Bulletin of the American Physical Society
APS April Meeting 2012
Volume 57, Number 3
Saturday–Tuesday, March 31–April 3 2012; Atlanta, Georgia
Session L11: Spin Structure of the Nucleon |
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Sponsoring Units: GHP Chair: Ernst Sichtermann, Lawrence Berkeley National Laboratory Room: Embassy F |
Sunday, April 1, 2012 3:30PM - 3:42PM |
L11.00001: Cross sections and double helicity asymmetryies of mid-rapidity single inclusive non-identified charged hadron production in p+p collisions at $\sqrt{s}$ = 62.4 GeV Amaresh Datta We investigate hard interaction in QCD through the measurement of cross sections of mid-rapidity production of non-identified charged hadrons from $p+p$ collisions at $\sqrt{s} = 62.4$ GeV. Measurements are made in the transverse momentum range from 0.5 GeV/$c$ to 4.5 GeV/$c$ by the PHENIX experiment at RHIC. Predictions based on perturbative QCD calculations at next-to-leading order (NLO) are consistent with the cross section results. The data are also consistent with resummed perturbative QCD calculations, which include terms with next-to-leading log (NLL) accuracy and have correspondingly reduced theoretical uncertainties. The double helicity asymmetry measurements of mid-rapidity non-identified charged hadrons in the measured transverse momentum range are sensitive at leading order to the polarization of gluons in a momentum fraction range $0.05 \leq x_{gluon} \leq 0.2$. [Preview Abstract] |
Sunday, April 1, 2012 3:42PM - 3:54PM |
L11.00002: Transverse single spin asymmetries in PHENIX David Kleinjan Inclusive transverse single spin asymmetries from high energetic polarized proton proton collisions provide insight into the spin-momentum correlations in QCD. Originally expected to be small in collinear perturbative QCD, results from PHENIX and other experiments show significant asymmetries in the forward momentum direction of the polarized proton over a wide range of center-of-mass energies. Several mechanisms have been proposed that attempt to explain these asymmetries, which include initial and final state effects. In order to disentangle these effects, a variety of probes is needed in different kinematic regions. In the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC), we study polarized p+p collisions at center-of-mass energies up to 500 GeV. We will show transverse asymmetries at forward ($3.1 < \vert \eta \vert < $3.8) and central rapidities ($\vert \eta \vert < $0.35) and discuss their possible implications for intitial and final state effects. [Preview Abstract] |
Sunday, April 1, 2012 3:54PM - 4:06PM |
L11.00003: Neutral Pion Double Helicity Asymmetry in Polarized Proton-Proton Collisions at $\sqrt{s}$=200 GeV at STAR William Leight One of the primary goals of the spin physics program at the STAR experiment is to constrain the polarized gluon distribution function $\Delta(g)(x,Q^{2})$ by measuring the double helicity asymmetry, $A_{LL}$, of various final-state channels. Neutral pions are a potentially powerful final state because they are copiously produced in p+p collisions and have few backgrounds. STAR can identify neutral pions using its large-acceptance electromagnetic calorimeter, combined with a track veto from the STAR Time Projection Chamber. I will present progress towards measuring an $A_{LL}$ for neutral pions using $\sim$14 pb$^{-1}$ of integrated luminosity taken during the 2009 200 GeV p+p run. [Preview Abstract] |
Sunday, April 1, 2012 4:06PM - 4:18PM |
L11.00004: Charged Pion + Jet Longitudinal Double Spin Asymmetry in Polarized Proton-Proton Collisions at $\sqrt{s} =200$ GeV at STAR James Hays-Wehle Inclusive measurements from polarized proton-proton collisions at RHIC have constrained $ \Delta g$, the polarized gluon distribution function of the proton. Correlation observables, such as this pion+jet measurement, allow for reconstruction of initial parton kinematics and are thus sensitive to the x dependence of $ \Delta g$. By measuring charged pions opposite a jet, this particular measurement can be sensitive to the flavor of the struck parton. This measurement, which is dominated by the quark-gluon subprocess, can be divided into terms proportional to $\Delta u\Delta g$ and $\Delta d \Delta g$. The relatively larger quark polarization amplifies the measured asymmetry thereby enhancing the statistical power. I will present progress on the mid-rapidity pion+jet longitudinal double spin asymmetry analysis from 10.6 pb$^{-1}$ of luminosity collected in the 2009 200 GeV p+p run. [Preview Abstract] |
Sunday, April 1, 2012 4:18PM - 4:30PM |
L11.00005: Longitudinal Double-Spin Asymmetry Measurements in p+p and Their Limitation by Systematic Uncertainty in Relative Luminosity Andrew Manion We present longitudinal double-spin asymmetries $A_{LL}$ in neutral $\pi^0$ production in the PHENIX detector at RHIC. This measurement has been shown to constrain the gluon spin contribution to the proton, $\Delta G$. We will also discuss the main systematic uncertainty, which originates from the relative luminosity of the different spin states in RHIC, and new ways to possibly understand the source of this uncertainty. [Preview Abstract] |
Sunday, April 1, 2012 4:30PM - 4:42PM |
L11.00006: Constraining $\Delta G$ at Low-x with Double Longitudinal Spin Asymmetries of Hadrons at Forward Rapidity in PHENIX Scott Wolin At low Bjorken-x, $x<0.05$, the proton structure is heavily gluon dominated. However, in this kinematic region, the gluon polarization, $\Delta G$, and hence its contribution to the net proton spin, remains weakly constrained. To map out the gluon polarization at low-x and distinguish between various theoretical models with the best sensitivity, it is necessary to measure the asymmetry, $A_{LL}$, in high $p_{T}$ hadrons in the forward direction ($3.1<|\eta|<3.9$) from longitudinally polarized protons. We will report the current status of the single $\pi^{0}$ measurements. In addition, we have upgraded the electronics and triggering of our forward calorimeter to be able to trigger on di-hadron events as well. The new trigger will be used first during the 2012 RHIC run. This measurement is particularly interesting because it provides the best sensitivity to low-x gluons, with $x\sim$ few $\times10^{-3}$, that participate in highly asymmetric interactions. We will report on the performance of our new trigger as the run in progress continues. Both the single and di-hadron measurements will provide valuable low-x input for future global analyses of $\Delta G$. [Preview Abstract] |
Sunday, April 1, 2012 4:42PM - 4:54PM |
L11.00007: $W^{\pm}$ Boson Production at Mid-rapidity in 500 GeV $p+p$ Collisions in the PHENIX Experiment Mikhail Stepanov We search for $W^{\pm}$ boson decays through $e^{\pm}$ channels in polarized $p+p$ collisions at $\sqrt{s}$ = 500 GeV at RHIC with the PHENIX central arm detectors, which cover $\mid \eta \mid \le 0.35$. The $W^{\pm}$ production is an important probe of the flavor-separated quark and antiquark helicity distributions in the proton. In 2011, PHENIX collected data with an integrated luminosity of $\sim$17 pb$^{-1}$ in 500 GeV $p+p$ collisions which is increased approximately by a factor of two in comparison with the previous 2009 data set; improved beam polarization was 46$\%$. The status of the analysis of the new data will be reported. In 2011, the detector configuration was changed by important detector upgrades, which leads to an increased background from conversion in additional material. A supplementary analysis technique is required and developed to extract the signal in these background conditions. [Preview Abstract] |
Sunday, April 1, 2012 4:54PM - 5:06PM |
L11.00008: $W$ Production at Forward Rapidity in 500 GeV p+p Collisions at PHENIX Murad Sarsour A major emphasis of the RHIC spin program at BNL is to study the spin-flavor structure of the proton based on the production of $W^{-(+)}$ bosons. $W^{-(+)}$ bosons are produced at leading order in $\bar{u}+d\,(\bar{d}+u)$ collisions and detected at RHIC through their leptonic decays, $l+\bar{\nu}_{l}\,(\bar{l}+\nu_{l})$, where only the respective charged lepton is measured. At forward rapidity, PHENIX completed the needed upgrades of the muon spectrometers to observe muons from $W^\pm$ decays and is ready for polarized p+p collisions at $\sqrt{s}=500$ GeV in 2012. The upgrades included new electronics transferring information from the muon tracking systems to the level 1 trigger processors and new fast Resistive Plate Chamber (RPC) tracking stations up and down stream of the PHENIX muon spectrometers. In 2011, the up stream RPC tracking stations were not yet installed, PHENIX collected approximately 17 pb$^{-1}$ of polarized p+p collisions at $\sqrt{s}=500$ GeV with the forward muon detectors. The status of the data analysis towards $W^\pm$ cross sections for the $\mu^\pm$ channels, at forward rapidity, will be presented. The proton beams had a longitudinal polarization of approximately 46$\%$, and progress on extracting $W$-decay muon single spin asymmetry will be reported. [Preview Abstract] |
Sunday, April 1, 2012 5:06PM - 5:18PM |
L11.00009: Single-Spin Asymmetries in SIDIS at JLab Harut Avagyan Measurements of spin and azimuthal asymmetries in semi-inclusive processes emerged as an important tool to access Transverse Momentum Dependent (TMD) parton distributions containing information on both the longitudinal and transverse motion of partons inside a fast moving nucleon. CLAS collaboration at Jefferson Lab collected recently approximately 19 billion electron triggers with hydrogen and 7 billion electron triggers with deuterium using solid state ammonia and deuterated ammonia targets. Kinematical dependences of single and double spin asymmetries have been measured for a longitudinally polarized proton target, providing access to transverse momentum distributions of quarks and spin orbit correlations in the nucleon. In this talk we present latest studies of TMDs and discuss newly released results, ongoing activities, as well as planed near term and future measurements. [Preview Abstract] |
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