance → 3 gluons
NASA Astrophysics Data System (ADS)
Ahmed, Taushif; Mahakhud, Maguni; Mathews, Prakash; Rana, Narayan; Ravindran, V.
2014-05-01
We present the virtual QCD corrections to the process h → g + g + g due to interference of born and two-loop amplitudes, where h is a massive spin-2 particle and g is the gluon. We assume that the SM fields couple to h through the SM energy momentum tensor. Our result constitutes one of the ingredients to full NNLO QCD contribution to production of a massive spin-2 particle along with a jet in the scattering process at the LHC. In particular, this massive spin-2 could be a KK mode of a ADD graviton in large extra dimensional model or a RS KK mode in warped extra dimensional model or a generic massive spin-2. In addition, it provides an opportunity to study the ultraviolet and infrared structures of QCD amplitudes involving tensorial coupling resulting from energy momentum operator. Using dimensional regularization, we find that infrared poles of this amplitude are in agreement with the proposal by Catani confirming the factorization property of QCD amplitudes with tensorial insertion.
Next-To-Leading Order QCD Corrections to pp->ttbb+X at the LHC
Bredenstein, A.; Denner, A.; Dittmaier, S.; Pozzorini, S.
2009-07-03
We report on the calculation of the full next-to-leading-order QCD corrections to the production of ttbb final states at the LHC, which deliver a serious background contribution to the production of a Higgs boson (decaying into a bb pair) in association with a tt pair. While the corrections significantly reduce the unphysical scale dependence of the leading-order cross section, our results predict an enhancement of the ttbb production cross section by a K factor of about 1.8.
QCD corrections to lifetime differences of B{sub s} mesons
Ulrich Nierste
2000-09-28
The calculation of QCD corrections to the width difference {Delta}{Lambda} in the B{sub s}meson system is presented. The next-to-leading order corrections reduce the dependence on the renormalization scale significantly and allow for a meaningful use of hadronic matrix elements from lattice gauge theory. At present the uncertainty of the lattice calculations limits the prediction of {Delta}{Lambda}. The presented work has been performed in collaboration with Martin Beneke, Gerhard Buchalla, Christoph Greub and Alexander Lenz.
SUSY-QCD corrections to scalar quark pair production in e+ e- annihilation
NASA Astrophysics Data System (ADS)
Eberl, H.; Bartl, A.; Majerotto, W.
1996-02-01
We calculate the supersymmetric O( αs) QCD corrections to the cross section e+e- → q˜ iq˜ j ( i, j = 1,2) within the Minimal Supersymmetric Standard Model. We pay particular attention to the case of the left-right squark mixing and to the renormalization of the mixing angle. The corrections due to gluino exchange turn out to be smaller than those due to gluon exchange, but they can be significant at higher energies, even for a gluino mass of a few hundred GeV.
Norniella, Olga; /Barcelona, IFAE
2005-01-01
Recent QCD measurements from the CDF collaboration at the Tevatron are presented, together with future prospects as the luminosity increases. The measured inclusive jet cross section is compared to pQCD NLO predictions. Precise measurements on jet shapes and hadronic energy flows are compared to different phenomenological models that describe gluon emissions and the underlying event in hadron-hadron interactions.
Two-loop QCD corrections to the MSSM Higgs masses beyond the effective-potential approximation
NASA Astrophysics Data System (ADS)
Degrassi, G.; Di Vita, S.; Slavich, P.
2015-02-01
We compute the two-loop QCD corrections to the neutral Higgs-boson masses in the Minimal Supersymmetric Standard Model, including the effect of non-vanishing external momenta in the self-energies. We obtain corrections of and , i.e., all two-loop corrections that involve the strong gauge coupling when the only non-vanishing Yukawa coupling is the top one. We adopt either the renormalization scheme or a mixed on-shell (OS)- scheme where the top/stop parameters are renormalized on-shell. We compare our results with those of earlier calculations, pointing out an inconsistency in a recent result obtained in the mixed OS- scheme. The numerical impact of the new corrections on the prediction for the lightest-scalar mass is moderate, but already comparable to the accuracy of the Higgs-mass measurement at the Large Hadron Collider.
NASA Astrophysics Data System (ADS)
Fleming, Sean
In this talk I review recent experimental and theoretical results in QCD. Since the topic is too vast to cover within given time constraints I choose to highlight some of the subjects that I find particularly exciting. On the experimental side I focus on measurements made at the Tevatron. Specifically jet production rates, and the cross section for B meson production. In addition I discuss an interesting measurement made by the Belle collaboration of double exclusive charmonium production. On the theory side I quickly review recent advances in computing hadronic cross sections at subleading order in perturbation theory. I then move on to soft-collinear effective theory. After a lightning review of the formalism I discuss recently published results on color-suppressed B → D decays.
Zhang Yue; Li Bohua; Li Chongsheng; Gao Jun; Zhu Huaxing
2011-05-01
We present the complete next-to-leading order (NLO) QCD predictions for the t{gamma} associated production induced by model-independent tq{gamma} and tqg flavor-changing neutral-current (FCNC) couplings at hadron colliders, respectively. We also consider the mixing effects between the tq{gamma} and tqg FCNC couplings for this process. Our results show that, for the tq{gamma} couplings, the NLO QCD corrections can enhance the total cross sections by about 50% and 40% at the Tevatron and LHC, respectively. Including the contributions from the tq{gamma}, tqg FCNC couplings and their mixing effects, the NLO QCD corrections can enhance the total cross sections by about 50% for the tu{gamma} and tug FCNC couplings, and by about 80% for the tc{gamma} and tcg FCNC couplings at the LHC, respectively. Moreover, the NLO corrections reduce the dependence of the total cross section on the renormalization and factorization scale significantly. We also evaluate the NLO corrections for several important kinematic distributions.
Next-to-leading order QCD corrections to the decay width H → Zγ
NASA Astrophysics Data System (ADS)
Bonciani, Roberto; Del Duca, Vittorio; Frellesvig, Hjalte; Henn, Johannes M.; Moriello, Francesco; Smirnov, Vladimir A.
2015-08-01
We present the analytic calculation of the two-loop QCD corrections to the decay width of a Higgs boson into a photon and a Z boson. The calculation is carried out using integration-by-parts identities for the reduction to master integrals of the scalar integrals, in terms of which we express the amplitude. The calculation of the master integrals is performed using differential equations applied to a set of functions suitably chosen to be of uniform weight. The final result is expressed in terms of logarithms and polylogarithmic functions Li2, Li3, Li4 and Li2,2.
Perturbative corrections to Λ b → Λ form factors from QCD light-cone sum rules
NASA Astrophysics Data System (ADS)
Wang, Yu-Ming; Shen, Yue-Long
2016-02-01
We compute radiative corrections to Λ b → Λ from factors, at next-to-leading logarithmic accuracy, from QCD light-cone sum rules with Λ b -baryon distribution amplitudes. Employing the diagrammatic approach factorization of the vacuum-to-Λ b -baryon correlation function is justified at leading power in Λ /m b , with the aid of the method of regions. Hard functions entering the factorization formulae are identical to the corresponding matching coefficients of heavy-to-light currents from QCD onto soft-collinear effective theory. The universal jet function from integrating out the hard-collinear fluctuations exhibits richer structures compared with the one involved in the factorization expressions of the vacuum-to- B-meson correlation function. Based upon the QCD resummation improved sum rules we observe that the perturbative corrections at {O}({α}_s) shift the Λ b → Λ from factors at large recoil significantly and the dominant contribution originates from the next-to-leading order jet function instead of the hard coefficient functions. Having at hand the sum rule predictions for the Λ b → Λ from factors we further investigate several decay observables in the electro-weak penguin Λ b → Λ ℓ + ℓ - transitions in the factorization limit (i.e., ignoring the "non-factorizable" hadronic effects which cannot be expressed in terms of the Λ b → Λ from factors), including the invariant mass distribution of the lepton pair, the forward-backward asymmetry in the dilepton system and the longitudinal polarization fraction of the leptonic sector.
Multi-jet Cross Sections at NLO with BlackHat and Sherpa
Berger, C.F.; Bern, Z.; Dixon, L.J.; Cordero, F.Febres; Forde, D.; Gleisberg, T.; Ita, H.; Kosower, D.A.; Maitre, D.
2009-05-20
In this talk, we report on a recent next-to-leading order QCD calculation of the production of a W boson in association with three jets at hadron colliders. The computation is performed by combining two programs, BlackHat for the computation of the virtual one-loop matrix elements and Sherpa for the real emission part. The addition of NLO corrections greatly reduces the factorization and renormalization scale dependence of the theory prediction for this process. This result demonstrates the applicability of unitarity-based methods for hadron collider physics.
QCD corrections to B → π form factors from light-cone sum rules
NASA Astrophysics Data System (ADS)
Wang, Yu-Ming; Shen, Yue-Long
2015-09-01
We compute perturbative corrections to B → π form factors from QCD light-cone sum rules with B-meson distribution amplitudes. Applying the method of regions we demonstrate factorization of the vacuum-to-B-meson correlation function defined with an interpolating current for pion, at one-loop level, explicitly in the heavy quark limit. The short-distance functions in the factorization formulae of the correlation function involves both hard and hard-collinear scales; and these functions can be further factorized into hard coefficients by integrating out the hard fluctuations and jet functions encoding the hard-collinear information. Resummation of large logarithms in the short-distance functions is then achieved via the standard renormalization-group approach. We further show that structures of the factorization formulae for fBπ+ (q2) and fBπ0 (q2) at large hadronic recoil from QCD light-cone sum rules match that derived in QCD factorization. In particular, we perform an exploratory phenomenological analysis of B → π form factors, paying attention to various sources of perturbative and systematic uncertainties, and extract |Vub | = (3.05-0.38+0.54|th. ± 0.09|exp.) ×10-3 with the inverse moment of the B-meson distribution amplitude ϕB+ (ω) determined by reproducing fBπ+ (q2 = 0) obtained from the light-cone sum rules with π distribution amplitudes. Furthermore, we present the invariant-mass distributions of the lepton pair for B → πℓνℓ (ℓ = μ, τ) in the whole kinematic region. Finally, we discuss non-valence Fock state contributions to the B → π form factors fBπ+ (q2) and fBπ0 (q2) in brief.
NLO Vector Boson Production With Light Jets
Bern, Z.; Diana, G.; Dixon, L.J.; Febres Cordero, F.; Forde, D.; Gleisberg, T.; Hoeche, S.; Ita, H.; Kosower, D.A.; Maitre, D.; Ozeren, K.
2012-02-15
In this contribution we present recent progress in the computation of next-to-leading order (NLO) QCD corrections for the production of an electroweak vector boson in association with jets at hadron colliders. We focus on results obtained using the virtual matrix element library BlackHat in conjunction with SHERPA, focusing on results relevant to understanding the background to top production. The production of a vector boson in association with several jets at the Large Hadron Collider (LHC) is an important background for other Standard Model processes as well as new physics signals. In particular, the production of a W boson in association with many jets is an important background for processes involving one or more top quarks. Precise predictions for the backgrounds are crucial to measurement of top-quark processes. Vector boson production in association with multiple jets is also a very important background for many SUSY searches, as it mimics the signatures of many typical decay chains. Here we will discuss how polarization information can be used as an additional handle to differentiate top pair production from 'prompt' W-boson production. More generally, ratios of observables, for example for events containing a W boson versus those containing a Z boson, are expected to be better-behaved as many uncertainties cancel in such ratios. Precise calculation of ratios, along with measurement of one of the two processes in the ratio, can be used in data-driven techniques for estimating backgrounds.
Electroweak Corrections at the LHC with MCFM
Campbell, John M.; Wackeroth, Doreen; Zhou, Jia
2015-07-10
Electroweak (EW) corrections at the LHC can be enhanced at high energies due to soft/collinear radiation of W and Z bosons, being dominated by Sudakov-like corrections in the form of $\\alpha_W^l\\log^n(Q^2/M_W^2)$ $(n \\le 2l, \\alpha_W = \\alpha/(4\\pi\\sin\\theta_W^2))$ when the energy scale $Q$ enters the TeV regime. Thus, the inclusion of EW corrections in LHC predictions is important for the search of possible signals of new physics in tails of kinematic distributions. EW corrections should also be taken into account in virtue of their comparable size ($\\mathcal{O}(\\alpha)$) to that of higher order QCD corrections ($\\mathcal{O}(\\alpha_s^2)$). We calculated the next-to-leading-order (NLO) weak corrections to the neutral-current (NC) Drell-Yan process, top-quark pair production and di-jet producion, and implemented them in the Monte-Carlo program MCFM. This enables a combined study with the corresponding NLO QCD corrections. We provide both the full NLO weak corrections and their weak Sudakov approximation valid at high energies. The latter is often used for a fast evaluation of weak effects, and having the exact result available as well allows to quantify the validity of the Sudakov approximation.
Dru Renner, Xu Feng, Karl Jansen, Marcus Petschlies
2011-08-01
We present a reliable nonperturbative calculation of the QCD correction, at leading-order in the electromagnetic coupling, to the anomalous magnetic moment of the electron, muon and tau leptons using two-flavor lattice QCD. We use multiple lattice spacings, multiple volumes and a broad range of quark masses to control the continuum, infinite-volume and chiral limits. We examine the impact of the commonly ignored disconnected diagrams and introduce a modification to the previously used method that results in a well-controlled lattice calculation. We obtain 1.513 (43) 10^-12, 5.72 (16) 10^-8 and 2.650 (54) 10^-6 for the leading-order QCD correction to the anomalous magnetic moment of the electron, muon and tau respectively, each accurate to better than 3%.
Leading QCD corrections for indirect dark matter searches: A fresh look
NASA Astrophysics Data System (ADS)
Bringmann, Torsten; Galea, Ahmad J.; Walia, Parampreet
2016-02-01
The annihilation of nonrelativistic dark matter particles at tree level can be strongly enhanced by the radiation of an additional gauge boson. This is particularly true for the helicity-suppressed annihilation of Majorana particles, like neutralinos, into fermion pairs. Surprisingly, and despite the potentially large effect due to the strong coupling, this has so far been studied in much less detail for the internal bremsstrahlung of gluons than for photons or electroweak gauge bosons. Here, we aim at bridging that gap by presenting a general analysis of neutralino annihilation into quark anti-quark pairs and a gluon, allowing e.g. for arbitrary neutralino compositions and keeping the leading quark mass dependence at all stages in the calculation. We find in some cases largely enhanced annihilation rates, especially for scenarios with squarks being close to degenerate in mass with the lightest neutralino, but also notable distortions in the associated antiproton and gamma-ray spectra. Both effects significantly impact limits from indirect searches for dark matter and are thus important to be taken into account in, e.g., global scans. For extensive scans, on the other hand, full calculations of QCD corrections are numerically typically too expensive to perform for each point in parameter space. We present here for the first time an efficient, numerically fast implementation of QCD corrections, extendable in a straightforward way to nonsupersymmetric models, which avoids computationally demanding full one-loop calculations or event generator runs and yet fully captures the leading effects relevant for indirect dark matter searches. In this context, we also present updated constraints on dark matter annihilation from cosmic-ray antiproton data. Finally, we comment on the impact of our results on relic density calculations.
Electroweak corrections and Bloch-Nordsieck violations in 2-to-2 processes at the LHC
NASA Astrophysics Data System (ADS)
Stirling, W. J.; Vryonidou, E.
2013-04-01
We consider the effect of next-to-leading order (NLO) electroweak corrections to Standard Model 2 → 2 processes, taking into account the potentially large double logarithms originating from both real and virtual corrections. A study of the leading Sudakov logarithms is presented and Bloch-Nordsieck (BN) violations are discussed for processes at the CERN Large Hadron Collider. In particular, we focus on the processes Z/γ+jet and also the ratio of Z to γ production. This ratio is known to be insensitive to NLO QCD corrections but this is not expected to be the case for the electroweak corrections. We also comment on the effect of electroweak corrections and the presence of BN violation for QCD processes, in particular dijet production, and also for purely electroweak processes such as W + H and W + Z associated production.
Up and Down Quark Masses and Corrections to Dashen's Theorem from Lattice QCD and Quenched QED.
Fodor, Z; Hoelbling, C; Krieg, S; Lellouch, L; Lippert, Th; Portelli, A; Sastre, A; Szabo, K K; Varnhorst, L
2016-08-19
In a previous Letter [Borsanyi et al., Phys. Rev. Lett. 111, 252001 (2013)] we determined the isospin mass splittings of the baryon octet from a lattice calculation based on N_{f}=2+1 QCD simulations to which QED effects have been added in a partially quenched setup. Using the same data we determine here the corrections to Dashen's theorem and the individual up and down quark masses. Our ensembles include 5 lattice spacings down to 0.054 fm, lattice sizes up to 6 fm, and average up-down quark masses all the way down to their physical value. For the parameter which quantifies violations to Dashen's theorem, we obtain ϵ=0.73(2)(5)(17), where the first error is statistical, the second is systematic, and the third is an estimate of the QED quenching error. For the light quark masses we obtain, m_{u}=2.27(6)(5)(4) and m_{d}=4.67(6)(5)(4) MeV in the modified minimal subtraction scheme at 2 GeV and the isospin breaking ratios m_{u}/m_{d}=0.485(11)(8)(14), R=38.2(1.1)(0.8)(1.4), and Q=23.4(0.4)(0.3)(0.4). Our results exclude the m_{u}=0 solution to the strong CP problem by more than 24 standard deviations. PMID:27588847
Up and Down Quark Masses and Corrections to Dashen's Theorem from Lattice QCD and Quenched QED
NASA Astrophysics Data System (ADS)
Fodor, Z.; Hoelbling, C.; Krieg, S.; Lellouch, L.; Lippert, Th.; Portelli, A.; Sastre, A.; Szabo, K. K.; Varnhorst, L.; Budapest-Marseille-Wuppertal Collaboration
2016-08-01
In a previous Letter [Borsanyi et al., Phys. Rev. Lett. 111, 252001 (2013)] we determined the isospin mass splittings of the baryon octet from a lattice calculation based on Nf=2 +1 QCD simulations to which QED effects have been added in a partially quenched setup. Using the same data we determine here the corrections to Dashen's theorem and the individual up and down quark masses. Our ensembles include 5 lattice spacings down to 0.054 fm, lattice sizes up to 6 fm, and average up-down quark masses all the way down to their physical value. For the parameter which quantifies violations to Dashen's theorem, we obtain ɛ =0.73 (2 )(5 )(17 ), where the first error is statistical, the second is systematic, and the third is an estimate of the QED quenching error. For the light quark masses we obtain, mu=2.27 (6 )(5 )(4 ) and md=4.67 (6 )(5 )(4 ) MeV in the modified minimal subtraction scheme at 2 G e V and the isospin breaking ratios mu/md=0.485 (11 )(8 )(14 ), R =38.2 (1.1 )(0.8 )(1.4 ), and Q =23.4 (0.4 )(0.3 )(0.4 ). Our results exclude the mu=0 solution to the strong C P problem by more than 24 standard deviations.
Matching next-to-leading order predictions to parton showers in supersymmetric QCD
Degrande, Céline; Fuks, Benjamin; Hirschi, Valentin; Proudom, Josselin; Shao, Hua-Sheng
2016-02-03
We present a fully automated framework based on the FeynRules and MadGraph5_aMC@NLO programs that allows for accurate simulations of supersymmetric QCD processes at the LHC. Starting directly from a model Lagrangian that features squark and gluino interactions, event generation is achieved at the next-to-leading order in QCD, matching short-distance events to parton showers and including the subsequent decay of the produced supersymmetric particles. As an application, we study the impact of higher-order corrections in gluino pair-production in a simplified benchmark scenario inspired by current gluino LHC searches.
Single-inclusive production of hadrons and jets in lepton-nucleon scattering at NLO
NASA Astrophysics Data System (ADS)
Hinderer, Patriz; Schlegel, Marc; Vogelsang, Werner
2015-07-01
We present next-to-leading order (NLO) perturbative-QCD calculations of the cross sections for ℓN →h X and ℓN →jet X . The main feature of these processes is that the scattered lepton is not observed, so that the hard scale that makes them perturbative is set by the transverse momentum of the hadron or jet. Kinematically, the two processes thus become direct analogs of single-inclusive production in hadronic collisions which, as has been pointed out in the literature, makes them promising tools for exploring transverse spin phenomena in QCD when the incident nucleon is transversely polarized. We find that the NLO corrections are sizable for the spin-averaged cross section. We also investigate in how far the scattering is dominated by the exchange of almost real (Weizsäcker-Williams) photons. We present numerical estimates of the cross sections for present-day fixed target experiments and for a possible future electron-ion collider.
Xiao Zhenjun; Zhang Zhiqing; Liu Xin; Guo Libo
2008-12-01
We calculate the branching ratios and CP-violating asymmetries of the four B{yields}K{eta}{sup (')} decays in the perturbative QCD (pQCD) factorization approach. Besides the full leading-order contributions, the partial next-to-leading-order (NLO) contributions from the QCD vertex corrections, the quark-loops, and the chromomagnetic penguins are also taken into account. The NLO pQCD predictions for the CP-averaged branching ratios are Br(B{sup +}{yields}K{sup +}{eta}){approx_equal}3.2x10{sup -6}, Br(B{sup {+-}}{yields}K{sup {+-}}{eta}{sup '}){approx_equal}51.0x10{sup -6}, Br(B{sup 0}{yields}K{sup 0}{eta}){approx_equal}2.1x10{sup -6}, and Br(B{sup 0}{yields}K{sup 0}{eta}{sup '}){approx_equal}50.3x10{sup -6}. The NLO contributions can provide a 70% enhancement to the LO Br(B{yields}K{eta}{sup '}), but a 30% reduction to the LO Br(B{yields}K{eta}), which play the key role in understanding the observed pattern of branching ratios. The NLO pQCD predictions for the CP-violating asymmetries, such as A{sub CP}{sup dir}(K{sub S}{sup 0}{eta}{sup '}){approx}2.3% and A{sub CP}{sup mix}(K{sub S}{sup 0}{eta}{sup '}){approx}63%, agree very well with currently available data. This means that the deviation {delta}S=A{sub CP}{sup mix}(K{sub S}{sup 0}{eta}{sup '})-sin2{beta} in pQCD approach is also very small.
NASA Astrophysics Data System (ADS)
Goldman, Jesse Matthew
This dissertation details the results of a NLO QCD analysis of overlinenoverline Fe and overlinenoverline Fe scattering at the Fermilab Tevatron. Recently an increasing number of measurements by a variety of experiments have led to a good understanding of the partonic contents of the nucleon. Accurate parameterisations of these contents and the fact that neutrino Deep Inelastic Scattering is an ideal probe of the nucleus allow for a unique understanding of QCD and related phenomena in the kinematic region for which Q2 > 5 GeV 2 and 0.1 < x < 0.7. Perturbative QCD and such non-perturbative effects as the EMC correction, the longitudinal structure function, RL, and higher twist corrections are studied and χ2 comparisons are made with the NuTeV charged current data sample. These comparisons indicate that a NLO perturbative QCD) model combined with the EMC correction and higher twist best agrees with the NuTeV data. Using this resultant model and altering the cuts to include all data for which 0.003 < x < 0.7 leads to a NLO measurement of the strange sea level, κ. Combining this result with the measurement of κ from the NuTeV dimuon analysis leads to limits on the Cabbibo-Kobayashi-Masakawa matrix element, Vcs, which are consistent with currently accepted values.
NASA Astrophysics Data System (ADS)
Balossini, Giovanni; Montagna, Guido; Carloni Calame, Carlo Michel; Moretti, Mauro; Nicrosini, Oreste; Piccinini, Fulvio; Treccani, Michele; Vicini, Alessandro
2010-01-01
Precision studies of the production of a high-transverse momentum lepton in association with missing energy at hadron colliders require that electroweak and QCD higher-order contributions are simultaneously taken into account in theoretical predictions and data analysis. Here we present a detailed phenomenological study of the impact of electroweak and strong contributions, as well as of their combination, to all the observables relevant for the various facets of the pmathop {p}limits^{left( - right)} to {text{lepton}} + X physics programme at hadron colliders, including luminosity monitoring and Parton Distribution Functions constraint, W precision physics and search for new physics signals. We provide a theoretical recipe to carefully combine electroweak and strong corrections, that are mandatory in view of the challenging experimental accuracy already reached at the Fermilab Tevatron and aimed at the CERN LHC, and discuss the uncertainty inherent the combination. We conclude that the theoretical accuracy of our calculation can be conservatively estimated to be about 2% for standard event selections at the Tevatron and the LHC, and about 5% in the very high W transverse mass/lepton transverse momentum tails. We also provide arguments for a more aggressive error estimate (about 1% and 3%, respectively) and conclude that in order to attain a one per cent accuracy: 1) exact mixed mathcal{O}left( {α {α_s}} right) corrections should be computed in addition to the already available NNLO QCD contributions and two-loop electroweak Sudakov logarithms; 2) QCD and electroweak corrections should be coherently included into a single event generator.
The SM and NLO Multileg Working Group: Summary Report
Andersen, J.R.; Archibald, J.; Badger, S.; Ball, R.D.; Bevilacqua, G.; Bierenbaum, I.; Binoth, T.; Boudjema, F.; Boughezal, R.; Bredenstein, A.; Britto, R.; Campanelli, M.; Campbell, J.; Carminati, L.; Chachamis, G.; Ciulli, V.; Cullen, G.; Czakon, M.; Del Debbio, L.; Denner, A.; Dissertori, G.; /Edinburgh U. /Zurich, ETH /Michigan State U. /CAFPE, Granada /CERN /Durham U., IPPP /DESY, Zeuthen /Democritos Nucl. Res. Ctr. /Valencia U., IFIC /Annecy, LAPTH /Zurich U. /KEK, Tsukuba /Saclay, SPhT /University Coll. London /Fermilab /INFN, Milan /Milan U. /PSI, Villigen /Florence U. /INFN, Florence /RWTH Aachen U.
2012-04-10
and added to in 2007. This list includes cross sections which are experimentally important, and which are theoretically feasible (if difficult) to calculate. Basically all 2-3 cross sections of interest have been calculated, with the frontier now extending to 2 {yields} 4 calculations. Often these calculations exist only as private codes. Since 2007, two additional calculations have been completed: t{bar t}b{bar b} and W+3 jets, reflecting the advance of the NLO technology to 2 {yields} 4 processes. In addition, the cross section for b{bar b}b{bar b} has been calculated for the q{bar q} initial state with the gg initial state calculation in progress. Final states of such complexity usually lead to multi-scale problems, and the correct choice of scales to use can be problematic not only at LO, but also at NLO. The size of the higher order corrections and of the residual scale dependence at NLOcan depend strongly on whether the considered cross section is inclusive, or whether a jet veto cut has been applied. Depending on the process, dramatically different behavior can be observed upon the application of a jet veto. There is a trade-off between suppressing the NLO cross section and increasing the perturbative uncertainty, with application of a jet veto sometimes destroying the cancellation between infra-red logs of real and virtual origin, and sometimes just suppressing large (and very scale-sensitive) tree-level contributions. So far, there is no general rule predicting the type of behavior to be expected, but this is an important matter for further investigation. From the experimental side, an addition to the above wish-list that will be crucial is the determination of the accuracy to which each of the calculations needs to be known. This is clearly related to the experimental accuracy at which the cross sections can be measured at the LHC, and can determine, for example, for what processes it may be necessary to calculate electo-weak corrections, in addition to the
Next-to-leading order QCD factorization for semi-inclusive deep inelastic scattering at twist 4.
Kang, Zhong-Bo; Wang, Enke; Wang, Xin-Nian; Xing, Hongxi
2014-03-14
Within the framework of a high-twist approach, we calculate the next-to-leading order (NLO) perturbative QCD corrections to the transverse momentum broadening in semi-inclusive hadron production in deeply inelastic e+A collisions, as well as lepton pair production in p+A collisions. With explicit calculations of both real and virtual contributions, we verify, for the first time, the factorization theorem at twist 4 in NLO for the nuclear-enhanced transverse momentum weighted differential cross section and demonstrate the universality of the associated twist-4 quark-gluon correlation function. We also identify the QCD evolution equation for the twist-4 quark-gluon correlation function in a large nucleus, which can be solved to determine the scale dependence of the jet transport parameter in the study of jet quenching. PMID:24679281
Next-to-Leading Order QCD Factorization for Semi-Inclusive Deep Inelastic Scattering at Twist 4
NASA Astrophysics Data System (ADS)
Kang, Zhong-Bo; Wang, Enke; Wang, Xin-Nian; Xing, Hongxi
2014-03-01
Within the framework of a high-twist approach, we calculate the next-to-leading order (NLO) perturbative QCD corrections to the transverse momentum broadening in semi-inclusive hadron production in deeply inelastic e +A collisions, as well as lepton pair production in p +A collisions. With explicit calculations of both real and virtual contributions, we verify, for the first time, the factorization theorem at twist 4 in NLO for the nuclear-enhanced transverse momentum weighted differential cross section and demonstrate the universality of the associated twist-4 quark-gluon correlation function. We also identify the QCD evolution equation for the twist-4 quark-gluon correlation function in a large nucleus, which can be solved to determine the scale dependence of the jet transport parameter in the study of jet quenching.
Zykunov, V. A.
2010-07-15
With an eye to future experiments at the Large Hadron Collider (LHC), O(aa{sub s}) QCD corrections to the Drell-Yan process are calculated for vertex functions and gluon bremsstrahlung. Use is made of fully differential cross sections, so that the result obtained in the present study can readily be applied in analyzing experimental data (in correcting data from future experiments at LHC). It is shown both analytically and numerically that the results are independent of unphysical parameters, including the parameter separating the regions of soft and hard gluons and the quark mass. A numerical analysis of radiative effects was performed by means of the FORTRAN code READY with allowance for the experimental cuts used at the Compact Muon Solenoid (CMS) detector
High-Energy QCD Asymptotics of Photon--Photon Collisions
Brodsky, Stanley J.
2002-07-26
The high-energy behavior of the total cross section for highly virtual photons, as predicted by the BFKL equation at next-to-leading order (NLO) in QCD, is discussed. The NLO BFKL predictions, improved by the BLM optimal scale setting, are in good agreement with recent OPAL and L3 data at CERN LEP2. NLO BFKL predictions for future linear colliders are presented.
Next-to-Leading Order QCD Corrections to Three-Jet Cross Sections with Massive Quarks
Bernreuther, W.; Brandenburg, A.; Uwer, P.
1997-07-01
We calculate the cross section for e{sup +}e{sup {minus}} annihilation into three jets for massive quarks at next-to-leading order in perturbative QCD, both on and off the Z resonance. Our computation allows the implementation of any jet clustering algorithm. We give results for the three-jet cross section involving b quarks for the JADE and Durham algorithms at c.m.energies {radical}(s)=m{sub Z} . We also discuss a three-jet observable that is sensitive to the mass of the b quark. {copyright} {ital 1997} {ital The American Physical Society}
Next-to-leading order QCD predictions for the hadronic WH+jet production
Su Jijuan; Ma Wengan; Zhang Renyou; Guo Lei
2010-06-01
We calculate the next-to-leading order (NLO) QCD corrections to the WH{sup 0} production in association with a jet at hadron colliders. We study the impacts of the complete NLO QCD radiative corrections to the integrated cross sections, the scale dependence of the cross sections, and the differential cross sections ((d{sigma}/dcos{theta}), (d{sigma}/dp{sub T})) of the final W-, Higgs boson and jet. We find that the corrections significantly modify the physical observables, and reduce the scale uncertainty of the leading-order cross section. Our results show that by applying the inclusive scheme with p{sub T,j}{sup cut}=20 GeV and taking m{sub H}=120 GeV, {mu}={mu}{sub 0{identical_to}}(1/2)(m{sub W}+m{sub H}), the K-factor is 1.15 for the process pp{yields}W{sup {+-}H0}j+X at the Tevatron, while the K-factors for the processes pp{yields}W{sup -}H{sup 0}j+X and pp{yields}W{sup +}H{sup 0}j+X at the LHC are 1.12 and 1.08, respectively. We conclude that to understand the hadronic associated WH{sup 0} production, it is necessary to study the NLO QCD corrections to the WH{sup 0}j production process which is part of the inclusive WH{sup 0} production.
Gorishny, S.G.; Kataev, A.L.; Larin, S.A.; Surgaladze, L.R. )
1990-12-30
Analytical results of a re-evaluation of the massless three-loop next-to-leading OCD correction to the correlator of the quark scalar currents and {Gamma}{sub tot} (H{sup 0} {yields} hadrons) are presented. The states of some other QCD perturbative results is discussed.
Foundations of Perturbative QCD
NASA Astrophysics Data System (ADS)
Collins, John
2011-04-01
1. Introduction; 2. Why QCD?; 3. Basics of QCD; 4. Infra-red safety and non-safety; 5. Libby-Sterman analysis and power counting; 6. Parton model to parton theory I; 7. Parton model to parton theory II; 8. Factorization; 9. Corrections to the parton model in QCD; 10. Factorization and subtractions; 11. DIS in QCD; 12. Fragmentation; 13. TMD factorization; 14. Hadron-hadron collisions; 15. More advanced topics; Appendices; References; Index.
Foundations of Perturbative QCD
NASA Astrophysics Data System (ADS)
Collins, John
2013-11-01
1. Introduction; 2. Why QCD?; 3. Basics of QCD; 4. Infra-red safety and non-safety; 5. Libby-Sterman analysis and power counting; 6. Parton model to parton theory I; 7. Parton model to parton theory II; 8. Factorization; 9. Corrections to the parton model in QCD; 10. Factorization and subtractions; 11. DIS in QCD; 12. Fragmentation; 13. TMD factorization; 14. Hadron-hadron collisions; 15. More advanced topics; Appendices; References; Index.
Berger, C.F.; Bern, Z.; Dixon, L.J.; Cordero, F.Febres; Forde, D.; Gleisberg, T.; Ita, H.; Kosower, D.A.; Maitre, D.; /Durham U.
2010-02-15
We present several results obtained using the BLACKHAT next-to-leading order QCD program library, in conjunction with SHERPA. In particular, we present distributions for vector boson plus 1,2,3-jet production at the Tevatron and at the asymptotic running energy of the Large Hadron Collider, including new Z + 3-jet distributions. The Z + 2-jet predictions for the second-jet P{sub T} distribution are compared to CDF data. We present the jet-emission probability at NLO in W + 2-jet events at the LHC, where the tagging jets are taken to be the ones furthest apart in pseudorapidity. We analyze further the large left-handed W{sup {+-}} polarization, identified in our previous study, for W bosons produced at high P{sub T} at the LHC.
Transport Processes in High Temperature QCD Plasmas
NASA Astrophysics Data System (ADS)
Hong, Juhee
The transport properties of high temperature QCD plasmas can be described by kinetic theory based on the Boltzmann equation. At a leading-log approximation, the Boltzmann equation is reformulated as a Fokker-Planck equation. First, we compute the spectral densities of
NASA Astrophysics Data System (ADS)
Borowka, S.; Hahn, T.; Heinemeyer, S.; Heinrich, G.; Hollik, W.
2015-09-01
Reaching a theoretical accuracy in the prediction of the lightest MSSM Higgs-boson mass, , at the level of the current experimental precision requires the inclusion of momentum-dependent contributions at the two-loop level. Recently two groups presented the two-loop QCD momentum-dependent corrections to (Borowka et al., Eur Phys J C 74(8):2994, 2014; Degrassi et al., Eur Phys J C 75(2):61, 2015), using a hybrid on-shell- scheme, with apparently different results. We show that the differences can be traced back to a different renormalization of the top-quark mass, and that the claim in Ref. Degrassi et al. (Eur Phys J C 75(2):61, 2015) of an inconsistency in Ref. Borowka et al. (Eur Phys J C 74(8):2994, 2014) is incorrect. We furthermore compare consistently the results for obtained with the top-quark mass renormalized on-shell and . The latter calculation has been added to the FeynHiggs package and can be used to estimate missing higher-order corrections beyond the two-loop level.
Precise QCD Predictions for the Production of a Z Boson in Association with a Hadronic Jet.
Gehrmann-De Ridder, A; Gehrmann, T; Glover, E W N; Huss, A; Morgan, T A
2016-07-01
We compute the cross section and differential distributions for the production of a Z boson in association with a hadronic jet to next-to-next-to-leading order (NNLO) in perturbative QCD, including the leptonic decay of the Z boson. We present numerical results for the transverse momentum and rapidity distributions of both the Z boson and the associated jet at the LHC. We find that the NNLO corrections increase the NLO predictions by approximately 1% and significantly reduce the scale variation uncertainty. PMID:27447500
Precise QCD Predictions for the Production of a Z Boson in Association with a Hadronic Jet
NASA Astrophysics Data System (ADS)
Gehrmann-De Ridder, A.; Gehrmann, T.; Glover, E. W. N.; Huss, A.; Morgan, T. A.
2016-07-01
We compute the cross section and differential distributions for the production of a Z boson in association with a hadronic jet to next-to-next-to-leading order (NNLO) in perturbative QCD, including the leptonic decay of the Z boson. We present numerical results for the transverse momentum and rapidity distributions of both the Z boson and the associated jet at the LHC. We find that the NNLO corrections increase the NLO predictions by approximately 1% and significantly reduce the scale variation uncertainty.
Short path length pQCD corrections to energy loss in the quark gluon plasma
NASA Astrophysics Data System (ADS)
Kolbe, Isobel; Horowitz, W. A.
2016-01-01
The twin identifications of high-pT enhancement and low-pT collective behaviour in the shockingly small systems of interacting particles created in pA collisions calls for a detailed theoretical energy loss analysis. We study the way in which energy is dissipated in the QGP created in pA collisions by calculating the short path length corrections to the DGLV energy loss formulae that have produced excellent predictions for AA collisions. We find that, shockingly, because of the large formation time assumption (used in the DGLV calculation), a highly non-trivial cancellation of correction terms results in a null short path length correction to the DGLV energy loss formula. We investigate the effect of relaxing the large formation time assumption in the final stages of the calculation and find, because of the separation distance between production and scattering centre is integrated over from 0 to ∞, ≳ 100% corrections, even in the large path length approximation employed by DGLV.
QCD measurements at the Tevatron
Bandurin, Dmitry; /Florida State U.
2011-12-01
Selected quantum chromodynamics (QCD) measurements performed at the Fermilab Run II Tevatron p{bar p} collider running at {radical}s = 1.96 TeV by CDF and D0 Collaborations are presented. The inclusive jet, dijet production and three-jet cross section measurements are used to test perturbative QCD calculations, constrain parton distribution function (PDF) determinations, and extract a precise value of the strong coupling constant, {alpha}{sub s}(m{sub Z}) = 0.1161{sub -0.0048}{sup +0.0041}. Inclusive photon production cross-section measurements reveal an inability of next-to-leading-order (NLO) perturbative QCD (pQCD) calculations to describe low-energy photons arising directly in the hard scatter. The diphoton production cross-sections check the validity of the NLO pQCD predictions, soft-gluon resummation methods implemented in theoretical calculations, and contributions from the parton-to-photon fragmentation diagrams. Events with W/Z+jets productions are used to measure many kinematic distributions allowing extensive tests and tunes of predictions from pQCD NLO and Monte-Carlo (MC) event generators. The charged-particle transverse momenta (p{sub T}) and multiplicity distributions in the inclusive minimum bias events are used to tune non-perturbative QCD models, including those describing the multiple parton interactions (MPI). Events with inclusive production of {gamma} and 2 or 3 jets are used to study increasingly important MPI phenomenon at high p{sub T}, measure an effective interaction cross section, {sigma}{sub eff} = 16.4 {+-} 2.3 mb, and limit existing MPI models.
NLO thermal dilepton rate at non-zero momentum
NASA Astrophysics Data System (ADS)
Laine, M.
2013-11-01
The vector channel spectral function and the dilepton production rate from a QCD plasma at a temperature above a few hundred MeV are evaluated up to next-to-leading order (NLO) including their dependence on a non-zero momentum with respect to the heat bath. The invariant mass of the virtual photon is taken to be in the range ~ ( πT)2 ~ (1GeV)2, generalizing previous NLO results valid for ≫ ( πT)2. In the opposite regime 0 < ≪ ( πT)2 the loop expansion breaks down, but agrees nevertheless in order of magnitude with a previous result obtained through resummations. Ways to test the vector spectral function through comparisons with imaginary-time correlators measured on the lattice are discussed.
NLO evolution of color dipoles in N=4 SYM
Balitsky, Ian; Chirilli, Giovanni
2009-01-01
High-energy behavior of amplitudes in a gauge theory can be reformulated in terms of the evolution of Wilson-line operators. In the leading logarithmic approximation it is given by the conformally invariant BK equation for the evolution of color dipoles. In QCD, the next-to-leading order BK equation has both conformal and non-conformal parts, the latter providing the running of the coupling constant. To separate the conformally invariant effects from the running-coupling effects, we calculate the NLO evolution of the color dipoles in the conformal ${\\cal N}$=4 SYM theory. We define the ``composite dipole operator' with the rapidity cutoff preserving conformal invariance. The resulting M\\"obius invariant kernel agrees with the forward NLO BFKL calculation of Ref. 1
Dimension Six Correction to the Vector Sector of AdS/QCD Model
Hovhannes Grigoryan
2007-09-06
We study the effect of dimension six term F^3 on the predictions of the holographic model for the vector meson form factor. It is shown that the dimensionless parameter with which this term enters the action determines the corrections to the electric radius, magnetic and quadrupole moments of the rho meson. The results suggest that the addition of higher order terms may improve the holographic model.
Next-to-next-to-leading order QCD corrections in models of TeV-scale gravity
NASA Astrophysics Data System (ADS)
de Florian, Daniel; Mahakhud, Maguni; Mathews, Prakash; Mazzitelli, Javier; Ravindran, V.
2014-04-01
We compute the next-to-next-to-leading order QCD corrections to the graviton production in models of TeV-scale gravity, within the soft-virtual approximation. For the Arkani-Hamed, Dimopoulos and Dvali (ADD) model we evaluate the contribu-tion to the Drell-Yan cross section, and we present distributions for the di-lepton invariant mass at the LHC with a center-of-mass energy = 14 TeV. We find a large K factor ( K ≃ 1 .8) for large values of invariant mass, which is the region where the ADD graviton contribution dominates the cross section. The increase in the cross section with respect to the previous order result is larger than 10% in the same invariant mass region. We also observe a substantial reduction in the scale uncertainty. For the Randall-Sundrum (RS) model we computed the total single graviton production cross section at the LHC. We find an increase between 10% and 13% with respect to the next-to-leading order prediction, depending on the model parameters. We provide an analytic expression for the NNLO K factor as a function of the lightest RS graviton mass.
On the precision of the computation of the QCD corrections to electroweak vacuum polarizations
NASA Astrophysics Data System (ADS)
Gonzalez-Garcia, M. C.; Halzen, F.; Vázquez, R. A.
1994-02-01
We demonstrate that the dispersive computation of the threshold enhancements to heavy quark vacuum polarizations is unstable. Because of the slow convergence of the dispersion relations the result critically depends on the intermediate energy region where the non-relativistic approximation, intrinsic to threshold calculations, is invalid. We discuss other ambiguities precluding a reliable calculation of the threshold contribution to the vacuum polarizations. In the absence of a solution prudence should force one to assign an error to the radiative corrections not far below the level of the perturbative O( ααs) contributions. This may preclude the extraction of the Higgs mass from precision measurements.
NLO evolution of color dipoles in N=4 SYM
Chirilli, Giovanni A.; Balitsky, Ian
2009-07-04
Here, high-energy behavior of amplitudes in a gauge theory can be reformulated in terms of the evolution of Wilson-line operators. In the leading logarithmic approximation it is given by the conformally invariant BK equation for the evolution of color dipoles. In QCD, the next-to-leading order BK equation has both conformal and non-conformal parts, the latter providing the running of the coupling constant. To separate the conformally invariant effects from the running-coupling effects, we calculate the NLO evolution of the color dipoles in the conformal ${\\cal N}$=4 SYM theory. We define the "composite dipole operator" with the rapidity cutoff preserving conformal invariance.
Gluonic Spin Contribution to Proton Spin at NLO
Casey, Andrew
2011-05-24
In 1988, when the EMC results showed that the quarks had a much smaller contribution to the spin of the proton than previously thought, the 'Proton Spin Crisis' began. Since then, considerable effort has been directed into discovering the main contributors to proton spin and how much each contributes. One such contributor is the gluonic spin component. QCD NLO evolution equations are combined with boundary conditions obtained from heavy quark decoupling expressions to evolve the equations from infinity to the mass of the charm quark in order to determine the gluonic spin contribution.
Zykunov, V. A.
2011-01-15
The contributions of inverse gluon emission to the lowest order QCD corrections to the Drell-Yan process for future experiments at LHC are calculated. The use of fully differential cross sections makes it possible to apply readily the results of these calculations for experimental purposes (in correcting data from future experiments at LHC). It is shown analytically that the present results are independent of the quark mass. A numerical analysis of respective radiative effects is performed by means of the READY FORTRAN code with allowance for the experimental cuts used at the Compact Muon Solenoid (CMS) detector.
tt¯+large missing energy from top-quark partners: A comprehensive study at next-to-leading order QCD
NASA Astrophysics Data System (ADS)
Boughezal, Radja; Schulze, Markus
2013-12-01
We perform a detailed study of top-quark partner production in the tt¯ plus large missing energy final state at the LHC, presenting results for both scalar and fermionic top-quark partners in the semileptonic and dileptonic decay modes of the top quarks. We compare the results of several simulation tools: leading order matrix elements, next-to-leading order (NLO) matrix elements, leading order plus parton shower simulations, and merged samples that contain the signal process with an additional hard jet radiated. We find that predictions from leading order plus parton shower simulations can significantly deviate from NLO QCD or LO merged samples and do not correctly model the kinematics of the tt¯+ET,miss signature. They are therefore not a good framework for modeling this new physics signature. On the other hand, the acceptances obtained with a merged sample of the leading-order process together with the radiation of an additional hard jet are in agreement with the NLO predictions. We also demonstrate that the scale variation of the inclusive cross section, plus that of the acceptance, does not accurately reflect the uncertainty of the cross section after cuts, which is typically larger. We show the importance of including higher-order QCD corrections when using kinematic distributions to determine the spin of the top-quark partner.
NASA Astrophysics Data System (ADS)
Anitha, K.; Balachandran, V.
2015-07-01
Vibrational spectral analysis and quantum chemical computations based on density functional theory have been performed on the N-(2-cyanoethyl)-N-butylaniline. The geometry, structural properties, intermolecular hydrogen bond, and harmonic vibrational frequencies of the title molecule have been investigated with the help of DFT (B3LYP) and LC-DFT (CAM-B3LYP) method. Molecular electrostatic potential (MEP) have been performed. The various intramolecular interactions have been exposed by natural bond orbital analysis. The distribution of atomic charges and bending of natural hybrid orbitals also reflect the presence of intramolecular hydrogen bonding. Global reactivity and local reactivity descriptors of the title molecule have been calculated. The analysis of the electron density of HOMO and LUMO gives an idea of the delocalization and low value of energy gap indicated the electron transport in the molecule and thereby NLO activity. The effect of solvent on second-order NLO properties has been studied using polarized continuum model (PCM) in the tetrahydrofuran (THF) solution. The solvent leads to a slight enhancement of the NLO responses for the studied complexes relevant to their NLO responses in gas phase. The electronic absorption spectra were investigated by the TDDFT methods. The frequency-dependent first hyperpolarizabilities of the N-(2-cyanoethyl)-N-butylaniline were also evaluated. The 1H and 13C NMR chemical shifts have been calculated by gauge-indepedent atomic orbital (GIAO) method with B3LYP/6-311++G(d, p) approach.
Wγ production in hadronic collisions using the POWHEG+MiNLO method
NASA Astrophysics Data System (ADS)
Barzè, Luca; Chiesa, Mauro; Montagna, Guido; Nason, Paolo; Nicrosini, Oreste; Piccinini, Fulvio; Prosperi, Valeria
2014-12-01
We detail a calculation of W γ production in hadronic collision, at Next-to- Leading Order (NLO) QCD interfaced to a shower generator according to the POWHEG prescription supplemented with the MiNLO procedure. The fixed order result is matched to an interleaved QCD+QED parton shower, in such a way that the contribution arising from hadron fragmentation into photons is fully modeled. In general, our calculation illustrates a new approach to the fully exclusive simulation of prompt photon production processes accurate at the NLO level in QCD. We compare our predictions to those of the NLO program MCFM, which treats the fragmentation contribution in terms of a photon fragmentation functions. We also perform comparisons to available LHC data at 7 TeV, for which we observe good agreement, and provide phenomenological results for physics studies of the W γ production process at the Run II of the LHC. The new tool, which includes W leptonic decays and the contribution of anomalous gauge couplings, allows a fully exclusive, hadron-level description of the W γ process, and is publicly available at the repository of the POWHEG BOX. Our approach can be easily adapted to deal with other relevant isolated photon production processes in hadronic collisions.
Spin polarisation of tt¯γγ production at NLO+PS with GoSam interfaced to MadGraph5_aMC@NLO
van Deurzen, Hans; Frederix, Rikkert; Hirschi, Valentin; Luisoni, Gionata; Mastrolia, Pierpaolo; Ossola, Giovanni
2016-04-22
Here, we present an interface between the multipurpose Monte Carlo tool MadGraph5_aMC@NLO and the automated amplitude generator GoSam. As a first application of this novel framework, we compute the NLO corrections to pp→ tt¯H and pp→ tt¯γγ matched to a parton shower. In the phenomenological analyses of these processes, we focus our attention on observables which are sensitive to the polarisation of the top quarks.
NASA Astrophysics Data System (ADS)
Sun, Junfeng; Chang, Qin; Hu, Xiaohui; Yang, Yueling
2015-04-01
In this paper, we investigate the contributions of hard spectator scattering and annihilation in B → PV decays within the QCD factorization framework. With available experimental data on B → πK* , ρK , πρ and Kϕ decays, comprehensive χ2 analyses of the parameters XA,Hi,f (ρA,Hi,f, ϕA,Hi,f) are performed, where XAf (XAi) and XH are used to parameterize the endpoint divergences of the (non)factorizable annihilation and hard spectator scattering amplitudes, respectively. Based on χ2 analyses, it is observed that (1) The topology-dependent parameterization scheme is feasible for B → PV decays; (2) At the current accuracy of experimental measurements and theoretical evaluations, XH = XAi is allowed by B → PV decays, but XH ≠ XAf at 68% C.L.; (3) With the simplification XH = XAi, parameters XAf and XAi should be treated individually. The above-described findings are very similar to those obtained from B → PP decays. Numerically, for B → PV decays, we obtain (ρA,Hi ,ϕA,Hi [ ° ]) = (2.87-1.95+0.66 , -145-21+14) and (ρAf, ϕAf [ ° ]) = (0.91-0.13+0.12 , -37-9+10) at 68% C.L. With the best-fit values, most of the theoretical results are in good agreement with the experimental data within errors. However, significant corrections to the color-suppressed tree amplitude α2 related to a large ρH result in the wrong sign for ACPdir (B- →π0K*-) compared with the most recent BABAR data, which presents a new obstacle in solving "ππ" and "πK" puzzles through α2. A crosscheck with measurements at Belle (or Belle II) and LHCb, which offer higher precision, is urgently expected to confirm or refute such possible mismatch.
Triple vector boson production through Higgs-Strahlung with NLO multijet merging
Hoeche, Stefan; Kraus, Frank; Pozzorini, Stephano; Schoenherr, Marek; Thompson, Jennifer M.; Zapp, Korinna C.
2014-07-25
Triple gauge boson hadroproduction, in particular the production of three W-bosons at the LHC, is considered at next-to leading order accuracy in QCD. The NLO matrix elements are combined with parton showers. Multijet merging is invoked such that NLO matrix elements with one additional jet are also included. The studies here incorporate both the signal and all relevant backgrounds for V H production with the subsequent decay of the Higgs boson into W– or τ–- pairs. They have been performed using SHERPA+OPENLOOPS in combination with COLLIER.
Kniehl, B. A.; Maniatis, M.; Weber, M. M.
2011-01-01
The discovery of charged Higgs bosons is of particular importance, since their existence is predicted by supersymmetry and they are absent in the standard model (SM). If the charged Higgs bosons are too heavy to be produced in pairs at future linear colliders, single production associated with a top and a bottom quark is enhanced in parts of the parameter space. We present the next-to-leading-order calculation in supersymmetric QCD within the minimal supersymmetric SM, completing a previous calculation of the SM-QCD corrections. In addition to the usual approach to perform the loop integration analytically, we apply a numerical approach based on the Bernstein-Tkachov theorem. In this framework, we avoid some of the generic problems connected with the analytical method.
Kovacs, E.; CDF Collaboration
1996-02-01
We present results for the inclusive jet cross section and the dijet mass distribution. The inclusive cross section and dijet mass both exhibit significant deviations from the predictions of NLO QCD for jets with E{sub T}>200 GeV, or dijet masses > 400 GeV/c{sup 2}. We show that it is possible, within a global QCD analysis that includes the CDF inclusive jet data, to modify the gluon distribution at high x. The resulting increase in the jet cross-section predictions is 25-35%. Owing to the presence of k{sub T} smearing effects, the direct photon data does not provide as strong a constraint on the gluon distribution as previously thought. A comparison of the CDF and UA2 jet data, which have a common range in x, is plagued by theoretical and experimental uncertainties, and cannot at present confirm the CDF excess or the modified gluon distribution.
Graudenz, D. )
1994-04-01
Jet cross sections in deeply inelastic scattering in the case of transverse photon exchange for the production of (1+1) and (2+1) jets are calculated in next-to-leading-order QCD (here the +1'' stands for the target remnant jet, which is included in the jet definition). The jet definition scheme is based on a modified JADE cluster algorithm. The calculation of the (2+1) jet cross section is described in detail. Results for the virtual corrections as well as for the real initial- and final-state corrections are given explicitly. Numerical results are stated for jet cross sections as well as for the ratio [sigma][sub (2+1) jet]/[sigma][sub tot] that can be expected at E665 and DESY HERA. Furthermore the scale ambiguity of the calculated jet cross sections is studied and different parton density parametrizations are compared.
Bornyakov, V.G.
2005-06-01
Possibilities that are provided by a lattice regularization of QCD for studying nonperturbative properties of QCD are discussed. A review of some recent results obtained from computer calculations in lattice QCD is given. In particular, the results for the QCD vacuum structure, the hadron mass spectrum, and the strong coupling constant are considered.
NASA Astrophysics Data System (ADS)
Backović, Mihailo; Krämer, Michael; Maltoni, Fabio; Martini, Antony; Mawatari, Kentarou; Pellen, Mathieu
2015-10-01
Weakly interacting dark matter particles can be pair-produced at colliders and detected through signatures featuring missing energy in association with either QCD/EW radiation or heavy quarks. In order to constrain the mass and the couplings to standard model particles, accurate and precise predictions for production cross sections and distributions are of prime importance. In this work, we consider various simplified models with s-channel mediators. We implement such models in the FeynRules/ MadGraph5_aMC@NLO framework, which allows to include higher-order QCD corrections in realistic simulations and to study their effect systematically. As a first phenomenological application, we present predictions for dark matter production in association with jets and with a top-quark pair at the LHC, at next-to-leading order accuracy in QCD, including matching/merging to parton showers. Our study shows that higher-order QCD corrections to dark matter production via s-channel mediators have a significant impact not only on total production rates, but also on shapes of distributions. We also show that the inclusion of next-to-leading order effects results in a sizeable reduction of the theoretical uncertainties.
NLO conformal symmetry in the Regge limit of QCD
Coriano, C.; White, A.R.; Wuesthoff, M.
1996-09-18
The authors show that a scale invariant approximation to the next-to-leading order BFKL kernel, constructed via transverse momentum diagrams, has a simple conformally invariant representation in impact parameter space. That a conformally invariant representation exists is shown first by relating the kernel directly to Feynman diagrams contributing to two photon diffractive dissociation.
Photon impact factor in the NLO
Balitsky, Ian
2013-04-01
The photon impact factor for the BFKL pomeron is calculated in the next-to-leading order (NLO) approximation using the operator expansion in Wilson lines. The result is represented as a NLO k{sub T}-factorization formula for the structure functions of small-x deep inelastic scattering.
A SUSY GUT of flavour with S 4 × SU(5) to NLO
NASA Astrophysics Data System (ADS)
Hagedorn, Claudia; King, Stephen F.; Luhn, Christoph
2010-06-01
We construct a Supersymmetric (SUSY) Grand Unified Theory (GUT) of Flavour based on S 4 × SU(5), together with an additional (global or local) Abelian symmetry, and study it to next-to-leading order (NLO) accuracy. The model includes a successful description of quark and lepton masses and mixing angles at leading order (LO) incorporating the Gatto-Sartori-Tonin (GST) relation and the Georgi-Jarlskog (GJ) relations. We study the vacuum alignment arising from F-terms to NLO and such corrections are shown to have a negligible effect on the results for fermion masses and mixings achieved at LO. Tri-bimaximal (TB) mixing in the neutrino sector is predicted very accurately up to NLO corrections of order 0.1%. Including charged lepton mixing corrections implies small deviations from TB mixing described by a precise sum rule, accurately maximal atmospheric mixing and a reactor mixing angle close to three degrees.
NASA Astrophysics Data System (ADS)
Akan, Tarik; Guo, Feng-Kun; Meißner, Ulf-G.
2014-09-01
Nucleon electric dipole moments originating from strong CP-violation are being calculated by several groups using lattice QCD. We revisit the finite volume corrections to the CP-odd nucleon matrix elements of the electromagnetic current, which can be related to the electric dipole moments in the continuum, in the framework of chiral perturbation theory up to next-to-leading order taking into account the breaking of Lorentz symmetry. A chiral extrapolation of the recent lattice results of both the neutron and proton electric dipole moments is performed, which results in dn=(-2.7±1.2)×10-16eθ0 cm and dp=(2.1±1.2)×10-16eθ0 cm.
NLO evolution of color dipoles in N=4 SYM
Chirilli, Giovanni A.; Balitsky, Ian
2009-07-04
Here, high-energy behavior of amplitudes in a gauge theory can be reformulated in terms of the evolution of Wilson-line operators. In the leading logarithmic approximation it is given by the conformally invariant BK equation for the evolution of color dipoles. In QCD, the next-to-leading order BK equation has both conformal and non-conformal parts, the latter providing the running of the coupling constant. To separate the conformally invariant effects from the running-coupling effects, we calculate the NLO evolution of the color dipoles in the conformalmore » $${\\cal N}$$=4 SYM theory. We define the "composite dipole operator" with the rapidity cutoff preserving conformal invariance.« less
Linear vs non-linear QCD evolution in the neutrino-nucleon cross section
NASA Astrophysics Data System (ADS)
Albacete, Javier L.; Illana, José I.; Soto-Ontoso, Alba
2016-03-01
Evidence for an extraterrestrial flux of ultra-high-energy neutrinos, in the order of PeV, has opened a new era in Neutrino Astronomy. An essential ingredient for the determination of neutrino fluxes from the number of observed events is the precise knowledge of the neutrino-nucleon cross section. In this work, based on [1], we present a quantitative study of σνN in the neutrino energy range 104 < Eν < 1014 GeV within two transversal QCD approaches: NLO DGLAP evolution using different sets of PDFs and BK small-x evolution with running coupling and kinematical corrections. Further, we translate this theoretical uncertainty into upper bounds for the ultra-high-energy neutrino flux for different experiments.
Nathan Isgur
1997-03-01
The author presents an idiosyncratic view of baryons which calls for a marriage between quark-based and hadronic models of QCD. He advocates a treatment based on valence quark plus glue dominance of hadron structure, with the sea of q pairs (in the form of virtual hadron pairs) as important corrections.
Perturbative QCD factorization of ρ γ⋆→ρ
NASA Astrophysics Data System (ADS)
Zhang, Ya-lan; Cheng, Shan; Hua, Jun; Xiao, Zhen-Jun
2016-02-01
In this paper we first demonstrate step by step that the factorization hypothesis is valid at the next-to-leading order (NLO) for the exclusive process ρ γ⋆→ρ by employing the collinear factorization approach, and then extend this proof to the case of the kT factorization by taking into account the transversal momentum of the light external quark (antiquark) lines in the ρ meson. At the NLO level, we then show that the soft divergences from different subdiagrams will cancel each other in the quark level, while the remaining collinear divergences can be absorbed into the NLO meson wave functions. The full NLO amplitudes can therefore be factorized as the convolution of the NLO wave functions Φρ(1 ) and the infrared-finite leading order (LO) hard kernels GX,I J ,k l 0 in the kT factorization. We also write down the polarized NLO ρ meson wave functions in the form of nonlocal hadron matrix elements with the gauge factor integral path deviating from the light cone. These NLO ρ meson wave functions can be used to calculate the NLO hard corrections to some relevant exclusive processes, such as B →ρ transition.
The perturbative QCD gradient flow to three loops
NASA Astrophysics Data System (ADS)
Harlander, Robert V.; Neumann, Tobias
2016-06-01
The gradient flow in QCD is treated perturbatively through next-to-next-to-leading order in the strong coupling constant. The evaluation of the relevant momentum and flow-time integrals is described, including various means of validation. For the vacuum expectation value of the action density, which turns out to be a useful quantity in lattice calculations, we find a very well-behaved perturbative series through NNLO. Quark mass effects are taken into account through NLO. The theoretical uncertainty due to renormalization-scale variation is significantly reduced with respect to LO and NLO, as long as the flow time is smaller than about 0.1 fm.
Beneke, M.; Braun, V.M.
1996-05-01
Resummation of large infrared logarithms in perturbation theory can, in certain circumstances, enhance the sensitivity to small gluon momenta and introduce spurious nonperturbative contributions. In particular, different procedures--equivalent in perturbation theory--to organize this resummation can differ by 1/Q power corrections. The question arises whether one can formulate resummation procedures that are explicitly consistent with the infrared behavior of finite-order Feynman diagrams. They explain how this problem can be treated and resolved in Drell-Yan (lepton pair) production and briefly discuss more complicated cases, such as top quark production and event shape variables in the e{sup +}e{sup {minus}} annihilation.
Multi-jet Merging with NLO Matrix Elements
Siegert, Frank; Hoche, Stefan; Krauss, Frank; Schonherr, Marek; /Dresden, Tech. U.
2011-08-18
In the algorithm presented here, the ME+PS approach to merge samples of tree-level matrix elements into inclusive event samples is combined with the POWHEG method, which includes exact next-to-leading order matrix elements in the parton shower. The advantages of the method are discussed and the quality of its implementation in SHERPA is exemplified by results for e{sup +}e{sup -} annihilation into hadrons at LEP, for deep-inelastic lepton-nucleon scattering at HERA, for Drell-Yan lepton-pair production at the Tevatron and for W{sup +}W{sup -}-production at LHC energies. The simulation of hard QCD radiation in parton-shower Monte Carlos has seen tremendous progress over the last years. It was largely stimulated by the need for more precise predictions at LHC energies where the large available phase space allows additional hard QCD radiation alongside known Standard Model processes or even signals from new physics. Two types of algorithms have been developed, which allow to improve upon the soft-collinear approximations made in the parton shower, such that hard radiation is simulated according to exact matrix elements. In the ME+PS approach [1] higher-order tree-level matrix elements for different final-state jet multiplicity are merged with each other and with subsequent parton shower emissions to generate an inclusive sample. Such a prescription is invaluable for analyses which are sensitive to final states with a large jet multiplicity. The only remaining deficiency of such tree-level calculations is the large uncertainty stemming from scale variations. The POWHEG method [2] solves this problem for the lowest multiplicity subprocess by combining full NLO matrix elements with the parton shower. While this leads to NLO accuracy in the inclusive cross section and the exact radiation pattern for the first emission, it fails to describe higher-order emissions with improved accuracy. Thus it is not sufficient if final states with high jet multiplicities are considered
2015-11-01
In the article by Heuslein et al, which published online ahead of print on September 3, 2015 (DOI: 10.1161/ATVBAHA.115.305775), a correction was needed. Brett R. Blackman was added as the penultimate author of the article. The article has been corrected for publication in the November 2015 issue. PMID:26490278
QCD Analysis of the semi-inclusive HERMES and COMPASS data
NASA Astrophysics Data System (ADS)
Shevchenko, O. Yu.; Akhunzyanov, R. R.; Lavrentyev, V. Yu.
2013-05-01
The first moments of polarized valence PDFs, responsible for the respective contributions to the nucleon spin, are extracted in NLO QCD from the data of COMPASS and HERMES collaborations on the semi-inclusive difference asymmetries. To this end the new method of QCD analysis (alternative to the usual global fit analysis) is applied. Using the obtained results on valence PDFs the first moments of polarized sea PDFs are reconstructed. They turn out surprisingly small: compatible with zeros within the errors.
Seven topics in perturbative QCD
Buras, A.J.
1980-09-01
The following topics of perturbative QCD are discussed: (1) deep inelastic scattering; (2) higher order corrections to e/sup +/e/sup -/ annihilation, to photon structure functions and to quarkonia decays; (3) higher order corrections to fragmentation functions and to various semi-inclusive processes; (4) higher twist contributions; (5) exclusive processes; (6) transverse momentum effects; (7) jet and photon physics.
2015-12-01
In the article by Narayan et al (Narayan O, Davies JE, Hughes AD, Dart AM, Parker KH, Reid C, Cameron JD. Central aortic reservoir-wave analysis improves prediction of cardiovascular events in elderly hypertensives. Hypertension. 2015;65:629–635. doi: 10.1161/HYPERTENSIONAHA.114.04824), which published online ahead of print December 22, 2014, and appeared in the March 2015 issue of the journal, some corrections were needed.On page 632, Figure, panel A, the label PRI has been corrected to read RPI. In panel B, the text by the upward arrow, "10% increase in kd,” has been corrected to read, "10% decrease in kd." The corrected figure is shown below.The authors apologize for these errors. PMID:26558821
NASA Astrophysics Data System (ADS)
1995-04-01
Seismic images of the Brooks Range, Arctic Alaska, reveal crustal-scale duplexing: Correction Geology, v. 23, p. 65 68 (January 1995) The correct Figure 4A, for the loose insert, is given here. See Figure 4A below. Corrected inserts will be available to those requesting copies of the article from the senior author, Gary S. Fuis, U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025. Figure 4A. P-wave velocity model of Brooks Range region (thin gray contours) with migrated wide-angle reflections (heavy red lines) and migreated vertical-incidence reflections (short black lines) superimposed. Velocity contour interval is 0.25 km/s; 4,5, and 6 km/s contours are labeled. Estimated error in velocities is one contour interval. Symbols on faults shown at top are as in Figure 2 caption.
Soft and hard contributions to QCD processes
Slavnov, D.A.; Bakulina, E.N.
1995-06-01
QCD corrections of order {alpha}{sub s} for deep inelastic lepton scattering and the Drell-Yan process are considered. The common soft part of these corrections is found. This result makes it possible to determine the modified parton distribution functions unambiguously beyond the leading logarithmic approximation. These distribution functions are used to obtain QCD corrections that are free of infrared and collinear ambiguities. 6 refs., 2 figs.
2016-02-01
Neogi T, Jansen TLTA, Dalbeth N, et al. 2015 Gout classification criteria: an American College of Rheumatology/European League Against Rheumatism collaborative initiative. Ann Rheum Dis 2015;74:1789–98. The name of the 20th author was misspelled. The correct spelling is Janitzia Vazquez-Mellado. We regret the error. PMID:26881284
Global QCD Analysis and Hadron Collider Physics
Tung, W.-K.
2005-03-22
The role of global QCD analysis of parton distribution functions (PDFs) in collider physics at the Tevatron and LHC is surveyed. Current status of PDF analyses are reviewed, emphasizing the uncertainties and the open issues. The stability of NLO QCD global analysis and its prediction on 'standard candle' W/Z cross sections at hadron colliders are discussed. The importance of the precise measurement of various W/Z cross sections at the Tevatron in advancing our knowledge of PDFs, hence in enhancing the capabilities of making significant progress in W mass and top quark parameter measurements, as well as the discovery potentials of Higgs and New Physics at the Tevatron and LHC, is emphasized.
2016-02-01
In the article by Guessous et al (Guessous I, Pruijm M, Ponte B, Ackermann D, Ehret G, Ansermot N, Vuistiner P, Staessen J, Gu Y, Paccaud F, Mohaupt M, Vogt B, Pechère-Bertschi A, Martin PY, Burnier M, Eap CB, Bochud M. Associations of ambulatory blood pressure with urinary caffeine and caffeine metabolite excretions. Hypertension. 2015;65:691–696. doi: 10.1161/HYPERTENSIONAHA.114.04512), which published online ahead of print December 8, 2014, and appeared in the March 2015 issue of the journal, a correction was needed.One of the author surnames was misspelled. Antoinette Pechère-Berstchi has been corrected to read Antoinette Pechère-Bertschi.The authors apologize for this error. PMID:26763012
Charm and bottom photoproduction at HERA with MC@NLO
Toll T.; Frixione, S.
2011-12-01
We apply the MC@NLO formalism to the production of heavy-quark pairs in pointlike photon-hadron collisions. By combining this result with its analogue relevant to hadron-hadron collisions, we obtain NLO predictions matched to parton showers for the photoproduction of Q{bar Q} pairs. We compare MC{at}NLO results to the measurements of c- and b-flavored hadron observables performed by the H1 and ZEUS Collaborations at HERA.
2015-05-22
The Circulation Research article by Keith and Bolli (“String Theory” of c-kitpos Cardiac Cells: A New Paradigm Regarding the Nature of These Cells That May Reconcile Apparently Discrepant Results. Circ Res. 2015:116:1216-1230. doi: 10.1161/CIRCRESAHA.116.305557) states that van Berlo et al (2014) observed that large numbers of fibroblasts and adventitial cells, some smooth muscle and endothelial cells, and rare cardiomyocytes originated from c-kit positive progenitors. However, van Berlo et al reported that only occasional fibroblasts and adventitial cells derived from c-kit positive progenitors in their studies. Accordingly, the review has been corrected to indicate that van Berlo et al (2014) observed that large numbers of endothelial cells, with some smooth muscle cells and fibroblasts, and more rarely cardiomyocytes, originated from c-kit positive progenitors in their murine model. The authors apologize for this error, and the error has been noted and corrected in the online version of the article, which is available at http://circres.ahajournals.org/content/116/7/1216.full ( PMID:25999426
NASA Astrophysics Data System (ADS)
1998-12-01
Alleged mosasaur bite marks on Late Cretaceous ammonites are limpet (patellogastropod) home scars Geology, v. 26, p. 947 950 (October 1998) This article had the following printing errors: p. 947, Abstract, line 11, “sepia” should be “septa” p. 947, 1st paragraph under Introduction, line 2, “creep” should be “deep” p. 948, column 1, 2nd paragraph, line 7, “creep” should be “deep” p. 949, column 1, 1st paragraph, line 1, “creep” should be “deep” p. 949, column 1, 1st paragraph, line 5, “19774” should be “1977)” p. 949, column 1, 4th paragraph, line 7, “in particular” should be “In particular” CORRECTION Mammalian community response to the latest Paleocene thermal maximum: An isotaphonomic study in the northern Bighorn Basin, Wyoming Geology, v. 26, p. 1011 1014 (November 1998) An error appeared in the References Cited. The correct reference appears below: Fricke, H. C., Clyde, W. C., O'Neil, J. R., and Gingerich, P. D., 1998, Evidence for rapid climate change in North America during the latest Paleocene thermal maximum: Oxygen isotope compositions of biogenic phosphate from the Bighorn Basin (Wyoming): Earth and Planetary Science Letters, v. 160, p. 193 208.
Synthesis of Polymers Containing Covalently Bonded NLO Chromophores
NASA Technical Reports Server (NTRS)
Denga, Xiao-Hua; Sanghadasa, Mohan; Walton, Connie; Penn, Benjamin B.; Amai, Robert L. S.; Clark, Ronald D.
1998-01-01
Polymers containing covalently bonded nonlinear optical (NLO) chromophores are expected to possess special properties such as greater stability, better mechanical processing, and easier film formation than their non-polymeric equivalent. For the present work, polymethylmethacrylate (PMMA) was selected as the basic polymer unit on which to incorporate different NLO chromophores. The NLO components were variations of DIVA {[2-methoxyphenyl methylidene]-propanedinitrile} which we prepared from vanillin derivatives and malononitrile. These were esterified with methacrylic acid and polymerized either directly or with methyl methacrylate to form homopolymers or copolymers respectively. Characterization of the polymers and NLO property studies are underway.
Hess, Peter O.
2006-09-25
A review is presented on the contributions of Mexican Scientists to QCD phenomenology. These contributions range from Constituent Quark model's (CQM) with a fixed number of quarks (antiquarks) to those where the number of quarks is not conserved. Also glueball spectra were treated with phenomenological models. Several other approaches are mentioned.
Blossier, B.; Boucaud, Ph.; Gravina, M.; Pene, O.; De soto, F.; Morenas, V.
2010-08-01
We present results concerning the nonperturbative evaluation of the ghost-gluon running QCD coupling constant from N{sub f}=2 twisted-mass lattice calculations. A novel method for calibrating the lattice spacing, independent of the string tension and hadron spectrum, is presented with results in agreement with previous estimates. The value of {Lambda}{sub MS} is computed from the running of the QCD coupling only after extrapolating to zero dynamical quark mass and after removing a nonperturbative operator-product expansion contribution that is assumed to be dominated by the dimension-two gluon condensate. The effect due to the dynamical quark mass in the determination of {Lambda}{sub MS} is discussed.
NLO Hierarchy of Wilson Lines Evolution
Balitsky, Ian
2015-03-01
The high-energy behavior of QCD amplitudes can be described in terms of the rapidity evolution of Wilson lines. I present the hierarchy of evolution equations for Wilson lines in the next-to-leading order.
Heavy to light Higgs boson decays at NLO in the singlet extension of the Standard Model
NASA Astrophysics Data System (ADS)
Bojarski, F.; Chalons, G.; López-Val, D.; Robens, T.
2016-02-01
We study the decay of a heavy Higgs boson into a light Higgs pair at one loop in the singlet extension of the Standard Model. To this purpose, we construct several renormalization schemes for the extended Higgs sector of the model. We apply these schemes to calculate the heavy-to-light Higgs decay width Γ H → hh at next-to-leading order electroweak accuracy, and demonstrate that certain prescriptions lead to gauge-dependent results. We comprehensively examine how the NLO predictions depend on the relevant singlet model parameters, with emphasis on the trademark behavior of the quantum effects, and how these change under different renormalization schemes and a variable renormalization scale. Once all present constraints on the model are included, we find mild NLO corrections, typically of few percent, and with small theoretical uncertainties.
NLO error propagation exercise data collection system
Keisch, B.; Bieber, A.M. Jr.
1983-01-01
A combined automated and manual system for data collection is described. The system is suitable for collecting, storing, and retrieving data related to nuclear material control at a bulk processing facility. The system, which was applied to the NLO operated Feed Materials Production Center, was successfully demonstrated for a selected portion of the facility. The instrumentation consisted of off-the-shelf commercial equipment and provided timeliness, convenience, and efficiency in providing information for generating a material balance and performing error propagation on a sound statistical basis.
η(c) production at the LHC challenges nonrelativistic QCD factorization.
Butenschoen, Mathias; He, Zhi-Guo; Kniehl, Bernd A
2015-03-01
We analyze the first measurement of η_{c} production, performed by the LHCb Collaboration, in the nonrelativistic QCD (NRQCD) factorization framework at next-to-leading order (NLO) in the strong-coupling constant α_{s} and the relative velocity v of the bound quarks including the feeddown from h_{c} mesons. Converting the long-distance matrix elements extracted by various groups from J/ψ yield and polarization data to the η_{c} case using heavy-quark spin symmetry, we find that the resulting NLO NRQCD predictions greatly overshoot the LHCb data, while the color-singlet model provides an excellent description. PMID:25793805
NASA Astrophysics Data System (ADS)
Bolzoni, Paolo
2007-09-01
In this PhD thesis, we analyze and generalize the renormalization group approach to the resummation of large logarithms in the perturbative expansion due to soft and collinear multiparton emissions. In particular, we present a generalization of this approach to prompt photon production. It is interesting to see that also with the more intricate two-scale kinematics that characterizes prompt photon production in the soft limit, it remains true that resummation simply follows from general kinematic properties of the phase space. Also, this approach does not require a separate treatment of individual colour structures when more than one colour structure contributes to fixed order results. However, the resummation formulae obtained here turn out to be less predictive than previous results: this depends on the fact that here neither specific factorization properties of the cross section in the soft limit is assumed, nor that soft emission satisfies eikonal-like relations. We also derive resumation formulae to all logarithmic accuracy and valid for all values of rapidity for the prompt photon production and the Drell-Yan rapidity distributions. We show that for the fixed-target experiment E866/NuSea, the NLL resummation corrections are comparable to NLO fixed-order corrections and are crucial to obtain agreement with the data. Finally we outline also possible future applications of the renormalization group approach.
Off-shell single-top production at NLO matched to parton showers
Frederix, R.; Frixione, S.; Papanastasiou, A. S.; Prestel, S.; Torrielli, P.
2016-06-06
We study the hadroproduction of a W b pair in association with a light jet, focusing on the dominant t -channel contribution and including exactly at the matrix-element level all non-resonant and off-shell effects induced by the finite top-quark width. Our simulations are accurate to the next-to-leading order in QCD, and are matched to the Herwig6 and Pythia8 parton showers through the MC@NLO method. We present phenomenological results relevant to the 8 TeV LHC, and carry out a thorough comparison to the case of on-shell t -channel single-top production. Furthermore, we formulate our approach so that it can be appliedmore » to the general case of matrix elements that feature coloured intermediate resonances and are matched to parton showers.« less
Off-shell single-top production at NLO matched to parton showers
NASA Astrophysics Data System (ADS)
Frederix, R.; Frixione, S.; Papanastasiou, A. S.; Prestel, S.; Torrielli, P.
2016-06-01
We study the hadroproduction of a W b pair in association with a light jet, focusing on the dominant t-channel contribution and including exactly at the matrix-element level all non-resonant and off-shell effects induced by the finite top-quark width. Our simulations are accurate to the next-to-leading order in QCD, and are matched to the Herwig6 and Pythia8 parton showers through the MC@NLO method. We present phenomenological results relevant to the 8 TeV LHC, and carry out a thorough comparison to the case of on-shell t-channel single-top production. We formulate our approach so that it can be applied to the general case of matrix elements that feature coloured intermediate resonances and are matched to parton showers.
QCD: Challenges for the future
Burrows, P.; Dawson, S.; Orr, L.; Smith, W.H.
1997-01-13
Despite many experimental verifications of the correctness of our basic understanding of QCD, there remain numerous open questions in strong interaction physics and we focus on the role of future colliders in addressing these questions. We discuss possible advances in the measurement of {alpha}{sub s}, in the study of parton distribution functions, and in the understanding of low x physics at present colliders and potential new facilities. We also touch briefly on the role of spin physics in advancing our understanding of QCD.
Top-pair production and decay at NLO matched with parton showers
Campbell, John M.; Ellis, R. Keith; Nason, Paolo; Re, Emanuele
2015-04-21
We present a next-to-leading order (NLO) calculation of tt¯ production in hadronic collisions interfaced to shower generators according to the POWHEG method. We start from an NLO result from previous work, obtained in the zero width limit, where radiative corrections to both production and decays are included. The POWHEG interface required an extension of the POWHEG BOX framework, in order to deal with radiation from the decay of resonances. This extension is fully general (i.e. it can be applied in principle to any process considered in the zero width limit), and is here applied for the first time. In order to perform a realistic simulation, we introduce finite width effects using different approximations, that we validated by comparing with published exact NLO results. We have interfaced our POWHEG code to the PYTHIA8 shower Monte Carlo generator. At this stage, we dealt with novel issues related to the treatment of resonances, especially with regard to the initial scale for the shower that needs to be set appropriately. This procedure affects, for example, the fragmentation function of the b quark, that we have studied with particular attention. We believe that the tool presented here improves over previous generators for all aspects that have to do with top decays, and especially for the study of issues related to top mass measurements that involve B hadrons or b jets. As a result, the work presented here also constitutes a first step towards a fully consistent matching of NLO calculations involving intermediate resonances decaying into coloured particles, with parton showers.
Top-pair production and decay at NLO matched with parton showers
Campbell, John M.; Ellis, R. Keith; Nason, Paolo; Re, Emanuele
2015-04-21
We present a next-to-leading order (NLO) calculation of tt¯ production in hadronic collisions interfaced to shower generators according to the POWHEG method. We start from an NLO result from previous work, obtained in the zero width limit, where radiative corrections to both production and decays are included. The POWHEG interface required an extension of the POWHEG BOX framework, in order to deal with radiation from the decay of resonances. This extension is fully general (i.e. it can be applied in principle to any process considered in the zero width limit), and is here applied for the first time. In ordermore » to perform a realistic simulation, we introduce finite width effects using different approximations, that we validated by comparing with published exact NLO results. We have interfaced our POWHEG code to the PYTHIA8 shower Monte Carlo generator. At this stage, we dealt with novel issues related to the treatment of resonances, especially with regard to the initial scale for the shower that needs to be set appropriately. This procedure affects, for example, the fragmentation function of the b quark, that we have studied with particular attention. We believe that the tool presented here improves over previous generators for all aspects that have to do with top decays, and especially for the study of issues related to top mass measurements that involve B hadrons or b jets. As a result, the work presented here also constitutes a first step towards a fully consistent matching of NLO calculations involving intermediate resonances decaying into coloured particles, with parton showers.« less
Simple analytic QCD model with perturbative QCD behavior at high momenta
Contreras, Carlos; Espinosa, Olivier; Cvetic, Gorazd; Martinez, Hector E.
2010-10-01
Analytic QCD models are those where the QCD running coupling has the physically correct analytic behavior, i.e., no Landau singularities in the Euclidean regime. We present a simple analytic QCD model in which the discontinuity function of the running coupling at high momentum scales is the same as in perturbative QCD (just like in the analytic QCD model of Shirkov and Solovtsov), but at low scales it is replaced by a delta function which parametrizes the unknown behavior there. We require that the running coupling agree to a high degree with the perturbative coupling at high energies, which reduces the number of free parameters of the model from four to one. The remaining parameter is fixed by requiring the reproduction of the correct value of the semihadronic tau decay ratio.
NLO matrix elements and truncated showers
NASA Astrophysics Data System (ADS)
Höche, Stefan; Krauss, Frank; Schönherr, Marek; Siegert, Frank
2011-08-01
In this publication, an algorithm is presented that combines the ME+PS approach to merge sequences of tree-level matrix elements into inclusive event samples [1] with the P owheg method, which combines exact next-to-leading order matrix element results with the parton shower [2, 3]. It was developed in parallel to the ME nloPS technique discussed in [4] and has been implemented in the event generator S herpa [5, 6]. The benefits of this approach are exemplified by some first predictions for a number of processes, namely the production of jets in e + e --annihilation, in deep-inelastic ep scattering, in association with single W, Z or Higgs bosons, and with vector boson pairs at hadron colliders.
NLO error propagation exercise: statistical results
Pack, D.J.; Downing, D.J.
1985-09-01
Error propagation is the extrapolation and cumulation of uncertainty (variance) above total amounts of special nuclear material, for example, uranium or /sup 235/U, that are present in a defined location at a given time. The uncertainty results from the inevitable inexactness of individual measurements of weight, uranium concentration, /sup 235/U enrichment, etc. The extrapolated and cumulated uncertainty leads directly to quantified limits of error on inventory differences (LEIDs) for such material. The NLO error propagation exercise was planned as a field demonstration of the utilization of statistical error propagation methodology at the Feed Materials Production Center in Fernald, Ohio from April 1 to July 1, 1983 in a single material balance area formed specially for the exercise. Major elements of the error propagation methodology were: variance approximation by Taylor Series expansion; variance cumulation by uncorrelated primary error sources as suggested by Jaech; random effects ANOVA model estimation of variance effects (systematic error); provision for inclusion of process variance in addition to measurement variance; and exclusion of static material. The methodology was applied to material balance area transactions from the indicated time period through a FORTRAN computer code developed specifically for this purpose on the NLO HP-3000 computer. This paper contains a complete description of the error propagation methodology and a full summary of the numerical results of applying the methodlogy in the field demonstration. The error propagation LEIDs did encompass the actual uranium and /sup 235/U inventory differences. Further, one can see that error propagation actually provides guidance for reducing inventory differences and LEIDs in future time periods.
Diffractive heavy quark production in AA collisions at the LHC at NLO
Machado, M. M.; Ducati, M. B. Gay; Machado, M. V. T.
2011-07-15
The single and double diffractive cross sections for heavy quarks production are evaluated at NLO accuracy for hadronic and heavy ion collisions at the LHC. Diffractive charm and bottom production is the main subject of this work, providing predictions for CaCa, PbPb and pPb collisions. The hard diffraction formalism is considered using the Ingelman-Schlein model where a recent parametrization for the Pomeron structure function (DPDF) is applied. Absorptive corrections are taken into account as well. The diffractive ratios are estimated and theoretical uncertainties are discussed. Comparison with competing production channels is also presented.
NASA Astrophysics Data System (ADS)
Bevilacqua, G.; Hartanto, H. B.; Kraus, M.; Worek, M.
2016-02-01
We present a complete description of top quark pair production in association with a jet in the dilepton channel. Our calculation is accurate to next-to-leading order (NLO) in QCD and includes all nonresonant diagrams, interferences, and off-shell effects of the top quark. Moreover, nonresonant and off-shell effects due to the finite W gauge boson width are taken into account. This calculation constitutes the first fully realistic NLO computation for top quark pair production with a final state jet in hadronic collisions. Numerical results for differential distributions as well as total cross sections are presented for the Large Hadron Collider at 8 TeV. With our inclusive cuts, NLO predictions reduce the unphysical scale dependence by more than a factor of 3 and lower the total rate by about 13% compared to leading-order QCD predictions. In addition, the size of the top quark off-shell effects is estimated to be below 2%.
DOUBLE TRANSVERSE SPIN ASYMMETRIES AT NEXT-TO-LEADING ORDER IN QCD.
MUKHERJEE,A.; STRATMANN,M.; VOGELSANG,W.
2004-10-10
We present a technique to calculate the cross sections and spin asymmetries for transversely polarized pp collisions at NLO in QCD and report on the use of this technique for the processes p{up_arrow}p{up_arrow} {yields} {gamma}X, p{up_arrow}p{up_arrow} {yields} {pi}X and p{up_arrow}p{up_arrow} {yields} {ell}{sup +}{ell}{sup -} X.
Heavy Quarks, QCD, and Effective Field Theory
Thomas Mehen
2012-10-09
The research supported by this OJI award is in the area of heavy quark and quarkonium production, especially the application Soft-Collinear E ective Theory (SCET) to the hadronic production of quarkonia. SCET is an e ffective theory which allows one to derive factorization theorems and perform all order resummations for QCD processes. Factorization theorems allow one to separate the various scales entering a QCD process, and in particular, separate perturbative scales from nonperturbative scales. The perturbative physics can then be calculated using QCD perturbation theory. Universal functions with precise fi eld theoretic de nitions describe the nonperturbative physics. In addition, higher order perturbative QCD corrections that are enhanced by large logarithms can be resummed using the renormalization group equations of SCET. The applies SCET to the physics of heavy quarks, heavy quarkonium, and similar particles.
Conformal kernel for NLO BFKL equation in ${\\cal N}$=4 SYM
Balitsky, Ian; Chirilli, Giovanni
2009-01-01
Using the requirement of M\\"{o}bius invariance of ${\\cal N}$=4 SYM amplitudes in the Regge limit we restore the conformal NLO BFKL kernel out of the eigenvalues known from the forward NLO BFKL result.
Global NLO Analysis of Nuclear Parton Distribution Functions
Hirai, M.; Kumano, S.; Nagai, T.-H.
2008-02-21
Nuclear parton distribution functions (NPDFs) are determined by a global analysis of experimental measurements on structure-function ratios F{sub 2}{sup A}/F{sub 2}{sup A{sup '}} and Drell-Yan cross section ratios {sigma}{sub DY}{sup A}/{sigma}{sub DY}{sup A{sup '}}, and their uncertainties are estimated by the Hessian method. The NPDFs are obtained in both leading order (LO) and next-to-leading order (NLO) of {alpha}{sub s}. As a result, valence-quark distributions are relatively well determined, whereas antiquark distributions at x>0.2 and gluon distributions in the whole x region have large uncertainties. The NLO uncertainties are slightly smaller than the LO ones; however, such a NLO improvement is not as significant as the nucleonic case.
Development of Polyimides-Based NLO Materials for Electrooptical Applications
NASA Technical Reports Server (NTRS)
Rutherford, Jacqueline; Li, Xiang; Mintz, Eric A.; Bu, Xiu R.
1998-01-01
Development of thermally stable optical materials for nonlinear optics have recently focused on the covalent incorporation of NLO chromophores into high performance polymers, especially thermally stable and processable polyamides. One key aspect for the incorporation of robust NLO chromophores into high Tg polymers is to sustain poling induced order. Other advantages include high loading level of chromophores, and elimination of possible phase separation as well as chromophore sublimation at processing or working temperature. We have prepared several polyimide based polymers which are covalently linked with thermally stable chromophores that we have developed, since polyamides generally exhibit high Tg and good film transparency. Here, we report the development and subsequent incorporation of indoline based chromophores into polyamides, leading to thermally stable NLO polymers.
Highly Non-Linear Optical (NLO) organic crystals
NASA Technical Reports Server (NTRS)
Harris, J. Milton
1987-01-01
This research project involves the synthesis and characterization of organic materials having powerful nonlinear optical (NLO) properties and the growth of highly ordered crystals and monomolecular films of these materials. Research in four areas is discussed: theoretical design of new materials, characterization of NLO materials, synthesis of new materials and development of coupling procedures for forming layered films, and improvement of the techniques for vapor phase and solution phase growth of high quality organic crystals. Knowledge gained from these experiments will form the basis for experiments in the growth of these crystals.
NASA Astrophysics Data System (ADS)
Majhi, S. K.; Mukhopadhyay, A.; Ward, B. F. L.; Yost, S. A.
2014-11-01
We present a phenomenological study of the current status of the application of our approach of exact amplitude-based resummation in quantum field theory to precision QCD calculations, by realistic MC event generator methods, as needed for precision LHC physics. We discuss recent results as they relate to the interplay of the attendant IR-improved DGLAP-CS theory of one of us and the precision of exact NLO matrix-element matched parton shower MC's in the Herwig6.5 environment as determined by comparison to recent LHC experimental observations on single heavy gauge boson production and decay. The level of agreement between the new theory and the data continues to be a reason for optimism. In the spirit of completeness, we discuss as well other approaches to the same theoretical predictions that we make here from the standpoint of physical precision with an eye toward the (sub-)1% QCD ⊗ EW total theoretical precision regime for LHC physics.
NASA Astrophysics Data System (ADS)
Jecs, E.; Kreicberga, J.; Kampars, V.; Jurgis, A.; Rutkis, M.
2009-09-01
For the development of electro optical active polyurethanes six new derivatives of 2-{(2-hydroxyethyl)-[4-(4-nitrophenylazo)phenyl]amino}ethanol and two of 2-{(2-hydroxyethyl)-[4-(5-nitropyridin-2-ylazo)phenyl]amino}ethanol were synthesized by azocoupling reaction. Molecular geometry, hyperpolarizability β FF and ground state dipole moment μ g were acquired by RHF ab initio (6-31G∗∗) calculations using HyperChem software package. To characterize NLO performance of synthesized azo compounds second order non linear coefficients d31 and d33 were measured as function of chromophore load in guest-host films (PMMA). Eight synthesized compounds can be grouped in four similar gross formula pairs (different position of octyloxy group) with almost equal μ g β FF product and different μ g values. At low chromophore concentrations higher dipole moment compounds perform better. Lower dipole moment compounds have better NLO efficiency at high chromophore loads. Accurate ranking of all chromophores, based on two-level model corrected zero frequency d33(0) values, was not viable due to overestimation of the dispersion factor.
QCD Results from the Fermilab Tevatron proton-antiproton Collider
Warburton, Andreas; CDF, for the; Collaborations, D0
2010-01-01
Selected recent quantum chromodynamics (QCD) measurements are reviewed for Fermilab Run II Tevatron proton-antiproton collisions studied by the Collider Detector at Fermilab (CDF) and D0 Collaborations at a centre-of-mass energy of {radical}s = 1.96 TeV. Tantamount to Rutherford scattering studies at the TeV scale, inclusive jet and dijet production cross-section measurements are used to seek and constrain new particle physics phenomena, test perturbative QCD calculations, inform parton distribution function (PDF) determinations, and extract a precise value of the strong coupling constant, a{sub s}(m{sub Z}) = 0.1161{sub -0.0048}{sup +0.0041}. Inclusive photon production cross-section measurements reveal an inability of next-to-leading-order (NLO) perturbative QCD (pQCD) calculations to describe low-energy photons arising directly in the hard scatter. Events with {gamma} + 3-jet configurations are used to measure the increasingly important double parton scattering (DPS) phenomenon, with an obtained effective interaction cross section of {sigma}{sub eff} = 16.4 {+-} 2.3 mb. Observations of central exclusive particle production demonstrate the viability of observing the Standard Model Higgs boson using similar techniques at the Large Hadron Collider (LHC). Three areas of inquiry into lower energy QCD, crucial to understanding high-energy collider phenomena, are discussed: the examination of intra-jet track kinematics to infer that jet formation is dominated by pQCD, and not hadronization, effects; detailed studies of the underlying event and its universality; and inclusive minimum-bias charged-particle momentum and multiplicity measurements, which are shown to challenge the Monte Carlo generators.
Parton energy loss and momentum broadening at NLO in high temperature QCD plasmas
NASA Astrophysics Data System (ADS)
Ghiglieri, Jacopo; Teaney, Derek
2015-10-01
We present an overview of a perturbative-kinetic approach to jet propagation, energy loss, and momentum broadening in a high temperature quark-gluon plasma. The leading-order kinetic equations describe the interactions between energetic jet-particles and a non-abelian plasma, consisting of on-shell thermal excitations and soft gluonic fields. These interactions include ↔ scatterings, collinear bremsstrahlung, and drag and momentum diffusion. We show how the contribution from the soft gluonic fields can be factorized into a set of Wilson line correlators on the light-cone. We review recent field-theoretical developments, rooted in the causal properties of these correlators, which simplify the calculation of the appropriate Wilson lines in thermal field theory. With these simplifications lattice measurements of transverse momentum broadening have become possible, and the kinetic equations describing parton transport have been extended to next-to-leading order in the coupling g.
Parton Energy Loss and Momentum Broadening at NLO in High Temperature QCD Plasmas
NASA Astrophysics Data System (ADS)
Ghiglieri, Jacopo; Teaney, Derek
We present an overview of a perturbative-kinetic approach to jet propagation, energy loss, and momentum broadening in a high temperature quark-gluon plasma. The leading-order kinetic equations describe the interactions between energetic jet-particles and a non-abelian plasma, consisting of on-shell thermal excitations and soft gluonic fields. These interactions include 2 ↔ 2 scatterings, collinear bremsstrahlung, and drag and momentum diffusion. We show how the contribution from the soft gluonic fields can be factorized into a set of Wilson line correlators on the light-cone. We review recent field-theoretical developments, rooted in the causal properties of these correlators, which simplify the calculation of the appropriate Wilson lines in thermal field theory. With these simplifications lattice measurements of transverse momentum broadening have become possible, and the kinetic equations describing parton transport have been extended to next-to-leading order in the coupling g.
None
2011-10-06
Modern QCD - Lecture 3 We will introduce processes with initial-state hadrons and discuss parton distributions, sum rules, as well as the need for a factorization scale once radiative corrections are taken into account. We will then discuss the DGLAP equation, the evolution of parton densities, as well as ways in which parton densities are extracted from data.
Effective charges and expansion parameters in QCD
Braaten, E.; Leveille, J.P.
1981-10-01
The momentum subtraction scheme MOM has been empirically successful in producing small QCD corrections to physical quantities at one loop order. By explicit calculations, we show that with a suitable shift in the renormalization scale, the minimal subtraction scheme coupling constant ..cap alpha../sub MS/ coincides with typical momentum scheme coupling constants at both one and two loop order.
NASA Astrophysics Data System (ADS)
Wilczek, Frank
Introduction Symmetry and the Phenomena of QCD Apparent and Actual Symmetries Asymptotic Freedom Confinement Chiral Symmetry Breaking Chiral Anomalies and Instantons High Temperature QCD: Asymptotic Properties Significance of High Temperature QCD Numerical Indications for Quasi-Free Behavior Ideas About Quark-Gluon Plasma Screening Versus Confinement Models of Chiral Symmetry Breaking More Refined Numerical Experiments High-Temperature QCD: Phase Transitions Yoga of Phase Transitions and Order Parameters Application to Glue Theories Application to Chiral Transitions Close Up on Two Flavors A Genuine Critical Point! (?) High-Density QCD: Methods Hopes, Doubts, and Fruition Another Renormalization Group Pairing Theory Taming the Magnetic Singularity High-Density QCD: Color-Flavor Locking and Quark-Hadron Continuity Gauge Symmetry (Non)Breaking Symmetry Accounting Elementary Excitations A Modified Photon Quark-Hadron Continuity Remembrance of Things Past More Quarks Fewer Quarks and Reality
Urban, Federico R.; Zhitnitsky, Ariel R.
2010-08-30
We review two mechanisms rooted in the infrared sector of QCD which, by exploiting the properties of the QCD ghost, as introduced by Veneziano, provide new insight on the cosmological dark energy problem, first, in the form of a Casimir-like energy from quantising QCD in a box, and second, in the form of additional, time-dependent, vacuum energy density in an expanding universe. Based on [1, 2].
Electroweak absorptive parts in the matching conditions of nonrelativistic QCD
Hoang, Andre H.; Reisser, Christoph J.
2005-04-01
Electroweak corrections associated with the instability of the top quark to the next-to-next-to-leading logarithmic (NNLL) total top pair threshold cross section in e{sup +}e{sup -} annihilation are determined. Our method is based on absorptive parts in electroweak matching conditions of the operators of nonrelativistic QCD and the optical theorem. The corrections lead to ultraviolet phase space divergences that have to be renormalized and lead to NLL mixing effects. Numerically, the corrections can amount to several percent and are comparable to the known NNLL QCD corrections.
QCD sign problem for small chemical potential
Splittorff, K.; Verbaarschot, J. J. M.
2007-06-01
The expectation value of the complex phase factor of the fermion determinant is computed in the microscopic domain of QCD at nonzero chemical potential. We find that the average phase factor is nonvanishing below a critical value of the chemical potential equal to half the pion mass and vanishes exponentially in the volume for larger values of the chemical potential. This holds for QCD with dynamical quarks as well as for quenched and phase quenched QCD. The average phase factor has an essential singularity for zero chemical potential and cannot be obtained by analytic continuation from imaginary chemical potential or by means of a Taylor expansion. The leading order correction in the p-expansion of the chiral Lagrangian is calculated as well.
Hadronic and nuclear interactions in QCD
Not Available
1982-01-01
Despite the evidence that QCD - or something close to it - gives a correct description of the structure of hadrons and their interactions, it seems paradoxical that the theory has thus far had very little impact in nuclear physics. One reason for this is that the application of QCD to distances larger than 1 fm involves coherent, non-perturbative dynamics which is beyond present calculational techniques. For example, in QCD the nuclear force can evidently be ascribed to quark interchange and gluon exchange processes. These, however, are as complicated to analyze from a fundamental point of view as is the analogous covalent bond in molecular physics. Since a detailed description of quark-quark interactions and the structure of hadronic wavefunctions is not yet well-understood in QCD, it is evident that a quantitative first-principle description of the nuclear force will require a great deal of theoretical effort. Another reason for the limited impact of QCD in nuclear physics has been the conventional assumption that nuclear interactions can for the most part be analyzed in terms of an effective meson-nucleon field theory or potential model in isolation from the details of short distance quark and gluon structure of hadrons. These lectures, argue that this view is untenable: in fact, there is no correspondence principle which yields traditional nuclear physics as a rigorous large-distance or non-relativistic limit of QCD dynamics. On the other hand, the distinctions between standard nuclear physics dynamics and QCD at nuclear dimensions are extremely interesting and illuminating for both particle and nuclear physics.
Subtractive Renormalization Group Invariance: Pionless EFT at NLO
Timoteo, Varese S.; Szpigel, Sergio; Duraes, Francisco O.
2010-11-12
We show some results concerning the renormalization group (RG) invariance of the nucleon-nucleon (NN) interaction in pionless effective field theory at next-to-leading order (NLO), using a non-relativistic Callan-Symanzik equation (NRCS) for the driving term of the Lippmann-Schwinger (LS) equation with three recursive subtractions. The phase-shifts obtained for the RG evolved potential are same as those for the original potential, apart from relative differences of order 10{sup -15}.
The development of new NLO crystals in the borate series
NASA Astrophysics Data System (ADS)
Chen, Chuangtian; Wu, Yicheng; Li, Rukang
1990-01-01
It is well known that the inorganic borates exist in numerous structural types, and some crystals such as KB5 (KB 5O 8·4H 2O) and BBO(β-BaB 2O 4) are excellent nonlinear optical (NLO) materials, particularly in the ultraviolet region. In this review, we are going to approach our topic from the anionic group theory, which we have begun to develop in the late 1960's. A systematic classification has been made of the borate series in terms of the structural types of the anionic groups. Calculations have been made for the linear and NLO properties for most of the important borate anionic groups, including second-order susceptibilities and absorption edges in the ultraviolet spectral region. We have therefore been led to the formulation of a series of structural criteria, which serve as useful guidelines for the screening, characterization, and development of certain borate crystals, such as BBO (β-BaB 2O 4, i.e., BaB 2O 4 in its low-temperature modification) and LBO (LiB 3O 5) as new materials. The characteristic features of BBO and LBO crystals, excellent NLO materials developed during the past few years in China at the Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, are also discussed.
Electroweak radiative corrections to triple photon production at the ILC
NASA Astrophysics Data System (ADS)
Zhang, Yu; Li, Wei-Hua; Duan, Peng-Fei; Song, Mao; Li, Gang
2016-07-01
In this paper, we present the precision predictions for three photon production in the standard model (SM) at the ILC including the full next-to-leading (NLO) electroweak (EW) corrections, high order initial state radiation (h.o.ISR) contributions and beamstrahlung effects. We present the LO and the NLO EW + h.o.ISR + beamstrahlung corrected total cross sections for various colliding energy when √{ s} ≥ 200 GeV and the kinematic distributions of final photons with √{ s} = 500 GeV at ILC, and find that the NLO EW corrections, the h.o.ISR contributions and the beamstrahlung effects are important in exploring the process e+e- → γγγ.
Lattice QCD in rotating frames.
Yamamoto, Arata; Hirono, Yuji
2013-08-23
We formulate lattice QCD in rotating frames to study the physics of QCD matter under rotation. We construct the lattice QCD action with the rotational metric and apply it to the Monte Carlo simulation. As the first application, we calculate the angular momenta of gluons and quarks in the rotating QCD vacuum. This new framework is useful to analyze various rotation-related phenomena in QCD. PMID:24010426
Markovian Monte Carlo program EvolFMC v.2 for solving QCD evolution equations
NASA Astrophysics Data System (ADS)
Jadach, S.; Płaczek, W.; Skrzypek, M.; Stokłosa, P.
2010-02-01
We present the program EvolFMC v.2 that solves the evolution equations in QCD for the parton momentum distributions by means of the Monte Carlo technique based on the Markovian process. The program solves the DGLAP-type evolution as well as modified-DGLAP ones. In both cases the evolution can be performed in the LO or NLO approximation. The quarks are treated as massless. The overall technical precision of the code has been established at 5×10. This way, for the first time ever, we demonstrate that with the Monte Carlo method one can solve the evolution equations with precision comparable to the other numerical methods. New version program summaryProgram title: EvolFMC v.2 Catalogue identifier: AEFN_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEFN_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including binary test data, etc.: 66 456 (7407 lines of C++ code) No. of bytes in distributed program, including test data, etc.: 412 752 Distribution format: tar.gz Programming language: C++ Computer: PC, Mac Operating system: Linux, Mac OS X RAM: Less than 256 MB Classification: 11.5 External routines: ROOT ( http://root.cern.ch/drupal/) Nature of problem: Solution of the QCD evolution equations for the parton momentum distributions of the DGLAP- and modified-DGLAP-type in the LO and NLO approximations. Solution method: Monte Carlo simulation of the Markovian process of a multiple emission of partons. Restrictions:Limited to the case of massless partons. Implemented in the LO and NLO approximations only. Weighted events only. Unusual features: Modified-DGLAP evolutions included up to the NLO level. Additional comments: Technical precision established at 5×10. Running time: For the 10 6 events at 100 GeV: DGLAP NLO: 27s; C-type modified DGLAP NLO: 150s (MacBook Pro with Mac OS X v.10
Production of heavy neutrino in next-to-leading order QCD at the LHC and beyond
NASA Astrophysics Data System (ADS)
Das, Arindam; Konar, Partha; Majhi, Swapan
2016-06-01
Majorana and pseudo-Dirac heavy neutrinos are introduced into the type-I and inverse seesaw models, respectively, in explaining the naturally small neutrino mass. TeV scale heavy neutrinos can also be accommodated to have a sizable mixing with the Standard Model light neutrinos, through which they can be produced and detected at the high energy colliders. In this paper we consider the Next-to-Leading Order QCD corrections to the heavy neutrino production, and study the scale variation in cross-sections as well as the kinematic distributions with different final states at 14 TeV LHC and also in the context of 100 TeV hadron collider. The repertoire of the Majorana neutrino is realized through the characteristic signature of the same-sign dilepton pair, whereas, due to a small lepton number violation, the pseudo-Dirac heavy neutrino can manifest the trileptons associated with missing energy in the final state. Using the √{s}=8 TeV, 20 .3 fb-1 and 19 .7 fb-1 data at the ATLAS and CMS respectively, we obtain prospective scale dependent upper bounds of the light-heavy neutrino mixing angles for the Majorana heavy neutrinos at the 14 TeV LHC and 100 TeV collider. Further exploiting a recent study on the anomalous multilepton search by CMS at √{s}=8 TeV with 19 .5 fb-1 data, we also obtain the prospective scale dependent upper bounds on the mixing angles for the pseudo-Dirac neutrinos. We thus project a scale dependent prospective reach using the NLO processes at the 14 TeV LHC.
NLO vertex for a forward jet plus a rapidity gap at high energies
Hentschinski, Martin; Madrigal Martínez, José Daniel; Murdaca, Beatrice; Vera, Agustín Sabio
2015-04-10
We present the calculation of the forward jet vertex associated to a rapidity gap (coupling of a hard pomeron to the jet) in the BFKL formalism at next-to-leading order (NLO). Real emission contributions are computed via Lipatov’s effective action. The NLO jet vertex turns out to be finite within collinear factorization and allows, together with the NLO non-forward gluon Green’s function, to perform NLO studies of jet production in diffractive events (e.g. Mueller-Tang dijets)
NASA Astrophysics Data System (ADS)
Lutz, Matthias F. M.; Lange, Jens Sören; Pennington, Michael; Bettoni, Diego; Brambilla, Nora; Crede, Volker; Eidelman, Simon; Gillitzer, Albrecht; Gradl, Wolfgang; Lang, Christian B.; Metag, Volker; Nakano, Takashi; Nieves, Juan; Neubert, Sebastian; Oka, Makoto; Olsen, Stephen L.; Pappagallo, Marco; Paul, Stephan; Pelizäus, Marc; Pilloni, Alessandro; Prencipe, Elisabetta; Ritman, Jim; Ryan, Sinead; Thoma, Ulrike; Uwer, Ulrich; Weise, Wolfram
2016-04-01
We report on the EMMI Rapid Reaction Task Force meeting 'Resonances in QCD', which took place at GSI October 12-14, 2015. A group of 26 people met to discuss the physics of resonances in QCD. The aim of the meeting was defined by the following three key questions: What is needed to understand the physics of resonances in QCD? Where does QCD lead us to expect resonances with exotic quantum numbers? What experimental efforts are required to arrive at a coherent picture? For light mesons and baryons only those with up, down and strange quark content were considered. For heavy-light and heavy-heavy meson systems, those with charm quarks were the focus. This document summarizes the discussions by the participants, which in turn led to the coherent conclusions we present here.
NASA Astrophysics Data System (ADS)
Deur, Alexandre; Brodsky, Stanley J.; de Téramond, Guy F.
2016-09-01
We review the present theoretical and empirical knowledge for αs, the fundamental coupling underlying the interactions of quarks and gluons in Quantum Chromodynamics (QCD). The dependence of αs(Q2) on momentum transfer Q encodes the underlying dynamics of hadron physics-from color confinement in the infrared domain to asymptotic freedom at short distances. We review constraints on αs(Q2) at high Q2, as predicted by perturbative QCD, and its analytic behavior at small Q2, based on models of nonperturbative dynamics. In the introductory part of this review, we explain the phenomenological meaning of the coupling, the reason for its running, and the challenges facing a complete understanding of its analytic behavior in the infrared domain. In the second, more technical, part of the review, we discuss the behavior of αs(Q2) in the high momentum transfer domain of QCD. We review how αs is defined, including its renormalization scheme dependence, the definition of its renormalization scale, the utility of effective charges, as well as "Commensurate Scale Relations" which connect the various definitions of the QCD coupling without renormalization-scale ambiguity. We also report recent significant measurements and advanced theoretical analyses which have led to precise QCD predictions at high energy. As an example of an important optimization procedure, we discuss the "Principle of Maximum Conformality", which enhances QCD's predictive power by removing the dependence of the predictions for physical observables on the choice of theoretical conventions such as the renormalization scheme. In the last part of the review, we discuss the challenge of understanding the analytic behavior αs(Q2) in the low momentum transfer domain. We survey various theoretical models for the nonperturbative strongly coupled regime, such as the light-front holographic approach to QCD. This new framework predicts the form of the quark-confinement potential underlying hadron spectroscopy and
Skands, Peter Z.; /Fermilab
2005-07-01
Recent developments in QCD phenomenology have spurred on several improved approaches to Monte Carlo event generation, relative to the post-LEP state of the art. In this brief review, the emphasis is placed on approaches for (1) consistently merging fixed-order matrix element calculations with parton shower descriptions of QCD radiation, (2) improving the parton shower algorithms themselves, and (3) improving the description of the underlying event in hadron collisions.
Compass Measurement of g1 and QCD Fits
NASA Astrophysics Data System (ADS)
Kunne, Fabienne
2016-02-01
We present the latest COMPASS results on the proton spin structure function g1p(x) at 200GeV. The data improve the statistical precision by a factor of ˜2 at low x. A reevaluation of the Bjorken sum rule based on COMPASS proton and deuteron data confirms its validation to a 9% accuracy. Finally, results from a global NLO QCD fit of g1 world data are shown. The extracted spin singlet distribution leads to an integrated value of 0.26 < ΔΣ < 0.34 at Q2 = 3 (GeV/c)2. The large uncertainty is mainly driven by the unknown shape of the distribution.
On-Shell Unitarity Bootstrap for QCD Amplitudes
Berger, Carola F.; Bern, Zvi; Dixon, Lance J.; Forde, Darren; Kosower, David A.
2006-10-17
Seeking and measuring new physics at the imminent Large Hadron Collider (LHC) will require extensive calculations of high-multiplicity backgrounds in perturbative QCD to next-to-leading order (NLO). The Les Houches 2005 workshop defined a target list, reproduced in table 1, for theorists to attack. In addition to the processes in the table, one would also like to compute processes such as W, Z + 4 jets, which are important backgrounds to searches for supersymmetry and other models of new electroweak physics. Such computations require one-loop amplitudes with seven external particles, including the vector boson, as depicted in figure 1. These are challenging calculations and Feynman-diagrammatic computations have only recently reached six-point amplitudes. Some of this progress has been described in this conference.
QCD analysis of the semi-inclusive COMPASS and HERMES data
NASA Astrophysics Data System (ADS)
Akhunzyanov, R. R.; Shevchenko, O. Yu.
2014-01-01
The first moments of polarized valence parton distribution functions truncated to the wide Bjorken x region 0.004 < x < 0.7 are directly (without any fitting procedure) extracted in the NLO QCD from combined semi-inclusive DIS data of COMPASS and HERMES collaborations. Two scenarios for fragmentation functions are considered. Applying the proposed original procedure to these results we estimate the contributions of sea u and d quarks to the proton spin, which turn out to be simply zero within the errors.
NASA Astrophysics Data System (ADS)
Nefedov, M. A.; Saleev, V. A.
2015-11-01
The hadroproduction of prompt isolated photon pairs at high energies is studied in the framework of the parton Reggeization approach. The real part of the NLO corrections is computed (the NLO⋆ approximation), and the procedure for the subtraction of double counting between real parton emissions in the hard-scattering matrix element and unintegrated parton distribution function is constructed for the amplitudes with Reggeized quarks in the initial state. The matrix element of the important next-to-next-to-leading-order subprocess R R →γ γ with full dependence on the transverse momenta of the initial-state Reggeized gluons is obtained. We compare obtained numerical results with diphoton spectra measured at the Tevatron and the LHC and find a good agreement of our predictions with experimental data at the high values of diphoton transverse momentum, pT, and especially at the pT larger than the diphoton invariant mass, M . In this multi-Regge kinematics region, the NLO correction is strongly suppressed, demonstrating the self-consistency of the parton Reggeization approach.
FOREWORD: Extreme QCD 2012 (xQCD)
NASA Astrophysics Data System (ADS)
Alexandru, Andrei; Bazavov, Alexei; Liu, Keh-Fei
2013-04-01
The Extreme QCD 2012 conference, held at the George Washington University in August 2012, celebrated the 10th event in the series. It has been held annually since 2003 at different locations: San Carlos (2011), Bad Honnef (2010), Seoul (2009), Raleigh (2008), Rome (2007), Brookhaven (2006), Swansea (2005), Argonne (2004), and Nara (2003). As usual, it was a very productive and inspiring meeting that brought together experts in the field of finite-temperature QCD, both theoretical and experimental. On the experimental side, we heard about recent results from major experiments, such as PHENIX and STAR at Brookhaven National Laboratory, ALICE and CMS at CERN, and also about the constraints on the QCD phase diagram coming from astronomical observations of one of the largest laboratories one can imagine, neutron stars. The theoretical contributions covered a wide range of topics, including QCD thermodynamics at zero and finite chemical potential, new ideas to overcome the sign problem in the latter case, fluctuations of conserved charges and how they allow one to connect calculations in lattice QCD with experimentally measured quantities, finite-temperature behavior of theories with many flavors of fermions, properties and the fate of heavy quarkonium states in the quark-gluon plasma, and many others. The participants took the time to write up and revise their contributions and submit them for publication in these proceedings. Thanks to their efforts, we have now a good record of the ideas presented and discussed during the workshop. We hope that this will serve both as a reminder and as a reference for the participants and for other researchers interested in the physics of nuclear matter at high temperatures and density. To preserve the atmosphere of the event the contributions are ordered in the same way as the talks at the conference. We are honored to have helped organize the 10th meeting in this series, a milestone that reflects the lasting interest in this
The Top Quark, QCD, And New Physics.
DOE R&D Accomplishments Database
Dawson, S.
2002-06-01
The role of the top quark in completing the Standard Model quark sector is reviewed, along with a discussion of production, decay, and theoretical restrictions on the top quark properties. Particular attention is paid to the top quark as a laboratory for perturbative QCD. As examples of the relevance of QCD corrections in the top quark sector, the calculation of e{sup+}e{sup -}+ t{bar t} at next-to-leading-order QCD using the phase space slicing algorithm and the implications of a precision measurement of the top quark mass are discussed in detail. The associated production of a t{bar t} pair and a Higgs boson in either e{sup+}e{sup -} or hadronic collisions is presented at next-to-leading-order QCD and its importance for a measurement of the top quark Yulrawa coupling emphasized. Implications of the heavy top quark mass for model builders are briefly examined, with the minimal supersymmetric Standard Model and topcolor discussed as specific examples.
THE TOP QUARK, QCD, AND NEW PHYSICS.
DAWSON,S.
2002-06-01
The role of the top quark in completing the Standard Model quark sector is reviewed, along with a discussion of production, decay, and theoretical restrictions on the top quark properties. Particular attention is paid to the top quark as a laboratory for perturbative QCD. As examples of the relevance of QCD corrections in the top quark sector, the calculation of e{sup +}e{sup -} + t{bar t} at next-to-leading-order QCD using the phase space slicing algorithm and the implications of a precision measurement of the top quark mass are discussed in detail. The associated production of a t{bar t} pair and a Higgs boson in either e{sup +}e{sup -} or hadronic collisions is presented at next-to-leading-order QCD and its importance for a measurement of the top quark Yulrawa coupling emphasized. Implications of the heavy top quark mass for model builders are briefly examined, with the minimal supersymmetric Standard Model and topcolor discussed as specific examples.
Harris, R.
1992-05-01
We present measurements of jet production and isolated prompt photon production in p{bar p} collisions at {radical}s = 1.8 TeV from the 1988--89 run of the Collider Detector at Fermilab (CDF). To test QCD with jets, the inclusive jet cross section (p{bar p} {yields} J + X) and two jet angular distributions (p{bar P} {yields} JJ + X) are compared to QCD predictions and are used to search for composite quarks. The ratio of the scaled jet cross sections at two Tevatron collision energies ({radical}s= 546 and 1800 GeV) is compared to QCD predictions for X{sub T} scaling violations. Also, we present the first evidence for QCD interference effects (color coherence) in third jet production (p{bar p} {yields} JJJ + X). To test QCD with photons, we present measurements of the transverse momentum spectrum of single isolated prompt photon production (p{bar p} {yields} {gamma} + X), double isolated prompt photon production (p{bar p} {yields} {gamma}{gamma} + X), and the angular distribution of photon-jet events (p{bar p} {yields} {gamma} J + X). We have also measured the isolated production ratio of {eta} and {pi}{sup 0} mesons (p{bar p} {yields} {eta} + X)/(p{bar p} {yields} {pi}{sup 0} + X) = 1.02 {plus minus} .15(stat) {plus minus} .23(sys).
Harris, R.; The CDF Collaboration
1992-05-01
We present measurements of jet production and isolated prompt photon production in p{bar p} collisions at {radical}s = 1.8 TeV from the 1988--89 run of the Collider Detector at Fermilab (CDF). To test QCD with jets, the inclusive jet cross section (p{bar p} {yields} J + X) and two jet angular distributions (p{bar P} {yields} JJ + X) are compared to QCD predictions and are used to search for composite quarks. The ratio of the scaled jet cross sections at two Tevatron collision energies ({radical}s= 546 and 1800 GeV) is compared to QCD predictions for X{sub T} scaling violations. Also, we present the first evidence for QCD interference effects (color coherence) in third jet production (p{bar p} {yields} JJJ + X). To test QCD with photons, we present measurements of the transverse momentum spectrum of single isolated prompt photon production (p{bar p} {yields} {gamma} + X), double isolated prompt photon production (p{bar p} {yields} {gamma}{gamma} + X), and the angular distribution of photon-jet events (p{bar p} {yields} {gamma} J + X). We have also measured the isolated production ratio of {eta} and {pi}{sup 0} mesons (p{bar p} {yields} {eta} + X)/(p{bar p} {yields} {pi}{sup 0} + X) = 1.02 {plus_minus} .15(stat) {plus_minus} .23(sys).
Majhi, S.K.; Mukhopadhyay, A.; Ward, B.F.L.; Yost, S.A.
2014-11-15
We present a phenomenological study of the current status of the application of our approach of exact amplitude-based resummation in quantum field theory to precision QCD calculations, by realistic MC event generator methods, as needed for precision LHC physics. We discuss recent results as they relate to the interplay of the attendant IR-improved DGLAP-CS theory of one of us and the precision of exact NLO matrix-element matched parton shower MC’s in the Herwig6.5 environment as determined by comparison to recent LHC experimental observations on single heavy gauge boson production and decay. The level of agreement between the new theory and the data continues to be a reason for optimism. In the spirit of completeness, we discuss as well other approaches to the same theoretical predictions that we make here from the standpoint of physical precision with an eye toward the (sub-)1% QCD⊗EW total theoretical precision regime for LHC physics. - Highlights: • Using LHC data, we show that IR-improved DGLAP-CS kernels with exact NLO Shower/ME matching improves MC precision. • We discuss other possible approaches in comparison with ours. • We propose experimental tests to discriminate between competing approaches.
The renormalization scale problem and novel perspectives for QCD
NASA Astrophysics Data System (ADS)
Brodsky, Stanley J.
2015-11-01
I discuss a number of novel tests of QCD, measurements which can illuminate fundamental features of hadron physics. These include the origin of the “ridge” in proton-proton collisions; the production of the Higgs at high xF; the role of digluon-initiated processes for quarkonium production; flavor-dependent anti-shadowing; the effect of nuclear shadowing on QCD sum rules; direct production of hadrons at high transverse momentum; and leading-twist lensing corrections; and the breakdown of perturbative QCD factorization. I also review the “Principle of Maximum Conformalit” (PMC) which systematically sets the renormalization scale order-by-order in pQCD, independent of the choice of renormalization scheme, thus eliminating an unnecessary theoretical uncertainty.
Deur, Alexandre; Brodsky, Stanley J.; de Téramond, Guy F.
2016-05-09
Here, we review present knowledge onmore » $$\\alpha_{s}$$, the Quantum Chromodynamics (QCD) running coupling. The dependence of $$\\alpha_s(Q^2)$$ on momentum transfer $Q$ encodes the underlying dynamics of hadron physics --from color confinement in the infrared domain to asymptotic freedom at short distances. We will survey our present theoretical and empirical knowledge of $$\\alpha_s(Q^2)$$, including constraints at high $Q^2$ predicted by perturbative QCD, and constraints at small $Q^2$ based on models of nonperturbative dynamics. In the first, introductory, part of this review, we explain the phenomenological meaning of the coupling, the reason for its running, and the challenges facing a complete understanding of its analytic behavior in the infrared domain. In the second, more technical, part of the review, we discuss $$\\alpha_s(Q^2)$$ in the high momentum transfer domain of QCD. We review how $$\\alpha_s$$ is defined, including its renormalization scheme dependence, the definition of its renormalization scale, the utility of effective charges, as well as `` Commensurate Scale Relations" which connect the various definitions of the QCD coupling without renormalization scale ambiguity. We also report recent important experimental measurements and advanced theoretical analyses which have led to precise QCD predictions at high energy. As an example of an important optimization procedure, we discuss the ``Principle of Maximum Conformality" which enhances QCD's predictive power by removing the dependence of the predictions for physical observables on the choice of the gauge and renormalization scheme. In last part of the review, we discuss $$\\alpha_s(Q^2)$$ in the low momentum transfer domain, where there has been no consensus on how to define $$\\alpha_s(Q^2)$$ or its analytic behavior. We will discuss the various approaches used for low energy calculations. Among them, we will discuss the light-front holographic approach to QCD in the strongly coupled
NASA Astrophysics Data System (ADS)
These are the proceedings of the QCD Evolution 2015 Workshop which was held 26-30 May, 2015 at Jefferson Lab, Newport News, Virginia, USA. The workshop is a continuation of a series of workshops held during four consecutive years 2011, 2012, 2013 at Jefferson Lab, and in 2014 in Santa Fe, NM. With the rapid developments in our understanding of the evolution of parton distributions including low-x, TMDs, GPDs, higher-twist correlation functions, and the associated progress in perturbative QCD, lattice QCD and effective field theory techniques we look forward with great enthusiasm to the 2015 meeting. A special attention was also paid to participation of experimentalists as the topics discussed are of immediate importance for the JLab 12 experimental program and a future Electron Ion Collider.
R evolution: Improving perturbative QCD
Hoang, Andre H.; Jain, Ambar; Stewart, Iain W.; Scimemi, Ignazio
2010-07-01
Perturbative QCD results in the MS scheme can be dramatically improved by switching to a scheme that accounts for the dominant power law dependence on the factorization scale in the operator product expansion. We introduce the ''MSR scheme'' which achieves this in a Lorentz and gauge invariant way and has a very simple relation to MS. Results in MSR depend on a cutoff parameter R, in addition to the {mu} of MS. R variations can be used to independently estimate (i.) the size of power corrections, and (ii.) higher-order perturbative corrections (much like {mu} in MS). We give two examples at three-loop order, the ratio of mass splittings in the B*-B and D*-D systems, and the Ellis-Jaffe sum rule as a function of momentum transfer Q in deep inelastic scattering. Comparing to data, the perturbative MSR results work well even for Q{approx}1 GeV, and power corrections are reduced compared to MS.
R evolution: Improving perturbative QCD
NASA Astrophysics Data System (ADS)
Hoang, André H.; Jain, Ambar; Scimemi, Ignazio; Stewart, Iain W.
2010-07-01
Perturbative QCD results in the MS¯ scheme can be dramatically improved by switching to a scheme that accounts for the dominant power law dependence on the factorization scale in the operator product expansion. We introduce the “MSR scheme” which achieves this in a Lorentz and gauge invariant way and has a very simple relation to MS¯. Results in MSR depend on a cutoff parameter R, in addition to the μ of MS¯. R variations can be used to independently estimate (i.) the size of power corrections, and (ii.) higher-order perturbative corrections (much like μ in MS¯). We give two examples at three-loop order, the ratio of mass splittings in the B*-B and D*-D systems, and the Ellis-Jaffe sum rule as a function of momentum transfer Q in deep inelastic scattering. Comparing to data, the perturbative MSR results work well even for Q˜1GeV, and power corrections are reduced compared to MS¯.
Brodsky, Stanley J.; /SLAC
2007-07-06
I discuss a number of novel topics in QCD, including the use of the AdS/CFT correspondence between Anti-de Sitter space and conformal gauge theories to obtain an analytically tractable approximation to QCD in the regime where the QCD coupling is large and constant. In particular, there is an exact correspondence between the fifth-dimension coordinate z of AdS space and a specific impact variable {zeta} which measures the separation of the quark constituents within the hadron in ordinary space-time. This connection allows one to compute the analytic form of the frame-independent light-front wavefunctions of mesons and baryons, the fundamental entities which encode hadron properties and allow the computation of exclusive scattering amplitudes. I also discuss a number of novel phenomenological features of QCD. Initial- and final-state interactions from gluon-exchange, normally neglected in the parton model, have a profound effect in QCD hard-scattering reactions, leading to leading-twist single-spin asymmetries, diffractive deep inelastic scattering, diffractive hard hadronic reactions, the breakdown of the Lam Tung relation in Drell-Yan reactions, and nuclear shadowing and non-universal antishadowing--leading-twist physics not incorporated in the light-front wavefunctions of the target computed in isolation. I also discuss tests of hidden color in nuclear wavefunctions, the use of diffraction to materialize the Fock states of a hadronic projectile and test QCD color transparency, and anomalous heavy quark effects. The presence of direct higher-twist processes where a proton is produced in the hard subprocess can explain the large proton-to-pion ratio seen in high centrality heavy ion collisions.
Lattice QCD for parallel computers
NASA Astrophysics Data System (ADS)
Quadling, Henley Sean
Lattice QCD is an important tool in the investigation of Quantum Chromodynamics (QCD). This is particularly true at lower energies where traditional perturbative techniques fail, and where other non-perturbative theoretical efforts are not entirely satisfactory. Important features of QCD such as confinement and the masses of the low lying hadronic states have been demonstrated and calculated in lattice QCD simulations. In calculations such as these, non-lattice techniques in QCD have failed. However, despite the incredible advances in computer technology, a full solution of lattice QCD may still be in the too-distant future. Much effort is being expended in the search for ways to reduce the computational burden so that an adequate solution of lattice QCD is possible in the near future. There has been considerable progress in recent years, especially in the research of improved lattice actions. In this thesis, a new approach to lattice QCD algorithms is introduced, which results in very significant efficiency improvements. The new approach is explained in detail, evaluated and verified by comparing physics results with current lattice QCD simulations. The new sub-lattice layout methodology has been specifically designed for current and future hardware. Together with concurrent research into improved lattice actions and more efficient numerical algorithms, the very significant efficiency improvements demonstrated in this thesis can play an important role in allowing lattice QCD researchers access to much more realistic simulations. The techniques presented in this thesis also allow ambitious QCD simulations to be performed on cheap clusters of commodity computers.
Radyushkin, Anatoly V.; Efremov, Anatoly Vasilievich; Ginzburg, Ilya F.
2013-04-01
We discuss some problems concerning the application of perturbative QCD to high energy soft processes. We show that summing the contributions of the lowest twist operators for non-singlet $t$-channel leads to a Regge-like amplitude. Singlet case is also discussed.
Brodsky, Stanley J.; Deshpande, Abhay L.; Gao, Haiyan; McKeown, Robert D.; Meyer, Curtis A.; Meziani, Zein-Eddine; Milner, Richard G.; Qiu, Jianwei; Richards, David G.; Roberts, Craig D.
2015-02-26
This White Paper presents the recommendations and scientific conclusions from the Town Meeting on QCD and Hadronic Physics that took place in the period 13-15 September 2014 at Temple University as part of the NSAC 2014 Long Range Planning process. The meeting was held in coordination with the Town Meeting on Phases of QCD and included a full day of joint plenary sessions of the two meetings. The goals of the meeting were to report and highlight progress in hadron physics in the seven years since the 2007 Long Range Plan (LRP07), and present a vision for the future by identifying the key questions and plausible paths to solutions which should define the next decade. The introductory summary details the recommendations and their supporting rationales, as determined at the Town Meeting on QCD and Hadron Physics, and the endorsements that were voted upon. The larger document is organized as follows. Section 2 highlights major progress since the 2007 LRP. It is followed, in Section 3, by a brief overview of the physics program planned for the immediate future. Finally, Section 4 provides an overview of the physics motivations and goals associated with the next QCD frontier: the Electron-Ion-Collider.
Andreas S. Kronfeld
2002-09-30
After reviewing some of the mathematical foundations and numerical difficulties facing lattice QCD, I review the status of several calculations relevant to experimental high-energy physics. The topics considered are moments of structure functions, which may prove relevant to search for new phenomena at the LHC, and several aspects of flavor physics, which are relevant to understanding CP and flavor violation.
Lincoln, Don
2016-06-28
The strongest force in the universe is the strong nuclear force and it governs the behavior of quarks and gluons inside protons and neutrons. The name of the theory that governs this force is quantum chromodynamics, or QCD. In this video, Fermilab?s Dr. Don Lincoln explains the intricacies of this dominant component of the Standard Model.
Devlin, T.; CDF Collaboration
1996-10-01
The CDF collaboration is engaged in a broad program of QCD measurements at the Fermilab Tevatron Collider. I will discuss inclusive jet production at center-of-mass energies of 1800 GeV and 630 GeV, properties of events with very high total transverse energy and dijet angular distributions.
Plunkett, R.; The CDF Collaboration
1991-10-01
Results are presented for hadronic jet and direct photon production at {radical}{bar s} = 1800 GeV. The data are compared with next-to-leading QCD calculations. A new limit on the scale of possible composite structure of the quarks is also reported. 12 refs., 4 figs.
The {Lambda}(1405) in Full QCD
Menadue, Benjamin J.; Kamleh, Waseem; Leinweber, Derek B.; Mahbub, M. Selim
2011-12-14
At 1405.1 MeV, the lowest-lying negative-parity state of the {Lambda} baryon lies surprising low. Indeed, this is lower than the lowest negative-parity state of the nucleon, even though the {Lambda}(1405) possesses a valence strange quark. However, previous Lattice QCD studies have been unable to identify such a low-lying state. Using the PACS-CS (2+1)-flavour full-QCD ensembles, available through the ILDG, we utilise a variational analysis with source and sink smearing to isolate this elusive state. We find three low-lying odd-parity states, and for the first time reproduce the correct level ordering with respect to the nearby scattering thresholds.
QCD at DOe: A Review of Recent Results
Sawyer, Lee
2011-04-26
We report a variety of measurements of hadronic final states, ranging from elastic scattering of protons to events with highly energetic jets, based on data taken with the DOe experiment at the Fermilab Tevatron proton-antiproton collider.Starting with the non-perturbative regime, we report measurement of the pp-bar elastic differential scattering cross section, using DOe's Forward Proton Detectors (FPD). We present a new way to describe minimum bias events based on angular distributions in {approx_equal}5 million minimum bias pp-bar collisions collected between April 2002 and February 2006 with the DOe detector. We demonstrate that the distribution of {Delta}{phi} in the detector transverse plane between the leading track and all other tracks is a robust observable that can be used for tuning of multiple color interaction models. Pseudorapidity correlations of the {Delta}{phi} distributions are also studied. In addition, we present a measurement of the effective cross section for events produced by double parton scattering.DOe has produced a wide-variety of analyzes of final states involving jets, using a well-understood and calibrated data sample. Inclusive jet cross-sections, dijet production, and multi-jet production have been studied and compared to next-to-leading order (NLO) perturbative Quantum Chromodynamics (pQCD) predictions. After reviewing several published measurements, including the inclusive jet cross section and extraction of the strong coupleing constant {alpha}{sub s}, and the dijet angular dependence and azimuthal decorrelation, we present several recent analyszes. The differential inclusive dijet as a function of the dijet invariant mass Mjj, and the three-jet cross section as a function of the invariant three-jet mass (M{sub 3jet}), are measured in a data set corresponding to an integrated luminosity of 0.7 fb{sup -1}. NLO pQCD calculations are found to be in a reasonable agreement with the measured cross sections.Based on the same data set
Nawa, Kanabu; Suganuma, Hideo; Kojo, Toru
2007-04-15
We study baryons in holographic QCD with D4/D8/D8 multi-D-brane system. In holographic QCD, the baryon appears as a topologically nontrivial chiral soliton in a four-dimensional effective theory of mesons. We call this topological soliton brane-induced Skyrmion. Some review of D4/D8/D8 holographic QCD is presented from the viewpoints of recent hadron physics and QCD phenomenologies. A four-dimensional effective theory with pions and {rho} mesons is uniquely derived from the non-Abelian Dirac-Born-Infeld (DBI) action of D8 brane with D4 supergravity background at the leading order of large N{sub c}, without small amplitude expansion of meson fields to discuss chiral solitons. For the hedgehog configuration of pion and {rho}-meson fields, we derive the energy functional and the Euler-Lagrange equation of brane-induced Skyrmion from the meson effective action induced by holographic QCD. Performing the numerical calculation, we obtain the soliton solution and figure out the pion profile F(r) and the {rho}-meson profile G-tilde(r) of the brane-induced Skyrmion with its total energy, energy density distribution, and root-mean-square radius. These results are compared with the experimental quantities of baryons and also with the profiles of standard Skyrmion without {rho} mesons. We analyze interaction terms of pions and {rho} mesons in brane-induced Skyrmion, and find a significant {rho}-meson component appearing in the core region of a baryon.
Brodsky, Stanley J.; /SLAC /Southern Denmark U., CP3-Origins
2011-08-12
I review a number of topics where conventional wisdom in hadron physics has been challenged. For example, hadrons can be produced at large transverse momentum directly within a hard higher-twist QCD subprocess, rather than from jet fragmentation. Such 'direct' processes can explain the deviations from perturbative QCD predictions in measurements of inclusive hadron cross sections at fixed x{sub T} = 2p{sub T}/{radical}s, as well as the 'baryon anomaly', the anomalously large proton-to-pion ratio seen in high centrality heavy ion collisions. Initial-state and final-state interactions of the struck quark, the soft-gluon rescattering associated with its Wilson line, lead to Bjorken-scaling single-spin asymmetries, diffractive deep inelastic scattering, the breakdown of the Lam-Tung relation in Drell-Yan reactions, as well as nuclear shadowing and antishadowing. The Gribov-Glauber theory predicts that antishadowing of nuclear structure functions is not universal, but instead depends on the flavor quantum numbers of each quark and antiquark, thus explaining the anomalous nuclear dependence measured in deep-inelastic neutrino scattering. Since shadowing and antishadowing arise from the physics of leading-twist diffractive deep inelastic scattering, one cannot attribute such phenomena to the structure of the nucleus itself. It is thus important to distinguish 'static' structure functions, the probability distributions computed from the square of the target light-front wavefunctions, versus 'dynamical' structure functions which include the effects of the final-state rescattering of the struck quark. The importance of the J = 0 photon-quark QCD contact interaction in deeply virtual Compton scattering is also emphasized. The scheme-independent BLM method for setting the renormalization scale is discussed. Eliminating the renormalization scale ambiguity greatly improves the precision of QCD predictions and increases the sensitivity of searches for new physics at the LHC
NLO evolution of 3-quark Wilson loop operator
Balitsky, I.; Grabovsky, A. V.
2015-01-07
It is well known that high-energy scattering of a meson from some hadronic target can be described by the interaction of that target with a color dipole formed by two Wilson lines corresponding to fast quark-antiquark pair. Moreover, the energy dependence of the scattering amplitude is governed by the evolution equation of this color dipole with respect to rapidity. Similarly, the energy dependence of scattering of a baryon can be described in terms of evolution of a three-Wilson-lines operator with respect to the rapidity of the Wilson lines. We calculate the evolution of the 3-quark Wilson loop operator in the next-to-leading order (NLO) and present a quasi-conformal evolution equation for a composite 3-Wilson-lines operator. Thus we also obtain the linearized version of that evolution equation describing the amplitude of the odderon exchange at high energies.
NLO evolution of 3-quark Wilson loop operator
Balitsky, I.; Grabovsky, A. V.
2015-01-07
It is well known that high-energy scattering of a meson from some hadronic target can be described by the interaction of that target with a color dipole formed by two Wilson lines corresponding to fast quark-antiquark pair. Moreover, the energy dependence of the scattering amplitude is governed by the evolution equation of this color dipole with respect to rapidity. Similarly, the energy dependence of scattering of a baryon can be described in terms of evolution of a three-Wilson-lines operator with respect to the rapidity of the Wilson lines. We calculate the evolution of the 3-quark Wilson loop operator in themore » next-to-leading order (NLO) and present a quasi-conformal evolution equation for a composite 3-Wilson-lines operator. Thus we also obtain the linearized version of that evolution equation describing the amplitude of the odderon exchange at high energies.« less
QCD with many fermions and QCD topology
NASA Astrophysics Data System (ADS)
Shuryak, Edward
2013-04-01
Major nonperturbative phenomena in QCD - confinement and chiral symmetry breaking - are known to be related with certain topological objects. Recent lattice advances into the domain of many Nf = O(10) fermion flavors have shown that both phase transitions had shifted in this case to much stronger coupling. We discuss confinement in terms of monopole Bose condensation, and discuss how it is affected by fermions "riding" on the monopoles, ending with the Nf dependence of the critical line. Chiral symmetry breaking is discussed in terms of the (anti)selfdual dyons, the instanton constituents. The fermionic zero modes of those have a different meaning and lead to strong interaction between dyons and antidyons. We report some qualitative consequences of this theory and also some information about our first direct numerical study of the dyonic ensemble, in respect to both chiral symmetry breaking and confinement (via back reaction to the holonomy potential).
Extended analytic QCD model with perturbative QCD behavior at high momenta
NASA Astrophysics Data System (ADS)
Ayala, César; Contreras, Carlos; Cvetič, Gorazd
2012-06-01
In contrast to perturbative QCD, the analytic QCD models have running coupling whose analytic properties correctly mirror those of spacelike observables. The discontinuity (spectral) function of such running coupling is expected to agree with the perturbative case at large timelike momenta; however, at low timelike momenta, it is not known. In the latter regime, we parametrize the unknown behavior of the spectral function as a sum of (two) delta functions; while the onset of the perturbative behavior of the spectral function is set to be 1.0-1.5GeV. This is in close analogy with the “minimal hadronic ansatz” used in the literature for modeling spectral functions of correlators. For the running coupling itself, we impose the condition that it basically merges with the perturbative coupling at high spacelike momenta. In addition, we require that the well-measured nonstrange semihadronic (V+A) tau decay ratio value be reproduced by the model. We thus obtain a QCD framework which is basically indistinguishable from perturbative QCD at high momenta (Q>1GeV), and at low momenta, it respects the basic analyticity properties of spacelike observables as dictated by the general principles of the local quantum field theories.
NASA Astrophysics Data System (ADS)
Dudek, Jozef J.
2016-03-01
I describe how hadron-hadron scattering amplitudes are related to the eigenstates of QCD in a finite cubic volume. The discrete spectrum of such eigenstates can be determined from correlation functions computed using lattice QCD, and the corresponding scattering amplitudes extracted. I review results from the Hadron Spectrum Collaboration who have used these finite volume methods to study ππ elastic scattering, including the ρ resonance, as well as coupled-channel πK, ηK scattering. The very recent extension to the case where an external current acts is also presented, considering the reaction πγ* → ππ, from which the unstable ρ → πγ transition form factor is extracted. Ongoing calculations are advertised and the outlook for finite volume approaches is presented.
Exponentially modified QCD coupling
Cvetic, Gorazd; Valenzuela, Cristian
2008-04-01
We present a specific class of models for an infrared-finite analytic QCD coupling, such that at large spacelike energy scales the coupling differs from the perturbative one by less than any inverse power of the energy scale. This condition is motivated by the Institute for Theoretical and Experimental Physics operator product expansion philosophy. Allowed by the ambiguity in the analytization of the perturbative coupling, the proposed class of couplings has three parameters. In the intermediate energy region, the proposed coupling has low loop-level and renormalization scheme dependence. The present modification of perturbative QCD must be considered as a phenomenological attempt, with the aim of enlarging the applicability range of the theory of the strong interactions at low energies.
Dudek, Jozef J.; Edwards, Robert G.
2012-03-21
In this study, we present the first comprehensive study of hybrid baryons using lattice QCD methods. Using a large basis of composite QCD interpolating fields we extract an extensive spectrum of baryon states and isolate those of hybrid character using their relatively large overlap onto operators which sample gluonic excitations. We consider the spectrum of Nucleon and Delta states at several quark masses finding a set of positive parity hybrid baryons with quantum numbers $N_{1/2^+},\\,N_{1/2^+},\\,N_{3/2^+},\\, N_{3/2^+},\\,N_{5/2^+},\\,$ and $\\Delta_{1/2^+},\\, \\Delta_{3/2^+}$ at an energy scale above the first band of `conventional' excited positive parity baryons. This pattern of states is compatible with a color octet gluonic excitation having $J^{P}=1^{+}$ as previously reported in the hybrid meson sector and with a comparable energy scale for the excitation, suggesting a common bound-state construction for hybrid mesons and baryons.
Gupta, R.
1998-12-31
The goal of the lectures on lattice QCD (LQCD) is to provide an overview of both the technical issues and the progress made so far in obtaining phenomenologically useful numbers. The lectures consist of three parts. The author`s charter is to provide an introduction to LQCD and outline the scope of LQCD calculations. In the second set of lectures, Guido Martinelli will discuss the progress they have made so far in obtaining results, and their impact on Standard Model phenomenology. Finally, Martin Luescher will discuss the topical subjects of chiral symmetry, improved formulation of lattice QCD, and the impact these improvements will have on the quality of results expected from the next generation of simulations.
Bjorken, J.D.
1996-10-01
New directions for exploring QCD at future high-energy colliders are sketched. These include jets within jets. BFKL dynamics, soft and hard diffraction, searches for disoriented chiral condensate, and doing a better job on minimum bias physics. The new experimental opportunities include electron-ion collisions at HERA, a new collider detector at the C0 region of the TeVatron, and the FELIX initiative at the LHC.
Kronfeld, A.S.; Allison, I.F.; Aubin, C.; Bernard, C.; Davies, C.T.H.; DeTar, C.; Di Pierro, M.; Freeland, E.D.; Gottlieb, Steven; Gray, A.; Gregor, E.; Heller, U.M.; Hetrick, J.E.; El-Khadra, Aida X.; Levkova, L.; Mackenzie, P.B.; Maresca, F.; Menscher, D.; Nobes, M.; Okamoto, M.; Oktay, M.B.; /Fermilab /Glasgow U. /Columbia U. /Washington U., St. Louis /Utah U. /DePaul U. /Art Inst. of Chicago /Indiana U. /Ohio State U. /Arizona U. /APS, New York /U. Pacific, Stockton /Illinois U., Urbana /Cornell U., LEPP /Simon Fraser U. /UC, Santa Barbara
2005-09-01
In the past year, we calculated with lattice QCD three quantities that were unknown or poorly known. They are the q{sup 2} dependence of the form factor in semileptonic D {yields} K/{nu} decay, the decay constant of the D meson, and the mass of the B{sub c} meson. In this talk, we summarize these calculations, with emphasis on their (subsequent) confirmation by experiments.
Giannetti, P. )
1991-05-01
Recent analysis of jet data taken at the Fermilab Tevatron Collider at {radical}S = 1.8 Tev are presented. Inclusive jet, dijet, trijet and direct photon measurements are compared to QCD parton level calculations, at orders {alpha}{sub s}{sup 3} or {alpha}{sub s}{sup 2}. The large total transverse energy events are well described by the Herwig shower Montecarlo. 19 refs., 20 figs., 1 tab.
Roberts, C.D.
1994-09-01
The Dyson-Schwinger equations (DSEs) are a tower of coupled integral equations that relate the Green functions of QCD to one another. Solving these equations provides the solution of QCD. This tower of equations includes the equation for the quark self-energy, which is the analogue of the gap equation in superconductivity, and the Bethe-Salpeter equation, the solution of which is the quark-antiquark bound state amplitude in QCD. The application of this approach to solving Abelian and non-Abelian gauge theories is reviewed. The nonperturbative DSE approach is being developed as both: (1) a computationally less intensive alternative and; (2) a complement to numerical simulations of the lattice action of QCD. In recent years, significant progress has been made with the DSE approach so that it is now possible to make sensible and direct comparisons between quantities calculated using this approach and the results of numerical simulations of Abelian gauge theories. Herein the application of the DSE approach to the calculation of pion observables is described: the {pi}-{pi} scattering lengths (a{sub 0}{sup 0}, a{sub 0}{sup 2}, A{sub 1}{sup 1}, a{sub 2}{sup 2}) and associated partial wave amplitudes; the {pi}{sup 0} {yields} {gamma}{gamma} decay width; and the charged pion form factor, F{sub {pi}}(q{sup 2}). Since this approach provides a straightforward, microscopic description of dynamical chiral symmetry breaking (D{sub X}SB) and confinement, the calculation of pion observables is a simple and elegant illustrative example of its power and efficacy. The relevant DSEs are discussed in the calculation of pion observables and concluding remarks are presented.
Hadronic Resonances from Lattice QCD
Lichtl, Adam C.; Bulava, John; Morningstar, Colin; Edwards, Robert; Mathur, Nilmani; Richards, David; Fleming, George; Juge, K. Jimmy; Wallace, Stephen J.
2007-10-26
The determination of the pattern of hadronic resonances as predicted by Quantum Chromodynamics requires the use of non-perturbative techniques. Lattice QCD has emerged as the dominant tool for such calculations, and has produced many QCD predictions which can be directly compared to experiment. The concepts underlying lattice QCD are outlined, methods for calculating excited states are discussed, and results from an exploratory Nucleon and Delta baryon spectrum study are presented.
Hadronic Resonances from Lattice QCD
John Bulava; Robert Edwards; George Fleming; K. Jimmy Juge; Adam C. Lichtl; Nilmani Mathur; Colin Morningstar; David Richards; Stephen J. Wallace
2007-06-16
The determination of the pattern of hadronic resonances as predicted by Quantum Chromodynamics requires the use of non-perturbative techniques. Lattice QCD has emerged as the dominant tool for such calculations, and has produced many QCD predictions which can be directly compared to experiment. The concepts underlying lattice QCD are outlined, methods for calculating excited states are discussed, and results from an exploratory Nucleon and Delta baryon spectrum study are presented.
Al-Yasari, Ahmed; Van Steerteghem, Nick; El Moll, Hani; Clays, Koen; Fielden, John
2016-02-21
We show that polyoxometalates (POMs) are an excellent redox-active acceptor on which to base high performance 2(nd) order non-linear optical (NLO) chromophores. This is demonstrated through three new organoimido-Lindqvist derivatives with HRS β0-values exceeding those of any dipolar organic system with comparable donor, π-system and absorption profile. Thus, organoimido POMs may provide a new generation of high performance, high transparency, and potentially redox-switchable NLO materials. PMID:26815652
Bevilacqua, G; Hartanto, H B; Kraus, M; Worek, M
2016-02-01
We present a complete description of top quark pair production in association with a jet in the dilepton channel. Our calculation is accurate to next-to-leading order (NLO) in QCD and includes all nonresonant diagrams, interferences, and off-shell effects of the top quark. Moreover, nonresonant and off-shell effects due to the finite W gauge boson width are taken into account. This calculation constitutes the first fully realistic NLO computation for top quark pair production with a final state jet in hadronic collisions. Numerical results for differential distributions as well as total cross sections are presented for the Large Hadron Collider at 8 TeV. With our inclusive cuts, NLO predictions reduce the unphysical scale dependence by more than a factor of 3 and lower the total rate by about 13% compared to leading-order QCD predictions. In addition, the size of the top quark off-shell effects is estimated to be below 2%. PMID:26894704
Resource Letter QCD-1: Quantum chromodynamics
NASA Astrophysics Data System (ADS)
Kronfeld, Andreas S.; Quigg, Chris
2010-11-01
This Resource Letter provides a guide to the literature on quantum chromodynamics (QCD), the relativistic quantum field theory of the strong interactions. Journal articles, books, and other documents are cited for the following topics: Quarks and color, the parton model, Yang-Mills theory, experimental evidence for color, QCD as a color gauge theory, asymptotic freedom, QCD for heavy hadrons, QCD on the lattice, the QCD vacuum, pictures of quark confinement, early and modern applications of perturbative QCD, the determination of the strong coupling and quark masses, QCD and the hadron spectrum, hadron decays, the quark-gluon plasma, the strong nuclear interaction, and QCD's role in nuclear physics.
Color Glass Condensate in Schwinger–Keldysh QCD
Jeon, Sangyong
2014-01-15
Within the Schwinger–Keldysh representation of many-body QCD, it is shown that the leading quantum corrections to the strong classical color field are “classical” in the sense that the fluctuation field still obeys the classical Jacobi-field equation, while the quantum effects solely reside in the fluctuations of the initial field configurations. Within this context, a systematic derivation of the JIMWLK renormalization group equation is presented. A clear identification of the correct form of gauge transformation rules and the correct form of the matter-field Lagrangian in the Schwinger–Keldysh QCD is also presented. -- Highlights: •Application of the Schwinger–Keldysh formalism to many-body QCD. •Clean separation of classical and quantum degrees of freedom. •Identification of the correct coupling between the gluon field and the color source. •Identification of the correct gauge transformation rules. •Sources of the classicality and quantum corrections to JIMWLK clarified.
Jet quenching from QCD evolution
NASA Astrophysics Data System (ADS)
Chien, Yang-Ting; Emerman, Alexander; Kang, Zhong-Bo; Ovanesyan, Grigory; Vitev, Ivan
2016-04-01
Recent advances in soft-collinear effective theory with Glauber gluons have led to the development of a new method that gives a unified description of inclusive hadron production in reactions with nucleons and heavy nuclei. We show how this approach, based on the generalization of the DGLAP evolution equations to include final-state medium-induced parton shower corrections for large Q2 processes, can be combined with initial-state effects for applications to jet quenching phenomenology. We demonstrate that the traditional parton energy loss calculations can be regarded as a special soft-gluon emission limit of the general QCD evolution framework. We present phenomenological comparison of the SCETG -based results on the suppression of inclusive charged hadron and neutral pion production in √{sNN }=2.76 TeV lead-lead collisions at the Large Hadron Collider to experimental data. We also show theoretical predictions for the upcoming √{sNN }≃5.1 TeV Pb +Pb run at the LHC.
NASA Astrophysics Data System (ADS)
Bartels, Jochen
2006-06-01
I summarize the present status of the AGK cutting rules in perturbative QCD. Particular attention is given to the application of the AGK analysis to diffraction and multiple scattering in DIS at HERA and to pp collisions at the LHC. I also discuss the bootstrap conditions which appear in pQCD.
QCD: Questions, challenges, and dilemmas
Bjorken, J.
1996-11-01
An introduction to some outstanding issues in QCD is presented, with emphasis on work by Diakonov and co-workers on the influence of the instanton vacuum on low-energy QCD observables. This includes the calculation of input valence-parton distributions for deep-inelastic scattering. 35 refs., 3 figs.
QCD coupling constants and VDM
Erkol, G.; Ozpineci, A.; Zamiralov, V. S.
2012-10-23
QCD sum rules for coupling constants of vector mesons with baryons are constructed. The corresponding QCD sum rules for electric charges and magnetic moments are also derived and with the use of vector-meson-dominance model related to the coupling constants. The VDM role as the criterium of reciprocal validity of the sum rules is considered.
Optical and structural properties of chalcone NLO single crystals
NASA Astrophysics Data System (ADS)
Rajesh Kumar, P. C.; Ravindrachary, V.; Janardhana, K.; Manjunath, H. R.; Karegouda, Prakash; Crasta, Vincent; Sridhar, M. A.
2011-11-01
Organic compound (E)-1-(4-methoxyphenyl)-3-(2,3,5-trichlorophenyl)prop-2-en-1-one [MPTCPP] with molecular formula C 16H 11Cl 3O 2 was synthesized using Claisen-Schmidt condensation reaction method. 1H NMR spectra was recorded to identify the various functional groups present in the compound and confirm the chemical structure. The single crystals were grown using slow evaporation solution growth technique. The UV-Visible spectrum study reveals that the crystal is transparent in the entire visible region and the absorption is observed at 364 nm. The Kurtz powder second harmonic generation (SHG) test shows that the MPTCPP is NLO active and its SHG efficiency is three times that of urea. Single crystal XRD study shows that the compound crystallizes in the monoclinic system with a space group Cc. The corresponding lattice parameters of the crystal are a = 28.215(5) Å, b = 3.9740(4) Å, c = 16.178(3) Å and V = 1503.0(4) Å 3. The micro hardness test was carried out and the work hardening coefficient value ( n) of the crystal was found to be 1.48. This indicates that the crystal is hard and is suitable for device application. The thermal study reveals that the thermal stability of the crystal is good.
Sekhar Chivukula
2010-01-08
The symmetries of a quantum field theory can be realized in a variety of ways. Symmetries can be realized explicitly, approximately, through spontaneous symmetry breaking or, via an anomaly, quantum effects can dynamically eliminate a symmetry of the theory that was present at the classical level. Quantum Chromodynamics (QCD), the modern theory of the strong interactions, exemplify each of these possibilities. The interplay of these effects determine the spectrum of particles that we observe and, ultimately, account for 99% of the mass of ordinary matter.
Sakai, Tadakatsu; Sugimoto, Shigeki
2005-12-02
We propose a holographic dual of QCD with massless flavors on the basis of a D4/D8-brane configuration within a probe approximation. We are led to a five-dimensional Yang-Mills theory on a curved space-time along with a Chern-Simons five-form on it, both of which provide us with a unifying framework to study the massless pion and an infinite number of massive vector mesons. We make sample computations of the physical quantities that involve the mesons and compare them with the experimental data. It is found that most of the results of this model are compatible with the experiments.
NASA Astrophysics Data System (ADS)
Sakai, Tadakatsu; Sugimoto, Shigeki
2005-12-01
We propose a holographic dual of QCD with massless flavors on the basis of a D4/D8-brane configuration within a probe approximation. We are led to a five-dimensional Yang-Mills theory on a curved space-time along with a Chern-Simons five-form on it, both of which provide us with a unifying framework to study the massless pion and an infinite number of massive vector mesons. We make sample computations of the physical quantities that involve the mesons and compare them with the experimental data. It is found that most of the results of this model are compatible with the experiments.
QCD THERMODYNAMICS AT ZERO AND NON-ZERO DENSITY.
SCHMIDT, C.
2007-07-03
We present recent results on thermodynamics of QCD with almost physical light quark masses and a physical strange quark mass value. These calculations have been performed with an improved staggered action especially designed for finite temperature lattice QCD. In detail we present a calculation of the transition temperature, using a combined chiral and continuum extrapolation. Furthermore we present preliminary results on the interaction measure and energy density at almost realistic quark masses. Finally we discuss the response of the pressure to a finite quark chemical potential. Within the Taylor expansion formalism we calculate quark number susceptibilities and leading order corrections to finite chemical potential. This is particularly useful for mapping out the critical region in the QCD phase diagram.
Resonance photo and electoproduction as a probe of QCD
Close, F.E.
1988-01-01
Analogies have been drawn between QCD where quarks build up hadrons, which in turn build up nuclei, and QED where electrons build up atoms, which in turn build up molecules. There has been a lot of talk about creating a quark theory of the nucleus in QCD by analogy with the way electrons build up molecules in QED. However, this seems to me to be a case of trying to run before you can walk, in that in QED the first step has been achieved, namely understanding atoms in terms of their electronic structure, but understanding molecules in QED is only understood in rather simple cases. In QCD the situation is even worse, in that we haven't even achieved the first step, namely in understanding how hadrons are built from quarks. We all believe that quarks are in the hadrons, and that at high momentum transfer we can apply perturbative QCD(pQCD). But to build the hadrons, we need pQCD and also non-perturbative QCD, which, at present, means building models to simulate the effects of the confinement. Insofar as any successful model of the nucleus will have it looking to a very good approximation as if it is made of nucleons, then I believe that first we have to understand the dynamics of quarks building the individual nucleons. Throughout this talk, I wanted to show how low-energy electron beams may help us deepen that understanding, and hopefully lead us towards the correct dynamical picture of the nucleon. 28 refs., 1 fig., 2 tabs.
Cool QCD: Hadronic Physics and QCD in Nuclei
NASA Astrophysics Data System (ADS)
Cates, Gordon
2015-10-01
QCD is the only strongly-coupled theory given to us by Nature, and it gives rise to a host of striking phenomena. Two examples in hadronic physics include the dynamic generation of mass and the confinement of quarks. Indeed, the vast majority of the mass of visible matter is due to the kinetic and potential energy of the massless gluons and the essentially massless quarks. QCD also gives rise to the force that binds protons and neutrons into nuclei, including subtle effects that have historically been difficult to understand. Describing these phenomena in terms of QCD has represented a daunting task, but remarkable progress has been achieved in both theory and experiment. Both CEBAF at Jefferson Lab and RHIC at Brookhaven National Lab have provided unprecedented experimental tools for investigating QCD, and upgrades at both facilities promise even greater opportunities in the future. Also important are programs at FermiLab as well as the LHC at CERN. Looking further ahead, an electron ion collider (EIC) has the potential to answer whole new sets of questions regarding the role of gluons in nuclear matter, an issue that lies at the heart of the generation of mass. On the theoretical side, rapid progress in supercomputers is enabling stunning progress in Lattice QCD calculations, and approximate forms of QCD are also providing deep new physical insight. In this talk I will describe both recent advances in Cool QCD as well as the exciting scientific opportunities that exist for the future.
Soltz, R; Vranas, P; Blumrich, M; Chen, D; Gara, A; Giampap, M; Heidelberger, P; Salapura, V; Sexton, J; Bhanot, G
2007-04-11
The theory of the strong nuclear force, Quantum Chromodynamics (QCD), can be numerically simulated from first principles on massively-parallel supercomputers using the method of Lattice Gauge Theory. We describe the special programming requirements of lattice QCD (LQCD) as well as the optimal supercomputer hardware architectures that it suggests. We demonstrate these methods on the BlueGene massively-parallel supercomputer and argue that LQCD and the BlueGene architecture are a natural match. This can be traced to the simple fact that LQCD is a regular lattice discretization of space into lattice sites while the BlueGene supercomputer is a discretization of space into compute nodes, and that both are constrained by requirements of locality. This simple relation is both technologically important and theoretically intriguing. The main result of this paper is the speedup of LQCD using up to 131,072 CPUs on the largest BlueGene/L supercomputer. The speedup is perfect with sustained performance of about 20% of peak. This corresponds to a maximum of 70.5 sustained TFlop/s. At these speeds LQCD and BlueGene are poised to produce the next generation of strong interaction physics theoretical results.
Nonperturbative QCD Calculations
NASA Astrophysics Data System (ADS)
Dellby, Niklas
1995-01-01
The research described in this thesis is an exact transformation of the Yang-Mills quantum chromodynamics (QCD) Lagrangrian into a form that is suitable for nonperturbative calculations. The conventional Yang-Mills Lagrangian has proven to be an excellent basis for perturbative calculations, but in nonperturbative calculations it is difficult to separate gauge problems from physical properties. To mitigate this problem, I develop a new equivalent Lagrangian that is not only expressed completely in terms of the field strengths ofthe gauge field but is also manifestly Lorentz and gauge invariant. The new Lagrangian is quadratic in derivatives, with non-linear local couplings, thus it is ideally suited for a numerical calculation. The field-strength Lagrangian is of such a form that it is possible to do a straightforward numerical stationary path expansion and find the fundamental QCD properties. This thesis examines several approximations analytically, investigating different ways to utilize the new Lagrangian. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253 -1690.).
Dudek, Jozef J.; Edwards, Robert G.
2012-03-21
In this study, we present the first comprehensive study of hybrid baryons using lattice QCD methods. Using a large basis of composite QCD interpolating fields we extract an extensive spectrum of baryon states and isolate those of hybrid character using their relatively large overlap onto operators which sample gluonic excitations. We consider the spectrum of Nucleon and Delta states at several quark masses finding a set of positive parity hybrid baryons with quantum numbersmore » $$N_{1/2^+},\\,N_{1/2^+},\\,N_{3/2^+},\\, N_{3/2^+},\\,N_{5/2^+},\\,$$ and $$\\Delta_{1/2^+},\\, \\Delta_{3/2^+}$$ at an energy scale above the first band of `conventional' excited positive parity baryons. This pattern of states is compatible with a color octet gluonic excitation having $$J^{P}=1^{+}$$ as previously reported in the hybrid meson sector and with a comparable energy scale for the excitation, suggesting a common bound-state construction for hybrid mesons and baryons.« less
NASA Astrophysics Data System (ADS)
Chen, Shi-Yong; Shen, Ke-Ming; Dai, Wei; Zhang, Ben-Wei; Zhang, Han-Zhong; Wang, En-Ke
2015-07-01
By using the recent spatially dependent nuclear PDF set EPS09s, we investigated the centrality-dependent Cold Nuclear Matter (CNM) effects for neutral π, η mesons and inclusive jets at RHIC in d+Au collisions and at LHC in p+Pb collisions. The nuclear modification factors as functions of transverse momentum are plotted at different centralities bins respectively. At all fixed centralities, the nuclear modification factors show no significant suppressions, contrast to the strong suppressions observed for central Au+Au collisions. Our results are consistent with the PHENIX preliminary Data in minimum bias and central d+Au collisions. The LHC experimental Data also support our predictions for both single inclusive hadron and inclusive jets productions in central p+Pb collisions. And the centrality dependence of the nuclear suppressions for all the observations in our calculations are lower than the RHIC and LHC Data. Supported by Ministry of Science and Technology in China under Grant Nos. 2014CB845404, 2014DFG02050, and by Natural Science Foundation of China under Grant Nos. 11322546, 11435004, 11221504
None
2011-10-06
Modern QCD - Lecture 1 Starting from the QCD Lagrangian we will revisit some basic QCD concepts and derive fundamental properties like gauge invariance and isospin symmetry and will discuss the Feynman rules of the theory. We will then focus on the gauge group of QCD and derive the Casimirs CF and CA and some useful color identities.
QCD Factorization and PDFs from Lattice QCD Calculation
NASA Astrophysics Data System (ADS)
Ma, Yan-Qing; Qiu, Jian-Wei
2015-02-01
In this talk, we review a QCD factorization based approach to extract parton distribution and correlation functions from lattice QCD calculation of single hadron matrix elements of quark-gluon operators. We argue that although the lattice QCD calculations are done in the Euclidean space, the nonperturbative collinear behavior of the matrix elements are the same as that in the Minkowski space, and could be systematically factorized into parton distribution functions with infrared safe matching coefficients. The matching coefficients can be calculated perturbatively by applying the factorization formalism on to asymptotic partonic states.
Carborane tuning on iridium complexes: redox-switchable second-order NLO responses.
Wang, Jiao; Wang, Wen-Yong; Fang, Xin-Yan; Qiu, Yong-Qing
2015-04-01
Much effort has been devoted to investigating the molecular geometries, electronic structures, redox properties and nonlinear optical (NLO) properties of Ir complexes involving o-, m- or p-carborane groups by density functional theory (DFT) methods. Switchable second-order NLO properties were induced by redox processes involving these complexes, and it was found that mainly the coordination bonds of Ir complexes changed during the oxidation process. Our calculations revealed that oxidation reactions have a significant influence on the second-order NLO response owing to the change in charge transfer pattern. The β tot values of oxidized species are at least ∼9 times larger for set I and ∼5 times larger for set II than those of the corresponding parent complexes. Introduction of carborane groups into ppy (phenylpyridine) ligands can enhance the second-order NLO response by 1.2- 1.6 times by a metal-to-ligand charge transfer (MLCT) transition between the Ir atom and carborane. The β tot of complex 2 [(ppy)2Ir(phen)](+) (phen = phenanthroline) is 3.3 times larger than that of complex 1 (ppy)2Ir(acce) (acce = acetylacetonate), which is caused by ligand-to-ligand charge transfer (LLCT) between ppy ligands and the ancillary ligand. Therefore, it can be concluded that the second-order NLO response can be effectively enhanced by oxidation reactions. PMID:25791353
Lattice QCD and Nuclear Physics
Konstantinos Orginos
2007-03-01
A steady stream of developments in Lattice QCD have made it possible today to begin to address the question of how nuclear physics emerges from the underlying theory of strong interactions. Central role in this understanding play both the effective field theory description of nuclear forces and the ability to perform accurate non-perturbative calculations in lo w energy QCD. Here I present some recent results that attempt to extract important low energy constants of the effective field theory of nuclear forces from lattice QCD.
Hadron physics in holographic QCD
NASA Astrophysics Data System (ADS)
Santra, A. B.; Lombardo, U.; Bonanno, A.
2012-07-01
Hadron physics deals with the study of strongly interacting subatomic particles such as neutrons, protons, pions and others, collectively known as baryons and mesons. Physics of strong interaction is difficult. There are several approaches to understand it. However, in the recent years, an approach called, holographic QCD, based on string theory (or gauge-gravity duality) is becoming popular providing an alternative description of strong interaction physics. In this article, we aim to discuss development of strong interaction physics through QCD and string theory, leading to holographic QCD.
Higher twist QCD terms in high-p/sub T/ pion production
Berger, E.L.; Gottschalk, T.; Sivers, D.
1980-08-01
The higher twist subprocesses qG ..-->.. q..pi../sup + -/ and q anti q ..-->.. G..pi../sup + -/ in the framework of perturbative Quantum Chromodynamics (QCD) are investigated. Cross sections for these processes are compared with the minimum twist QCD results for q anti q ..-->.. q anti q and qG ..-->.. qG. The higher twist terms give sizeable corrections to the inclusive pion yields, particularly for q anti q initial states. The effects of higher twist QCD terms for the charge ratio, N(..pi../sup -/N ..-->.. ..pi../sup -/X)/N(..pi../sup -/N ..-->.. ..pi../sup +/X) are examined.
NASA Astrophysics Data System (ADS)
Ellis, R. Keith
2009-05-01
Recent progress in perturbative QCD is described, with special emphasis on one-loop corrections to processes with large numbers of jets. These processes constitute important backgrounds for new physics searches at hadron colliders.
NASA Astrophysics Data System (ADS)
Mahmood, Asif; Abdullah, Muhammad Imran; Khan, Salah Ud-Din
2015-03-01
In this study, indigo based dyes with high non-linear optical response have been investigated. Density functional theory (DFT) was used to study non-linear optical properties of indigo and newly designed dyes (IM-Dye-0, IM-Dye-1, IM-Dye-2 and IM-Dye-3). The time dependant density functional theory (TDDFT) was used to calculate the excitation energies. The HOMO-LUMO energy gaps of newly designed dyes were smaller as compare with indigo dye. Absorption maxima of newly designed dyes strongly red shifted as compare with indigo dye. High non-linear optical (NLO) response of newly designed dyes revealed that these materials would be excellent for NLO applications. This theoretical approach of designing will pave the way for experimentalists to synthesize high response NLO compound.
Hadronic Higgs production through NLO PS in the SM, the 2HDM and the MSSM
NASA Astrophysics Data System (ADS)
Mantler, Hendrik; Wiesemann, Marius
2015-06-01
The next-to-leading order (NLO) cross section of the gluon fusion process is matched to parton showers in the MC@NLO approach. We work in the framework of MadGraph5_aMC@NLO and document the inclusion of the full quark-mass dependence in the Standard Model (SM) as well as the state-of-the-art squark and gluino effects within the Minimal Supersymmetric SM embodied in the program SusHi. The combination of the two programs is realized by a script which is publicly available and whose usage is detailed. We discuss the input cards and the relevant parameter switches. One of our focuses is on the shower scale which is specifically important for gluon-induced Higgs production, particularly in models with enhanced Higgs-bottom Yukawa coupling.
Leptonic decay of the ϒ(1S) meson at third order in QCD.
Beneke, Martin; Kiyo, Yuichiro; Marquard, Peter; Penin, Alexander; Piclum, Jan; Seidel, Dirk; Steinhauser, Matthias
2014-04-18
We present the complete next-to-next-to-next-to-leading order short-distance and bound-state QCD correction to the leptonic decay rate Γ(ϒ(1S)→ℓ+ℓ-) of the lowest-lying spin-1 bottomonium state. The perturbative QCD prediction is compared to the measurement Γ(ϒ(1S)→e+e-)=1.340(18) keV. PMID:24785029
Precise tests of QCD in e{sup +}e{sup {minus}} annihilation
Burrows, P.N.
1997-03-01
A pedagogical review is given of precise tests of QCD in electron-positron annihilation. Emphasis is placed on measurements that have served to establish QCD as the correct theory of strong interactions, as well as measurements of the coupling parameter {alpha}{sub s}. An outlook is given for future important tests at a high-energy e{sup +}e{sup {minus}} collider.
Excited Baryons in Holographic QCD
de Teramond, Guy F.; Brodsky, Stanley J.; /SLAC /Southern Denmark U., CP3-Origins
2011-11-08
The light-front holographic QCD approach is used to describe baryon spectroscopy and the systematics of nucleon transition form factors. Baryon spectroscopy and the excitation dynamics of nucleon resonances encoded in the nucleon transition form factors can provide fundamental insight into the strong-coupling dynamics of QCD. The transition from the hard-scattering perturbative domain to the non-perturbative region is sensitive to the detailed dynamics of confined quarks and gluons. Computations of such phenomena from first principles in QCD are clearly very challenging. The most successful theoretical approach thus far has been to quantize QCD on discrete lattices in Euclidean space-time; however, dynamical observables in Minkowski space-time, such as the time-like hadronic form factors are not amenable to Euclidean numerical lattice computations.
QCD analogy for quantum gravity
NASA Astrophysics Data System (ADS)
Holdom, Bob; Ren, Jing
2016-06-01
Quadratic gravity presents us with a renormalizable, asymptotically free theory of quantum gravity. When its couplings grow strong at some scale, as in QCD, then this strong scale sets the Planck mass. QCD has a gluon that does not appear in the physical spectrum. Quadratic gravity has a spin-2 ghost that we conjecture does not appear in the physical spectrum. We discuss how the QCD analogy leads to this conjecture and to the possible emergence of general relativity. Certain aspects of the QCD path integral and its measure are also similar for quadratic gravity. With the addition of the Einstein-Hilbert term, quadratic gravity has a dimensionful parameter that seems to control a quantum phase transition and the size of a mass gap in the strong phase.
Synthesis of several novel multifunctionalized chromophores for second-order NLO
NASA Astrophysics Data System (ADS)
Luo, Jingdong; Zhan, Caimao; Qin, Jingui
1998-08-01
4-[4-disubstituted-amino-phenylazo]-(alpha) - cyanocinnamates with two or more functional groups (such as hydroxyl, allyl) at both ends of the molecule to be used as novel chromophores for second-order NLO polymeric materials are synthesized by diazonium coupling and Knoevenagel condensation. In this two-step method, the tediousness of functionalization at the electron-acceptor end is avoided by selecting (alpha) -cyanoacrylate as electron-acceptor. The products are easy to purify, and the whole procedure is simple and time-saving, which facilitates the choice of polymer system for effective hardened NLO lattice in a broader range.
NLO predictions for a lepton, missing transverse momentum and dijets at the Tevatron
Campbell, John M.; Martin, Adam; Williams, Ciaran; /Fermilab
2011-05-01
In this paper we investigate the various processes that can contribute to a final state consisting of a lepton, missing transverse momentum, and two jets at next-to-leading order (NLO) at the Tevatron. In particular we consider the production of W/Z+2 jets, diboson pairs, single top, and the t{bar t} process with both fully leptonic and semileptonic decays. We present distributions for the invariant mass of the dijet system and normalizations of the various processes, accurate to NLO.
Next-to-Leading Order QCD Predictions for Z, gamma^* 3-Jet Distributions at the Tevatron
Berger, C.F.; Bern, Z.; Dixon, L.J.; Cordero, F.Febres; Forde, D.; Gleisberg, T.; Ita, H.; Kosower, D.A.; Maitre, D.; /Durham U.
2010-06-02
Using BlackHat in conjunction with SHERPA, we have computed next-to-leading order QCD predictions for a variety of distributions in Z, {gamma}{sup {asterisk}}+ 1, 2, 3-jet production at the Tevatron, where the Z boson or off-shell photon decays into an electron-positron pair. We find good agreement between the NLO results for jet {sub pT} distributions and measurements by CDF and D0. We also present jetproduction ratios, or probabilities of finding one additional jet. As a function of vector-boson {sub pT} , the ratios have distinctive features which we describe in terms of a simple model capturing leading logarithms and phase-space and parton-distribution-function suppression.
Savin, I. A.
2007-06-13
The fits of all published data on g1, including the new COMPASS measurements of g{sub 1}{sup d}(x,Q{sup 2}), have been performed by using two different QCD evolution formalisms in the next-to-leading-order (NLO) approximation. In both methods we obtain two solutions for fitted parameters of the parton distribution functions (PDFs), one with {delta}G>0 and the other - with {delta}G<0, where {delta}G is the first moment of the polarized gluon distribution in nucleon.
On the loop approximation in nucleon QCD sum rules
Drukarev, E. G. Ryskin, M. G.; Sadovnikova, V. A.
2015-10-15
There was a general belief that the nucleon QCD sum rules which include only the quark loops and thus contain only the condensates of dimension d = 3 and d = 4 have only a trivial solution. We demonstrate that there is also a nontrivial solution. We show that it can be treated as the lowest order approximation to the solution which includes the higher terms of the Operator Product Expansion. Inclusion of the radiative corrections improves the convergence of the series.
Andersen, Jens O.; Leganger, Lars E.; Strickland, Michael; Su, Nan
2011-10-15
In this brief report we compare the predictions of a recent next-to-next-to-leading order hard-thermal-loop perturbation theory (HTLpt) calculation of the QCD trace anomaly to available lattice data. We focus on the trace anomaly scaled by T{sup 2} in two cases: N{sub f}=0 and N{sub f}=3. When using the canonical value of {mu}=2{pi}T for the renormalization scale, we find that for Yang-Mills theory (N{sub f}=0) agreement between HTLpt and lattice data for the T{sup 2}-scaled trace anomaly begins at temperatures on the order of 8T{sub c}, while treating the subtracted piece as an interaction term when including quarks (N{sub f}=3) agreement begins already at temperatures above 2T{sub c}. In both cases we find that at very high temperatures the T{sup 2}-scaled trace anomaly increases with temperature in accordance with the predictions of HTLpt.
X-Ray Diffraction Analysis of NLO Crystals: Traditional Applications and More New Opportunities
NASA Technical Reports Server (NTRS)
Antipin, Mikhail Yu.; Clark, Ronald D.; Nesterov, Vladimir N.
1998-01-01
Single crystal X-ray diffraction analysis is one of the more important methods for the molecular and crystal structure determination of matter and therefore it has a great importance in material science including design and engineering of different compounds with non-linear optical (NLO) properties. It was shown in our previous publications that this method provides unique information about molecular structure of NLO compounds, their crystal symmetry and crystal packing arrays, molecular conformation and geometries and many other structural and electronic characteristics that are important for understanding the nature of NLO properties of solids. A very new application of the X-ray diffraction method is related to analysis of the electron density distribution p(r) in crystals and some of its characteristics (atomic and group charges, dipole and higher multipole moments, etc.), that may be obtained directly form the diffraction measurements. In the present work, we will discuss our preliminary low temperature high-resolution X-ray data for the m-nitroaniline (mNA) single crystal (VI). This is one of the "classical" organic NLO materials and electron density distribution analysis in this simple compound has a great scientific interest.
Highly Non-Linear Optical (NLO) organic crystals and films. Electrooptical organic materials
NASA Technical Reports Server (NTRS)
Mcmanus, Samuel P.; Rosenberger, Franz; Matthews, John
1987-01-01
Devices employing nonlinear optics (NLO) hold great promise for important applications in integrated optics, optical information processing and telecommunications. Properly designed organics possess outstanding optical and electrooptical properties which will substantially advance many technologies including electrooptical switching, optical amplification for communications, and parallel processing for hybrid optical computers. A brief comparison of organic and inorganic materials is given.
Feynman rules for Coulomb gauge QCD
Andrasi, A.; Taylor, J.C.
2012-10-15
The Coulomb gauge in nonabelian gauge theories is attractive in principle, but beset with technical difficulties in perturbation theory. In addition to ordinary Feynman integrals, there are, at 2-loop order, Christ-Lee (CL) terms, derived either by correctly ordering the operators in the Hamiltonian, or by resolving ambiguous Feynman integrals. Renormalization theory depends on the sub-graph structure of ordinary Feynman graphs. The CL terms do not have a sub-graph structure. We show how to carry out renormalization in the presence of CL terms, by re-expressing these as 'pseudo-Feynman' integrals. We also explain how energy divergences cancel. - Highlights: Black-Right-Pointing-Pointer In Coulomb gauge QCD, we re-express Christ-Lee terms in the Hamiltonian as pseudo-Feynman integrals. Black-Right-Pointing-Pointer This gives a subgraph structure, and allows the ordinary renormalization process. Black-Right-Pointing-Pointer It also leads to cancellation of energy-divergences.
Electroproduction of tensor mesons in QCD
NASA Astrophysics Data System (ADS)
Braun, V. M.; Kivel, N.; Strohmaier, M.; Vladimirov, A. A.
2016-06-01
Due to multiple possible polarizations hard exclusive production of tensor mesons by virtual photons or in heavy meson decays offers interesting possibilities to study the helicity structure of the underlying short-distance process. Motivated by the first measurement of the transition form factor γ∗γ → f 2(1270) at large momentum transfers by the BELLE collaboration we present an improved QCD analysis of this reaction in the framework of collinear factorization including contributions of twist-three quark-antiquark-gluon operators and an estimate of soft end-point corrections using light-cone sum rules. The results appear to be in good agreement with the data, in particular the predicted scaling behavior is reproduced in all cases.
Subcritical string and large N QCD
Thorn, Charles B.
2008-10-15
We pursue the possibility of using subcritical string theory in 4 spacetime dimensions to establish a string dual for large N QCD. In particular we study the even G-parity sector of the 4 dimensional Neveu-Schwarz dual resonance model as the natural candidate for this string theory. Our point of view is that the open string dynamics given by this model will determine the appropriate subcritical closed string theory, a tree level background of which should describe the sum of planar multiloop open string diagrams. We examine the one-loop open string diagram, which contains information about the closed string spectrum at weak coupling. Higher loop open string diagrams will be needed to determine closed string interactions. We also analyze the field theory limit of the one-loop open string diagram and recover the correct running coupling behavior of the limiting gauge theory.
Recent QCD results from the Tevatron
Pickarz, Henryk; CDF and DO collaboration
1997-02-01
Recent QCD results from the CDF and D0 detectors at the Tevatron proton-antiproton collider are presented. An outlook for future QCD tests at the Tevatron collider is also breifly discussed. 27 refs., 11 figs.
Kenneth Wilson and Lattice QCD
NASA Astrophysics Data System (ADS)
Ukawa, Akira
2015-09-01
We discuss the physics and computation of lattice QCD, a space-time lattice formulation of quantum chromodynamics, and Kenneth Wilson's seminal role in its development. We start with the fundamental issue of confinement of quarks in the theory of the strong interactions, and discuss how lattice QCD provides a framework for understanding this phenomenon. A conceptual issue with lattice QCD is a conflict of space-time lattice with chiral symmetry of quarks. We discuss how this problem is resolved. Since lattice QCD is a non-linear quantum dynamical system with infinite degrees of freedom, quantities which are analytically calculable are limited. On the other hand, it provides an ideal case of massively parallel numerical computations. We review the long and distinguished history of parallel-architecture supercomputers designed and built for lattice QCD. We discuss algorithmic developments, in particular the difficulties posed by the fermionic nature of quarks, and their resolution. The triad of efforts toward better understanding of physics, better algorithms, and more powerful supercomputers have produced major breakthroughs in our understanding of the strong interactions. We review the salient results of this effort in understanding the hadron spectrum, the Cabibbo-Kobayashi-Maskawa matrix elements and CP violation, and quark-gluon plasma at high temperatures. We conclude with a brief summary and a future perspective.
LATTICE QCD THERMODYNAMICS WITH WILSON QUARKS.
EJIRI,S.
2007-11-20
We review studies of QCD thermodynamics by lattice QCD simulations with dynamical Wilson quarks. After explaining the basic properties of QCD with Wilson quarks at finite temperature including the phase structure and the scaling properties around the chiral phase transition, we discuss the critical temperature, the equation of state and heavy-quark free energies.
Next-to-leading-order correction to pion form factor in k{sub T} factorization
Li Hsiangnan; Shen Yuelong; Wang Yuming; Zou Hao
2011-03-01
We calculate the next-to-leading-order (NLO) correction to the pion electromagnetic form factor at leading twist in the k{sub T} factorization theorem. Partons off-shell by k{sub T}{sup 2} are considered in both quark diagrams and effective diagrams for the transverse-momentum-dependent pion wave function. The light-cone singularities in the transverse-momentum-dependent pion wave function are regularized by rotating the Wilson lines away from the light cone. The soft divergences from gluon exchanges among initial- and fal-state partons cancel exactly. We derive the infrared-finite k{sub T}-dependent NLO hard kernel for the pion electromagnetic form factor by taking the difference of the above two sets of diagrams. Varying the renormalization and factorization scales, we find that the NLO correction is smaller, when both the scales are set to the invariant masses of internal particles: it becomes lower than 40% of the leading-order contribution for momentum transfer squared Q{sup 2}>7 GeV{sup 2}. It is observed that the NLO leading-twist correction does not play an essential role in explaining the experimental data, but the leading-order higher-twist contribution does.
Unparticles in diphoton production to next-to-leading order in QCD at the LHC
NASA Astrophysics Data System (ADS)
Kumar, M. C.; Mathews, Prakash; Ravindran, V.; Tripathi, Anurag
2009-04-01
We compute to next-to-leading order in QCD the tensor unparticle contribution to the diphoton production at the LHC, wherein the unparticle sector is a consequence of (a) scale invariance but not full conformal invariance and (b) conformal invariance. We use the semianalytical two cutoff phase-space slicing method to handle the O(αs) corrections to the pp→γγX and show that our results are insensitive to the soft and collinear cutoffs. In order to avoid the contribution of the photons due to fragmentation, we employ the smooth cone isolation criterion. Significance of the QCD corrections to the diphoton events including unparticles is highlighted.
Rapidity distributions in Drell-Yan and Higgs productions at threshold to third order in QCD.
Ahmed, Taushif; Mandal, M K; Rana, Narayan; Ravindran, V
2014-11-21
We present the threshold N(3)LO perturbative QCD corrections to the rapidity distributions of dileptons in the Drell-Yan process and Higgs boson in gluon fusion. Sudakov resummation of QCD amplitudes, renormalization group invariance, and the mass factorization theorem provide useful guidelines to obtain them in an elegant manner. We use various state of the art three loop results that have been recently available to obtain these distributions. For the Higgs boson, we demonstrate numerically the importance of these corrections at the LHC. PMID:25479490
Neutron star structure from QCD
NASA Astrophysics Data System (ADS)
Fraga, Eduardo S.; Kurkela, Aleksi; Vuorinen, Aleksi
2016-03-01
In this review article, we argue that our current understanding of the thermodynamic properties of cold QCD matter, originating from first principles calculations at high and low densities, can be used to efficiently constrain the macroscopic properties of neutron stars. In particular, we demonstrate that combining state-of-the-art results from Chiral Effective Theory and perturbative QCD with the current bounds on neutron star masses, the Equation of State of neutron star matter can be obtained to an accuracy better than 30% at all densities.
The supercritical pomeron in QCD.
White, A. R.
1998-06-29
Deep-inelastic diffractive scaling violations have provided fundamental insight into the QCD pomeron, suggesting a single gluon inner structure rather than that of a perturbative two-gluon bound state. This talk outlines a derivation of a high-energy, transverse momentum cut-off, confining solution of QCD. The pomeron, in first approximation, is a single reggeized gluon plus a ''wee parton'' component that compensates for the color and particle properties of the gluon. This solution corresponds to a super-critical phase of Reggeon Field Theory.
QCD inequalities for hadron interactions.
Detmold, William
2015-06-01
We derive generalizations of the Weingarten-Witten QCD mass inequalities for particular multihadron systems. For systems of any number of identical pseudoscalar mesons of maximal isospin, these inequalities prove that near threshold interactions between the constituent mesons must be repulsive and that no bound states can form in these channels. Similar constraints in less symmetric systems are also extracted. These results are compatible with experimental results (where known) and recent lattice QCD calculations, and also lead to a more stringent bound on the nucleon mass than previously derived, m_{N}≥3/2m_{π}. PMID:26196617
Yun, J.C.
1990-10-10
In this paper we report recent QCD analysis with the new data taken from CDF detector. CDF recorded an integrated luminosity of 4.4 nb{sup {minus}1} during the 1988--1989 run at center of mass system (CMS) energy of 1.8 TeV. The major topics of this report are inclusive jet, dijet, trijet and direct photon analysis. These measurements are compared of QCD predictions. For the inclusive jet an dijet analysis, tests of quark compositeness are emphasized. 11 refs., 6 figs.
Lattice QCD clusters at Fermilab
Holmgren, D.; Mackenzie, Paul B.; Singh, Anitoj; Simone, Jim; /Fermilab
2004-12-01
As part of the DOE SciDAC ''National Infrastructure for Lattice Gauge Computing'' project, Fermilab builds and operates production clusters for lattice QCD simulations. This paper will describe these clusters. The design of lattice QCD clusters requires careful attention to balancing memory bandwidth, floating point throughput, and network performance. We will discuss our investigations of various commodity processors, including Pentium 4E, Xeon, Opteron, and PPC970. We will also discuss our early experiences with the emerging Infiniband and PCI Express architectures. Finally, we will present our predictions and plans for future clusters.
Glueball decay in holographic QCD
Hashimoto, Koji; Tan, C.-I; Terashima, Seiji
2008-04-15
Using holographic QCD based on D4-branes and D8-anti-D8-branes, we have computed couplings of glueballs to light mesons. We describe glueball decay by explicitly calculating its decay widths and branching ratios. Interestingly, while glueballs remain less well understood both theoretically and experimentally, our results are found to be consistent with the experimental data for the scalar glueball candidate f{sub 0}(1500). More generally, holographic QCD predicts that decay of any glueball to 4{pi}{sup 0} is suppressed, and that mixing of the lightest glueball with qq mesons is small.
Nucleon Structure from Lattice QCD
David Richards
2007-09-05
Recent advances in lattice field theory, in computer technology and in chiral perturbation theory have enabled lattice QCD to emerge as a powerful quantitative tool in understanding hadron structure. I describe recent progress in the computation of the nucleon form factors and moments of parton distribution functions, before proceeding to describe lattice studies of the Generalized Parton Distributions (GPDs). In particular, I show how lattice studies of GPDs contribute to building a three-dimensional picture of the proton, I conclude by describing the prospects for studying the structure of resonances from lattice QCD.
Realization of chiral symmetry breaking and restoration in holographic QCD
NASA Astrophysics Data System (ADS)
Chelabi, Kaddour; Fang, Zhen; Huang, Mei; Li, Danning; Wu, Yue-Liang
2016-05-01
With proper profiles of the scalar potential and the dilaton field, for the first time, the spontaneous chiral symmetry breaking in the vacuum and its restoration at finite temperature are correctly realized in the holographic QCD framework. In the chiral limit, a nonzero chiral condensate develops in the vacuum and decreases with temperature, and the phase transition is of the second order for a two-flavor case and of the first order for a three-flavor case. In the case of explicit chiral symmetry breaking, in the two-flavor case, the second-order phase transition turns into a crossover with any nonzero current quark mass, and in the three-flavor case, the first-order phase transition turns into a crossover at a finite current quark mass. The correct description of chiral symmetry breaking and restoration makes the holographic QCD models more powerful in dealing with nonperturbative QCD phenomena. This framework can be regarded as a general setup in an application of AdS/CFT to describe conventional Ginzburg-Landau-Wilson-type phase transitions, e.g. in condensed matter and cosmology systems.
NASA Astrophysics Data System (ADS)
Boz, Tamer; Giudice, Pietro; Hands, Simon; Skullerud, Jon-Ivar; Williams, Anthony G.
2016-01-01
QCD at high chemical potential has interesting properties such as deconfinement of quarks. Two-color QCD, which enables numerical simulations on the lattice, constitutes a laboratory to study QCD at high chemical potential. Among the interesting properties of two-color QCD at high density is the diquark condensation, for which we present recent results obtained on a finer lattice compared to previous studies. The quark propagator in two-color QCD at non-zero chemical potential is referred to as the Gor'kov propagator. We express the Gor'kov propagator in terms of form factors and present recent lattice simulation results.
Dark Energy from graviton-mediated interactions in the QCD vacuum
Pasechnik, Roman; Beylin, Vitaly; Vereshkov, Grigory E-mail: vbey@rambler.ru
2013-06-01
Adopting the hypothesis about the exact cancellation of vacuum condensates contributions to the ground state energy in particle physics to the leading order in graviton-mediated interactions, we argue that the observable cosmological constant can be dynamically induced by an uncompensated quantum gravity correction to them after the QCD phase transition epoch. To start with, we demonstrate a possible cancellation of the quark-gluon condensate contribution to the total vacuum energy density of the Universe at temperatures T < 100 MeV without taking into account the graviton-mediated effects. In order to incorporate the latter, we then calculate the leading-order quantum correction to the classical Einstein equations due to metric fluctuations induced by the non-perturbative vacuum fluctuations of the gluon and quark fields in the quasiclassical approximation. It has been demonstrated that such a correction to the vacuum energy density has a form ε{sub Λ} ∼ GΛ{sub QCD}{sup 6}, where G is the gravitational constant, and Λ{sub QCD} is the QCD scale parameter. We analyze capabilities of this approach based on the synthesis between quantum gravity in quasiclassical approximation and theory of non-perturbative QCD vacuum for quantitative explanation of the observed Dark Energy density.
PDF and QCD effects in the precision measurement of the W boson mass at CDF
Beecher, Daniel
2011-01-01
A sample of W → ev (W → μν) and Z^{0} → e^{+}e^{-} (Z^{0} → μ^{+}μ^{-}) events recorded by the CDF detector for p$\\bar{p}$ collisions at √s = 1.96 TeV are used to evaluate the systematic uncertainty in the determination of the W boson mass arising from uncertainties in the parton distribution functions and higher-order QCD effects. The systematic contribution of PDFs is determined to be 10 MeV/c^{2} for MSTW2008 NLO and 12 MeV/c^{2} for CTEQ6.6. The total systematic contribution arising from higher-order QCD effects in 9 MeV/c^{2}. The Z^{0} events are used to extract improved estimates of the phenomenological parameters in the BLNY model that describes low transverse momentum.
Renormalization in Coulomb gauge QCD
NASA Astrophysics Data System (ADS)
Andraši, A.; Taylor, John C.
2011-04-01
In the Coulomb gauge of QCD, the Hamiltonian contains a non-linear Christ-Lee term, which may alternatively be derived from a careful treatment of ambiguous Feynman integrals at 2-loop order. We investigate how and if UV divergences from higher order graphs can be consistently absorbed by renormalization of the Christ-Lee term. We find that they cannot.
Nuclear reactions from lattice QCD
Briceño, Raúl A.; Davoudi, Zohreh; Luu, Thomas C.
2015-01-13
In this study, one of the overarching goals of nuclear physics is to rigorously compute properties of hadronic systems directly from the fundamental theory of strong interactions, Quantum Chromodynamics (QCD). In particular, the hope is to perform reliable calculations of nuclear reactions which will impact our understanding of environments that occur during big bang nucleosynthesis, the evolution of stars and supernovae, and within nuclear reactors and high energy/density facilities. Such calculations, being truly ab initio, would include all two-nucleon and three- nucleon (and higher) interactions in a consistent manner. Currently, lattice QCD provides the only reliable option for performing calculations of some of the low-energy hadronic observables. With the aim of bridging the gap between lattice QCD and nuclear many-body physics, the Institute for Nuclear Theory held a workshop on Nuclear Reactions from Lattice QCD on March 2013. In this review article, we report on the topics discussed in this workshop and the path planned to move forward in the upcoming years.
Nuclear reactions from lattice QCD
Briceño, Raúl A.; Davoudi, Zohreh; Luu, Thomas C.
2015-01-13
In this study, one of the overarching goals of nuclear physics is to rigorously compute properties of hadronic systems directly from the fundamental theory of strong interactions, Quantum Chromodynamics (QCD). In particular, the hope is to perform reliable calculations of nuclear reactions which will impact our understanding of environments that occur during big bang nucleosynthesis, the evolution of stars and supernovae, and within nuclear reactors and high energy/density facilities. Such calculations, being truly ab initio, would include all two-nucleon and three- nucleon (and higher) interactions in a consistent manner. Currently, lattice QCD provides the only reliable option for performing calculationsmore » of some of the low-energy hadronic observables. With the aim of bridging the gap between lattice QCD and nuclear many-body physics, the Institute for Nuclear Theory held a workshop on Nuclear Reactions from Lattice QCD on March 2013. In this review article, we report on the topics discussed in this workshop and the path planned to move forward in the upcoming years.« less
QCD Phase Transitions, Volume 15
Schaefer, T.; Shuryak, E.
1999-03-20
The title of the workshop, ''The QCD Phase Transitions'', in fact happened to be too narrow for its real contents. It would be more accurate to say that it was devoted to different phases of QCD and QCD-related gauge theories, with strong emphasis on discussion of the underlying non-perturbative mechanisms which manifest themselves as all those phases. Before we go to specifics, let us emphasize one important aspect of the present status of non-perturbative Quantum Field Theory in general. It remains true that its studies do not get attention proportional to the intellectual challenge they deserve, and that the theorists working on it remain very fragmented. The efforts to create Theory of Everything including Quantum Gravity have attracted the lion share of attention and young talent. Nevertheless, in the last few years there was also a tremendous progress and even some shift of attention toward emphasis on the unity of non-perturbative phenomena. For example, we have seen some efforts to connect the lessons from recent progress in Supersymmetric theories with that in QCD, as derived from phenomenology and lattice. Another example is Maldacena conjecture and related development, which connect three things together, string theory, super-gravity and the (N=4) supersymmetric gauge theory. Although the progress mentioned is remarkable by itself, if we would listen to each other more we may have chance to strengthen the field and reach better understanding of the spectacular non-perturbative physics.
Lattice QCD in Background Fields
William Detmold, Brian Tiburzi, Andre Walker-Loud
2009-06-01
Electromagnetic properties of hadrons can be computed by lattice simulations of QCD in background fields. We demonstrate new techniques for the investigation of charged hadron properties in electric fields. Our current calculations employ large electric fields, motivating us to analyze chiral dynamics in strong QED backgrounds, and subsequently uncover surprising non-perturbative effects present at finite volume.
Basics of QCD perturbation theory
Soper, D.E.
1997-06-01
This is an introduction to the use of QCD perturbation theory, emphasizing generic features of the theory that enable one to separate short-time and long-time effects. The author also covers some important classes of applications: electron-positron annihilation to hadrons, deeply inelastic scattering, and hard processes in hadron-hadron collisions. 31 refs., 38 figs.
Experimenting with Langevin lattice QCD
Gavai, R.V.; Potvin, J.; Sanielevici, S.
1987-05-01
We report on the status of our investigations of the effects of systematic errors upon the practical merits of Langevin updating in full lattice QCD. We formulate some rules for the safe use of this updating procedure and some observations on problems which may be common to all approximate fermion algorithms.
QCD tests and large momentum-transfer reactions at CBA
Longacre, R.; Tannenbaum, M.J.
1983-03-01
It is desirable to try to find fundamental tests of QCD which are sensitive to the specific properties of gluons and the non-Alelian structure of the theory, which would show that the theory is computable above leading order, and which are insensitive to the extraneous parameters such as structure functions, fragmentation functions and the like. Such tests can occur when higher-order corrections produce interference effects which must be zero in lowest order. One such effect is the linear polarization of direct single photons produced in p-p collisions. It is claimed that this polarization provides a rigorous test of perturbative QCD as well as an important check on the color hypothesis. This latter aspect is particularly attractive because the polarization involves the three-gluon interaction and the equality of the quark-gluon and three-gluon coupling in an essential way. Plans for studies at the CBA are discussed. (WHK)
Report of the 2005 Snowmass Top/QCD Working Group
Juste, A.; Kiyo, Y.; Petriello, F.; Teubner, T.; Agashe, K.; Batra, P.; Baur, U.; Berger, C.F.; Cembranos, J.A.R.; Gehrmann-De Ridder, A.; Gehrmann, T.; Glover, E.W.N.; Godfrey, S.; Hoang, A.; Perelstein, M.; Sullivan, Z.; Tait, T.; Zhu, S.; /Johns Hopkins U. /Princeton, Inst. Advanced Study /Syracuse U. /Argonne /SUNY, Buffalo /SLAC /UC, Irvine /Zurich, ETH /Zurich U. /Durham U., IPPP /Ottawa Carleton Inst. Phys. /Munich, Max Planck Inst. /Cornell U., CIHEP /Peking U.
2006-01-17
This report discusses several topics in both top quark physics and QCD at an International Linear Collider (ILC). Issues such as measurements at the t tbar threshold, including both theoretical and machine requirements, and the determination of electroweak top quark couplings are reviewed. New results concerning the potential of a 500 GeV e+e collider for measuring Wtb couplings and the top quark Yukawa coupling are presented. The status of higher order QCD corrections to jet production cross sections, heavy quark form factors, and longitudinal gauge boson scattering, needed for percent-level studies at the ILC, are reviewed. A new study of the measurement of the hadronic structure of the photon at a gamma gamma collider is presented. The effects on top quark properties from several models of new physics, including composite models, Little Higgs theories, and CPT violation, are studied.
The QCD/SM working group: Summary report
W. Giele et al.
2004-01-12
Quantum Chromo-Dynamics (QCD), and more generally the physics of the Standard Model (SM), enter in many ways in high energy processes at TeV Colliders, and especially in hadron colliders (the Tevatron at Fermilab and the forthcoming LHC at CERN), First of all, at hadron colliders, QCD controls the parton luminosity, which rules the production rates of any particle or system with large invariant mass and/or large transverse momentum. Accurate predictions for any signal of possible ''New Physics'' sought at hadron colliders, as well as the corresponding backgrounds, require an improvement in the control of uncertainties on the determination of PDF and of the propagation of these uncertainties in the predictions. Furthermore, to fully exploit these new types of PDF with uncertainties, uniform tools (computer interfaces, standardization of the PDF evolution codes used by the various groups fitting PDF's) need to be proposed and developed. The dynamics of colour also affects, both in normalization and shape, various observables of the signals of any possible ''New Physics'' sought at the TeV scale, such as, e.g. the production rate, or the distributions in transverse momentum of the Higgs boson. Last, but not least, QCD governs many backgrounds to the searches for this ''New Physics''. Large and important QCD corrections may come from extra hard parton emission (and the corresponding virtual corrections), involving multi-leg and/or multi-loop amplitudes. This requires complex higher order calculations, and new methods have to be designed to compute the required multi-legs and/or multi-loop corrections in a tractable form. In the case of semi-inclusive observables, logarithmically enhanced contributions coming from multiple soft and collinear gluon emission require sophisticated QCD resummation techniques. Resummation is a catch-all name for efforts to extend the predictive power of QCD by summing the large logarithmic corrections to all orders in perturbation theory. In
Drell-Yan lepton angular distributions in perturbative QCD
NASA Astrophysics Data System (ADS)
Lambertsen, Martin; Vogelsang, Werner
2016-06-01
We present a comprehensive comparison of the available experimental data for the Drell-Yan lepton angular coefficients λ and ν to calculations at leading and next-to-leading order of perturbative QCD. To obtain the next-to-leading order corrections, we make use of publicly available numerical codes that allow us to compute the Drell-Yan cross section at second order in perturbation theory and from which the contributions we need can be extracted. Our comparisons reveal that perturbative QCD is able to describe the experimental data overall rather well, especially at colliders, but also in the fixed-target regime. On the basis of the angular coefficients alone, there appears to be little (if any) convincing evidence for effects that go beyond fixed-order collinear factorized perturbation theory, although the presence of such effects is not ruled out.
Plans for Jet Energy Corrections at CMS
NASA Astrophysics Data System (ADS)
Mishra, Kalanand
2009-05-01
We present a plan for Jet Energy Corrections at CMS. Jet corrections at CMS will come initially from simulation tuned on test beam data, directly from collision data when available, and ultimately from a simulation tuned on collision data. The corrections will be factorized into a fixed sequence of sub-corrections associated with different detector and physics effects. The following three factors are minimum requirements for most analysis: offset corrections for pile-up and noise; correction for the response of the calorimeter as a function of jet pseudorapidity relative to the barrel; correction for the absolute response as a function of transverse momentum in the barrel. The required correction gives a jet Lorentz vector equivalent to the sum of particles in the jet cone emanating from a QCD hard collision. We discuss the status of these corrections, the planned data-driven techniques for their derivation, and their anticipated evolution with the stages of the CMS experiment.
The QCD equation of state with charm quarks from lattice QCD
NASA Astrophysics Data System (ADS)
Cheng, Michael
Recently, there have been several calculations of the QCD equation of state (EoS) on the lattice. These calculations take into account the two light quarks and the strange quark, but have ignored the effects of the charm quark, assuming that the charm mass (mc ≈ 1300 MeV) is exponentially suppressed at the temperatures which are explored. However, future heavy ion collisions, such as those planned at the LHC, may well probe temperature regimes where the charm quarks play an important role in the dynamics of the QGP. We present a calculation of the charm quark contribution to the QCD EoS using p4-improved staggered fermions at Nt = 4, 6, 8. This calculation is done with a quenched charm quark, i.e. the relevant operators are measured using a valence charm quark mass on a 2+1 flavor gauge field background. The charm quark masses are determined by calculating charmonium masses (metac and mJ/Psi) and fixing these mesons to their physical masses. The interaction measure, pressure, energy density, and entropy density are calculated. We find that the charm contribution makes a significant contribution, even down to temperatures as low as the pseudo-critical temperature, Tc. However, there are significant scaling corrections at the lattice spacings that we use, preventing a reliable continuum extrapolation.
Effective field theories for QCD with rooted staggered fermions
Bernard, Claude; Golterman, Maarten; Shamir, Yigal
2008-04-01
Even highly improved variants of lattice QCD with staggered fermions show significant violations of taste symmetry at currently accessible lattice spacings. In addition, the 'rooting trick' is used in order to simulate with the correct number of light sea quarks, and this makes the lattice theory nonlocal, even though there is good reason to believe that the continuum limit is in the correct universality class. In order to understand scaling violations, it is thus necessary to extend the construction of the Symanzik effective theory to include rooted staggered fermions. We show how this can be done, starting from a generalization of the renormalization-group approach to rooted staggered fermions recently developed by one of us. We then explain how the chiral effective theory follows from the Symanzik action, and show that it leads to 'rooted' staggered chiral perturbation theory as the correct chiral theory for QCD with rooted staggered fermions. We thus establish a direct link between the renormalization-group based arguments for the correctness of the continuum limit and the success of rooted staggered chiral perturbation theory in fitting numerical results obtained with the rooting trick. In order to develop our argument, we need to assume the existence of a standard partially-quenched chiral effective theory for any local partially-quenched theory. Other technical, but standard, assumptions are also required.
Diphoton production in the ADD model to NLO + parton shower accuracy at the LHC
NASA Astrophysics Data System (ADS)
Frederix, R.; Mandal, Manoj K.; Mathews, Prakash; Ravindran, V.; Seth, Satyajit; Torrielli, P.; Zaro, M.
2012-12-01
In this paper, we present the next-to-leading order predictions for diphoton production in the ADD model, matched to the HERWIG parton shower using the MC@NLO formalism. A selection of the results is presented for d = 2-6 extra dimensions, using generic cuts as well as analysis cuts mimicking the search strategies as pursued by the ATLAS and CMS experiments.
A comparison of NNLO QCD predictions with 7 TeV ATLAS and CMS data for V+jet processes
NASA Astrophysics Data System (ADS)
Boughezal, Radja; Liu, Xiaohui; Petriello, Frank
2016-09-01
We perform a detailed comparison of next-to-next-to-leading order (NNLO) QCD predictions for the W+jet and Z+jet processes with 7 TeV experimental data from ATLAS and CMS. We observe excellent agreement between theory and data for most studied observables, which span several orders of magnitude in both cross section and energy. For some observables, such as the HT distribution, the NNLO QCD corrections are essential for resolving existing discrepancies between theory and data.
Calculation of the nucleon axial charge in lattice QCD
D. B. Renner; R. G. Edwards; G. Fleming; Ph. Hagler; J. W. Negele; K. Orginos; A. V. Pochinsky; D. G. Richards; W. Schroers
2006-09-01
Protons and neutrons have a rich structure in terms of their constituents, the quarks and gluons. Understanding this structure requires solving Quantum Chromodynamics (QCD). However QCD is extremely complicated, so we must numerically solve the equations of QCD using a method known as lattice QCD. Here we describe a typical lattice QCD calculation by examining our recent computation of the nucleon axial charge.
Jet-medium interactions at NLO in a weakly-coupled quark-gluon plasma
NASA Astrophysics Data System (ADS)
Ghiglieri, Jacopo; Moore, Guy D.; Teaney, Derek
2016-03-01
We present an extension to next-to-leading order in the strong coupling constant g of the AMY effective kinetic approach to the energy loss of high momentum particles in the quark-gluon plasma. At leading order, the transport of jet-like particles is determined by elastic scattering with the thermal constituents, and by inelastic collinear splittings induced by the medium. We reorganize this description into collinear splittings, high-momentum-transfer scatterings, drag and diffusion, and particle conversions (momentum-preserving identity-changing processes). We show that this reorganized description remains valid to NLO in g, and compute the appropriate modifications of the drag, diffusion, particle conversion, and inelastic splitting coefficients. In addition, a new kinematic regime opens at NLO for wider-angle collinear bremsstrahlung. These semi-collinear emissions smoothly interpolate between the leading order high-momentum-transfer scatterings and collinear splittings. To organize the calculation, we introduce a set of Wilson line operators on the light-cone which determine the diffusion and identity changing coefficients, and we show how to evaluate these operators at NLO.
Physicochemical and solvatochromic analysis of an imidazole derivative as NLO material
NASA Astrophysics Data System (ADS)
Jayabharathi, Jayaraman; Thanikachalam, Venugopal; Perumal, Marimuthu Venkatesh
2012-01-01
Bioactive imidazole derivative, 2-(2,4-difluorophenyl)-1-phenyl-1H-imidazo[4,5-f][1,10]phenanthroline, has been synthesized and characterized by IR, UV-vis, NMR and elemental (CHN) analysis. The electric dipole moment ( μ) and the hyperpolarizability ( β) have been studied both experimentally and theoretically, which reveals that the synthesized imidazole derivative possesses non-linear optical (NLO) behavior. This chromophore possess more appropriate ratio of off-diagonal versus diagonal β tensorial component ( r = βxyy/ βxxx = -0.19) which reflects the in plane nonlinearity anisotropy. Since they have largest μβ 0 value, the reported imidazole can be used as potential NLO material. Within this context, reasonable conclusions concerning the steric hindrance in the chromospheres, push-pull character, hyperpolarizability of the imidazole and their application as NLO materials will be drawn. The solvent effect on the absorption and fluorescence bands was analyzed by a multi-component linear regression in which several solvent parameters were analyzed simultaneously.
QCD with chiral 4-fermion interactions ({chi}QCD)
Kogut, J.B.; Sinclair, D.K.
1996-10-01
Lattice QCD with staggered quarks is augmented by the addition of a chiral 4-fermion interaction. The Dirac operator is now non-singular at m{sub q}=0, decreasing the computing requirements for light quark simulations by at least an order of magnitude. We present preliminary results from simulations at finite and zero temperatures for m{sub q}=0, with and without gauge fields. Chiral QCD enables simulations at physical u and d quark masses with at least an order of magnitude saving in CPU time. It also enables simulations with zero quark masses which is important for determining the equation of state. A renormalization group analysis will be needed to continue to the continuum limit. 7 refs., 2 figs.
NASA Astrophysics Data System (ADS)
Boyle, P. A.; Christ, N. H.; Garron, N.; Jung, C.; Jüttner, A.; Kelly, C.; Mawhinney, R. D.; McGlynn, G.; Murphy, D. J.; Ohta, S.; Portelli, A.; Sachrajda, C. T.
2016-03-01
We have performed fits of the pseudoscalar masses and decay constants, from a variety of the RBC-UKQCD Collaboration's domain wall fermion ensembles, to S U (2 ) partially quenched chiral perturbation theory at next-to-leading order (NLO) and next-to-next-to-leading order (NNLO). We report values for nine NLO and eight linearly independent combinations of NNLO partially quenched low-energy constants, which we compare to other lattice and phenomenological determinations. We discuss the size of successive terms in the chiral expansion and use our large set of low-energy constants to make predictions for mass splittings due to QCD isospin-breaking effects and the S-wave π π scattering lengths. We conclude that, for the range of pseudoscalar masses explored in this work, 115 MeV ≲mPS≲430 MeV , the NNLO S U (2 ) expansion is quite robust and can fit lattice data with percent-scale accuracy.
anQCD: Fortran programs for couplings at complex momenta in various analytic QCD models
NASA Astrophysics Data System (ADS)
Ayala, César; Cvetič, Gorazd
2016-02-01
We provide three Fortran programs which evaluate the QCD analytic (holomorphic) couplings Aν(Q2) for complex or real squared momenta Q2. These couplings are holomorphic analogs of the powers a(Q2)ν of the underlying perturbative QCD (pQCD) coupling a(Q2) ≡αs(Q2) / π, in three analytic QCD models (anQCD): Fractional Analytic Perturbation Theory (FAPT), Two-delta analytic QCD (2 δanQCD), and Massive Perturbation Theory (MPT). The index ν can be noninteger. The provided programs do basically the same job as the Mathematica package anQCD.m published by us previously (Ayala and Cvetič, 2015), but are now written in Fortran.
Dru Renner
2012-04-01
Precision computation of hadronic physics with lattice QCD is becoming feasible. The last decade has seen precent-level calculations of many simple properties of mesons, and the last few years have seen calculations of baryon masses, including the nucleon mass, accurate to a few percent. As computational power increases and algorithms advance, the precise calculation of a variety of more demanding hadronic properties will become realistic. With this in mind, I discuss the current lattice QCD calculations of generalized parton distributions with an emphasis on the prospects for well-controlled calculations for these observables as well. I will do this by way of several examples: the pion and nucleon form factors and moments of the nucleon parton and generalized-parton distributions.
Quark eigenmodes and lattice QCD
NASA Astrophysics Data System (ADS)
Liu, Guofeng
In this thesis, we study a number of topics in lattice QCD through the low-lying quark eigenmodes in the domain wall fermion (DWF) formulation in the quenched approximation. Specifically, we present results for the chiral condensate measured from these eigenmodes; we investigate the QCD vacuum structure by looking at the correlation between the magnitude of the chirality density, |psi†(x)gamma5psi( x)|, and the normal density, psi†( x)psi(x), for these states; we study the behavior of DWF formulation at large quark masses by investigating the mass dependence of the eigenvalues of the physical four dimensional-states as well as the bulk, five-dimensional states.
LATTICE QCD AT FINITE DENSITY.
SCHMIDT, C.
2006-07-23
I discuss different approaches to finite density lattice QCD. In particular, I focus on the structure of the phase diagram and discuss attempts to determine the location of the critical end-point. Recent results on the transition line as function of the chemical potential (T{sub c}({mu}{sub q})) are reviewed. Along the transition line, hadronic fluctuations have been calculated; which can be used to characterize properties of the Quark Gluon plasma and eventually can also help to identify the location of the critical end-point in the QCD phase diagram on the lattice and in heavy ion experiments. Furthermore, I comment on the structure of the phase diagram at large {mu}{sub q}.
Innovations in Lattice QCD Algorithms
Konstantinos Orginos
2006-06-25
Lattice QCD calculations demand a substantial amount of computing power in order to achieve the high precision results needed to better understand the nature of strong interactions, assist experiment to discover new physics, and predict the behavior of a diverse set of physical systems ranging from the proton itself to astrophysical objects such as neutron stars. However, computer power alone is clearly not enough to tackle the calculations we need to be doing today. A steady stream of recent algorithmic developments has made an important impact on the kinds of calculations we can currently perform. In this talk I am reviewing these algorithms and their impact on the nature of lattice QCD calculations performed today.
Sudakov safety in perturbative QCD
NASA Astrophysics Data System (ADS)
Larkoski, Andrew J.; Marzani, Simone; Thaler, Jesse
2015-06-01
Traditional calculations in perturbative quantum chromodynamics (pQCD) are based on an order-by-order expansion in the strong coupling αs. Observables that are calculable in this way are known as "safe." Recently, a class of unsafe observables was discovered that do not have a valid αs expansion but are nevertheless calculable in pQCD using all-orders resummation. These observables are called "Sudakov safe" since singularities at each αs order are regulated by an all-orders Sudakov form factor. In this paper, we give a concrete definition of Sudakov safety based on conditional probability distributions, and we study a one-parameter family of momentum sharing observables that interpolate between the safe and unsafe regimes. The boundary between these regimes is particularly interesting, as the resulting distribution can be understood as the ultraviolet fixed point of a generalized fragmentation function, yielding a leading behavior that is independent of αs.
Huston, J. |; CDF Collaboration
1994-01-01
CDF has recently concluded a very successful 1992--93 data run in which an integrated luminosity of 21.3 pb {sup {minus}1} was written to tape. The large data sample allows for a greater discovery potential for new phenomena and for better statistical and systematic precision in analysis of conventional physics. This paper summarizes some of the new results from QCD analyses for this run.
Brodsky, Stanley J.; de Teramond, Guy F.; /Costa Rica U. /SLAC
2007-02-21
The AdS/CFT correspondence between string theory in AdS space and conformal .eld theories in physical spacetime leads to an analytic, semi-classical model for strongly-coupled QCD which has scale invariance and dimensional counting at short distances and color confinement at large distances. Although QCD is not conformally invariant, one can nevertheless use the mathematical representation of the conformal group in five-dimensional anti-de Sitter space to construct a first approximation to the theory. The AdS/CFT correspondence also provides insights into the inherently non-perturbative aspects of QCD, such as the orbital and radial spectra of hadrons and the form of hadronic wavefunctions. In particular, we show that there is an exact correspondence between the fifth-dimensional coordinate of AdS space z and a specific impact variable {zeta} which measures the separation of the quark and gluonic constituents within the hadron in ordinary space-time. This connection allows one to compute the analytic form of the frame-independent light-front wavefunctions, the fundamental entities which encode hadron properties and allow the computation of decay constants, form factors, and other exclusive scattering amplitudes. New relativistic lightfront equations in ordinary space-time are found which reproduce the results obtained using the 5-dimensional theory. The effective light-front equations possess remarkable algebraic structures and integrability properties. Since they are complete and orthonormal, the AdS/CFT model wavefunctions can also be used as a basis for the diagonalization of the full light-front QCD Hamiltonian, thus systematically improving the AdS/CFT approximation.
Yamamoto, Arata
2016-07-29
We propose the lattice QCD calculation of the Berry phase, which is defined by the ground state of a single fermion. We perform the ground-state projection of a single-fermion propagator, construct the Berry link variable on a momentum-space lattice, and calculate the Berry phase. As the first application, the first Chern number of the (2+1)-dimensional Wilson fermion is calculated by the Monte Carlo simulation. PMID:27517766
DeGrand, T.
1997-06-01
These lectures provide an introduction to lattice methods for nonperturbative studies of Quantum Chromodynamics. Lecture 1: Basic techniques for QCD and results for hadron spectroscopy using the simplest discretizations; lecture 2: Improved actions--what they are and how well they work; lecture 3: SLAC physics from the lattice-structure functions, the mass of the glueball, heavy quarks and {alpha}{sub s} (M{sub z}), and B-{anti B} mixing. 67 refs., 36 figs.
Brodsky, Stanley J.; de Teramond, Guy F.; /Costa Rica U.
2012-02-16
The relation between the hadronic short-distance constituent quark and gluon particle limit and the long-range confining domain is yet one of the most challenging aspects of particle physics due to the strong coupling nature of Quantum Chromodynamics, the fundamental theory of the strong interactions. The central question is how one can compute hadronic properties from first principles; i.e., directly from the QCD Lagrangian. The most successful theoretical approach thus far has been to quantize QCD on discrete lattices in Euclidean space-time. Lattice numerical results follow from computation of frame-dependent moments of distributions in Euclidean space and dynamical observables in Minkowski spacetime, such as the time-like hadronic form factors, are not amenable to Euclidean lattice computations. The Dyson-Schwinger methods have led to many important insights, such as the infrared fixed point behavior of the strong coupling constant, but in practice, the analyses are limited to ladder approximation in Landau gauge. Baryon spectroscopy and the excitation dynamics of nucleon resonances encoded in the nucleon transition form factors can provide fundamental insight into the strong-coupling dynamics of QCD. New theoretical tools are thus of primary interest for the interpretation of the results expected at the new mass scale and kinematic regions accessible to the JLab 12 GeV Upgrade Project. The AdS/CFT correspondence between gravity or string theory on a higher-dimensional anti-de Sitter (AdS) space and conformal field theories in physical space-time has led to a semiclassical approximation for strongly-coupled QCD, which provides physical insights into its nonperturbative dynamics. The correspondence is holographic in the sense that it determines a duality between theories in different number of space-time dimensions. This geometric approach leads in fact to a simple analytical and phenomenologically compelling nonperturbative approximation to the full light
FermiQCD: A tool kit for parallel lattice QCD applications
Di Pierro, M.
2002-03-01
We present here the most recent version of FermiQCD, a collection of C++ classes, functions and parallel algorithms for lattice QCD, based on Matrix Distributed Processing. FermiQCD allows fast development of parallel lattice applications and includes some SSE2 optimizations for clusters of Pentium 4 PCs.
None
2011-10-06
Modern QCD - Lecture 2 We will start discussing the matter content of the theory and revisit the experimental measurements that led to the discovery of quarks. We will then consider a classic QCD observable, the R-ratio, and use it to illustrate the appearance of UV divergences and the need to renormalize the coupling constant of QCD. We will then discuss asymptotic freedom and confinement. Finally, we will examine a case where soft and collinear infrared divergences appear, will discuss the soft approximation in QCD and will introduce the concept of infrared safe jets.
Tuning the NLO properties of polymethineimine chains by chemical substitution
NASA Astrophysics Data System (ADS)
Medved', Miroslav; Jacquemin, Denis
2013-03-01
Structure and molecular electronic properties including dipole moment, polarizability and first hyperpolarizability of polymethineimine (PMI) oligomers (up to hexadecamers) and its experimentally known amino-, methyl-, and cyano-derivatives are investigated using several ab initio methods (HF, MP2 and DFT). It is shown that side-chain substitutions have significant effects both on the structure and molecular properties of PMI chains. Depending on the substitution, two types of structures have been identified. The first is characterized by a bent skeleton and encompasses PMI, polyacetonitrile (PAcN), and polycyanonitrile (PCN). The second, represented by polyaminonitrile (PAN), remains quasi-linear with the plane of the unit cell (UC) only slightly rotating around the longitudinal molecular axis. These structural differences are also reflected in molecular properties; while in case of PMI, PAcN, and PCN the longitudinal component of properties (reduced per UC) reaches its maximum value for medium-size oligomers and then decreases for longer chains, the linear and nonlinear properties of PAN steadily increase towards the polymeric limit. In addition, we have assessed the performances of long-range corrected DFT functionals (LR-DFT), namely LC-BLYP, CAM-B3LYP, and ωB97X within the present framework: they provide results in qualitative agreement with MP2, a success not reached with B3LYP.
Simultaneous QCD analysis of diffractive and inclusive DIS data
NASA Astrophysics Data System (ADS)
Watt, G.; Martin, A. D.; Ryskin, M. G.
2005-09-01
We present a novel analysis of diffractive DIS data, in which the input parton distributions of the Pomeron are parameterised using perturbative QCD expressions. In addition to the usual two-gluon model for the perturbative Pomeron, we allow for the possibility that it may be made from two sea quarks. In particular, we treat individually the components of the Pomeron of different size. This property allows the absorptive corrections to the inclusive DIS structure function F to be calculated using the AGK cutting rules. The absorptive effects are found to enhance the size of the gluon distribution of the proton at small x.
Advancing QCD-based calculations of energy loss
NASA Astrophysics Data System (ADS)
Tywoniuk, Konrad
2013-08-01
We give a brief overview of the basics and current developments of QCD-based calculations of radiative processes in medium. We put an emphasis on the underlying physics concepts and discuss the theoretical uncertainties inherently associated with the fundamental parameters to be extracted from data. An important area of development is the study of the single-gluon emission in medium. Moreover, establishing the correct physical picture of multi-gluon emissions is imperative for comparison with data. We will report on progress made in both directions and discuss perspectives for the future.
General QED/QCD aspects of simple systems
Telegdi, V.L.; Brodsky, S.J.
1989-09-01
This paper discusses the following topics: renormalization theory; the Kinoshita-Lee-Nauenberg theorem; the Yennie-Frautschi-Suura relation; scale invariance at large momentum transfer; scaling and scaling violation at large momentum transfers; low-energy theorem in Compton scattering; does the perturbation series in QED converge; renormalization of the weak angle /Theta//sub w/; the Nambu-Bethe-Salpeter (NBS) equation; the decay rate of /sup 3/S, positronium; radiative corrections to QCD Born cross section; and progress on the relativistic 2-body equation.
One-loop QCD contribution to the potential of QQ¯
NASA Astrophysics Data System (ADS)
Liu, Li-Quan; Zhao, Shu-Min; Zhang, Jian-Jun; Yang, Bao-Zhu; Huang, De-Bao
2011-02-01
Without the non-relativistic approximation in one-loop function, the dominating one-loop contribution to the quark-antiquark potential is studied numerically in terms of perturbative Quantum Chromo Dynamics (QCD). For Coulomb-like potential, the ratio of the one-loop correction to the tree diagram contribution is presented, whose absolute value is about 20%. Our result is consistent with the analysis that the one-loop contribution should be suppressed by a factor αs/π to the leading order contribution. This work can deepen the comprehension of αs in Cornel potential.
The role of ion pairs in the second-order NLO response of 4-X-1-methylpiridinium salts.
Tessore, Francesca; Cariati, Elena; Cariati, Franco; Roberto, Dominique; Ugo, Renato; Mussini, Patrizia; Zuccaccia, Cristiano; Macchioni, Alceo
2010-02-01
A series of 4-X-1-methylpyridinium cationic nonlinear optical (NLO) chromophores (X = (E)-CH=CHC(6)H(5); (E)-CH=CHC(6)H(4)-4'-C(CH(3))(3); (E)-CH=CHC(6)H(4)-4'-N(CH(3))(2); (E)-CH=CHC(6)H(4)-4'-N(C(4)H(9))(2); (E,E)-(CH=CH)(2)C(6)H(4)-4'-N(CH(3))(2)) with various organic (CF(3)SO(3)(-), p-CH(3)C(6)H(4)SO(3)(-)), inorganic (I(-), ClO(4)(-), SCN(-), [Hg(2)I(6)](2-)) and organometallic (cis-[Ir(CO)(2)I(2)](-)) counter anions are studied with the aim of investigating the role of ion pairing and of ionic dissociation or aggregation of ion pairs in controlling their second-order NLO response in anhydrous chloroform solution. The combined use of electronic absorption spectra, conductimetric measurements and pulsed field gradient spin echo (PGSE) NMR experiments show that the second-order NLO response, investigated by the electric-field-induced second harmonic generation (EFISH) technique, of the salts of the cationic NLO chromophores strongly depends upon the nature of the counter anion and concentration. The ion pairs are the major species at concentration around 10(-3) M, and their dipole moments were determined. Generally, below 5x10(-4) M, ion pairs start to dissociate into ions with parallel increase of the second-order NLO response, due to the increased concentration of purely cationic NLO chromophores with improved NLO response. At concentration higher than 10(-3) M, some multipolar aggregates, probably of H type, are formed, with parallel slight decrease of the second-order NLO response. Ion pairing is dependent upon the nature of the counter anion and on the electronic structure of the cationic NLO chromophore. It is very strong for the thiocyanate anion in particular and, albeit to a lesser extent, for the sulfonated anions. The latter show increased tendency to self-aggregate. PMID:20029883
Hao, Ming; Flynn, Kevin; Nien-Shy, Chyong; Jester, Bryan E.; Winkler, Moritz; Brown, Donald J.; La Schiazza, Olivier; Bille, Josef; Jester, James V.
2010-01-01
Imaging of non-linear optical (NLO) signals generated from the eye using ultrafast pulsed lasers has been limited to the study of ex vivo tissues because of the use of conventional microscopes with slow scan speeds. The purpose of this study was to evaluate the ability of a novel, high scan rate ophthalmoscope to generate NLO signals using an attached femtosecond laser. NLO signals were generated and imaged in live, anesthetized albino rabbits using a newly designed Heidelberg Two-Photon Laser Ophthalmoscope with attached 25 mW femtosecond laser having a central wavelength of 780 nm, pulsewidth of 75 fs, and a repetition rate of 50 MHz. To assess two-photon excited fluorescent (TPEF) signal generation, cultured rabbit corneal fibroblasts (RCF) were first labeled by Blue-green fluorescent FluoSpheres (1 μm diameter) and then cells were micro-injected into the central cornea. Clumps of RCF cells could be detected by both reflectance and TPEF imaging at 6 hours after injection. By 6 days, RCF containing fluorescent microspheres confirmed by TPEF showed a more spread morphology and had migrated from the original injection site. Overall, this study demonstrates the potential of using NLO microscopy to sequentially detect TPEF signals from live, intact corneas. We conclude that further refinement of the Two-photon laser Ophthalmoscope should lead to the development of an important, new clinical instrument capable of detecting NLO signals from patient corneas. PMID:20558159
Family of dilatons and metrics for AdS/QCD models
NASA Astrophysics Data System (ADS)
Vega, Alfredo; Cabrera, Paulina
2016-06-01
We explore some possibilities for obtaining useful metrics and dilatons for anti-de Sitter (AdS)/QCD models. As a guideline, we consider dilatons and/or metrics that on the one hand reproduce the mesonic spectrum, and that on the other hand allow us a correct implementation of chiral symmetry breaking in AdS/QCD models. We discuss two procedures: one is based on supersymmetric quantum mechanics techniques and the other considers the interpolation between some limits on dilatons and/or metrics.
Precise QCD Predictions for the Production of Dijet Final States in Deep Inelastic Scattering.
Currie, James; Gehrmann, Thomas; Niehues, Jan
2016-07-22
The production of two-jet final states in deep inelastic scattering is an important QCD precision observable. We compute it for the first time to next-to-next-to-leading order (NNLO) in perturbative QCD. Our calculation is fully differential in the lepton and jet variables and allows one to impose cuts on the jets in both the laboratory and the Breit frame. We observe that the NNLO corrections are moderate in size, except at kinematical edges, and that their inclusion leads to a substantial reduction of the scale variation uncertainty on the predictions. Our results will enable the inclusion of deep inelastic dijet data in precision phenomenology studies. PMID:27494466
Precise QCD Predictions for the Production of Dijet Final States in Deep Inelastic Scattering
NASA Astrophysics Data System (ADS)
Currie, James; Gehrmann, Thomas; Niehues, Jan
2016-07-01
The production of two-jet final states in deep inelastic scattering is an important QCD precision observable. We compute it for the first time to next-to-next-to-leading order (NNLO) in perturbative QCD. Our calculation is fully differential in the lepton and jet variables and allows one to impose cuts on the jets in both the laboratory and the Breit frame. We observe that the NNLO corrections are moderate in size, except at kinematical edges, and that their inclusion leads to a substantial reduction of the scale variation uncertainty on the predictions. Our results will enable the inclusion of deep inelastic dijet data in precision phenomenology studies.
Hard elastic scattering in QCD: Leading behavior
Botts, J.F.
1989-01-01
The author derives the asymptotic behavior of elastic meson-meson and baryon-baryon scattering at high energy and large angle t/s {approximately} O(1). The results organize both Sudakov and nonleading logarithmic corrections to independent (Landshoff) scatterings of valence quarks. He shows how to separate these contributions systematically from single scattering contributions, in a manner which suggests that the complete amplitudes should be computable perturbatively down to the dimensional counting power, in terms of hadronic wave functions. In the final chapter, the perturbative asymptotic amplitude and differential cross section for elastic pion-pion scattering is calculated numerically. For various choices of pion wave function and running coupling, the onset of power law behavior, d{sigma}/dt {approximately} s{sup {minus}5.8}, was observed. The dependence in d{sigma}/dt on the cutoff in gluon momentum, chosen to be O({Lambda}{sub QCD}/Q), was observed to be sharp for ln(s/1GeV{sup 2}) less than 1. Very small oscillations in d{sigma}/dt appear in physically realizable energies, but these are cutoff dependent, and their interpretation unclear. Higher twist effects were estimated to be roughly {approximately}15% for 2 < ln(s/1GeV{sup 2}) < 10.
QCD tests in electron-positron scattering
Maruyama, T.
1995-11-01
Recent results on QCD tests at the Z{sup o} resonance are described. Measurements of Color factor ratios, and studies of final state photon radiation are performed by the LEP experiments. QCD tests using a longitudinally polarized beam are reported by the SLD experiment.
Lattice QCD and High Baryon Density State
Nagata, Keitaro; Nakamura, Atsushi; Motoki, Shinji; Nakagawa, Yoshiyuki; Saito, Takuya
2011-10-21
We report our recent studies on the finite density QCD obtained from lattice QCD simulation with clover-improved Wilson fermions of two flavor and RG-improved gauge action. We approach the subject from two paths, i.e., the imaginary and chemical potentials.
Quantum properties of QCD string fragmentation
NASA Astrophysics Data System (ADS)
Todorova-Nová, Šárka
2016-07-01
A simple quantization concept for a 3-dim QCD string is used to derive properties of QCD flux tube from the mass spectrum of light mesons and to predict observable quantum effects in correlations between adjacent hadrons. The quantized fragmentation model is presented and compared with experimental observations.
Solvable models and hidden symmetries in QCD
Yepez-Martinez, Tochtli; Hess, P. O.; Civitarese, O.; Lerma H., S.
2010-12-23
We show that QCD Hamiltonians at low energy exhibit an SU(2) structure, when only few orbital levels are considered. In case many orbital levels are taken into account we also find a semi-analytic solution for the energy levels of the dominant part of the QCD Hamiltonian. The findings are important to propose the structure of phenomenological models.
Growth and Vibrational Spectroscopic Investigations of NLO Crystal Barium Thiourea Chloride
NASA Astrophysics Data System (ADS)
Kumari, M. Meena; Ravikumar, C.; Amalanathan, M.; Jayakumar, V. S.; Joe, I. Hubert
2008-11-01
The crystal of NLO interest, Barium thiourea chloride (BTC) has been crystallized and is subjected to FT-IR and NIR FT-Raman spectral studies along with the quantum chemical computations. The equilibrium geometry, first hyperpolarizability, various bonding features and vibrational wavenumbers have been calculated by B3LYP density functional theory (DFT) calculations at the LANL2DZ level. The predicted vibrational spectra are in fair agreement with the experiment. The broadening of NH2 stretching wavenumber indicates the intermolecular N-H…CI hydrogen bonding present in the molecule.
Physico-chemical studies of fused phenanthrimidazole derivative as sensitive NLO material
NASA Astrophysics Data System (ADS)
Jayabharathi, Jayaraman; Thanikachalam, Venugopal; Sathishkumar, Ramalingam; Jayamoorthy, Karunamoorthy
2013-01-01
Heterocyclic phenanthrimidazole derivative, 2-(4-fluorophenyl)-1-p-tolyl-1H-imidazo[4,5-f] [1,10] phenanthroline (FPTIP) has been synthesized and characterised by NMR, mass and CHN analysis. The FPTIP was evaluated concerning their solvatochromic properties and molecular optical nonlinearities. Their electric dipole moment (μ), polarizability (α) and hyperpolarizability (β) have been calculated theoretically and the results indicate that the extension of the π-framework of the ligands has an effect on the NLO properties. The energies of the HOMO and LUMO levels and the molecular electrostatic potential (MEP) energy surface studies have exploited the existence of intramolecular charge transfer (ICT) within the molecule.
Structure modulations in nonlinear optical (NLO) materials Cs(2)TB4O9 (T = Ge, Si).
Zhou, Zhengyang; Xu, Xiang; Fei, Rao; Mao, Jianggao; Sun, Junliang
2016-04-01
Incommensurately modulated borate structures of a new type were studied in detail in the nonlinear optical (NLO) materials Cs(2)TB4O9 (T = Ge, Si) using single-crystal X-ray diffraction techniques. The structures were solved by the charge-flipping algorithm in the superspace group I2(αβ0)0. The refinement results strongly suggest that the main structure modulation feature of Cs(2)TB4O9 is the ordering of the O atoms. With these modulated structure models, the unreasonable B-O distances in the average structures were explained as the ordering of BO4 and BO3. PMID:27048721
Growth, spectral and thermal studies of an efficient NLO material: Diaquadicinnamatocadmium(II)
Roy, Sunalya M.; Sudarsanakumar, M. R.; Dhanya, V. S.
2014-01-28
A nonlinear metal–organic crystal, diaquadicinnamatocadmium(II) has been grown by controlled gel diffusion technique. Sodium metasilicate was used to prepare the gel. The chemical composition of the crystal has been determined by CHN analysis. Powder X-ray diffraction studies confirm the crystalline nature of the grown crystal. Functional groups present in the compound were identified by FT-IR spectral analysis. The thermal decomposition of the compound was studied using thermogravimetry (TG). The optical transparency range and the lower cut-off wavelength were identified from the UV-Visible-NIR spectrum. The NLO activity of the grown crystal was confirmed using Kurtz and Perry powder test.
Scaffold characterization using NLO multimodal microscopy in metrology for regenerative medicine
NASA Astrophysics Data System (ADS)
Mortati, Leonardo; Divieto, Carla; Boffitto, Monica; Sartori, Susanna; Ciardelli, Gianluca; Sassi, Maria Paola
2013-09-01
Metrology in regenerative medicine aims to develop traceable measurement technologies for characterizing cellular and macromolecule behaviour in regenerative medicine products and processes. One key component in regenerative medicine is using three-dimensional porous scaffolds to guide cells during the regeneration process. The regeneration of specific tissues guided by tissue analogous substrates is dependent on diverse scaffold architectural properties that can be derived quantitatively from scaffolds images. This paper discuss the results obtained with the multimodal NLO microscope recently realized in our laboratory in characterizing 3D tissue engineered (TE) scaffolds colonized from human Mesenchimal stem cells (hMSC), focusing on the study of the three-dimensional metrological parameters.
Consistent Perturbative Fixed Point Calculations in QCD and Supersymmetric QCD
NASA Astrophysics Data System (ADS)
Ryttov, Thomas A.
2016-08-01
We suggest how to consistently calculate the anomalous dimension γ* of the ψ ¯ ψ operator in finite order perturbation theory at an infrared fixed point for asymptotically free theories. If the n +1 loop beta function and n loop anomalous dimension are known, then γ* can be calculated exactly and fully scheme independently in a Banks-Zaks expansion through O (Δfn) , where Δf=N¯ f-Nf , Nf is the number of flavors, and N¯f is the number of flavors above which asymptotic freedom is lost. For a supersymmetric theory, the calculation preserves supersymmetry order by order in Δf. We then compute γ* through O (Δf2) for supersymmetric QCD in the dimensional reduction scheme and find that it matches the exact known result. We find that γ* is astonishingly well described in perturbation theory already at the few loops level throughout the entire conformal window. We finally compute γ* through O (Δf3) for QCD and a variety of other nonsupersymmetric fermionic gauge theories. Small values of γ* are observed for a large range of flavors.
Consistent Perturbative Fixed Point Calculations in QCD and Supersymmetric QCD.
Ryttov, Thomas A
2016-08-12
We suggest how to consistently calculate the anomalous dimension γ_{*} of the ψ[over ¯]ψ operator in finite order perturbation theory at an infrared fixed point for asymptotically free theories. If the n+1 loop beta function and n loop anomalous dimension are known, then γ_{*} can be calculated exactly and fully scheme independently in a Banks-Zaks expansion through O(Δ_{f}^{n}), where Δ_{f}=N[over ¯]_{f}-N_{f}, N_{f} is the number of flavors, and N[over ¯]_{f} is the number of flavors above which asymptotic freedom is lost. For a supersymmetric theory, the calculation preserves supersymmetry order by order in Δ_{f}. We then compute γ_{*} through O(Δ_{f}^{2}) for supersymmetric QCD in the dimensional reduction scheme and find that it matches the exact known result. We find that γ_{*} is astonishingly well described in perturbation theory already at the few loops level throughout the entire conformal window. We finally compute γ_{*} through O(Δ_{f}^{3}) for QCD and a variety of other nonsupersymmetric fermionic gauge theories. Small values of γ_{*} are observed for a large range of flavors. PMID:27563948
QCD Collisional Energy Loss Reexamined
NASA Astrophysics Data System (ADS)
Peshier, A.
2006-11-01
It is shown that at a large temperature and E→∞ the QCD collisional energy loss reads dE/dx˜α(mD2)T2. Compared to previous approaches, which led to dEB/dx˜α2T2ln(ET/mD2) similar to the Bethe-Bloch formula in QED, we take into account the running of the strong coupling. As one significant consequence, due to asymptotic freedom, dE/dx becomes E independent for large parton energies. Some implications with regard to heavy ion collisions are pointed out.
QCD collisional energy loss reexamined.
Peshier, A
2006-11-24
It is shown that at a large temperature and E --> infinity the QCD collisional energy loss reads dE/dx approximately alpha(m(D)2)T2. Compared to previous approaches, which led to dE(B)/dx approximately alpha2 T2 ln(ET/m(D)2) similar to the Bethe-Bloch formula in QED, we take into account the running of the strong coupling. As one significant consequence, due to asymptotic freedom, dE/dx becomes E independent for large parton energies. Some implications with regard to heavy ion collisions are pointed out. PMID:17155739
"Quantum Field Theory and QCD"
Jaffe, Arthur M.
2006-02-25
This grant partially funded a meeting, "QFT & QCD: Past, Present and Future" held at Harvard University, Cambridge, MA on March 18-19, 2005. The participants ranged from senior scientists (including at least 9 Nobel Prize winners, and 1 Fields medalist) to graduate students and undergraduates. There were several hundred persons in attendance at each lecture. The lectures ranged from superlative reviews of past progress, lists of important, unsolved questions, to provocative hypotheses for future discovery. The project generated a great deal of interest on the internet, raising awareness and interest in the open questions of theoretical physics.
Nucleon Structure from Lattice QCD
Haegler, Philipp
2011-10-24
Hadron structure calculations in lattice QCD have seen substantial progress during recent years. We illustrate the achievements that have been made by discussing latest lattice results for a limited number of important observables related to nucleon form factors and generalized parton distributions. A particular focus is placed on the decomposition of the nucleon spin 1/2 in terms of quark spin and orbital angular momentum contributions. Results and limitations of the necessary chiral extrapolations based on ChPT will be briefly discussed.
Spectral continuity in dense QCD
Hatsuda, Tetsuo; Yamamoto, Naoki; Tachibana, Motoi
2008-07-01
The vector mesons in three-flavor quark matter with chiral and diquark condensates are studied using the in-medium QCD sum rules. The diquark condensate leads to a mass splitting between the flavor-octet and flavor-singlet channels. At high density, the singlet vector meson disappears from the low-energy spectrum, while the octet vector mesons survive as light excitations with a mass comparable to the fermion gap. A possible connection between the light gluonic modes and the flavor-octet vector mesons at high density is also discussed.
Nuclear Physics from Lattice QCD
William Detmold, Silas Beane, Konstantinos Orginos, Martin Savage
2011-01-01
We review recent progress toward establishing lattice Quantum Chromodynamics as a predictive calculational framework for nuclear physics. A survey of the current techniques that are used to extract low-energy hadronic scattering amplitudes and interactions is followed by a review of recent two-body and few-body calculations by the NPLQCD collaboration and others. An outline of the nuclear physics that is expected to be accomplished with Lattice QCD in the next decade, along with estimates of the required computational resources, is presented.
Single transverse-spin asymmetry in QCD
NASA Astrophysics Data System (ADS)
Koike, Yuji
2014-09-01
So far large single transverse-spin asymmetries (SSA) have been observed in many high-energy processes such as semi-inclusive deep inelastic scattering and proton-proton collisions. Since the conventional parton model and perturbative QCD can not accomodate such large SSAs, the framework for QCD hard processes had to be extended to understand the mechanism of SSA. In this extended frameworks of QCD, intrinsic transverse momentum of partons and the multi-parton (quark-gluon and pure-gluonic) correlations in the hadrons, which were absent in the conventional framework, play a crucial role to cause SSAs, and well-defined formulation of these effects has been a big challenge for QCD theorists. Study on these effects has greatly promoted our understanding on QCD dynamics and hadron structure. In this talk, I will present an overview on these theoretical activity, emphasizing the important role of the Drell-Yan process.
Hu, Gonghao; Miao, Hao; Mei, Hua; Zhou, Shuai; Xu, Yan
2016-05-10
The first polyoxometalates modified by a porphyrin-resembling planar Schiff base have been successfully designed and synthesized under hydrothermal conditions. The third-order NLO responses indicated that they are excellent third-order NLO materials. Their catalytic performances are also investigated. PMID:27117492
The decay of Λ _b→ p~K^- in QCD factorization approach
NASA Astrophysics Data System (ADS)
Zhu, Jie; Ke, Hong-Wei; Wei, Zheng-Tao
2016-05-01
With only the tree-level operator, the decay of Λ _b→ pK is predicted to be one order smaller than the experimental data. The QCD penguin effects should be taken into account. In this paper, we explore the one-loop QCD corrections to the decay of Λ _b→ pK within the framework of QCD factorization approach. For the baryon system, the diquark approximation is adopted. The transition hadronic matrix elements between Λ _b and p are calculated in the light-front quark model. The branching ratio of Λ _b→ pK is predicted to be about 4.85× 10^{-6}, which is consistent with experimental data (4.9± 0.9)× 10^{-6}. The CP violation is about 5 % in theory.
Pseudo-scalar Higgs boson production at threshold N^3LO and N^3LL QCD
NASA Astrophysics Data System (ADS)
Ahmed, Taushif; Kumar, M. C.; Mathews, Prakash; Rana, Narayan; Ravindran, V.
2016-06-01
We present the first results on the production of pseudo-scalar Higgs boson through gluon fusion at the LHC to N^3LO in QCD taking into account only soft-gluon effects. We have used the effective Lagrangian that describes the coupling of the pseudo-scalar Higgs boson with the gluons in the large top quark mass limit. We have used quantities that have recently become available, namely the three-loop pseudo-scalar Higgs boson form factor and the third order universal soft function in QCD to achieve this. Along with the fixed order results, we also present the process dependent resummation coefficient for a threshold resummation to N^3LL in QCD. Phenomenological impact of these threshold N^3LO corrections to pseudo-scalar Higgs boson production at the LHC is presented and their role in the reduction of the renormalization scale dependence is demonstrated.
Analysis of the QCD spectrum and chiral symmetry breaking with varying quark masses
Simonov, Yu. A.
2013-04-15
The meson spectrum of QCD is studied in the framework of nonperturbative QCD as a function of varying quark masses m{sub q}. It is shown that the total spectrum consists of two branches: 1) the standard one, which may be called the flux-tube spectrum, depending approximately linearly on m{sub q}, and 2) the chiral symmetry breaking (CSB) spectrum for pseudoscalar (PS) flavor nonsinglet mesons with mass dependence {radical}m{sub q}. The formalism for PS mesons is derived from the QCD Lagrangian with m{sub q} corrections, and a unified form of the PS propagator was derived. It is shown that the CSB branch of PS mesons joins to the flux-tube branch at around m{sub q} = 200 MeV. All these results are in close correspondence with recent numerical data on large lattices.
Nuclear Physics and Lattice QCD
Beane, Silas
2003-11-01
Impressive progress is currently being made in computing properties and interac- tions of the low-lying hadrons using lattice QCD. However, cost limitations will, for the foreseeable future, necessitate the use of quark masses, Mq, that are signif- icantly larger than those of nature, lattice spacings, a, that are not significantly smaller than the physical scale of interest, and lattice sizes, L, that are not sig- nificantly larger than the physical scale of interest. Extrapolations in the quark masses, lattice spacing and lattice volume are therefore required. The hierarchy of mass scales is: L 1 j Mq j â ºC j a 1 . The appropriate EFT for incorporating the light quark masses, the finite lattice spacing and the lattice size into hadronic observables is C-PT, which provides systematic expansions in the small parame- ters e m L, 1/ Lâ ºC, p/â ºC, Mq/â ºC and aâ ºC . The lattice introduces other unphysical scales as well. Lattice QCD quarks will increasingly be artificially separated
Smith, W.H.
1997-06-01
These lectures describe QCD physics studies over the period 1992--1996 from data taken with collisions of 27 GeV electrons and positrons with 820 GeV protons at the HERA collider at DESY by the two general-purpose detectors H1 and ZEUS. The focus of these lectures is on structure functions and jet production in deep inelastic scattering, photoproduction, and diffraction. The topics covered start with a general introduction to HERA and ep scattering. Structure functions are discussed. This includes the parton model, scaling violation, and the extraction of F{sub 2}, which is used to determine the gluon momentum distribution. Both low and high Q{sup 2} regimes are discussed. The low Q{sup 2} transition from perturbative QCD to soft hadronic physics is examined. Jet production in deep inelastic scattering to measure {alpha}{sub s}, and in photoproduction to study resolved and direct photoproduction, is also presented. This is followed by a discussion of diffraction that begins with a general introduction to diffraction in hadronic collisions and its relation to ep collisions, and moves on to deep inelastic scattering, where the structure of diffractive exchange is studied, and in photoproduction, where dijet production provides insights into the structure of the Pomeron. 95 refs., 39 figs.
NASA Astrophysics Data System (ADS)
Moorthy, N.; Prabakar, P. C. Jobe; Ramalingam, S.; Govindarajan, M.; Gnanamuthu, S. Joshua; Pandian, G. V.
2016-08-01
The prepared Acetaldehyde thiosemicarbazone (ATSC) have been investigated by both the experimental and theoretical methods; through this work, the essentiality of elucidation of molecular fragments source linear and non-linear optical properties was explored. The stability of the structure and entire calculations have been performed on HF and B3LYP methods with 6-311++G(d,p) level of basis set. The Mulliken charge profile, electronic, optical and hyper polarizability analyses have been carried out in order to evaluate nonlinear optical (NLO) performance of the present compound. The exact optical location of the ATSC was determined by executing UV-Visible calculations on TDSCF method. The existence of the molecular group for the inducement and tuning of NLO properties were thoroughly investigated by performing fundamental vibrational investigation. The optical energy transformation among frontier molecular levels has been described in UV-Visible region. The Gibbs energy coefficient of thermodynamic functions was monitored in different temperature and it was found constant irrespective of temperatures. The appearance of different chemical environment of H and C was monitored from the 1H and 13C NMR spectra. The vibrational optical polarization characteristics with respect to molecular composition in the compound have been studied by VCD spectrum. The bond critical point, Laplacian of electron density, electron kinetic energy density and total electron energy density have calculated and analysed using AIM study.
Wolfe, Carl E.; Maltman, Kim
2001-01-01
The strong isospin-breaking correction {Omega}{sub st}, which appears in estimates of the standard model value for the direct CP-violating ratio {epsilon}{prime}/{epsilon}, is evaluated to next-to-leading order (NLO) in the chiral expansion using chiral perturbation theory. The relevant linear combinations of the unknown NLO CP-odd weak low-energy constants (LEC's) which, in combination with one-loop and strong LEC contributions, are required for a complete determination at this order, are estimated using two different models. It is found that, to NLO, {Omega}{sub st}=0.08{+-}0.05, significantly reduced from the ''standard'' value, 0.25{+-}0.08, employed in recent analyses. The potentially significant numerical impact of this decrease on standard model predictions for {epsilon}{prime}/{epsilon}, associated with the decreased cancellation between gluonic penguin and electroweak penguin contributions, is also discussed.
Vranas, P
2007-06-18
Quantum Chromodynamics is the theory of nuclear and sub-nuclear physics. It is a celebrated theory and one of its inventors, F. Wilczek, has termed it as '... our most perfect physical theory'. Part of this is related to the fact that QCD can be numerically simulated from first principles using the methods of lattice gauge theory. The computational demands of QCD are enormous and have not only played a role in the history of supercomputers but are also helping define their future. Here I will discuss the intimate relation of QCD and massively parallel supercomputers with focus on the Blue Gene supercomputer and QCD thermodynamics. I will present results on the performance of QCD on the Blue Gene as well as physics simulation results of QCD at temperatures high enough that sub-nuclear matter transitions to a plasma state of elementary particles, the quark gluon plasma. This state of matter is thought to have existed at around 10 microseconds after the big bang. Current heavy ion experiments are in the quest of reproducing it for the first time since then. And numerical simulations of QCD on the Blue Gene systems are calculating the theoretical values of fundamental parameters so that comparisons of experiment and theory can be made.
The QCD vacuum, hadrons and superdense matter
Shuryak, E.
1986-01-01
This is probably the only textbook available that gathers QCD, many-body theory and phase transitions in one volume. The presentation is pedagogical and readable. Contents: The QCD Vacuum: Introduction; QCD on the Lattice Topological Effects in Gauges Theories. Correlation Functions and Microscopic Excitations: Introduction; Operator Product Expansion; The Sum Rules beyond OPE; Nonpower Contributions to Correlators and Instantons; Hadronic Spectroscopy on the Lattice. Dense Matter: Hadronic Matter; Asymptotically Dense Quark-Gluon Plasma; Instantons in Matter; Lattice Calculations at Finite Temperature; Phase Transitions; Macroscopic Excitations and Experiments: General Properties of High Energy Collisions; ''Barometers'', ''Thermometers'', Interferometric ''Microscope''; Experimental Perspectives.
Excited light isoscalar mesons from lattice QCD
Christopher Thomas
2011-07-01
I report a recent lattice QCD calculation of an excited spectrum of light isoscalar mesons, something that has up to now proved challenging for lattice QCD. With novel techniques we extract an extensive spectrum with high statistical precision, including spin-four states and, for the first time, light isoscalars with exotic quantum numbers. In addition, the hidden flavour content of these mesons is determined, providing a window on annihilation dynamics in QCD. I comment on future prospects including applications to the study of resonances.
QCD thermodynamics and missing hadron states
NASA Astrophysics Data System (ADS)
Petreczky, Peter
2016-03-01
Equation of State and fluctuations of conserved charges in hot strongly interacting matter are being calculated with increasing accuracy in lattice QCD, and continuum results at physical quark masses become available. At sufficiently low temperature the thermodynamic quantities can be understood in terms of hadron resonance gas model that includes known hadrons and hadronic resonances from Particle Data Book. However, for some quantities it is necessary to include undiscovered hadronic resonances (missing states) that are, however, predicted by quark model and lattice QCD study of hadron spectrum. Thus, QCD thermodynamics can provide indications for the existence of yet undiscovered hadron states.
Death to perturbative QCD in exclusive processes?
Eckardt, R.; Hansper, J.; Gari, M.F.
1994-04-01
The authors discuss the question of whether perturbative QCD is applicable in calculations of exclusive processes at available momentum transfers. They show that the currently used method of determining hadronic quark distribution amplitudes from QCD sum rules yields wave functions which are completely undetermined because the polynomial expansion diverges. Because of the indeterminacy of the wave functions no statement can be made at present as to whether perturbative QCD is valid. The authors emphasize the necessity of a rigorous discussion of the subject and the importance of experimental data in the range of interest.
Shape of mesons in holographic QCD
Torabian, Mahdi; Yee, Ho-Ung
2009-10-15
Based on the expectation that the constituent quark model may capture the right physics in the large N limit, we point out that the orbital angular momentum of the quark-antiquark pair inside light mesons of low spins in the constituent quark model may provide a clue for the holographic dual string model of large N QCD. Our discussion, relying on a few suggestive assumptions, leads to a necessity of world-sheet fermions in the bulk of dual strings that can incorporate intrinsic spins of fundamental QCD degrees of freedom. We also comment on the interesting issue of the size of mesons in holographic QCD.
Towards the chiral limit in QCD
Shailesh Chandrasekharan
2006-02-28
Computing hadronic observables by solving QCD from first principles with realistic quark masses is an important challenge in fundamental nuclear and particle physics research. Although lattice QCD provides a rigorous framework for such calculations many difficulties arise. Firstly, there are no good algorithms to solve lattice QCD with realistically light quark masses. Secondly, due to critical slowing down, Monte Carlo algorithms are able to access only small lattice sizes on coarse lattices. Finally, due to sign problems it is almost impossible to study the physics of finite baryon density. Lattice QCD contains roughly three mass scales: the cutoff (or inverse lattice spacing) a{sup -1}, the confinement scale {Lambda}{sub QCD}, and the pion mass m{sub {pi}}. Most conventional Monte Carlo algorithms for QCD become inefficient in two regimes: when {Lambda}{sub QCD} becomes small compared to a{sup -1} and when m{sub {pi}} becomes small compared to {Lambda}{sub QCD}. The former can be largely controlled by perturbation theory thanks to asymptotic freedom. The latter is more difficult since chiral extrapolations are typically non-analytic and can be unreliable if the calculations are not done at sufficiently small quark masses. For this reason it has been difficult to compute quantities close to the chiral limit. The essential goal behind this proposal was to develop a new approach towards understanding QCD and QCD-like theories with sufficiently light quarks. The proposal was based on a novel cluster algorithm discovered in the strong coupling limit with staggered fermions [1]. This algorithm allowed us to explore the physics of exactly massless quarks and as well as light quarks. Thus, the hope was that this discovery would lead to the complete solution of at least a few strongly coupled QCD-like theories. The solution would be far better than those achievable through conventional methods and thus would be able to shed light on the chiral physics from a new
Renormalons and 1/Q2 corrections
NASA Astrophysics Data System (ADS)
Akhoury, R.; Zakharov, V. I.
1997-06-01
We argue that the appearance of the Landau pole in the running coupling of QCD introduces 1/Q2 power corrections in current correlator functions. These terms are not accounted for by the standard operator product expansion and is the price to be paid for the lack of a unique definition of the running coupling at the 1/Q2 level. We review also possible phenomenological implications of the 1/Q2 terms in an alternative language of ultraviolet renormalon.
QCD at the Large Hadron Collider—Higgs Searches and Some Non-SUSY Extensions Beyond the SM
NASA Astrophysics Data System (ADS)
Mathews, Prakash; Ravindran, V.
We present a brief overview of the physics potential of the Large Hadron Collider (LHC) and the role of quantum chromody- namics (QCD) in predicting various observables at the LHC with unprecedented accuracy. We have studied the production of Standard Model (SM) Higgs boson through gluon fusion channel and various signals of physics beyond the Standard Model (BSM) restricted to non-supersymmetric scenarios. These are models with large extra-dimensions such as ADD and Randall- Sundrum models and also physics senario resulting from scale/conformal invariant sector, namely unparticle physics. We have presented QCD effects to several of the observables in these models through higher order perturbative QCD corrections and parton distribution functions. We have demonstrated how the these corrections reduce the scale ambiguities coming from renormalisation and factorisation. Our study shows that the precise and unambiguous predictions are possible for various BSM studies at the LHC.
Revisiting charmless hadronic B{sub u,d} decays in QCD factorization
Cheng, H.-Y.; Chua, C.-K.
2009-12-01
Within the framework of QCD factorization, we consider two different types of power correction effects in order to resolve the CP puzzles and rate deficit problems with penguin-dominated two-body decays of B mesons and color-suppressed tree-dominated {pi}{sup 0}{pi}{sup 0} and {rho}{sup 0}{pi}{sup 0} modes: penguin annihilation and soft corrections to the color-suppressed tree amplitude. We emphasize that the electroweak penguin solution to the B{yields}K{pi} CP puzzle via new physics is irrelevant for solving the CP and rate puzzles related to tree-dominated decays. While some channels, e.g. K{sup -}{pi}{sup +}, K{sup -}{rho}{sup 0}, {pi}{sup +}{pi}{sup -}, {rho}{sup {+-}}{pi}{sup {+-}} need penguin annihilation to induce the correct magnitudes and signs for their CP violation, some other decays such as B{sup -}{yields}K{sup -}{pi}{sup 0}, {pi}{sup -}{eta}, K{sup -}{eta} and B{sup 0}{yields}K*{sup 0}{eta}, {pi}{sup 0}{pi}{sup 0} require the presence of both power corrections to account for the measured CP asymmetries. In general, QCD factorization predictions for the branching fractions and direct CP asymmetries of B{yields}PP, VP, VV decays are in good agreement with experiment. The predictions of perturbative QCD and soft-collinear effective theory are included for comparison.
NASA Astrophysics Data System (ADS)
Anis, Mohd; Muley, G. G.; Hakeem, A.; Shirsat, M. D.; Hussaini, S. S.
2015-08-01
The aim of present investigation is to assess the impact of oxalic acid (OA) and maleic acid (MA) on nonlinearity (second and third order) and dielectric behavior of potassium dihydrogen phosphate (KDP) crystal by means of SHG efficiency test, Z-scan analysis and dielectric studies respectively. The enhancement in SHG efficiency of OA and MA doped KDP crystal has been confirmed by means of Kurtz-Perry powder test technique. The close and open aperture Z-scan technique has been employed to study the nature and origin of improved third order NLO behavior of doped KDP crystals at 632.8 nm. The magnitude of third order nonlinear susceptibility (χ3), nonlinear refraction (n2), nonlinear absorption coefficient (β) and figure of merit (FOM) of doped KDP crystals has been calculated using the Z-scan transmittance data to explore the suitability of crystals for distinct laser assisted applications. The dielectric constant and dielectric loss of pure, OA and MA doped KDP crystals were measured at different temperatures by means of dielectric studies.
From QCD to physical resonances
NASA Astrophysics Data System (ADS)
Bolton, Daniel R.; Briceño, Raúl A.; Wilson, David J.
2016-05-01
In this talk, we present the first chiral extrapolation of a resonant scattering amplitude obtained from lattice QCD. Finite-volume spectra, determined by the Hadron Spectrum Collaboration at mπ = 236 MeV [1], for the isotriplet ππ channel are analyzed using the Lüscher method to determine the infinite-volume scattering amplitude. Unitarized Chiral Perturbation Theory is then used to extrapolate the scattering amplitude to the physical light quark masses. The viability of this procedure is demonstrated by its agreement with the experimentally determined scattering phase shift up to center-of-mass energies of 1.2 GeV. Finally, we analytically continue the amplitude to the complex plane to obtain the ρ-pole at [ 755 (2 )(1 )(02 20 ) -i/2 129 (3 )(1 )(1 7 ) ] MeV.
QCD tests with polarized beams
Maruyama, Takashi; SLD Collaboration
1996-09-01
The authors present three QCD studies performed by the SLD experiment at SLAC, utilizing the highly polarized SLC electron beam. They examined particle production differences in light quark and antiquark hemispheres, and observed more high momentum baryons and K{sup {minus}}`s than antibaryons and K{sup +}`s in quark hemispheres, consistent with the leading particle hypothesis. They performed a search for jet handedness in light q- and {anti q}-jets. Assuming Standard Model values of quark polarization in Z{sup 0} decays, they have set an improved upper limit on the analyzing power of the handedness method. They studied the correlation between the Z{sup 0} spin and the event-plane orientation in polarized Z{sup 0} decays into three jets.
Gluonic transversity from lattice QCD
NASA Astrophysics Data System (ADS)
Detmold, W.; Shanahan, P. E.
2016-07-01
We present an exploratory study of the gluonic structure of the ϕ meson using lattice QCD (LQCD). This includes the first investigation of gluonic transversity via the leading moment of the twist-2 double-helicity-flip gluonic structure function Δ (x ,Q2). This structure function only exists for targets of spin J ≥1 and does not mix with quark distributions at leading twist, thereby providing a particularly clean probe of gluonic degrees of freedom. We also explore the gluonic analogue of the Soffer bound which relates the helicity flip and nonflip gluonic distributions, finding it to be saturated at the level of 80%. This work sets the stage for more complex LQCD studies of gluonic structure in the nucleon and in light nuclei where Δ (x ,Q2) is an "exotic glue" observable probing gluons in a nucleus not associated with individual nucleons.
Lattice QCD Beyond Ground States
Huey-Wen Lin; Saul D. Cohen
2007-09-11
In this work, we apply black box methods (methods not requiring input) to find excited-state energies. A variety of such methods for lattice QCD were introduced at the 3rd iteration of the numerical workshop series. We first review a selection of approaches that have been used in lattice calculations to determine multiple energy states: multiple correlator fits, the variational method and Bayesian fitting. In the second half, we will focus on a black box method, the multi-effective mass. We demonstrate the approach on a toy model, as well as on real lattice data, extracting multiple states from single correlators. Without complicated operator construction or specialized fitting programs, the black box method shows good consistency with the traditional approaches.
Nuclear Force from Lattice QCD
Ishii, N.; Aoki, S.; Hatsuda, T.
2007-07-13
The nucleon-nucleon (NN) potential is studied by lattice QCD simulations in the quenched approximation, using the plaquette gauge action and the Wilson quark action on a 32{sup 4} [{approx_equal}(4.4 fm){sup 4}] lattice. A NN potential V{sub NN}(r) is defined from the equal-time Bethe-Salpeter amplitude with a local interpolating operator for the nucleon. By studying the NN interaction in the {sup 1}S{sub 0} and {sup 3}S{sub 1} channels, we show that the central part of V{sub NN}(r) has a strong repulsive core of a few hundred MeV at short distances (r < or approx. 0.5 fm) surrounded by an attractive well at medium and long distances. These features are consistent with the known phenomenological features of the nuclear force.
Nuclear force from lattice QCD.
Ishii, N; Aoki, S; Hatsuda, T
2007-07-13
The nucleon-nucleon (NN) potential is studied by lattice QCD simulations in the quenched approximation, using the plaquette gauge action and the Wilson quark action on a 32(4) [approximately (4.4 fm)(4)] lattice. A NN potential V(NN)(r) is defined from the equal-time Bethe-Salpeter amplitude with a local interpolating operator for the nucleon. By studying the NN interaction in the (1)S(0) and (3)S(1) channels, we show that the central part of V(NN)(r) has a strong repulsive core of a few hundred MeV at short distances (r approximately < 0.5 fm) surrounded by an attractive well at medium and long distances. These features are consistent with the known phenomenological features of the nuclear force. PMID:17678213
Sivers Asymmetry with QCD Evolution
NASA Astrophysics Data System (ADS)
Echevarria, Miguel G.; Idilbi, Ahmad; Kang, Zhong-Bo; Vitev, Ivan
2015-02-01
We analyze the Sivers asymmetry in both Drell-Yan (DY) production and semi-inclusive deep inelastic scattering (SIDIS), while considering properly defined transverse momentum dependent parton distribution and fragmentation functions and their QCD evolution. After finding a universal non-perturbative spin-independent Sudakov factor that can describe reasonably well the world's data of SIDIS, DY lepton pair and W/Z production in unpolarized scatterings, we perform a global fitting of all the experimental data on the Sivers asymmetry in SIDIS from HERMES, COMPASS and Jefferson Lab. Then we make predictions for the asymmetry in DY lepton pair and W boson production, which could be compared to the future experimental data in order to test the sign change of the Sivers function.
Electroweak symmetry breaking via QCD.
Kubo, Jisuke; Lim, Kher Sham; Lindner, Manfred
2014-08-29
We propose a new mechanism to generate the electroweak scale within the framework of QCD, which is extended to include conformally invariant scalar degrees of freedom belonging to a larger irreducible representation of SU(3)c. The electroweak symmetry breaking is triggered dynamically via the Higgs portal by the condensation of the colored scalar field around 1 TeV. The mass of the colored boson is restricted to be 350 GeV≲mS≲3 TeV, with the upper bound obtained from perturbative renormalization group evolution. This implies that the colored boson can be produced at the LHC. If the colored boson is electrically charged, the branching fraction of the Higgs boson decaying into two photons can slightly increase, and moreover, it can be produced at future linear colliders. Our idea of nonperturbative electroweak scale generation can serve as a new starting point for more realistic model building in solving the hierarchy problem. PMID:25215976
Hormuzdiar, J.N.; Hsu, S.D.
1999-02-01
We describe a class of pionic breather solutions (PBS) which appear in the chiral Lagrangian description of low-energy QCD. These configurations are long lived, with lifetimes greater than 10{sup 3} fm/c, and could arise as remnants of disoriented chiral condensate (DCC) formation at RHIC. We show that the chiral Lagrangian equations of motion for a uniformly isospin-polarized domain reduce to those of the sine-Gordon model. Consequently, our solutions are directly related to the breather solutions of sine-Gordon theory in 3+1 dimensions. We investigate the possibility of PBS formation from multiple domains of DCC, and show that the probability of formation is non-negligible. {copyright} {ital 1999} {ital The American Physical Society}
Modeling QCD for Hadron Physics
NASA Astrophysics Data System (ADS)
Tandy, P. C.
2011-10-01
We review the approach to modeling soft hadron physics observables based on the Dyson-Schwinger equations of QCD. The focus is on light quark mesons and in particular the pseudoscalar and vector ground states, their decays and electromagnetic couplings. We detail the wide variety of observables that can be correlated by a ladder-rainbow kernel with one infrared parameter fixed to the chiral quark condensate. A recently proposed novel perspective in which the quark condensate is contained within hadrons and not the vacuum is mentioned. The valence quark parton distributions, in the pion and kaon, as measured in the Drell Yan process, are investigated with the same ladder-rainbow truncation of the Dyson-Schwinger and Bethe-Salpeter equations.
Modeling QCD for Hadron Physics
Tandy, P. C.
2011-10-24
We review the approach to modeling soft hadron physics observables based on the Dyson-Schwinger equations of QCD. The focus is on light quark mesons and in particular the pseudoscalar and vector ground states, their decays and electromagnetic couplings. We detail the wide variety of observables that can be correlated by a ladder-rainbow kernel with one infrared parameter fixed to the chiral quark condensate. A recently proposed novel perspective in which the quark condensate is contained within hadrons and not the vacuum is mentioned. The valence quark parton distributions, in the pion and kaon, as measured in the Drell Yan process, are investigated with the same ladder-rainbow truncation of the Dyson-Schwinger and Bethe-Salpeter equations.
The QCD/SM Working Group: Summary Report
M. Dobbs et al.
2004-08-05
synopsis of it is included here as the first contribution to this report. This report reflects the hard and creative work by the many contributors which took place in the working group. After the MC guide description, the next contributions report on progress in describing multiple interactions, important for the LHC, and underlying events. An announcement of a Monte Carlo database, under construction, is followed by a number of contributions improving parton shower descriptions. Subsequently, a large number of contributions address resummations in various forms, after which follow studies of QCD effects in pion pair, top quark pair and photon pair plus jet production. After a study of electroweak corrections to hadronic precision observables, the report ends by presenting recent progress in methods to compute finite order corrections at one-loop with many legs, and at two-loop.
The QCD/SM working group: Summary report
Dobbs, Matt; Frixione, S.; Laenen, E.; De Roeck, A.; Tollefson, K.; Andersen, J.; Balazs, C.; Banfi, A.; Bernreuther, W.; Binoth, T.; Brandenburg, A.; Buttar, C.; Cao, C-H.; Cruz, A.; Dawson, I.; DelDuca, V.; Drollinger, V.; Dudko, L.; Eynck, T.; Field, R.; Grazzini, M.; Guillet, J.P.; Heinrich, G.; Huston, J.; Kauer, N.; Kidonakis, N.; Kulesza, A.; Lassila-Perini, K.; Magnea, L.; Mahmoudi, F.; Maina, E.; Maltoni, F.; Nolten, M.; Moraes, A.; Moretti, S.; Mrenna, S.; Nagy, Z.; Olness, F.; Puljak, I.; Ross, D.A.; Sabio-Vera, A.; Salam, G.P.; Sherstnev, A.; Si, Z.G.; Sjostrand, T.; Skands, P.; Thome, E.; Trocsanyi, Z.; Uwer, P.; Weinzierl, S.; Yuan, C.P.; Zanderighi,G.; Zanderighi, G.
2004-04-09
synopsis of it is included here as the first contribution to this report. This report reflects the hard and creative work by the many contributors which took place in the working group. After the MC guide description, the next contributions report on progress in describing multiple interactions, important for the LHC, and underlying events. An announcement of a Monte Carlo database, under construction, is followed by a number of contributions improving parton shower descriptions. Subsequently, a large number of contributions address resummations in various forms, after which follow studies of QCD effects in pion pair, top quark pair and photon pair plus jet production. After a study of electroweak corrections to hadronic precision observables, the report ends by presenting recent progress in methods to compute finite order corrections at one-loop with many legs, and at two-loop.
NLO QED contributions to top-pair production at hadron colliders
Hollik, W.; Kollar, M.
2008-01-01
Electroweak one-loop calculations for production of top-quark pairs at colliders are completed by providing the missing QED type contributions from real and virtual photons, where also effects from interference between QED and QCD contributions have to be taken into account. Moreover, photon-induced tt production is included as another partonic channel.
Parton distributions from lattice QCD: an update
Detmold, W; Melnitchouk, W; Thomas, A W
2004-04-01
We review the extraction of parton distributions from their moments calculated in lattice QCD, focusing in particular on their extrapolation to the physical region. As examples, we consider both the unpolarized and polarized isovector parton distributions of the nucleon.
Opportunities, challenges, and fantasies in lattice QCD
NASA Astrophysics Data System (ADS)
Wilczek, Frank
2003-05-01
Some important problems in quantitative QCD will certainly yield to hard work and adequate investment of resources, others appear difficult but may be accessible, and still others will require essentially new ideas. Here I identify several examples in each class.
None
2011-10-06
Modern QCD - Lecture 4 We will consider some processes of interest at the LHC and will discuss the main elements of their cross-section calculations. We will also summarize the current status of higher order calculations.
Strange Baryon Physics in Full Lattice QCD
Huey-Wen Lin
2007-11-01
Strange baryon spectra and form factors are key probes to study excited nuclear matter. The use of lattice QCD allows us to test the strength of the Standard Model by calculating strange baryon quantities from first principles.
Excited light meson spectroscopy from lattice QCD
Christopher Thomas, Hadron Spectrum Collaboration
2012-04-01
I report on recent progress in calculating excited meson spectra using lattice QCD, emphasizing results and phenomenology. With novel techniques we can now extract extensive spectra of excited mesons with high statistical precision, including spin-four states and those with exotic quantum numbers. As well as isovector meson spectra, I will present new calculations of the spectrum of excited light isoscalar mesons, something that has up to now been a challenge for lattice QCD. I show determinations of the flavor content of these mesons, including the eta-eta' mixing angle, providing a window on annihilation dynamics in QCD. I will also discuss recent work on using lattice QCD to map out the energy-dependent phase shift in pi-pi scattering and future applications of the methodology to the study of resonances and decays.
Simplifying Multi-Jet QCD Computation
Peskin, Michael E.; /SLAC
2011-11-04
These lectures give a pedagogical discussion of the computation of QCD tree amplitudes for collider physics. The tools reviewed are spinor products, color ordering, MHV amplitudes, and the Britto-Cachazo-Feng-Witten recursion formula.
QCD mechanisms for heavy particle production
Brodsky, S.J.
1985-09-01
For very large pair mass, the production of heavy quarks and supersymmetric particles is expected to be governed by ACD fusion subprocesses. At lower mass scales other QCD mechanisms such as prebinding distortion and intrinsic heavy particle Fock states can become important, possibly accounting for the anomalies observed for charm hadroproduction. We emphasize the importance of final-state Coulomb interactions at low relative velocity in QCD and predict the existence of heavy narrow four quark resonances (c c-bar u u-bar) and (cc c-bar c-bar) in ..gamma gamma.. reactions. Coherent QCD contributions are discussed as a contribution to the non-additivity of nuclear structure functions and heavy particle production cross sections. We also predict a new type of amplitude zero for exclusive heavy meson pair production which follows from the tree-graph structure of QCD. 35 refs., 8 figs., 1 tab.
Hadronic final states in high -pT QCD at CDF
Matera, Keith
2013-11-18
The heavy quark content of gauge boson events is of great interest to studies of QCD. These events probe the gluon and heavy-quark parton distribution functions of the proton, and also provide a measurement of the rate of final state gluon splitting to heavy flavor. In addition, gauge boson plus heavy quark events are representative of backgrounds to Higgs, single top, and supersymmetric particle searches. Recent work with the CDF II detector at the Fermilab Tevatron has measured the cross-section of several gauge boson plus heavy flavor production processes, including the first Tevatron observation of specific charm process p{p bar} → W +c. Results are found to be in agreement with NLO predictions that include an enhanced rate of g → {cc bar}/bb splitting. Lastly, a new analysis promises to probe a lower pT (c) region than has been previously explored, by fully reconstructing D* → D0(Kπ)π decays in the full CDF dataset (9.7 fb−1).
Recent QCD Studies at the Tevatron
Group, Robert Craig
2008-04-01
Since the beginning of Run II at the Fermilab Tevatron the QCD physics groups of the CDF and D0 experiments have worked to reach unprecedented levels of precision for many QCD observables. Thanks to the large dataset--over 3 fb{sup -1} of integrated luminosity recorded by each experiment--important new measurements have recently been made public and will be summarized in this paper.
QCD and hard diffraction at the LHC
Albrow, Michael G.; /Fermilab
2005-09-01
As an introduction to QCD at the LHC the author gives an overview of QCD at the Tevatron, emphasizing the high Q{sup 2} frontier which will be taken over by the LHC. After describing briefly the LHC detectors the author discusses high mass diffraction, in particular central exclusive production of Higgs and vector boson pairs. The author introduces the FP420 project to measure the scattered protons 420m downstream of ATLAS and CMS.
Novel QCD effects in nuclear collisions
Brodsky, S.J.
1991-12-01
Heavy ion collisions can provide a novel environment for testing fundamental dynamical processes in QCD, including minijet formation and interactions, formation zone phenomena, color filtering, coherent co-mover interactions, and new higher twist mechanisms which could account for the observed excess production and anomalous nuclear target dependence of heavy flavor production. The possibility of using light-cone thermodynamics and a corresponding covariant temperature to describe the QCD phases of the nuclear fragmentation region is also briefly discussed.
Lattice and Phase Diagram in QCD
Lombardo, Maria Paola
2008-10-13
Model calculations have produced a number of very interesting expectations for the QCD Phase Diagram, and the task of a lattice calculations is to put these studies on a quantitative grounds. I will give an overview of the current status of the lattice analysis of the QCD phase diagram, from the quantitative results of mature calculations at zero and small baryochemical potential, to the exploratory studies of the colder, denser phase.
Precision lattice QCD: challenges and prospects
NASA Astrophysics Data System (ADS)
Hashimoto, Shoji
2013-04-01
With Peta-flops scale computational resources, lattice QCD simulation has recently reached one of its primary goals, i.e. reproducing the low-lying hadron spectrum starting from the QCD Lagrangian. Applications to various other phenomenological quantities, for which no other way of precise theoretical calculation is available, would become the next milestone. In this talk I will provide a brief overview of the field and summarize the remaining problems to be solved before achieving the precision calculations.
Random walk through recent CDF QCD results
C. Mesropian
2003-04-09
We present recent results on jet fragmentation, jet evolution in jet and minimum bias events, and underlying event studies. The results presented in this talk address significant questions relevant to QCD and, in particular, to jet studies. One topic discussed is jet fragmentation and the possibility of describing it down to very small momentum scales in terms of pQCD. Another topic is the studies of underlying event energy originating from fragmentation of partons not associated with the hard scattering.
Some new/old approaches to QCD
Gross, D.J.
1992-11-01
In this lecture I shall discuss some recent attempts to revive some old ideas to address the problem of solving QCD. I believe that it is timely to return to this problem which has been woefully neglected for the last decade. QCD is a permanent part of the theoretical landscape and eventually we will have to develop analytic tools for dealing with the theory in the infra-red. Lattice techniques are useful but they have not yet lived up to their promise. Even if one manages to derive the hadronic spectrum numerically, to an accuracy of 10% or even 1%, we will not be truly satisfied unless we have some analytic understanding of the results. Also, lattice Monte-Carlo methods can only be used to answer a small set of questions. Many issues of great conceptual and practical interest-in particular the calculation of scattering amplitudes, are thus far beyond lattice control. Any progress in controlling QCD in an explicit analytic, fashion would be of great conceptual value. It would also be of great practical aid to experimentalists, who must use rather ad-hoc and primitive models of QCD scattering amplitudes to estimate the backgrounds to interesting new physics. I will discuss an attempt to derive a string representation of QCD and a revival of the large N approach to QCD. Both of these ideas have a long history, many theorist-years have been devoted to their pursuit-so far with little success. I believe that it is time to try again. In part this is because of the progress in the last few years in string theory. Our increased understanding of string theory should make the attempt to discover a stringy representation of QCD easier, and the methods explored in matrix models might be employed to study the large N limit of QCD.
Probing QCD at high energy via correlations
Jalilian-Marian, Jamal
2011-04-26
A hadron or nucleus at high energy or small x{sub Bj} contains many gluons and may be described as a Color Glass Condensate. Angular and rapidity correlations of two particles produced in high energy hadron-hadron collisions is a sensitive probe of high gluon density regime of QCD. Evolution equations which describe rapidity dependence of these correlation functions are derived from a QCD effective action.
Some New/Old Approaches to QCD
DOE R&D Accomplishments Database
Gross, D. J.
1992-11-01
In this lecture I shall discuss some recent attempts to revive some old ideas to address the problem of solving QCD. I believe that it is timely to return to this problem which has been woefully neglected for the last decade. QCD is a permanent part of the theoretical landscape and eventually we will have to develop analytic tools for dealing with the theory in the infra-red. Lattice techniques are useful but they have not yet lived up to their promise. Even if one manages to derive the hadronic spectrum numerically, to an accuracy of 10% or even 1%, we will not be truly satisfied unless we have some analytic understanding of the results. Also, lattice Monte-Carlo methods can only be used to answer a small set of questions. Many issues of great conceptual and practical interest-in particular the calculation of scattering amplitudes, are thus far beyond lattice control. Any progress in controlling QCD in an explicit analytic, fashion would be of great conceptual value. It would also be of great practical aid to experimentalists, who must use rather ad-hoc and primitive models of QCD scattering amplitudes to estimate the backgrounds to interesting new physics. I will discuss an attempt to derive a string representation of QCD and a revival of the large N approach to QCD. Both of these ideas have a long history, many theorist-years have been devoted to their pursuit-so far with little success. I believe that it is time to try again. In part this is because of the progress in the last few years in string theory. Our increased understanding of string theory should make the attempt to discover a stringy representation of QCD easier, and the methods explored in matrix models might be employed to study the large N limit of QCD.
Lattice QCD and the Jefferson Laboratory Program
Jozef Dudek, Robert Edwards, David Richards, Konstantinos Orginos
2011-06-01
Lattice gauge theory provides our only means of performing \\textit{ab initio} calculations in the non-perturbative regime. It has thus become an increasing important component of the Jefferson Laboratory physics program. In this paper, we describe the contributions of lattice QCD to our understanding of hadronic and nuclear physics, focusing on the structure of hadrons, the calculation of the spectrum and properties of resonances, and finally on deriving an understanding of the QCD origin of nuclear forces.
Contact term, its holographic description in QCD and dark energy
NASA Astrophysics Data System (ADS)
Zhitnitsky, Ariel R.
2012-08-01
In this work we study the well-known contact term, which is the key element in resolving the so-called U(1)A problem in QCD. We study this term using the dual holographic description. We argue that in the dual picture the contact term is saturated by the D2-branes which can be interpreted as the tunneling events in Minkowski space-time. We quote a number of direct lattice results supporting this identification. We also argue that the contact term receives a Casimir-like correction ˜(ΛQCDR)-1 rather than the naively expected exp(-ΛQCDR) when the Minkowski space-time R3,1 is replaced by a large but finite manifold with a size R. Such a behavior is consistent with other quantum field theory (QFT)-based computations when powerlike corrections are due to nontrivial properties of topological sectors of the theory. In holographic description, such a behavior is due to a massless Ramond-Ramond (RR) field living in the bulk of multidimensional space when powerlike corrections is a natural outcome of a massless RR field. In many respects, the phenomenon is similar to the Aharonov-Casher effect when the “modular electric field” can penetrate into a superconductor where the electric field is exponentially screened. The role of “modular operator” from the Aharonov-Casher effect is played by a large-gauge transformation operator T in four-dimensional QCD, resulting in the transparency of the system to topologically nontrivial pure gauge configurations. We discuss some profound consequences of our findings. In particular, we speculate that a slow variation of the contact term in expanding universe might be the main source of the observed dark energy.
QCD: results from lattice quantum chromodynamics
Kronfeld, Andreas S.; /Fermilab
2006-10-01
Quantum chromodynamics (QCD) is the modern theory of the strong force. In this theory, the main objects are quarks and gluons, which are bound by the strong force into protons, neutrons, and other particles called hadrons. In the framework of QCD, the strong nuclear force binding protons and neutrons together into nuclei is actually only a residue of the much stronger forces acting between quarks and gluons. In fact, inside the proton, even the concept of force is not very useful. Within all hadrons they have a swirl of gluons being exchanged back and forth as a manifestation of the strong force. To make matters worse, gluons can split into two, and then rejoin, or they can split into a quark-antiquark pair. Even the simplest hadron is a complex system hosting constantly interacting components. Despite this complexity, QCD is well established experimentally. This is because at short distances (or high energies), the coupling between the particles is effectively small and particles move around with relative freedom. This is called asymptotic freedom and QCD is amenable to the traditional methods of quantum field theory in this regime. High-energy experiments have tested and confirmed QCD in this realm, which led to the 2004 Nobel Prize in Physics for Drs. David Gross, David Politzer, and Frank Wilczek, the theorists who provided the theory for short-range QCD and asymptotic freedom.
Higgs boson gluon-fusion production in QCD at three loops.
Anastasiou, Charalampos; Duhr, Claude; Dulat, Falko; Herzog, Franz; Mistlberger, Bernhard
2015-05-29
We present the cross section for the production of a Higgs boson at hadron colliders at next-to-next-to-next-to-leading order (N^{3}LO) in perturbative QCD. The calculation is based on a method to perform a series expansion of the partonic cross section around the threshold limit to an arbitrary order. We perform this expansion to sufficiently high order to obtain the value of the hadronic cross at N^{3}LO in the large top-mass limit. For renormalization and factorization scales equal to half the Higgs boson mass, the N^{3}LO corrections are of the order of +2.2%. The total scale variation at N^{3}LO is 3%, reducing the uncertainty due to missing higher order QCD corrections by a factor of 3. PMID:26066428
Unparticles in diphoton production to next-to-leading order in QCD at the LHC
Kumar, M. C.; Mathews, Prakash
2009-04-01
We compute to next-to-leading order in QCD the tensor unparticle contribution to the diphoton production at the LHC, wherein the unparticle sector is a consequence of (a) scale invariance but not full conformal invariance and (b) conformal invariance. We use the semianalytical two cutoff phase-space slicing method to handle the O({alpha}{sub s}) corrections to the pp{yields}{gamma}{gamma}X and show that our results are insensitive to the soft and collinear cutoffs. In order to avoid the contribution of the photons due to fragmentation, we employ the smooth cone isolation criterion. Significance of the QCD corrections to the diphoton events including unparticles is highlighted.
Can Nonrelativistic QCD Explain the γ γ*→ηc Transition Form Factor Data?
NASA Astrophysics Data System (ADS)
Feng, Feng; Jia, Yu; Sang, Wen-Long
2015-11-01
Unlike the bewildering situation in the γ γ*→π form factor, a widespread view is that perturbative QCD can decently account for the recent BABAR measurement of the γ γ*→ηc transition form factor. The next-to-next-to-leading-order perturbative correction to the γ γ*→ηc ,b form factor, is investigated in the nonrelativistic QCD (NRQCD) factorization framework for the first time. As a byproduct, we obtain, by far, the most precise order-αs2 NRQCD matching coefficient for the ηc ,b→γ γ process. After including the substantial negative order-αs2 correction, the good agreement between NRQCD prediction and the measured γ γ*→ηc form factor is completely ruined over a wide range of momentum transfer squared. This eminent discrepancy casts some doubts on the applicability of the NRQCD approach to hard exclusive reactions involving charmonium.
aMC fast: automation of fast NLO computations for PDF fits
NASA Astrophysics Data System (ADS)
Bertone, Valerio; Frederix, Rikkert; Frixione, Stefano; Rojo, Juan; Sutton, Mark
2014-08-01
We present the interface between M adG raph5_ aMC@NLO, a self-contained program that calculates cross sections up to next-to-leading order accuracy in an automated manner, and APPL grid, a code that parametrises such cross sections in the form of look-up tables which can be used for the fast computations needed in the context of PDF fits. The main characteristic of this interface, which we dub aMC fast, is its being fully automated as well, which removes the need to extract manually the process-specific information for additional physics processes, as is the case with other matrix-element calculators, and renders it straightforward to include any new process in the PDF fits. We demonstrate this by studying several cases which are easily measured at the LHC, have a good constraining power on PDFs, and some of which were previously unavailable in the form of a fast interface.
Fluorescence, spectroscopic and NLO properties of green tea extract in deoxyribonucleic acid
NASA Astrophysics Data System (ADS)
Manea, Ana-Maria; Rau, Ileana; Kajzar, Francois; Meghea, Aurelia
2013-11-01
Natural, purely biological deoxyribonucleic acid (DNA)-green tea extract (GTE) complexes at different concentrations were prepared and characterized for their spectroscopic, fluorescent, linear and nonlinear optical properties. The complexes can be processed into good optical quality thin films by solution casting. They fluoresce when excited in UV absorption band, with a significantly larger quantum yield for the DNA-GTE complex than for a pure GTE solution. The thin film refractive indices were determined by Fabry-Perot (FP) interference patterns. The third-order nonlinear optical (NLO) properties of thin films were determined by the optical third-harmonic generation technique at 1064.2 nm fundamental wavelength. The phase of THG susceptibility was determined from the concentration variation of THG susceptibility. It reveals presence of a two-photon resonance with a band lying in the optical gap.
NASA Astrophysics Data System (ADS)
Çatıkkaş, Berna; Aktan, Ebru; Yalçın, Ergin
2016-08-01
This work deals with the optimized molecular structure, vibrational spectra, nonlinear optic (NLO) and frontier molecule orbital (FMO) properties of 1-Methyl-2-phenyl-3-(1,3,4-thiadiazol-2-yldiazenyl)-1H-indole (MPI) by quantum chemical calculations. The Fourier transform infrared (FT-MIR and FT-FIR) and Raman spectra of 1-Methyl-2-phenyl-3-(1,3,4-thiadiazol-2-yldiazenyl)-1H-indole (MPI) were recorded in the region (4000-400 cm-1 and 400-30 cm-1) and (3200-92 cm-1), respectively. The analysis and complete vibrational assignments of the fundamental modes of the MPI molecule were carried out by using the observed FT-IR and FT-Raman data and calculated Total Energy Distribution (TED) according to Scaled Quantum Mechanics procedure. The calculated geometrical parameters of the MPI molecule are in agreement with the obtained values from XRD studies. On the other hand, the difference between the scaled and observed wavenumber values of the most of the fundamentals are very small. 1H NMR and 13C NMR chemical shift values, and energy gap between LUMO-HOMO and molecular electrostatic potential (MEP) were investigated by using density functional theory (B3LYP) methods. UV/Visible spectra and λ maximum absorption values, the oscillator strengths in the chloroform, methanol and DMSO solvation in combination with different basis sets were calculated by using the time-dependent density functional theory (TD-DFT). Additionally, the predicted nonlinear optical (NLO) properties of the MPI are quite greater than that of urea at the B3LYP/6-31++G(d,p) level.
NASA Astrophysics Data System (ADS)
Torres-Zúñiga, V.; Castañeda-Guzmán, R.; Morales-Saavedra, O. G.; Pérez-Martínez, A. L.; Ogawa, T.
2011-12-01
The pulsed-laser photoacoustic-technique (PLPA) was implemented to characterize molecular orientational order and anisotropy in push-pull poled polymeric films as function of temperature and laser polarization. Traditionally, photoacoustic signals are considered to be directly proportional to the linear optical absorption in amorphous media. In this work, however, it is shown that photoacoustic signals can also be highly sensitive to the material anisotropy when convenient polarization dependent photoacoustic analyses are performed. Thus, variation of the molecular orientation in organic films, comprising rod-like polar chromophores, can be unambiguously monitored via rms-analyses performed on the amplitude of the generated opto-acoustical PLPA-signals as function of the incident laser polarization. This result can be useful for the characterization of organic-based nonlinear optical (NLO) poled films and, in general, in studies of anisotropic materials. In fact, in this work we were able to accurately determine the molecular order parameter ( ϕ) of a NLO-active spin-coated polymeric film containing optically active push-pull chromophores. These molecules, previously oriented via an electrical-poling procedure, are capable to exhibit strong second harmonic generation (SHG) effects. The PLPA-measurements were systematically compared to the linear UV-vis optical absorbance spectra while heating the poled film sample in order to monitor the thermally induced molecular disorder, so that the order parameter may be photo-acoustically evaluated via the PLPA-signals generated from the poled to the unpoled film phase. These PLPA-experiments were performed taking into account the UV-vis reference spectra for calibration and comparison purposes in the evaluation of the order parameter. A significant advantage of the PLPA-technique over commonly used optical spectral methodologies is its convenient applicability in samples exhibiting poor or null optical transmission.
Synthesis and electro-optic properties of the chromophore-containing NLO polyarylate polymers
NASA Astrophysics Data System (ADS)
Ren, Haohui; Peng, Chengcheng; Bo, Shuhui; Fan, Guofang; Xu, Guangming; Zhao, Hui; Zhen, Zhen; Liu, Xinhou
2014-03-01
Base on the same two monomers, diphenolic acid (DPA) and isophthaloyl chloride (IPC), three chromophore-containing nonlinear optical (NLO) polyarylate polymers were prepared. A tricyanofuran (TCF)-acceptor type chromophore group was in main-chain (mPAR-chr1), side-chain (sPAR-chr1) and side-chain with a 1,1-bis(4-hydroxyphenyl)-1-phenyl-2,2,2-trifluoroethane (BPAPF) group (sPAR-F-chr1), respectively. The obtained polymers were characterized and evaluated by UV-Vis, 1H NMR, DSC and TGA. All the polymers exhibited good electro-optic (EO) activity. The relationship between EO coefficients (r33) and the chromophore concentration of the three polymers were also characterized and discussed. There were no obvious differences found in EO activity between mPAR-chr1 and sPAR-chr1 polyarylates with the same chromophore. The fluorinated block polyarylate sPAR-F-chr1 has the largest r33 value in these three polyarylates which is 52 pm/V at the wavelength of 1310 nm (which is almost twice the r33 value of normal polymers contained the same chormophore at the same content), when the concentration of chromophore 1 is 18wt.%. 85% of the r33 value was retained in the sPAR-F-chr1 after being heated at 85°C for 600 hours. The polymer sPAR-F-chr1, with good solubility, high Tg (above 200 °C) and side functional group at the same time, may probably be a practical NLO material. These properties make the new polyarylates have potential applications in EO devices such as EO modulators and switches.
Resumming double logarithms in the QCD evolution of color dipoles
NASA Astrophysics Data System (ADS)
Iancu, E.; Madrigal, J. D.; Mueller, A. H.; Soyez, G.; Triantafyllopoulos, D. N.
2015-05-01
The higher-order perturbative corrections, beyond leading logarithmic accuracy, to the BFKL evolution in QCD at high energy are well known to suffer from a severe lack-of-convergence problem, due to radiative corrections enhanced by double collinear logarithms. Via an explicit calculation of Feynman graphs in light cone (time-ordered) perturbation theory, we show that the corrections enhanced by double logarithms (either energy-collinear, or double collinear) are associated with soft gluon emissions which are strictly ordered in lifetime. These corrections can be resummed to all orders by solving an evolution equation which is non-local in rapidity. This equation can be equivalently rewritten in local form, but with modified kernel and initial conditions, which resum double collinear logs to all orders. We extend this resummation to the next-to-leading order BFKL and BK equations. The first numerical studies of the collinearly-improved BK equation demonstrate the essential role of the resummation in both stabilizing and slowing down the evolution.
QCD Prediction of ATT for Small QT Dimuon Production in pp and pp-bar Collisions
Kawamura, Hiroyuki; Kodaira, Jiro; Tanaka, Kazuhiro
2007-06-13
We present QCD prediction of double-spin asymmetries (ATT) in transversely polarized Drell-Yan process at small transverse momentum QT of dimuon. Resummation of large logarithmic corrections, relevant in small QT region, is performed up to next-to-leading logarithmic (NLL) accuracy. ATT at RHIC, J-PARC and GSI are studied numerically in the corresponding kinematic regions. We show that the large ATT is obtained for small QT and moderate energies.
Imaginary part of the static gluon propagator in an anisotropic (viscous) QCD plasma
Dumitru, Adrian; Guo, Yun; Strickland, Michael
2009-06-01
We determine viscosity corrections to the retarded, advanced and symmetric gluon self-energies and to the static propagator in the weak-coupling ''hard loop'' approximation to high-temperature QCD. We apply these results to calculate the imaginary part of the heavy-quark potential which is found to be smaller (in magnitude) than at vanishing viscosity. This implies a smaller decay width of quarkonium bound states in an anisotropic plasma.
Infrared modified QCD couplings and Bjorken sum rule
NASA Astrophysics Data System (ADS)
Khandramai, V. L.; Teryaev, O. V.; Gabdrakhmanov, I. R.
2016-02-01
We test the recently proposed “Massive” Perturbation Theory (MPT) for the description of the Γ1p-n data at low momentum transfers. The MPT constructed on the two grounds: the first is pQCD with only one parameter added, an effective “glueball mass” mp ≲ Mgl ≲ 1 GeV; serving as an infrared “regulator” the second stems out of the ghost- free Analytic Perturbation Theory comprising non-power perturbative expansion that makes it compatible with linear integral transformations. It is regular in the low-energy region and could serve as a practical means for the analysis of data below 1 GeV up to the IR-limit. We study the non-perturbative Bjorken sum rule higher twists correction by using the MPT, the integral representation for infinite sum of higher twists coefficients and the QCD-inspired model for the Q2-dependence of the generalized Gerasimov-Drell-Hearn sum rule.
Bootstrapping Multi-Parton Loop Amplitudes in QCD
Bern, Zvi; Dixon, Lance J.; Kosower, David A.; /Saclay, SPhT
2005-07-06
The authors present a new method for computing complete one-loop amplitudes, including their rational parts, in non-supersymmetric gauge theory. This method merges the unitarity method with on-shell recursion relations. It systematizes a unitarity-factorization bootstrap approach previously applied by the authors to the one-loop amplitudes required for next-to-leading order QCD corrections to the processes e{sup +}e{sup -} {yields} Z, {gamma}* {yields} 4 jets and pp {yields} W + 2 jets. We illustrate the method by reproducing the one-loop color-ordered five-gluon helicity amplitudes in QCD that interfere with the tree amplitude, namely A{sub 5;1}(1{sup -}, 2{sup -}, 3{sup +}, 4{sup +}, 5{sup +}) and A{sub 5;1}(1{sup -}, 2{sup +}, 3{sup -}, 4{sup +}, 5{sup +}). Then we describe the construction of the six- and seven-gluon amplitudes with two adjacent negative-helicity gluons, A{sub 6;1}(1{sup -}, 2{sup -}, 3{sup +}, 4{sup +}, 5{sup +}, 6{sup +}) and A{sub 7;1}(1{sup -}, 2{sup -}, 3{sup +}, 4{sup +}, 5{sup +}, 6{sup +}, 7{sup +}), which uses the previously-computed logarithmic parts of the amplitudes as input. They present a compact expression for the six-gluon amplitude. No loop integrals are required to obtain the rational parts.
The effective QCD phase diagram and the critical end point
NASA Astrophysics Data System (ADS)
Ayala, Alejandro; Bashir, Adnan; Cobos-Martínez, J. J.; Hernández-Ortiz, Saúl; Raya, Alfredo
2015-08-01
We study the QCD phase diagram on the temperature T and quark chemical potential μ plane, modeling the strong interactions with the linear sigma model coupled to quarks. The phase transition line is found from the effective potential at finite T and μ taking into account the plasma screening effects. We find the location of the critical end point (CEP) to be (μCEP /Tc, TCEP /Tc) ∼ (1.2, 0.8), where Tc is the (pseudo)critical temperature for the crossover phase transition at vanishing μ. This location lies within the region found by lattice inspired calculations. The results show that in the linear sigma model, the CEP's location in the phase diagram is expectedly determined solely through chiral symmetry breaking. The same is likely to be true for all other models which do not exhibit confinement, provided the proper treatment of the plasma infrared properties for the description of chiral symmetry restoration is implemented. Similarly, we also expect these corrections to be substantially relevant in the QCD phase diagram.
On aspects of holographic thermal QCD at finite coupling
NASA Astrophysics Data System (ADS)
Sil, Karunava; Misra, Aalok
2016-09-01
In the context of string theoretic dual of thermal QCD-like theories at finite gauge/string coupling of [1] (as part of the 'MQGP' limit of [2]), we obtain the QCD deconfinement temperature compatible with lattice results for the right number of light flavors Nf = 3, and the correct mass scale of the light (first generation) quarks. The type IIB background of [1] is also shown to be thermodynamically stable. Further, we show that the temperature dependence of DC electrical conductivity mimics a one-dimensional Luttinger liquid, and the requirement of the Einstein relation (ratio of electrical conductivity and charge susceptibility equal to the diffusion constant) to be satisfied requires a specific dependence of the Ouyang embedding parameter on the horizon radius. These results arise due to the non-Kählerity and non-conformality of the type IIB background. On the geometrical side we quantify the former (non-Kählerity) by evaluating the SU (3) /G2-structure torsion classes of the local type IIA mirror/M-theory uplift. Analogous to what was shown for the type IIB background in [5], we first show that the type IIA delocalized SYZ mirror (after fine tuning) can also be approximately supersymmetric. We then work out the G2-structure torsion classes of the local M-theory uplift of the mirror type IIA metric - in the large-N limit at finite coupling, G2 structure approaches G2 holonomy.
QCD structure of nuclear interactions
NASA Astrophysics Data System (ADS)
Granados, Carlos G.
The research presented in this dissertation investigated selected processes involving baryons and nuclei in hard scattering reactions. These processes are characterized by the production of particles with large energies and transverse momenta. Through these processes, this work explored both, the constituent (quark) structure of baryons (specifically nucleons and Delta-Isobars), and the mechanisms through which the interactions between these constituents ultimately control the selected reactions. The first of such reactions is the hard nucleon-nucleon elastic scattering, which was studied here considering the quark exchange between the nucleons to be the dominant mechanism of interaction in the constituent picture. In particular, it was found that an angular asymmetry exhibited by proton-neutron elastic scattering data is explained within this framework if a quark-diquark picture dominates the nucleon's structure instead of a more traditional SU(6) three quarks picture. The latter yields an asymmetry around 90o center of mass scattering with a sign opposite to what is experimentally observed. The second process is the hard breakup by a photon of a nucleon-nucleon system in light nuclei. Proton-proton (pp) and proton-neutron (pn) breakup in 3He, and DeltaDelta-isobars production in deuteron breakup were analyzed in the hard rescattering model (HRM), which in conjunction with the quark interchange mechanism provides a Quantum Chromodynamics (QCD) description of the reaction. Through the HRM, cross sections for both channels in 3He photodisintegration were computed without the need of a fitting parameter. The results presented here for pp breakup show excellent agreement with recent experimental data. In DeltaDelta-isobars production in deuteron breakup, HRM angular distributions for the two DeltaDelta channels were compared to the pn channel and to each other. An important prediction fromthis study is that the Delta++Delta- channel consistently dominates Delta+Delta0
QCD as a topologically ordered system
Zhitnitsky, Ariel R.
2013-09-15
We argue that QCD belongs to a topologically ordered phase similar to many well-known condensed matter systems with a gap such as topological insulators or superconductors. Our arguments are based on an analysis of the so-called “deformed QCD” which is a weakly coupled gauge theory, but nevertheless preserves all the crucial elements of strongly interacting QCD, including confinement, nontrivial θ dependence, degeneracy of the topological sectors, etc. Specifically, we construct the so-called topological “BF” action which reproduces the well known infrared features of the theory such as non-dispersive contribution to the topological susceptibility which cannot be associated with any propagating degrees of freedom. Furthermore, we interpret the well known resolution of the celebrated U(1){sub A} problem where the would be η{sup ′} Goldstone boson generates its mass as a result of mixing of the Goldstone field with a topological auxiliary field characterizing the system. We then identify the non-propagating auxiliary topological field of the BF formulation in deformed QCD with the Veneziano ghost (which plays the crucial role in resolution of the U(1){sub A} problem). Finally, we elaborate on relation between “string-net” condensation in topologically ordered condensed matter systems and long range coherent configurations, the “skeletons”, studied in QCD lattice simulations. -- Highlights: •QCD may belong to a topologically ordered phase similar to condensed matter (CM) systems. •We identify the non-propagating topological field in deformed QCD with the Veneziano ghost. •Relation between “string-net” condensates in CM systems and the “skeletons” in QCD lattice simulations is studied.
Two flavor QCD and confinement
D'Elia, Massimo; Di Giacomo, Adriano; Pica, Claudio
2005-12-01
We argue that the order of the chiral transition for N{sub f}=2 is a sensitive probe of the QCD vacuum, in particular, of the mechanism of color confinement. A strategy is developed to investigate the order of the transition by use of finite size scaling analysis. An in-depth numerical investigation is performed with staggered fermions on lattices with L{sub t}=4 and L{sub s}=12, 16, 20, 24, 32 and quark masses am{sub q} ranging from 0.01335 to 0.307036. The specific heat and a number of susceptibilities are measured and compared with the expectations of an O(4) second order and of a first order phase transition. A detailed comparison with previous works, which all use similar techniques as ours, is performed. A second order transition in the O(4) and O(2) universality classes are incompatible with our data, which seem to prefer a first order transition. However we have L{sub t}=4 and unimproved action, so that a check with improved techniques (algorithm and action) and possibly larger L{sub t} will be needed to assess this issue on a firm basis.
[Zn(C 7H 3O 5N)] n · nH 2O: A third-order NLO Zn coordination polymer with spiroconjugated structure
NASA Astrophysics Data System (ADS)
Zhou, Guo-Wei; Lan, You-Zhao; Zheng, Fa-Kun; Zhang, Xin; Lin, Meng-Hai; Guo, Guo-Cong; Huang, Jin-Shun
2006-08-01
[Zn(C 7H 3O 5N)] n · nH 2O ( 1) possesses an anticlockwise windmill-like framework structure and formats spiroconjugation over the infinite molecular layer that is predicted to have large static third-order polarizability and the convergence value of γxxxx reaches 6.86 × 10 -33 esu in the case of zero input photon energy. The third-order NLO properties of 1 were investigated via Z-scan techniques at wavelength of 532 nm. It showed strong third-order NLO absorptive properties, and its n2 value was calculated to be 4.15 × 10 -11 esu. The relationship between the spiroconjugated structure and the NLO property has been discussed, which supposed to be more valuable for the NLO research.
Importance of proper renormalization scale-setting for QCD testing at colliders
Wu, Xing -Gang; Wang, Sheng -Quan; Brodsky, Stanley J.
2015-12-22
A primary problem affecting perturbative quantum chromodynamic (pQCD) analyses is the lack of a method for setting the QCD running-coupling renormalization scale such that maximally precise fixed-order predictions for physical observables are obtained. The Principle of Maximum Conformality (PMC) eliminates the ambiguities associated with the conventional renormalization scale-setting procedure, yielding predictions that are independent of the choice of renormalization scheme. The QCD coupling scales and the effective number of quark flavors are set order-by-order in the pQCD series. The PMC has a solid theoretical foundation, satisfying the standard renormalization group invariance condition and all of the self-consistency conditions derived frommore » the renormalization group. The PMC scales at each order are obtained by shifting the arguments of the strong force coupling constant αs to eliminate all non-conformal {βi} terms in the pQCD series. The {βi} terms are determined from renormalization group equations without ambiguity. The correct behavior of the running coupling at each order and at each phase-space point can then be obtained. The PMC reduces in the NC → 0 Abelian limit to the Gell-Mann-Low method. In this brief report, we summarize the results of our recent application of the PMC to a number of collider processes, emphasizing the generality and applicability of this approach. A discussion of hadronic Z decays shows that, by applying the PMC, one can achieve accurate predictions for the total and separate decay widths at each order without scale ambiguities. We also show that, if one employs the PMC to determine the top-quark pair forward-backward asymmetry at the next-to-next-to-leading order level, one obtains a comprehensive, self-consistent pQCD explanation for the Tevatron measurements of the asymmetry. This accounts for the “increasing-decreasing” behavior observed by the D0 collaboration for increasing tt¯ invariant mass. At lower
Importance of proper renormalization scale-setting for QCD testing at colliders
Wu, Xing -Gang; Wang, Sheng -Quan; Brodsky, Stanley J.
2015-12-22
A primary problem affecting perturbative quantum chromodynamic (pQCD) analyses is the lack of a method for setting the QCD running-coupling renormalization scale such that maximally precise fixed-order predictions for physical observables are obtained. The Principle of Maximum Conformality (PMC) eliminates the ambiguities associated with the conventional renormalization scale-setting procedure, yielding predictions that are independent of the choice of renormalization scheme. The QCD coupling scales and the effective number of quark flavors are set order-by-order in the pQCD series. The PMC has a solid theoretical foundation, satisfying the standard renormalization group invariance condition and all of the self-consistency conditions derived from the renormalization group. The PMC scales at each order are obtained by shifting the arguments of the strong force coupling constant αs to eliminate all non-conformal {βi} terms in the pQCD series. The {βi} terms are determined from renormalization group equations without ambiguity. The correct behavior of the running coupling at each order and at each phase-space point can then be obtained. The PMC reduces in the N_{C} → 0 Abelian limit to the Gell-Mann-Low method. In this brief report, we summarize the results of our recent application of the PMC to a number of collider processes, emphasizing the generality and applicability of this approach. A discussion of hadronic Z decays shows that, by applying the PMC, one can achieve accurate predictions for the total and separate decay widths at each order without scale ambiguities. We also show that, if one employs the PMC to determine the top-quark pair forward-backward asymmetry at the next-to-next-to-leading order level, one obtains a comprehensive, self-consistent pQCD explanation for the Tevatron measurements of the asymmetry. This accounts for the “increasing-decreasing” behavior observed by the D0 collaboration for increasing tt¯ invariant mass. At lower
Importance of proper renormalization scale-setting for QCD testing at colliders
NASA Astrophysics Data System (ADS)
Wu, Xing-Gang; Wang, Sheng-Quan; Brodsky, Stanley J.
2016-02-01
A primary problem affecting perturbative quantum chromodynamic (pQCD) analyses is the lack of a method for setting the QCD running-coupling renormalization scale such that maximally precise fixed-order predictions for physical observables are obtained. The Principle of Maximum Conformality (PMC) eliminates the ambiguities associated with the conventional renormalization scale-setting procedure, yielding predictions that are independent of the choice of renormalization scheme. The QCD coupling scales and the effective number of quark flavors are set order-by-order in the pQCD series. The PMC has a solid theoretical foundation, satisfying the standard renormalization group invariance condition and all of the self-consistency conditions derived from the renormalization group. The PMC scales at each order are obtained by shifting the arguments of the strong force coupling constant α s to eliminate all non-conformal { β i } terms in the pQCD series. The { β i } terms are determined from renormalization group equations without ambiguity. The correct behavior of the running coupling at each order and at each phase-space point can then be obtained. The PMC reduces in the N C → 0 Abelian limit to the Gell-Mann-Low method. In this brief report, we summarize the results of our recent application of the PMC to a number of collider processes, emphasizing the generality and applicability of this approach. A discussion of hadronic Z decays shows that, by applying the PMC, one can achieve accurate predictions for the total and separate decay widths at each order without scale ambiguities. We also show that, if one employs the PMC to determine the top-quark pair forward-backward asymmetry at the next-to-next-to-leading order level, one obtains a comprehensive, self-consistent pQCD explanation for the Tevatron measurements of the asymmetry. This accounts for the "increasing-decreasing" behavior observed by the D0 collaboration for increasing t overline t invariant mass. At
Deuteron Electromagnetic Form Factors in AdS/QCD
NASA Astrophysics Data System (ADS)
Lyubovitskij, Valery E.; Gutsche, Thomas; Schmidt, Ivan; Vega, Alfredo
2016-03-01
We extend a soft-wall AdS/QCD approach to a description of deuteron properties. Our framework is based an effective action formulated in terms of AdS fields, which are holographically equivalent to the deuteron and photon fields. This action produces the equation of motion for the deuteron wave function and the Q^2 -dependent electromagnetic current, which are then used to calculate the deuteron electromagnetic form factors and structure functions in the Euclidean region. We show that the predicted deuteron quantities are expressed through a universal function, which is defined by a single scale parameter κ and which has the correct 1/Q^{10} power scaling at large Q^2.
Saturation and universality in QCD at small /x
NASA Astrophysics Data System (ADS)
Iancu, E.; McLerran, L.
2001-06-01
We find approximate solutions to the renormalization group equation which governs the quantum evolution of the effective theory for the Color Glass Condensate. This is a functional Fokker-Planck equation which generates in particular the non-linear evolution equations previously derived by Balitsky and Kovchegov within perturbative QCD. In the limit where the transverse momentum of the external probe is large compared to the saturation momentum, our approximations yield the Gaussian ansatz for the effective action of the McLerran-Venugopalan model. In the opposite limit, of a small external momentum, we find that the effective theory is governed by a scale-invariant universal action which has the correct properties to describe gluon saturation.
Deuteron Electromagnetic Form Factors in AdS/QCD
NASA Astrophysics Data System (ADS)
Lyubovitskij, Valery E.; Gutsche, Thomas; Schmidt, Ivan; Vega, Alfredo
2016-07-01
We extend a soft-wall AdS/QCD approach to a description of deuteron properties. Our framework is based an effective action formulated in terms of AdS fields, which are holographically equivalent to the deuteron and photon fields. This action produces the equation of motion for the deuteron wave function and the Q^2-dependent electromagnetic current, which are then used to calculate the deuteron electromagnetic form factors and structure functions in the Euclidean region. We show that the predicted deuteron quantities are expressed through a universal function, which is defined by a single scale parameter κ and which has the correct 1/Q^{10} power scaling at large Q^2.
Two-loop conformal generators for leading-twist operators in QCD
NASA Astrophysics Data System (ADS)
Braun, V. M.; Manashov, A. N.; Moch, S.; Strohmaier, M.
2016-03-01
QCD evolution equations in minimal subtraction schemes have a hidden symmetry: one can construct three operators that commute with the evolution kernel and form an SL(2) algebra, i.e. they satisfy (exactly) the SL(2) commutation relations. In this paper we find explicit expressions for these operators to two-loop accuracy going over to QCD in non-integer d = 4 - 2ɛ space-time dimensions at the intermediate stage. In this way conformal symmetry of QCD is restored on quantum level at the specially chosen (critical) value of the coupling, and at the same time the theory is regularized allowing one to use the standard renormalization procedure for the relevant Feynman diagrams. Quantum corrections to conformal generators in d = 4 - 2ɛ effectively correspond to the conformal symmetry breaking in the physical theory in four dimensions and the SL(2) commutation relations lead to nontrivial constraints on the renormalization group equations for composite operators. This approach is valid to all orders in perturbation theory and the result includes automatically all terms that can be identified as due to a nonvanishing QCD β-function (in the physical theory in four dimensions). Our result can be used to derive three-loop evolution equations for flavor-nonsinglet quark-antiquark operators including mixing with the operators containing total derivatives. These equations govern, e.g., the scale dependence of generalized hadron parton distributions and light-cone meson distribution amplitudes.
Aleksejevs, Aleksandrs; Barkanova, Svetlana; Ilyichev, Alexander; Zykunov, Vladimir
2010-11-01
We perform updated and detailed calculations of the complete NLO set of electroweak radiative corrections to parity violating e- e- --> e- e- (gamma) scattering asymmetries at energies relevant for the ultra-precise Moller experiment coming soon at JLab. Our numerical results are presented for a range of experimental cuts and relative importance of various contributions is analyzed. We also provide very compact expressions analytically free from non-physical parameters and show them to be valid for fast yet accurate estimations.
QCD at nonzero chemical potential: Recent progress on the lattice
NASA Astrophysics Data System (ADS)
Aarts, Gert; Attanasio, Felipe; Jäger, Benjamin; Seiler, Erhard; Sexty, Dénes; Stamatescu, Ion-Olimpiu
2016-01-01
We summarise recent progress in simulating QCD at nonzero baryon density using complex Langevin dynamics. After a brief outline of the main idea, we discuss gauge cooling as a means to control the evolution. Subsequently we present a status report for heavy dense QCD and its phase structure, full QCD with staggered quarks, and full QCD with Wilson quarks, both directly and using the hopping parameter expansion to all orders.
NASA Astrophysics Data System (ADS)
Tamer, Ömer; Avcı, Davut; Atalay, Yusuf
2015-02-01
Organic compounds which have one or more aromatic systems in conjugated positions show charge transfer interactions which are responsible for the non-linear properties of the compounds. A conjugated π electron system enables a pathway for the entire length of conjugation under the perturbation of an external electric field. When electron donating and withdrawing moieties are located at terminal position of conjugated backbone, nonlinear optical (NLO) properties have been increased significantly which involve the correlated and high delocalized π electron states. Recently synthesized organic complexes, 1-(4-fluorostyryl)-4-nitrostilbene (1), 4-Chloro 4-nitrostilbene (2), 4-Bromo 4-nitrostilbene (3) and 4-Iodo 4-nitrostilbene (4), were simulated using density functional theory (DFT). Based on the optimized geometries, spectroscopic and NLO properties of these complexes were discussed as compared with each other.
Holographic models and the QCD trace anomaly
Jose L. Goity, Roberto C. Trinchero
2012-08-01
Five dimensional dilaton models are considered as possible holographic duals of the pure gauge QCD vacuum. In the framework of these models, the QCD trace anomaly equation is considered. Each quantity appearing in that equation is computed by holographic means. Two exact solutions for different dilaton potentials corresponding to perturbative and non-perturbative {beta}-functions are studied. It is shown that in the perturbative case, where the {beta}-function is the QCD one at leading order, the resulting space is not asymptotically AdS. In the non-perturbative case, the model considered presents confinement of static quarks and leads to a non-vanishing gluon condensate, although it does not correspond to an asymptotically free theory. In both cases analyses based on the trace anomaly and on Wilson loops are carried out.
Quarkonium states in an anisotropic QCD plasma
Dumitru, Adrian; Guo Yun; Mocsy, Agnes; Strickland, Michael
2009-03-01
We consider quarkonium in a hot quantum chromodynamics (QCD) plasma which, due to expansion and nonzero viscosity, exhibits a local anisotropy in momentum space. At short distances the heavy-quark potential is known at tree level from the hard-thermal loop resummed gluon propagator in anisotropic perturbative QCD. The potential at long distances is modeled as a QCD string which is screened at the same scale as the Coulomb field. At asymptotic separation the potential energy is nonzero and inversely proportional to the temperature. We obtain numerical solutions of the three-dimensional Schroedinger equation for this potential. We find that quarkonium binding is stronger at nonvanishing viscosity and expansion rate, and that the anisotropy leads to polarization of the P-wave states.
Exploring hyperons and hypernuclei with lattice QCD
Beane, S.R.; Bedaque, P.F.; Parreno, A.; Savage, M.J.
2003-01-01
In this work we outline a program for lattice QCD that wouldprovide a first step toward understanding the strong and weakinteractions of strange baryons. The study of hypernuclear physics hasprovided a significant amount of information regarding the structure andweak decays of light nuclei containing one or two Lambda's, and Sigma's.From a theoretical standpoint, little is known about the hyperon-nucleoninteraction, which is required input for systematic calculations ofhypernuclear structure. Furthermore, the long-standing discrepancies inthe P-wave amplitudes for nonleptonic hyperon decays remain to beunderstood, and their resolution is central to a better understanding ofthe weak decays of hypernuclei. We present a framework that utilizesLuscher's finite-volume techniques in lattice QCD to extract thescattering length and effective range for Lambda-N scattering in both QCDand partially-quenched QCD. The effective theory describing thenonleptonic decays of hyperons using isospin symmetry alone, appropriatefor lattice calculations, is constructed.
Resolving B-CP puzzles in QCD factorization
Cheng, H.-Y.; Chua, C.-K.
2009-10-01
Within the framework of QCD factorization (QCDF), power corrections due to penguin annihilation can account for the observed rates of penguin-dominated two-body decays of B mesons and direct CP asymmetries A{sub CP}(K{sup -}{pi}{sup +}), A{sub CP}(K*{sup -}{pi}{sup +}), A{sub CP}(K{sup -}{rho}{sup 0}) and A{sub CP}({pi}{sup +}{pi}{sup -}). However, the predicted direct CP-violating effects in QCDF for B{sup -}{yields}K{sup -}{pi}{sup 0}, K{sup -}{eta}, {pi}{sup -}{eta} and B{sup 0}{yields}{pi}{sup 0}{pi}{sup 0} are wrong in signs when confronted with experiment. We show that subleading 1/m{sub b} power corrections to the color-suppressed tree amplitude due to spectator scattering or final-state interactions will yield correct signs for aforementioned CP asymmetries and accommodate the observed {pi}{sup 0}{pi}{sup 0} and {rho}{sup 0}{pi}{sup 0} rates simultaneously. Implications are discussed.
Brodsky, Stanley J.; de Teramond, Guy F.; /SLAC /Southern Denmark U., CP3-Origins /Costa Rica U.
2011-01-10
AdS/QCD, the correspondence between theories in a dilaton-modified five-dimensional anti-de Sitter space and confining field theories in physical space-time, provides a remarkable semiclassical model for hadron physics. Light-front holography allows hadronic amplitudes in the AdS fifth dimension to be mapped to frame-independent light-front wavefunctions of hadrons in physical space-time. The result is a single-variable light-front Schroedinger equation which determines the eigenspectrum and the light-front wavefunctions of hadrons for general spin and orbital angular momentum. The coordinate z in AdS space is uniquely identified with a Lorentz-invariant coordinate {zeta} which measures the separation of the constituents within a hadron at equal light-front time and determines the off-shell dynamics of the bound state wavefunctions as a function of the invariant mass of the constituents. The hadron eigenstates generally have components with different orbital angular momentum; e.g., the proton eigenstate in AdS/QCD with massless quarks has L = 0 and L = 1 light-front Fock components with equal probability. Higher Fock states with extra quark-anti quark pairs also arise. The soft-wall model also predicts the form of the nonperturbative effective coupling and its {beta}-function. The AdS/QCD model can be systematically improved by using its complete orthonormal solutions to diagonalize the full QCD light-front Hamiltonian or by applying the Lippmann-Schwinger method to systematically include QCD interaction terms. Some novel features of QCD are discussed, including the consequences of confinement for quark and gluon condensates. A method for computing the hadronization of quark and gluon jets at the amplitude level is outlined.
NASA Astrophysics Data System (ADS)
Altürk, Sümeyye; Avci, Davut; Tamer, Ömer; Atalay, Yusuf
2016-03-01
It is well known that the practical applications of second-order and third-order nonlinear optical (NLO) materials have been reported in modern technology, such as optical data processing, transmission and storage, etc. In this respect, the linear and nonlinear optical parameters (the molecular static polarizability (α), and the first-order static hyperpolarizability (β0), the second-order static hyperpolarizability (γ)), UV-vis spectra and HOMO and LUMO energies of 2-(1'-(4'''-Methoxyphenyl)-5'-(thien-2″-yl)pyrrol-2'-yl)-1,3-benzothiazole were investigated by using the HSEh1PBE/6-311G(d,p) level of density functional theory. The UV-vis spectra were simulated using TD/HSEh1PBE/6- 311G(d,p) level, and the major contributions to the electronic transitions were obtained. The molecular hardness (η) and electronegativity (χ) parameters were also obtained by using molecular frontier orbital energies. The NLO parameters of the title compound were calculated, and obtained data were compared with that of para-Nitroaniline (pNA) which is a typical NLO material and the corresponding experimental data. Obtained data of the chromosphere display significant molecular second-and third-nonlinearity.
NASA Astrophysics Data System (ADS)
Szablewski, Marek; Cross, Graham H.
2005-09-01
The conversion of the complex salt of TCNQ and triethylamine; TEA(TCNQ)2 into the zwitterionic NLO chromophore DEMI can be achieved in a polymeric guest host system. Synthesis of the chromophore in a thin polymer film can be monitored by observation of the SHG in an in-situ poling experiment. We discuss the characterization of the conversion process, which could potentially lead to the "writing" of very small areas of nonlinearly active material into otherwise inactive polymer films. We have found that the transformation from organic salt to NLO (Non linear Optical) chromophore occurs at approximately 160°C, the transformation is accompanied by a dramatic change in colour from green to blue and by an accompanying decrease in conductivity. The resultant blue spectrum is identical to that obtained by doping DEMI into PMMA. All characteristic TCNQ- peaks in the UV/Vis absorption spectrum are completely diminished, and the reaction appears to be almost 100% efficient. In-situ corona poling experiments, while heating a thin film of TEA(TCNQ)2 in PMMA above its glass transition temperature reveal no SHG from an input wavelength of 1.9 microns until the conversion temperature is achieved. At this point when DEMI has been "synthesised" in the sample the SHG can be observed and its relative intensity measured relative to that of a quartz plate. We also discuss the attempted synthesis in situ of a related zwitterionic NLO chromophore Me-P3CNQ.
High-Energy Amplitudes in the Next-to-Leading Order
Ian Balitsky
2011-03-01
High-energy scattering in the saturation region is described by the evolution of color dipoles. In the leading order this evolution is governed by the non-linear BK equation. To see if this equation is relevant for existing or future accelerators (like EIC or LHeC) one needs to know how big are the next-to-leading order (NLO) corrections. I review the calculation of the NLO corrections to high-energy amplitudes in QCD.
QCD unitarity constraints on Reggeon Field Theory
NASA Astrophysics Data System (ADS)
Kovner, Alex; Levin, Eugene; Lublinsky, Michael
2016-08-01
We point out that the s-channel unitarity of QCD imposes meaningful constraints on a possible form of the QCD Reggeon Field Theory. We show that neither the BFKL nor JIMWLK nor Braun's Hamiltonian satisfy the said constraints. In a toy, zero transverse dimensional case we construct a model that satisfies the analogous constraint and show that at infinite energy it indeed tends to a "black disk limit" as opposed to the model with triple Pomeron vertex only, routinely used as a toy model in the literature.
QCD subgroup on diffractive and forward physics
Albrow, M.G.; Baker, W.; Bhatti, A.
1997-09-01
Over the last few years, there has been a resurgence of interest in small-x or diffractive physics. This has been due to the realization that perturbative QCD techniques may be applicable to what was previously thought of as a non-perturbative problem and to the opening up of new energy regimes at HERA and the Tevatron collider. The goal is to understand the pomeron, and hence the behavior of total cross sections, elastic scattering and diffractive excitation, in terms of the underlying theory, QCD. This paper is divided into experiments of hadron-hadron colliders and electron-proton colliders.
Experimental Study of Nucleon Structure and QCD
Jian-Ping Chen
2012-03-01
Overview of Experimental Study of Nucleon Structure and QCD, with focus on the spin structure. Nucleon (spin) Structure provides valuable information on QCD dynamics. A decade of experiments from JLab yields these exciting results: (1) valence spin structure, duality; (2) spin sum rules and polarizabilities; (3) precision measurements of g{sub 2} - high-twist; and (4) first neutron transverse spin results - Collins/Sivers/A{sub LT}. There is a bright future as the 12 GeV Upgrade will greatly enhance our capability: (1) Precision determination of the valence quark spin structure flavor separation; and (2) Precision extraction of transversity/tensor charge/TMDs.
Chiral symmetry restoration in holographic noncommutative QCD
NASA Astrophysics Data System (ADS)
Nakajima, Tadahito; Ohtake, Yukiko; Suzuki, Kenji
2011-09-01
We consider the noncommutative deformation of the Sakai-Sugimoto model at finite temperature and finite baryon chemical potential. The space noncommutativity is possible to have an influence on the flavor dynamics of the QCD. The critical temperature and critical value of the chemical potential are modified by the space noncommutativity. The influence of the space noncommutativity on the flavor dynamics of the QCD is caused by the Wess-Zumino term in the effective action of the D8-branes. The intermediate temperature phase, in which the gluons deconfine but the chiral symmetry remains broken, is easy to be realized in some region of the noncommutativity parameter.
Hadron scattering and resonances in QCD
NASA Astrophysics Data System (ADS)
Dudek, Jozef J.
2016-05-01
I describe how hadron-hadron scattering amplitudes are related to the eigenstates of QCD in a finite cubic volume. The discrete spectrum of such eigenstates can be determined from correlation functions computed using lattice QCD, and the corresponding scattering amplitudes extracted. I review results from the Hadron Spectrum Collaboration who have used these finite volume methods to study ππ elastic scattering, including the ρ resonance, as well as coupled-channel π >K, ηK scattering. Ongoing calculations are advertised and the outlook for finite volume approaches is presented.
Exclusive hadronic and nuclear processes in QCD
Brodsky, S.J.
1985-12-01
Hadronic and nuclear processes are covered, in which all final particles are measured at large invariant masses compared with each other, i.e., large momentum transfer exclusive reactions. Hadronic wave functions in QCD and QCD sum rule constraints on hadron wave functions are discussed. The question of the range of applicability of the factorization formula and perturbation theory for exclusive processes is considered. Some consequences of quark and gluon degrees of freedom in nuclei are discussed which are outside the usual domain of traditional nuclear physics. 44 refs., 7 figs. (LEW)
QCD resummation for hadronic final states
NASA Astrophysics Data System (ADS)
Luisoni, Gionata; Marzani, Simone
2015-10-01
We review the basic concepts of all-order calculations in quantum chromodynamics (QCD) and their application to collider phenomenology. We start by discussing the factorization properties of QCD amplitudes and cross-sections in the soft and collinear limits and their resulting all-order exponentiation. We then discuss several applications of this formalism to observables which are of great interest at particle colliders. In this context, we describe the all-order resummation of event-shape distributions, as well as observables that probe the internal structure of hadronic jets.
String breaking in four dimensional lattice QCD
Duncan, A.; Eichten, E.; Thacker, H.
2001-06-01
Virtual quark pair screening leads to breaking of the string between fundamental representation quarks in QCD. For unquenched four dimensional lattice QCD, this (so far elusive) phenomenon is studied using the recently developed truncated determinant algorithm (TDA). The dynamical configurations were generated on a 650 MHz PC. Quark eigenmodes up to 420 MeV are included exactly in these TDA studies performed at low quark mass on large coarse [but O(a{sup 2}) improved] lattices. A study of Wilson line correlators in Coulomb gauge extracted from an ensemble of 1000 two-flavor dynamical configurations reveals evidence for flattening of the string tension at distances R{approx}>1 fm.
Massive photons: An infrared regularization scheme for lattice QCD+QED
Endres, Michael G.; Shindler, Andrea; Tiburzi, Brian C.; Walker-Loud, Andre
2016-08-10
The commonly adopted approach for including electromagnetic interactions in lattice QCD simulations relies on using finite volume as the infrared regularization for QED. The long-range nature of the electromagnetic interaction, however, implies that physical quantities are susceptible to power-law finite volume corrections, which must be removed by performing costly simulations at multiple lattice volumes, followed by an extrapolation to the infinite volume limit. In this work, we introduce a photon mass as an alternative means for gaining control over infrared effects associated with electromagnetic interactions. We present findings for hadron mass shifts due to electromagnetic interactions (i.e., for the proton,more » neutron, charged and neutral kaon) and corresponding mass splittings, and compare the results with those obtained from conventional QCD+QED calculations. Results are reported for numerical studies of three flavor electroquenched QCD using ensembles corresponding to 800 MeV pions, ensuring that the only appreciable volume corrections arise from QED effects. The calculations are performed with three lattice volumes with spatial extents ranging from 3.4 - 6.7 fm. As a result, we find that for equal computing time (not including the generation of the lattice configurations), the electromagnetic mass shifts can be extracted from computations on a single (our smallest) lattice volume with comparable or better precision than the conventional approach.« less
NASA Technical Reports Server (NTRS)
Waegell, Mordecai J.; Palacios, David M.
2011-01-01
Jitter_Correct.m is a MATLAB function that automatically measures and corrects inter-frame jitter in an image sequence to a user-specified precision. In addition, the algorithm dynamically adjusts the image sample size to increase the accuracy of the measurement. The Jitter_Correct.m function takes an image sequence with unknown frame-to-frame jitter and computes the translations of each frame (column and row, in pixels) relative to a chosen reference frame with sub-pixel accuracy. The translations are measured using a Cross Correlation Fourier transformation method in which the relative phase of the two transformed images is fit to a plane. The measured translations are then used to correct the inter-frame jitter of the image sequence. The function also dynamically expands the image sample size over which the cross-correlation is measured to increase the accuracy of the measurement. This increases the robustness of the measurement to variable magnitudes of inter-frame jitter
Setting the Renormalization Scale in QCD: The Principle of Maximum Conformality
Brodsky, Stanley J.; Di Giustino, Leonardo; /SLAC
2011-08-19
A key problem in making precise perturbative QCD predictions is the uncertainty in determining the renormalization scale {mu} of the running coupling {alpha}{sub s}({mu}{sup 2}): The purpose of the running coupling in any gauge theory is to sum all terms involving the {beta} function; in fact, when the renormalization scale is set properly, all non-conformal {beta} {ne} 0 terms in a perturbative expansion arising from renormalization are summed into the running coupling. The remaining terms in the perturbative series are then identical to that of a conformal theory; i.e., the corresponding theory with {beta} = 0. The resulting scale-fixed predictions using the 'principle of maximum conformality' (PMC) are independent of the choice of renormalization scheme - a key requirement of renormalization group invariance. The results avoid renormalon resummation and agree with QED scale-setting in the Abelian limit. The PMC is also the theoretical principle underlying the BLM procedure, commensurate scale relations between observables, and the scale-setting method used in lattice gauge theory. The number of active flavors nf in the QCD {beta} function is also correctly determined. We discuss several methods for determining the PMC/BLM scale for QCD processes. We show that a single global PMC scale, valid at leading order, can be derived from basic properties of the perturbative QCD cross section. The elimination of the renormalization scheme ambiguity using the PMC will not only increase the precision of QCD tests, but it will also increase the sensitivity of collider experiments to new physics beyond the Standard Model.
Light-like Wilson line in QCD without path ordering
NASA Astrophysics Data System (ADS)
Nayak, Gouranga C.
2016-07-01
Unlike the Wilson line in QED the Wilson line in QCD contains path ordering. In this paper we get rid of the path ordering in the light-like Wilson line in QCD by simplifying all the infinite number of noncommuting terms in the SU(3) pure gauge. We prove that the light-like Wilson line in QCD naturally emerges when path integral formulation of QCD is used to prove factorization of soft and collinear divergences at all order in coupling constant in QCD processes at high energy colliders.
Chiral logarithms in quenched QCD
Y. Chen; S. J. Dong; T. Draper; I. Horvath; F. X. Lee; K. F. Liu; N. Mathur; and J. B. Zhang
2004-08-01
The quenched chiral logarithms are examined on a 163x28 lattice with Iwasaki gauge action and overlap fermions. The pion decay constant fpi is used to set the lattice spacing, a = 0.200(3) fm. With pion mass as low as {approx}180 MeV, we see the quenched chiral logarithms clearly in mpi2/m and fP, the pseudoscalar decay constant. The authors analyze the data to determine how low the pion mass needs to be in order for the quenched one-loop chiral perturbation theory (chiPT) to apply. With the constrained curve-fitting method, they are able to extract the quenched chiral logarithmic parameter delta together with other low-energy parameters. Only for mpi<=300 MeV do we obtain a consistent and stable fit with a constant delta which they determine to be 0.24(3)(4) (at the chiral scale Lambdachi = 0.8 GeV). By comparing to the 123x28 lattice, they estimate the finite volume effect to be about 2.7% for the smallest pion mass. They also fitted the pion mass to the form for the re-summed cactus diagrams and found that its applicable region is extended farther than the range for the one-loop formula, perhaps up to mpi {approx}500-600 MeV. The scale independent delta is determined to be 0.20(3) in this case. The authors study the quenched non-analytic terms in the nucleon mass and find that the coefficient C1/2 in the nucleon mass is consistent with the prediction of one-loop chiPT. They also obtain the low energy constant L5 from fpi. They conclude from this study that it is imperative to cover only the range of data with the pion mass less than {approx}300 MeV in order to examine the chiral behavior of the hadron masses and decay constants in quenched QCD and match them with quenched one-loop chiPT.
NASA Astrophysics Data System (ADS)
Santhakumari, R.; Ramamurthi, K.
2011-02-01
Single crystals of the organic NLO material, benzaldehyde thiosemicarbazone (BTSC) monohydrate, were grown by slow evaporation method. Solubility of BTSC monohydrate was determined in ethanol at different temperatures. The grown crystals were characterized by single crystal X-ray diffraction analysis to determine the cell parameters and by FT-IR technique to study the presence of the functional groups. Thermogravimetric and differential thermal analyses reveal the thermal stability of the crystal. UV-vis-NIR spectrum shows excellent transmission in the region of 200-1100 nm. Theoretical calculations were carried out to determine the linear optical constants such as extinction coefficient and refractive index. Further the optical nonlinearities of BTSC have been investigated by Z-scan technique with He-Ne laser radiation of wavelength 632.8 nm. Mechanical properties of the grown crystal were studied using Vickers microhardness tester. Second harmonic generation efficiency of the powdered BTSC monohydrate was tested using Nd:YAG laser and it is found to be ˜5.3 times that of potassium dihydrogen orthophosphate.
DFT calculations on spectroscopic and structural properties of a NLO chromophore
NASA Astrophysics Data System (ADS)
Altürk, Sümeyye; Avci, Davut; Tamer, Ömer; Atalay, Yusuf
2016-03-01
The molecular geometry optimization, vibrational frequencies and gauge including atomic orbital (GIAO) 1H and 13C NMR chemical shift values of 2-(1'-(4'''-Methoxyphenyl)-5'-(thien-2″-yl)pyrrol-2'-yl)-1,3-benzothiazole as potential nonlinear optical (NLO) material were calculated using density functional theory (DFT) HSEh1PBE method with 6-311G(d,p) basis set. The best of our knowledge, this study have not been reported to date. Additionally, a detailed vibrational study was performed on the basis of potential energy distribution (PED) using VEDA program. It is noteworthy that NMR chemical shifts are quite useful for understanding the relationship between the molecular structure and electronic properties of molecules. The computed IR and NMR spectra were used to determine the types of the experimental bands observed. Predicted values of structural and spectroscopic parameters of the chromophore were compared with each other so as to display the effects of the different substituents on the spectroscopic and structural properties. Obtained data showed that there is an agreement between the predicted and experimental data.
A new promising nonlinear optical (NLO) crystal for visible and ultraviolet (UV) regions
Gheorghe, L.; Achim, A.; Voicu, F.
2012-08-17
Different La{sub 1−x}Gd{sub x}Sc{sub 3}(BO{sub 3}){sub 4} compounds with 0 ≤ x ≤ 0.5 were synthesized by solid-state reaction method. The X-ray diffraction studies revealed that the compounds containing more than 30 at.% Gd{sup 3+} ions have non-centrosymmetric trigonal structure (space group R32) and, consequently they are optically nonlinear. A crystal of La{sub x}Gd{sub y}Sc{sub z}(BO{sub 3}){sub 4} (x+y+z = 4) – LGSB with La{sub 0.75}Gd{sub 0.5}Sc{sub 2.75}(BO{sub 3}){sub 4} starting melt composition and relatively small dimensions (about 10 mm in diameter and 25 mm in length) was grown by the Czochralski method. In order to confirm the NLO property, the as-grown crystal was subjected to second-harmonic generation (SHG) test. The nonlinear coefficient d{sub 11} of LGSB crystal has been preliminary estimated to be about 1.9 pm/V, which is larger than that of YAl{sub 3}(BO{sub 3}){sub 4} (YAB) crystal. This article has been formally retracted, please refer to the article PDF for the full retraction notice.
Santhakumari, R; Ramamurthi, K
2011-02-01
Single crystals of the organic NLO material, benzaldehyde thiosemicarbazone (BTSC) monohydrate, were grown by slow evaporation method. Solubility of BTSC monohydrate was determined in ethanol at different temperatures. The grown crystals were characterized by single crystal X-ray diffraction analysis to determine the cell parameters and by FT-IR technique to study the presence of the functional groups. Thermogravimetric and differential thermal analyses reveal the thermal stability of the crystal. UV-vis-NIR spectrum shows excellent transmission in the region of 200-1100 nm. Theoretical calculations were carried out to determine the linear optical constants such as extinction coefficient and refractive index. Further the optical nonlinearities of BTSC have been investigated by Z-scan technique with He-Ne laser radiation of wavelength 632.8 nm. Mechanical properties of the grown crystal were studied using Vickers microhardness tester. Second harmonic generation efficiency of the powdered BTSC monohydrate was tested using Nd:YAG laser and it is found to be ∼5.3 times that of potassium dihydrogen orthophosphate. PMID:21186136
QCD Evolution of Helicity and Transversity TMDs
Prokudin, Alexei
2014-01-01
We examine the QCD evolution of the helicity and transversity parton distribution functions when including also their dependence on transverse momentum. Using an appropriate definition of these polarized transverse momentum distributions (TMDs), we describe their dependence on the factorization scale and rapidity cutoff, which is essential for phenomenological applications.
QCD Physics at the Tevatron Collider
Messina, Andrea
2005-10-12
In this contribution some of the prominent QCD physics results from CDF and D0 experiments in Run II are presented. The cross sections and the properties of jets are discussed for both the inclusive and the b-jet production. Results on the associate production of light and heavy flavour jets together with vector bosons are also reported.
Large Scale Commodity Clusters for Lattice QCD
A. Pochinsky; W. Akers; R. Brower; J. Chen; P. Dreher; R. Edwards; S. Gottlieb; D. Holmgren; P. Mackenzie; J. Negele; D. Richards; J. Simone; W. Watson
2002-06-01
We describe the construction of large scale clusters for lattice QCD computing being developed under the umbrella of the U.S. DoE SciDAC initiative. We discuss the study of floating point and network performance that drove the design of the cluster, and present our plans for future multi-Terascale facilities.
BRST invariance in Coulomb gauge QCD
NASA Astrophysics Data System (ADS)
Andraši, A.; Taylor, J. C.
2015-12-01
In the Coulomb gauge, the Hamiltonian of QCD contains terms of order ħ2, identified by Christ and Lee, which are non-local but instantaneous. The question is addressed how do these terms fit in with BRST invariance. Our discussion is confined to the simplest, O(g4) , example.
Toward lattice QCD simulation on AP1000
NASA Astrophysics Data System (ADS)
Ohta, Shigemi
AP1000 is Fujitsu Laboratory's experimental parallel computer consisting of up to 1024 microcomputers called cells. It is found that each AP1000 cell can sustain two to three megaflops computational speed for full QCD lattice numerical simulations in IEEE 64-bit floating point format
Phase structure of QCD for heavy quarks
NASA Astrophysics Data System (ADS)
Fischer, Christian S.; Luecker, Jan; Pawlowski, Jan M.
2015-01-01
We investigate the nature of the deconfinement and Roberge-Weiss transition in the heavy quark regime for finite real and imaginary chemical potential within the functional approach to continuum QCD. We extract the critical phase boundary between the first-order and crossover regions and also explore tricritical scaling. Our results confirm previous ones from finite volume lattice studies.
QCD PHASE TRANSITIONS-VOLUME 15.
SCHAFER,T.
1998-11-04
The title of the workshop, ''The QCD Phase Transitions'', in fact happened to be too narrow for its real contents. It would be more accurate to say that it was devoted to different phases of QCD and QCD-related gauge theories, with strong emphasis on discussion of the underlying non-perturbative mechanisms which manifest themselves as all those phases. Before we go to specifics, let us emphasize one important aspect of the present status of non-perturbative Quantum Field Theory in general. It remains true that its studies do not get attention proportional to the intellectual challenge they deserve, and that the theorists working on it remain very fragmented. The efforts to create Theory of Everything including Quantum Gravity have attracted the lion share of attention and young talent. Nevertheless, in the last few years there was also a tremendous progress and even some shift of attention toward emphasis on the unity of non-perturbative phenomena. For example, we have seen some. efforts to connect the lessons from recent progress in Supersymmetric theories with that in QCD, as derived from phenomenology and lattice. Another example is Maldacena conjecture and related development, which connect three things together, string theory, super-gravity and the (N=4) supersymmetric gauge theory. Although the progress mentioned is remarkable by itself, if we would listen to each other more we may have chance to strengthen the field and reach better understanding of the spectacular non-perturbative physics.
Quark screening lengths in finite temperature QCD
Gocksch, A. California Univ., Santa Barbara, CA . Inst. for Theoretical Physics)
1990-11-01
We have computed Landau gauge quark propagators in both the confined and deconfined phase of QCD. I discuss the magnitude of the resulting screening lengths as well as aspects of chiral symmetry relevant to the quark propagator. 12 refs., 1 fig., 1 tab.
The CKM Matrix from Lattice QCD
Mackenzie, Paul B.; /Fermilab
2009-07-01
Lattice QCD plays an essential role in testing and determining the parameters of the CKM theory of flavor mixing and CP violation. Very high precisions are required for lattice calculations analyzing CKM data; I discuss the prospects for achieving them. Lattice calculations will also play a role in investigating flavor mixing and CP violation beyond the Standard Model.
Exact Adler Function in Supersymmetric QCD
NASA Astrophysics Data System (ADS)
Shifman, M.; Stepanyantz, K.
2015-02-01
The Adler function D is found exactly in supersymmetric QCD. Our exact formula relates D (Q2) to the anomalous dimension of the matter superfields γ (αs(Q2)) . En route we prove another theorem: the absence of the so-called singlet contribution to D . While such singlet contributions are present in individual supergraphs, they cancel in the sum.
Marking up lattice QCD configurations and ensembles
P.Coddington; B.Joo; C.M.Maynard; D.Pleiter; T.Yoshie
2007-10-01
QCDml is an XML-based markup language designed for sharing QCD configurations and ensembles world-wide via the International Lattice Data Grid (ILDG). Based on the latest release, we present key ingredients of the QCDml in order to provide some starting points for colleagues in this community to markup valuable configurations and submit them to the ILDG.
On-Shell Methods in Perturbative QCD
Bern, Zvi; Dixon, Lance J.; Kosower, David A.
2007-04-25
We review on-shell methods for computing multi-parton scattering amplitudes in perturbative QCD, utilizing their unitarity and factorization properties. We focus on aspects which are useful for the construction of one-loop amplitudes needed for phenomenological studies at the Large Hadron Collider.
Exploring Hyperons and Hypernuclei with Lattice QCD
S.R. Beane; P.F. Bedaque; A. Parreno; M.J. Savage
2005-01-01
In this work we outline a program for lattice QCD that would provide a first step toward understanding the strong and weak interactions of strange baryons. The study of hypernuclear physics has provided a significant amount of information regarding the structure and weak decays of light nuclei containing one or two Lambda's, and Sigma's. From a theoretical standpoint, little is known about the hyperon-nucleon interaction, which is required input for systematic calculations of hypernuclear structure. Furthermore, the long-standing discrepancies in the P-wave amplitudes for nonleptonic hyperon decays remain to be understood, and their resolution is central to a better understanding of the weak decays of hypernuclei. We present a framework that utilizes Luscher's finite-volume techniques in lattice QCD to extract the scattering length and effective range for Lambda-N scattering in both QCD and partially-quenched QCD. The effective theory describing the nonleptonic decays of hyperons using isospin symmetry alone, appropriate for lattice calculations, is constructed.
Pluto collaboration
1981-02-01
Results obtained with the PLUTO detector at PETRA are presented. Multihadron final states have been analysed with respect to clustering, energy-energy correlations and transverse momenta in jets. QCD predictions for hard gluon emission and soft gluon-quark cascades are discussed. Results on ..cap alpha../sub s/ and the gluon spin are given.
Schvellinger, Martin
2008-07-28
We briefly review one of the current applications of the AdS/CFT correspondence known as AdS/QCD and discuss about the calculation of four-point quark-flavour current correlation functions and their applications to the calculation of observables related to neutral kaon decays and neutral kaon mixing processes.
The Chroma Software System for Lattice QCD
Robert Edwards; Balint Joo
2004-06-01
We describe aspects of the Chroma software system for lattice QCD calculations. Chroma is an open source C++ based software system developed using the software infrastructure of the US SciDAC initiative. Chroma interfaces with output from the BAGEL assembly generator for optimized lattice fermion kernels on some architectures. It can be run on workstations, clusters and the QCDOC supercomputer.
Varelas, N.; D0 Collaboration
1997-10-01
We present recent results on jet production, dijet angular distributions, W+ Jets, and color coherence from p{anti p} collisions at {radical}s = 1.8 TeV at the Fermilab Tevatron Collider using the D0 detector. The data are compared to perturbative QCD calculations or to predictions of parton shower based Monte Carlo models.
QCD in hadron-hadron collisions
Albrow, M.
1997-03-01
Quantum Chromodynamics provides a good description of many aspects of high energy hadron-hadron collisions, and this will be described, along with some aspects that are not yet understood in QCD. Topics include high E{sub T} jet production, direct photon, W, Z and heavy flavor production, rapidity gaps and hard diffraction.
Factorization and other novel effects in QCD
Brodsky, S.J.
1983-09-01
Recent progress in proving the validity of factorization for inclusive reactions in QCD is reviewed. A new necessary condition involving the target length is emphasized. We also discuss a number of novel effects in gauge theory including null zone phenomena, color transparency, formation zone conditions, and possible heavy quark Fock states components in ordinary hadrons. 36 references.
Dual condensate and QCD phase transition
Zhang Bo; Bruckmann, Falk; Fodor, Zoltan; Szabo, Kalman K.; Gattringer, Christof
2011-05-23
The dual condensate is a new QCD phase transition order parameter, which connnects confinement and chiral symmetry breaking as different mass limits. We discuss the relation between the fermion spectrum at general boundary conditions and the dual condensate and show numerical results for the latter from unquenched SU(3) lattice configurations.
Visualization Tools for Lattice QCD - Final Report
Massimo Di Pierro
2012-03-15
Our research project is about the development of visualization tools for Lattice QCD. We developed various tools by extending existing libraries, adding new algorithms, exposing new APIs, and creating web interfaces (including the new NERSC gauge connection web site). Our tools cover the full stack of operations from automating download of data, to generating VTK files (topological charge, plaquette, Polyakov lines, quark and meson propagators, currents), to turning the VTK files into images, movies, and web pages. Some of the tools have their own web interfaces. Some Lattice QCD visualization have been created in the past but, to our knowledge, our tools are the only ones of their kind since they are general purpose, customizable, and relatively easy to use. We believe they will be valuable to physicists working in the field. They can be used to better teach Lattice QCD concepts to new graduate students; they can be used to observe the changes in topological charge density and detect possible sources of bias in computations; they can be used to observe the convergence of the algorithms at a local level and determine possible problems; they can be used to probe heavy-light mesons with currents and determine their spatial distribution; they can be used to detect corrupted gauge configurations. There are some indirect results of this grant that will benefit a broader audience than Lattice QCD physicists.
Blazey, G.C.
1995-05-01
Selected recent Quantum Chromodynamics (QCD) results from the D0 and CDF experiments at the Fermilab Tevatron are presented and discussed. The inclusive jet and inclusive triple differential dijet cross sections are compared to next-to-leading order QCD calculations. The sensitivity of the dijet cross section to parton distribution functions (for hadron momentum fractions {approximately} 0.01 to {approximately} 0.4) will constrain the gluon distribution of the proton. Two analyses of dijet production at large rapidity separation are presented. The first analysis tests the contributions of higher order processes to dijet production and can be considered a test of BFKL or GLAP parton evolution. The second analysis yields a strong rapidity gap signal consistent with colorless exchange between the scattered partons. The prompt photon inclusive cross section is consistent with next-to-leading order QCD only at the highest transverse momenta. The discrepancy at lower momenta may be indicative of higher order processes impacting a transverse momentum or ``k{sub T}`` to the partonic interaction. The first measurement of the strong coupling constant from the Tevatron is also presented. The coupling constant can be determined from the ratio of W + 1jet to W + 0jet cross sections and a next-to-leading order QCD calculation.
Heavy quark masses from lattice QCD
NASA Astrophysics Data System (ADS)
Lytle, Andrew T.
2016-07-01
Progress in quark mass determinations from lattice QCD is reviewed, focusing on results for charm and bottom mass. These are of particular interest for precision Higgs studies. Recent determinations have achieved percent-level uncertainties with controlled systematics. Future prospects for these calculations are also discussed.