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Bathe, S.

Publications and source records attributed to Bathe, S..

87 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Charged-pion cross sections and double-helicity asymmetries in polarized p + p collisions at s = 200 GeV

In this paper, we present midrapidity charged-pion invariant cross sections, the ratio of the π - to π + cross sections and the charge-separated double-spin asymmetries in polarized p+p collisions at s = 200 GeV . While the cross section measurements are consistent within the errors of next-to-leading-order (NLO) perturbative quantum chromodynamics predictions (pQCD), the same calculations overestimate the ratio of the charged-pion cross sections. This discrepancy arises from the cancellation of the substantial systematic errors associated with the NLO-pQCD predictions in the ratio and highlights the constraints these data will place on flavor-dependent pion fragmentation functions. Lastly, the charge-separated pion asymmetries presented here sample an x range of ~0.03–0.16 and provide unique information on the sign of the gluon-helicity distribution.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Cross section for b b ¯ production via dielectrons in d + Au collisions at s N N = 200 GeV

We report a measurement of e⁺e⁻ pairs from semileptonic heavy-flavor decays in d+Au collisions at √s NN = 200 GeV. Thus, exploring the mass and transverse-momentum dependence of the yield, the bottom decay contribution can be isolated from charm, and quantified by comparison to PYTHIA and MC@NLO simulations. The resulting bb-production cross section is σ d Au bb =1.37±0.28(stat)±0.46(syst) mb, which is equivalent to a nucleon-nucleon cross section of σ NN bb =3.4 ± 0.8(stat)±1.1(syst) µb.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Nuclear matter effects on J/ψ production in asymmetric Cu + Au collisions at \(\sqrt{s_{\mathrm{NN}}} = 200\) GeV

We report on J/ψ production from asymmetric Cu+Au heavy-ion collisions at \(\sqrt{s_{\mathrm{NN}}} = 200\) GeV at the Relativistic Heavy Ion Collider at both forward (Cu-going direction) and backward (Au-going direction) rapidities. The nuclear modification of J/ψ yields in Cu+Au collisions in the Au-going direction is found to be comparable to that in Au+Au collisions when plotted as a function of the number of participating nucleons. In the Cu-going direction, J/ψ production shows a stronger suppression. This difference is comparable in magnitude and has the same sign as the difference expected from shadowing effects due to stronger low-x gluon suppression in the larger Au nucleus. Thus, the relative suppression is opposite to that expected from hot nuclear matter dissociation, since a higher energy density is expected in the Au-going direction.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Cross section and transverse single-spin asymmetry of eta mesons in p ↑ plus p collisions at √s=200 GeV at forward rapidity

We present a measurement of the cross section and transverse single-spin asymmetry (A N ) for η mesons at large pseudorapidity from √s=200 GeV p ↑ +p collisions. The measured cross section for 0.5 T <5.0 GeV/c and 3.0<|η|<3.8 is well described by a next-to-leading-order perturbative-quantum-chromodynamics calculation. The asymmetries A N have been measured as a function of Feynman-x (x F ) from 0.2<|x F |<0.7, as well as transverse momentum (p T ) from 1.0 T <4.5 GeV/c. The asymmetry averaged over positive x F is (A N ) = 0.061±0.014. The results are consistent with prior transverse single-spin measurements of forward η and π⁰ mesons at various energies in overlapping x F ranges. Comparison of different particle species can help to determine the origin of the large observed asymmetries in p ↑ +p collisions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

PHENIX highlights

Results from RHIC led to the discovery of the strongly coupled quark–gluon plasma (sQGP), a state of the QCD vacuum. In order to arrive at a coherent picture of this state, both the properties of the sQGP and the conditions under which the sQGP is measured have to be established. In this paper, we present recent experimental results of the PHENIX Collaboration, further constraining the conditions and the properties of the sQGP at RHIC: measurement of direct photon elliptic flow provides strong constraints for hydrodynamic models employed to derive the initial temperature; measurement of v 2 and v 3 disentangles effects from the initial state and η/s; flow and R AA measurements at lower $\sqrt{s}$ extend the results to a regime at lower temperature and higher baryon density.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Suppression of Back-to-Back Pairs at Forward Rapidity in d + Au Collisions sqrt(s_NN)=200 GeV

Back-to-back hadron pair yields in d+Au and p+p collisions at {radical}s{sub NN} = 200 GeV were measured with the PHENIX detector at the Relativistic Heavy Ion Collider. Rapidity separated hadron pairs were detected with the trigger hadron at pseudorapidity |{eta}| < 0.35 and the associated hadron at forward rapidity (deuteron direction, 3.0 < {eta} < 3.8). Pairs were also detected with both hadrons measured at forward rapidity; in this case, the yield of back-to-back hadron pairs in d+Au collisions with small impact parameters is observed to be suppressed by a factor of 10 relative to p+p collisions. The kinematics of these pairs is expected to probe partons in the Au nucleus with a low fraction x of the nucleon momenta, where the gluon densities rise sharply. The observed suppression as a function of nuclear thickness, p{sub T}, and {eta} points to cold nuclear matter effects arising at high parton densities.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Cold Nuclear Matter Effects on J/{psi} Yields as a Function of Rapidity and Nuclear Geometry in d+A Collisions at {radical}(s{sub NN})=200 GeV

We present measurements of J/{psi} yields in d+Au collisions at {radical}(s{sub NN})=200 GeV recorded by the PHENIX experiment and compare them with yields in p+p collisions at the same energy per nucleon-nucleon collision. The measurements cover a large kinematic range in J/{psi} rapidity (-2.2<y<2.4) with high statistical precision and are compared with two theoretical models: one with nuclear shadowing combined with final state breakup and one with coherent gluon saturation effects. In order to remove model dependent systematic uncertainties we also compare the data to a simple geometric model. The forward rapidity data are inconsistent with nuclear modifications that are linear or exponential in the density weighted longitudinal thickness, such as those from the final state breakup of the bound state.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Event structure and double helicity asymmetry in jet production from polarized p+p collisions at (sq rt) s = 200 GeV

We report on the event structure and double helicity asymmetry (A{sub LL}) of jet production in longitudinally polarized p+p collisions at {radical}s = 200 GeV. Photons and charged particles were measured by the PHENIX experiment at midrapidity |{eta}| < 0.35 with the requirement of a high-momentum (> 2 GeV/c) photon in the event. Event structure, such as multiplicity, p{sub T} density and thrust in the PHENIX acceptance, were measured and compared with the results from the pythia event generator and the geant detector simulation. The shape of jets and the underlying event were well reproduced at this collision energy. For the measurement of jet ALL, photons and charged particles were clustered with a seed-cone algorithm to obtain the cluster p{sub T} sum (p{sub T}{sup reco}). The effect of detector response and the underlying events on p{sub T}{sup reco} was evaluated with the simulation. The production rate of reconstructed jets is satisfactorily reproduced with the next-to-leading-order and perturbative quantum chromodynamics jet production cross section. For 4 < p{sub T}{sup reco} < 12 GeV/c with an average beam polarization of <P> = 49% we measured A{sub LL} = -0.0014 {+-} 0.0037{sup stat} at the lowest p{sub T}{sup reco} bin (4-5 GeV/c) and -0.0181 {+-} 0.0282{sup stat} at the highest p{sub T}{sup reco} bin (10-12 GeV/c) with a beam polarization scale error of 9.4% and a p{sub T} scale error of 10%. Jets in the measured p{sub T}{sup reco} range arise primarily from hard-scattered gluons with momentum fraction 0.02 < x < 0.3 according to pythia. The measured A{sub LL} is compared with predictions that assume various {Delta}G(x) distributions based on the Gluck-Reya-Stratmann-Vogelsang parameterization. The present result imposes the limit -1.1 < {integral}{sub 0.02}{sup 0.3}dx{Delta}G(x,{mu}{sup 2} = 1 GeV{sup 2}) < 0.4 at 95% confidence level or {integral}{sub 0.02}{sup 0.3}dx{Delta}G(x,{mu}2 = 1 GeV{sup 2}) < 0.5 at 99% confidence level.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗