Bulletin of the American Physical Society
2007 Annual Meeting of the Division of Nuclear Physics
Volume 52, Number 10
Wednesday–Saturday, October 10–13, 2007; Newport News, Virginia
Session EB: Mini-Symposium on the Global Analysis of Spin-Dependent Parton Distributions II |
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Chair: Krishna Kumar, The University of Massachusetts Room: Newport News Marriott at City Center Grand Salon III |
Friday, October 12, 2007 2:00PM - 2:36PM |
EB.00001: An update on the Next-to-Leading Order perturbative QCD analysis of the spin structure function data Invited Speaker: We present a next-to-leading order ($\alpha_{S}^{2}$) perturbative QCD analysis of the nucleon spin structure function data available from the fixed target deep inelastic scattering experiments. In the analysis we include the most recent available data sets available from CERN, SLAC and DESY. The polarized gluon distribution obtained from this analysis is then compared to the now available direct measurements of polarized gluons from COMPASS and RHIC data on inclusive neutral pions and jets. We also comment on the impact of possible future data from RHIC and the Electron Ion Collider (EIC). [Preview Abstract] |
Friday, October 12, 2007 2:36PM - 2:48PM |
EB.00002: ABSTRACT WITHDRAWN |
Friday, October 12, 2007 2:48PM - 3:00PM |
EB.00003: Longitudinal Double Spin Asymmetry and Cross Section for Direct Photon Production at Mid-rapidity in Polarized $\sqrt{s} = 200$ GeV $pp$ Collisions at PHENIX Robert Bennett Production of direct photons in collisions at RHIC is one of the important c hannels PHENIX will employ to determine the polarized gluon distribution. To es tablish the theoretical understanding of this process, we first present the comp arison the direct photon unpolarized cross section measured during $\sqrt{s} = 2 00$ GeV collisions, with the perturbative QCD calculations at next-to-leading or der. The extraction of the cross section relies on two techniques: First purify ing our sample by considering only isolated photons as direct photon candidates and second by a statistical subtraction of weighted spectra of known sources of decay photons from the total photon event sample. We then proceed to evaluate th e double helicity spin asymmetries, $A_{LL}$, from these data sets and compare w ith theoretical models. Since the direct photon $A_{LL}$ is linear in $\Delta G $, it is sensitive to both the sign and magnitude of $\Delta G$ and it will even tually be able to serve as a complementary measurement to the $\pi^0$ $A_{LL}$ a nalysis . A status of the analysis of data obtained in 2005, based on a luminos ity of $2.7$ pb$^{-1}$ and polarization 50\%, and 2006 with $7.5$ pb$^{-1}$ lumi nosity and $60\%$ polarization will be presented. [Preview Abstract] |
Friday, October 12, 2007 3:00PM - 3:12PM |
EB.00004: Longitudinal Spin Transfer of Hyperons in Polarized Proton-proton Collisions at $\sqrt s$ =200 GeV Qinghua Xu The study of the spin content of the nucleon with polarized proton collisions forms one of the main goals of the STAR (Solenoid Tracker At RHIC) spin physics program. The longitudinal spin transfer $D_{LL}$ of the Lambda and anti-Lambda hyperons at large transverse momenta is sensitive to the helicity distribution functions of strange quarks and anti-quarks, and to polarized fragmentation functions. This contribution reports on the measurement of $D_{LL}$ in inclusive $\Lambda$ and $\bar \Lambda$ production in longitudinally polarized proton-proton collisions at a center of mass energy of $\sqrt{s}$ = 200 GeV. The data were collected in the year 2005 with proton beam polarizations of about 50\%, and a sampled integrated luminosity of about 3 pb$^{-1}$. The $\Lambda$($\bar \Lambda$) candidates were reconstructed via the dominant decay channel $\Lambda\to p \pi^-$ ($\bar \Lambda \to \bar p \pi^+$) at mid-rapidity ($|\eta|<1$) using the STAR Time Projection Chamber. Preliminary results on $D_{LL}$, covering transverse momenta up to 4 GeV/c, will be presented together with an outlook on future hyperon spin transfer measurements. [Preview Abstract] |
Friday, October 12, 2007 3:12PM - 3:24PM |
EB.00005: The Polarization of Anti-Lambda Produced in $\sqrt{s}$=200GeV Longitudinal Polarized Proton-Proton Collision at PHENIX Ran Han The polarization of anti-lambdas produced in pp collisions as a function of rapidity is expected to be sensitive to the polarization of the anti-strange sea of the nucleon and also sensitive to the polarized fragmentation functions. ~ Substantially non-zero and rather large spin transfers have been observed by the FNAL E704 and E665 experiments.~ But the polarization reactions can be studied for the first time in longitudinal polarized pp scattering at higher collider energies at RHIC. ~ In this presentation, we discuss the anti-lambda polarization and its dependence on pseudo-rapidity in $\sqrt{s}$=200GeV polarized proton-proton collisions at RHIC/PHENIX, using 0.25 pb-1 of data collected collected in 2003 with beam polarizations 32{\%}. The anti-lambda candidates are reconstructed at mid-rapidity via its weak decay channel `anti-lambda-$>$bar(p)+pion(+)'; and the charged particles are measured with the PHENIX central arms. [Preview Abstract] |
Friday, October 12, 2007 3:24PM - 3:36PM |
EB.00006: Charm Content in Jets from p+p Collisions at $\sqrt{s}$ = 200GeV Xin Dong In hadron collisions at high energies, the charm content in jets can be calculated in perturbative QCD. Gluon fusion into heavy flavor pair results in a hard contribution to the fragmentation into charm hadrons, while gluon splitting process results in a soft contribution. We report the measurements of $D^{*\pm}$ production in jets from p+p collisions at $\sqrt{s}$ = 200 GeV with the STAR experiment at RHIC. The measurements give insight in the charm production mechanism, which is of importance to both the heavy ion and spin physics programs at RHIC. [Preview Abstract] |
Friday, October 12, 2007 3:36PM - 3:48PM |
EB.00007: New Measurements of the Proton Double-Spin Asymmetries $A_1$ and $A_2$ In and Above the Resonance Region Robert Fersch The CLAS EG1b experiment in Hall-B at Jefferson Laboratory utilized a polarized electron beam at various (1.6, 2.5, 4.2, 5.7 GeV) energies and polarized frozen NH$_3$ and ND$_3$ targets to measure double-polarization asymmetries of inclusive electron-nucleon scattering. The proton asymmetry $A_1$ has been extracted from the double-spin asymmetry (at $0.15$ GeV$^2 < Q^2 < 2.0$ GeV$^2$). Newly analyzed data at 2.5 and 4.2 GeV allows a more complete integration in $x$ of the $g_1$ structure function than provided by previous analysis, reducing models dependency in the calculation of $\Gamma_1$, the first moment of $g_1$. A linear regression of the asymmetries in terms of $\eta \equiv \epsilon\sqrt{Q^2}/(E - \epsilon{E'})$ also provides a rudimentary measurement of $A_2$ in the region of kinematic overlap for the varying beam energies. [Preview Abstract] |
Friday, October 12, 2007 3:48PM - 4:00PM |
EB.00008: Measurements of Double Longitudinal Spin Asymmetry in Dimuon Production at RHIC Ming Liu One of the main goals of RHIC-SPIN program is to determine the contribution of the polarized gluons to the proton spin. At RHIC energy, it is expected heavy quark (charm and beauty) production is dominated by gluon-gluon interactions, so measurement of double longitudinal spin asymmetry of heavy quark production in the polarized p+p collisions will allow us to directly probe the polarized gluon distribution inside the proton. The PHENIX experiment collected 7.5 $pb^{-1}$ (beam polarization about $60\%$) data from year 2006 run, and successfully reconstructed about 30K dimuon $J/\Psi$ candidates as well as 100K back-to-back dimuons with invariant mass above 5 GeV. These two probes cover very different kinematic ranges: for the forward $J/\Psi$ production, the covered x ranges are, $x_1$ ~0.2 and $x_2$ ~10$^{-3}$; for the back-to-back dimuons, $x_1$ ~$x_2$ ~0.1. In this talk, we present the current status of $A_{LL}$ measurements in the dimuon channels from the PHENIX experiment. [Preview Abstract] |
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