Bulletin of the American Physical Society
2010 Fall Meeting of the APS Division of Nuclear Physics
Volume 55, Number 14
Tuesday–Saturday, November 2–6, 2010; Santa Fe, New Mexico
Session FF: Spin Physics at RHIC |
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Chair: Patrick McGaughey, Los Alamos National Laboratory Room: Kearney |
Thursday, November 4, 2010 4:00PM - 4:12PM |
FF.00001: ABSTRACT WITHDRAWN |
Thursday, November 4, 2010 4:12PM - 4:24PM |
FF.00002: Physics with Tagged Forward Protons at STAR Ivan Koralt One of the goals of the physics program with tagged forward protons with the STAR detector at RHIC is the study of elastic scattering of polarized protons at small four-momentum transfer squared (-$t)$ in the RHIC center of mass (cms) energy range. Coulomb and nuclear amplitudes plus their interference describe elastic scattering of polarized protons at these ranges. Studying the kinematic region of low $\vert -t\vert $ provides also an opportunity to study the spin averaged nuclear amplitude. In order to achieve this goal, silicon strip detectors are installed inside Roman Pots at 55.5 m and 58.5 m on either side of the STAR interaction point (IP), detecting the very forward scattered protons. During the RHIC 2009 data taking period, the collaboration collected approximately 30M elastic triggers with transversely polarized proton beams at $\surd s $= 200 GeV and four-momentum transfer squared range of 0.005 GeV$^{2}$/$c^{2} \quad \le -t \le $ 0.035 GeV$^{2}$/$c^{2}$. In this talk, we describe the experimental setup and performance during the 2009 data taking period. We elaborate on the quality of the recorded data, techniques used for event reconstruction, and efficiencies of the Si detectors. We will present preliminary results, including the single spin asymmetry $A_{N}$. [Preview Abstract] |
Thursday, November 4, 2010 4:24PM - 4:36PM |
FF.00003: Longitudinal Spin Transfer of $\Lambda$ and $\bar\Lambda$ in Polarized Proton-Proton Collisions at $\sqrt{s} = 200$ GeV Ramon Cendejas The longitudinal spin transfer, $D_{LL}$, of $\Lambda$ and $\bar\Lambda$ hyperons in longitudinally polarized proton-proton collisions is sensitive to the polarization of strange quarks and anti-quarks in the polarized proton, and polarized fragmentation. The STAR collaboration previously reported $D_{LL}$ from a data sample obtained in 2005 that corresponds to an integrated luminosity of 2 $pb^{-1}$ with 50\% beam polarization. In 2006 and 2009 larger data samples were obtained, corresponding to 8.5 $pb^{-1}$ and 25 $pb^{-1}$ with beam polarizations of 53\% and 57\%, respectively. These data are expected to considerably improve the precision of the $D_{LL}$ measurement and extend their range to larger transverse momenta, $p_{T}$. Increased acceptance of jet triggered events in 2009 are expected to enhance the sample of $\Lambda$ and $\bar\Lambda$ hyperons associated to jets. The analysis status will be discussed. [Preview Abstract] |
Thursday, November 4, 2010 4:36PM - 4:48PM |
FF.00004: 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, for example, correlations between produced hadrons at forward rapidities, provides the opportunity to decipher between dynamical contributions to $A_{N}$, such as the Collins and Sivers mechanisms. Recent analysis at STAR investigates high pseudorapidity $\pi^{0}$-charged particle correlations from $\sqrt{s}=200$ GeV polarized proton collisions. The $\pi^{0}$'s are detected at $2.5<\eta<4$ with 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] |
Thursday, November 4, 2010 4:48PM - 5:00PM |
FF.00005: Measuring the Light Anti-Quark Asymmetry in Drell-Yan Scattering Kazutaka Nakahara The light anti-quark distributions within the nucleon give unique insight into the origin of the quark sea. Whereas the non-perturbative nature of this sea poses a challenge in performing quantitative calculations, experiments have been performed to constrain the assumptions that underlie various phenomenological models. One such assumption is the equality of $\bar{u}$ and $\bar{d}$ distributions within the nucleon. While the E866/NuSea experiment saw clear signs of a $\frac{\bar{d}}{\bar{u}}$ asymmetry at Bjorken x, the sea became flavor symmetric at higher x, suggesting a possible shift in the underlying mechanism generating the sea. The E906/SeaQuest Experiment, which is scheduled to take place at Fermilab, will determine the $\frac{\bar{d}}{\bar{u}}$ asymmetry over 0.04 $<$ x $<$ 0.45 by measuring the Drell-Yan cross section in p-p and p-d scattering. The Drell-Yan process, which involves a $q$$\bar{q}$ annihilation and a $\mu$$\bar{\mu}$ ($l$$\bar{l}$) production mediated by a virtual photon, gives a unique signature from which the $\frac{\bar{d}}{\bar{u}}$ fraction can be derived. The experiment will make use of a 120 GeV proton beam extracted from the Fermilab Main Injector. The low beam energy relative to E866 will allow for a 50$\times$ improvement in the statistical uncertainty of the cross section measurement compared to existing results. Physics motivation, project status, and the expected results from the E906/SeaQuest experiment will be presented. [Preview Abstract] |
Thursday, November 4, 2010 5:00PM - 5:12PM |
FF.00006: New Measurement of Nuclear Antiquark Distributions at E906/SeaQuest Joshua Rubin The E906/SeaQuest experiment at Fermilab will make a new measurement of the modification of the parton distributions of the nucleus with respect to those of the nucleon, an effect first observed by the EMC collaboration. To accomplish this, the Drell-Yan cross sections for a variety of targets will be measured using a 120 GeV proton beam from the FNAL main injector. The majority of nuclear modification measurements have been performed using deep inelastic scattering, which is sensitive to the charge-weighted sums of the parton densities. The cross-section ratios to be measured by E906, in contrast, will be sensitive to modification of the sea quark densities which provides essential new model constraints. E906/SeaQuest will access the x $>$ 0.2 regime, that is, the antishadowing region where the E772 Drell-Yan measurements were statistically limited and into the ``EMC Effect'' region. The results will also be valuable in revealing the nuclear corrections required to employ high luminosity neutrino data on nuclear targets in parton distribution fits. The experiment will begin in 2010 and run for two years. [Preview Abstract] |
Thursday, November 4, 2010 5:12PM - 5:24PM |
FF.00007: Dijet Cross Section and Longitudinal Double Spin Asymmetry in Polarized Proton-Proton Collisions at 200 GeV at STAR Matthew Walker The polarized gluon distribution function of the proton, $\Delta g(x,Q^2)$, has been constrained by inclusive measurements from polarized proton-proton collisions at RHIC. Correlation measurements, such as the dijet measurement, provide, at leading order, access to parton kinematics and are thus sensitive to the shape of $\Delta g(x,Q^2)$. STAR's large acceptance electromagnetic calorimetry and tracking make it well suited for this measurement. The statuses of the dijet cross-section analysis from the 2005 and 2006 RHIC data sets and the longitudinal double spin asymmetry analysis from the 2006 and 2009 data sets, all at mid-rapidity, will be presented. [Preview Abstract] |
Thursday, November 4, 2010 5:24PM - 5:36PM |
FF.00008: Toward a Dijet Measurement at Forward Rapidity Utilizing the STAR Endcap Electromagnetic Calorimeter B.S. Page To date, the STAR experiment at the Relativistic Heavy Ion Collider has probed the gluon helicity distribution of the proton, $\Delta g(x)$, primarily through inclusive channels. These inclusive measurements have resulted in a strong constraint on the integral of $\Delta g(x)$ over the Bjorken-$x$ range of $0.03$ to $0.3$; however, they have little sensitivity to the the shape of $\Delta g(x)$ as a function of $x$. In contrast, dijet measurements give sensitivity to partonic kinematics and thus allow for the investigation of the $x$ dependence of $\Delta g(x)$. The study of dijets at forward rapidity in STAR is complicated by the falling charged particle tracking efficiency of the Time Projection Chamber for $|\eta| > 1$, as well as a gap in electromagnetic calorimeter coverage for $1.0<\eta<1.086$. To study dijets at forward rapidity, and thus gain access to lower partonic $x$ values, it will therefore be necessary to have a detailed understanding of systematic changes in reconstructed jet properties as one moves into the Endcap region $(1.086 < \eta < 2)$. The status of studies investigating these systematic changes will be presented. [Preview Abstract] |
Thursday, November 4, 2010 5:36PM - 5:48PM |
FF.00009: The STAR $W$ Physics Program at RHIC Justin Stevens The production of $W^{-(+)}$ bosons in longitudinally polarized p+p collisions at RHIC provides a new means of studying the spin-flavor asymmetries of the proton sea quark distributions. $W^{-(+)}$ bosons are produced in $\bar{u}+d\,(\bar{d}+u)$ collisions and can be detected through their leptonic decays, $e^{-}+\bar{\nu}_{e}\,(e^{+}+\nu_{e})$, where only the charged lepton is detected. At mid-rapidity, the charge sign of the high $p_T$ $e^{-(+)}$ is determined from precise tracking information provided by the STAR Time Projection Chamber (TPC). At forward rapidity, new tracking capabilities will be provided by the Forward GEM Tracker, consisting of six triple-GEM detectors currently under construction. The large acceptance of the TPC and Electromagnetic Calorimeters is well suited to place isolation requirements on the $e^{-(+)}$ and to veto on the away side energy, which reduces the large QCD background by several orders of magnitude, yielding a clean $W$ signal. In 2009 the STAR Collaboration collected an integrated luminosity of $\sim$ 12 pb$^{-1}$ at $\sqrt{s}=500$ GeV with an average beam polarization of $\sim$ 39\%. Preliminary results for the $W^{-(+)}$ production cross section and parity-violating single-spin asymmetry, $A_L$, from the 2009 data, as well as future projections for the STAR $W$ spin program at mid-rapidity and forward rapidity, will be presented. [Preview Abstract] |
Thursday, November 4, 2010 5:48PM - 6:00PM |
FF.00010: Uncertainties in the $\Delta$G Extraction from a Global Analysis of Polarized Data Ciprian Gal, Daniel de Florian, Rodolfo Sassot, Marco Stratmann, Werner Vogelsang, Kieran Boyle, Swadhin Taneja, Abhay Deshpande In the latest global analysis from DSSV the $\Delta$G and its uncertainty are extracted based on polarized DIS and p+p collisions. Presently in the DSSV analysis the experimental uncertainties are all treated as uncorrelated. One way to improve our knowledge of $\Delta$G is to get a more complete understanding of these uncertainties. We do this by expanding the analysis to include experimental correlated uncertainties (like polarization). The results from this work together with an overview of the global analysis from DSSV will be discussed. [Preview Abstract] |
Thursday, November 4, 2010 6:00PM - 6:12PM |
FF.00011: PHENIX Measurements of the Double Helicity Asymmetry in Neutral Pion Production in Polarized p+p Collisions at $\sqrt{s}=200$ and 500 GeV Kieran Boyle Measurement of the gluon's contribution to the proton spin, $\Delta G$, is an important component of the RHIC spin program. One particular avenue for constraining $\Delta G$ is through the $\pi^{0}$ double helicity asymmetry, $A_{LL}$. The large $p+p \rightarrow \pi^{0}$ cross section coupled with the high resolution of the PHENIX EM-Calorimeter make this an attractive measurement. Significant constraints have already come from 2005 and 2006 PHENIX measurements in $\sqrt{s}=200$ GeV polarized proton collisions. In 2009, $\sqrt{s}=200$ GeV running saw a near doubling in the figure of merit ($P^4 L$) compared to 2006, due to a large increase in luminosity ($L$) with $\sim$57\% polarization ($P$). Also, the first data at $\sqrt{s}=500$ GeV were recorded, which will push the constraints to lower momentum fraction x. The status of the 200 and 500 GeV analyses will be presented. [Preview Abstract] |
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