Bulletin of the American Physical Society
2011 Fall Meeting of the APS Division of Nuclear Physics
Volume 56, Number 12
Wednesday–Saturday, October 26–29, 2011; East Lansing, Michigan
Session HC: Hadronic Physics I |
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Chair: Ernst Sichtermann, Lawrence Berkeley National Laboratory Room: 101 |
Friday, October 28, 2011 10:30AM - 10:42AM |
HC.00001: Forward Single Spin Asymmetries in Transversely Polarized Proton Collisions at STAR Yuxi Pan In transversely polarized proton collisions, single spin
asymmetries of particle production at forward rapidity are known
to be sensitive to the polarized quark degrees of freedom. Large
asymmetries for $\pi^{0}$ mesons in the region $0 |
Friday, October 28, 2011 10:42AM - 10:54AM |
HC.00002: Asymmetries in Forward-rapidity $\pi^{0}$-Charged Particle Correlations at STAR from $p^{\uparrow}+p$ Collisions at $\sqrt{s}=200$ GeV James Drachenberg RHIC experiments have observed large transverse single-spin asymmetries, $A_{N}$, in inclusive hadron production at forward rapidity. Extending the analysis beyond inclusive measurements provides the opportunity to decipher between dynamical contributions to $A_{N}$. Asymmetries in two-particle correlations provide access to so-called interference fragmentation functions and proton transversity. Recent analysis at STAR investigates single-spin asymmetries in high-pseudorapidity $\pi^{0}$-charged particle correlations from $\sqrt{s}=200$ GeV polarized-proton collisions recorded during 2008 with average fill polarization of 48\%. The $\pi^{0}$'s are detected at $2.5<\eta<4$ with a Pb-Glass calorimeter known as the Forward Meson Spectrometer, and the charged particles are detected in the same pseudorapidity region with the Forward Time Projection Chamber. The status of the analysis will be discussed. [Preview Abstract] |
Friday, October 28, 2011 10:54AM - 11:06AM |
HC.00003: Transverse Single Spin Asymmetry for Forward Direct Photon Production in $\sqrt{s}=200$ GeV $p^{\uparrow}+p$ Collisions at STAR Len K. Eun Experimental results for large transverse single spin asymmetries, $A_{N}$, continue to challenge our understanding of QCD. One important test of the current theoretical framework is the sign reversal of $A_{N}$ from SIDIS to Drell-Yan channels, a topic closely linked to QCD factorization. Theoretical models based on initial state effects predict the sign of $A_{N}$ for jets and prompt photons in hadron collisions to be the same as Drell-Yan, but opposite of what is observed for mesonic final states, such as previous STAR results for $\pi^0$ and $\eta$. The $A_{N}$ for direct photons (prompt + fragmentation) may serve as an indirect test of this model, especially if final state effects (Collins asymmetry) are small for fragmentation photons. We present the status update for the STAR measurement of $A_{N}$ for direct photon production at average pseudorapidity of 3.65. All data were collected for polarized p+p collisions at RHIC energies of $\sqrt{s}$ = 200 GeV. The integrated luminosity was 6.8 pb$^{-1}$, and the average polarization was 56\%. [Preview Abstract] |
Friday, October 28, 2011 11:06AM - 11:18AM |
HC.00004: Collins Asymmetry Contributions to Quark Transversity Constraints in Mid-Rapidity Jets in $p^\uparrow p$ Collisions at STAR Robert Fersch Proton quark transverse spin distributions ($\delta q(x,Q^2)$) are less well-constrained than longitudinal spin distributions ($\Delta q(x,Q^2)$) due to the limited amount of transverse spin data available to separate Collins and Sivers effects. Measurement of the azimuthal asymmetry of $\pi^\pm$ mesons within reconstructed jets in $p^{\uparrow}p\rightarrow$jet$(\pi^\pm)+X$ reactions observed in the Solenoidal Tracker at RHIC (STAR) at midrapidity ($|\eta|<1.0$) enables isolation of the Collins effect, and thus offers additional constraints to $\delta q(x,Q^2)$ parametrizations, which currently include Belle measurements of Collins fragmentation in e$^+$e$^-$ collisions and HERMES and COMPASS measurements of the Collins asymmetry in deep-inelastic lepton-nucleon scattering. We present progress toward asymmetry measurements from $\sqrt{s} = $200 GeV transversely polarized ($\sim$58\%) proton collision data (totalling $\sim$1 pb$^{-1}$), for average quark momentum fraction $\langle x \rangle \sim$ 0.2. [Preview Abstract] |
Friday, October 28, 2011 11:18AM - 11:30AM |
HC.00005: Single Spin Asymmetry Measurement for $W$-Boson Production in Longitudinally Polarized $p+p$ Collisions at $\sqrt{s}$ = 500 GeV in PHENIX Young Jin Kim One of main physics thrusts at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) is to understand the origin of proton spin structure. Parity violating single spin asymmetries for $W^\pm$-bosons in longitudinally polarized $p+p$ collisions at $\sqrt{s}$ = 500 GeV will give access to the flavor separated quark and anti-quark polarizations in the proton. The PHENIX experiment has measured $A_L$ for electrons from $W$-decay with its central arm spectrometers and will measure muons from $W$-decay with its forward muon spectrometers. Cross sections for $W^\pm$-bosons and the corresponding single spin asymmetries for $e^\pm$ in the central arms will be shown for the run 2009 data sample. The current status of the muon measurements from $W^\pm$ decays in muon arms during RHIC Run-11 will be presented. [Preview Abstract] |
Friday, October 28, 2011 11:30AM - 11:42AM |
HC.00006: Constraining $\Delta$ G at Low-x with Double Longitudinal Spin Asymmetries for Forward Hadron and Di-Hadron Pairs in PHENIX Scott Wolin The gluon polarization, $\Delta G=\int_{0}^{1}g(x)dx$, is
constrained in the region $0.05 |
Friday, October 28, 2011 11:42AM - 11:54AM |
HC.00007: Constraining $\Delta G$ at low-x with Double Longitudinal Spin Asymmetries for Forward Hadrons in PHENIX Cameron McKinney Currently, global fits of the gluon polarization $\Delta g(x)$ are constrained by PHENIX and STAR data from polarized p+p collisions at RHIC in the range $0.03< x <0.3$. These fits yield a first moment of the gluon polarization, $\Delta G$, consistent with zero, but they are not sensitive to possible contributions to $\Delta G$ from the low-x region. By measuring $A_{LL}$ for forward ($3.1<\eta<3.9$) $\pi^{0}$ production in the Muon Piston Calorimeter (MPC) at PHENIX, we aim to probe the structure of $\Delta g(x)$ in this low-x region. Production of hadrons at large pseudo-rapidities is favored in asymmetric collisions between a high-x quark and a low-x gluon that give the center of momentum frame a large forward boost. Simulations using the event generator PYTHIA have shown that measuring forward $\pi^{0}$'s can access $\Delta g(x)$ for $x \sim$ $10^{-3}$. Here, we present the analysis status of $A_{LL}$ for merged $\pi^{0}$'s in the MPC at $\sqrt{s}=500\: GeV$ from the 2009 dataset. This data along with data from polarized p+p runs at PHENIX through 2015 will help to provide stronger constraints on the form of $\Delta g(x)$ for ongoing global analyses. [Preview Abstract] |
Friday, October 28, 2011 11:54AM - 12:06PM |
HC.00008: HERMES Measurements of the Nucleon Transverse Spin Structure Francesca Giordano Azimuthal modulations appearing in the Semi-Inclusive Deep-Inelastic Scattering (SIDIS) cross section for hadrons are sensitive to the transverse degrees of freedom of quarks within the nucleon. Such modulations can be related to combinations of Transverse Momentum Dependent (TMD) parton distribution functions and fragmentation functions, which describe correlations between the quark or the nucleon spin with the quark transverse momentum (spin-orbit correlations), and could provide insights into the yet unmeasured quark orbital angular momentum. At HERMES, TMDs are probed for various hadron types through the analysis of specific azimuthal modulations of the SIDIS cross section. An overview of recent results obtained using transversely polarized target protons as well as using unpolarized beam and targets will be presented. [Preview Abstract] |
Friday, October 28, 2011 12:06PM - 12:18PM |
HC.00009: The MPC-EX Upgrade to the PHENIX Forward Spectrometers Arbin Timilsina The PHENIX detector has been one of the primary experimental tools at the Relativistic Heavy Ion Collider (RHIC). The MPC-EX upgrade to PHENIX will complement the existing Muon Piston Calorimeter (MPC) for measurements of inclusive direct photon and hadron production at forward rapidities. The MPC-EX will make possible a study of gluon distributions in cold nuclear matter via direct photon and neutral pion measurements, and direct measurements of spin-dependent fragmentation in polarized proton-proton collisions. The detector will cover pseudorapidity from 3.8 to 3.1 and consists of a novel Si+W preshower device with pad and strip readout. In this presentation I will discuss the design of the MPC-EX detector and the latest simulation results. [Preview Abstract] |
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