Bulletin of the American Physical Society
APS April Meeting 2013
Volume 58, Number 4
Saturday–Tuesday, April 13–16, 2013; Denver, Colorado
Session L9: Spin Structure of the Nucleon I |
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Sponsoring Units: GHP Chair: Kalyan Allada, Jefferson Laboratory Room: Governor's Square 11 |
Sunday, April 14, 2013 3:30PM - 3:42PM |
L9.00001: Persepectives of Polarized Drell-Yan Measurements with Future Fixed-Target and Collider Experiments Xiaodong Jiang, Kwangbok Lee Drell-Yan spin observable measurements with polarized proton or $^3$He beams on polarized proton or $^3$He targets provide valuable and unique probes to access the fundamental structure of nucleons. For example, comparing to Semi- Inclusive Deep Inelastic Scattering (SIDIS), double longitudinal spin asymmetries in Drell-Yan reactions provide a clean access to anti-quark helicity distributions without involving quark fragmentation functions. Transverse Single Spin Asymmetry (SSA) in Drell-Yan reactions can test the predicted sign change of quark Sivers function compared to that from SIDIS measurement, providing an important test of the fundamental QCD as well as our current understanding of the transverse spin phenomena. Drell-Yan SSA can also access other quark Transverse Momentum Dependent distributions (TMDs), for example, quark's transversity ($h_1$), and quark's ``longitudinal helicity'' ($h_{1L}^\perp$). We studied several options of polarized Drell-Yan measurements with polarized beams for fixed-target and collider cases, such as the Fermilab Main Injector's extracted proton beam, the future J-PARC 50 GeV/c beam and at the RHIC Collider. We will discuss the physics sensitivities of double-spin and single-spin Drell-Yan observable measurements. [Preview Abstract] |
Sunday, April 14, 2013 3:42PM - 3:54PM |
L9.00002: Sign Flip of Single Transverse Spin Asymmetries in Drell-Yan and DIS: The Role of Cuts and Complex Phases Matthew Sievert, Stanley Brodsky, Dae Sung Hwang, Yuri Kovchegov, Ivan Schmidt The transverse polarization of a hadron's spin can couple to its partons' transverse momentum distribution, resulting in an asymmetry known as the Sivers asymmetry. Depending on the scattering mechanism, this asymmetry of the parton distribution may persist into the final-state hadron distribution. Such single transverse spin asymmetries provide unique insights into the internal spin structure of hadrons and can couple to different scattering processes than the usual unpolarized cross-section. One hallmark prediction of transverse-momentum-dependent factorization is that the Sivers asymmetry should have equal magnitude and opposite sign between the Drell-Yan process and semi-inclusive deep inelastic scattering. We explicitly verify this prediction in greater detail than had previously been considered, using a toy model for the proton wave function. With an explicit representation of the transverse spinors, we demonstrate how $C/P/T$ invariance couples the asymmetry to the imaginary part, or cut, of the diagrams. To establish the validity of the predicted sign flip, we demonstrate a non-trivial equivalence between the cuts present in deep inelastic scattering and the Drell-Yan process. [Preview Abstract] |
Sunday, April 14, 2013 3:54PM - 4:06PM |
L9.00003: Feasibility study for measuring the Drell-Yan cross section and double-spin asymmetry (ALL) at PHENIX using the FVTX Tracker Gonaduwage Perera, Stephen Pate Analysis of di-muon pairs produced in the Drell-Yan process in high energy longitudinally polarized proton-proton collisions provides a tool to probe the proton spin structure. The new Forward Silicon Vertex Detector (FVTX) enables us to study the Drell-Yan process for forward di-muon production (1.2\textless \textbar $\eta $\textbar \textless 2.4) in the PHENIX experiment at RHIC with less background. In this talk we present the status of the analysis of simulation data and RHIC 2012 data for the intermediate mass region (4 GeV \textless M \textless 8 GeV) Drell-Yan process at a center of mass energy of 510 GeV in proton-proton collisions. [Preview Abstract] |
Sunday, April 14, 2013 4:06PM - 4:18PM |
L9.00004: The Double Helicity Asymmetry in Neutral Pion Production at PHENIX and Its Constraint on $\Delta G$ Through Global Analysis Kieran Boyle Understanding the gluon spin contribution to the proton spin, $\Delta G$, is a primary goal of the RHIC spin program. The abundant production of pions in $p+p$ collisions, coupled with the PHENIX detector's fine resolution Electromagnetic Calorimeter and high $p_T$ triggering capabilities, make neutral pions a prime candidate to study the proton spin structure in polarized $p+p$ collisions at RHIC. Measurements of the double helicity asymmetry, $A_{LL}$, in $\pi^0$ production from 2005 and 2006 were shown to significantly constrain the gluon helicity distribution, $\Delta G$, in the proton [1]. With improved luminosity and polarization, the figure of merit for the 2009 data set was a factor of 1.5 better that the previous runs combined. We present the 2009 results for $\pi^0$ $A_{LL}$, along with a discussion of the results from inclusion of these data in a recent update of the DSSV global analysis.\\[4pt] [1] D. de Florian, R. Sassot, M. Stratmann, W. Vogelsang (DSSV) Phys.Rev.Lett. 101 (2008) 072001 [Preview Abstract] |
Sunday, April 14, 2013 4:18PM - 4:30PM |
L9.00005: ABSTRACT WITHDRAWN |
Sunday, April 14, 2013 4:30PM - 4:42PM |
L9.00006: Recent Results on $W$ Boson Production in Polarized $p+p$ Collisions at STAR Justin Stevens The production of $W$ bosons in polarized $p+p$ collisions at RHIC provides an excellent tool to probe the proton's sea quark distributions. At leading order $W^{-(+)}$ bosons are produced in $\bar{u}+d\,(\bar{d}+u)$ collisions, and parity-violating single-spin asymmetries measured in longitudinally polarized $p+p$ collisions give access to the flavor-separated light quark and antiquark helicity distributions. In 2012 the STAR experiment collected an integrated luminosity of $\sim$80 pb$^{-1}$ at $\sqrt{s}=510$ GeV with an average beam polarization of $\sim$55\%. Preliminary results from this dataset for the single-spin asymmetry, $A_L$, will be presented as well as future projections for the STAR $W$ program. [Preview Abstract] |
Sunday, April 14, 2013 4:42PM - 4:54PM |
L9.00007: Measurement of $W^{\pm}$ Boson Production at Mid-rapidity in 510 GeV Polarized $p+p$ Collisions at PHENIX Mikhail Stepanov The measurement of $W^{\pm}$ production in polarized proton-proton collisions provides access to the flavor-separated quark and anti-quark polarized parton distribution functions. The PHENIX experiment at RHIC observes $W^{\pm}\rightarrow e^{\pm}$ decays at mid-rapidity with the PHENIX central arm detectors ($\mid \eta \mid \le 0.35$). In 2012, the new silicon VTX detector was fully operational, allowing for improved analysis techniques in order to reduce background from conversion electrons in the detector material. The recently recorded data in 2012 at $\sqrt{s}$ = 510 GeV with an integrated luminosity of $\approx $30 pb$^{-1}$ is about twice the size of previous data sets and also takes an advantage of improved beam polarization ($P\approx$ 52$\%$). We report the status of the analysis of the cross section and the parity violating longitudinal single-spin asymmetry of $e^{\pm}$ from $W^{\pm}$ decays. [Preview Abstract] |
Sunday, April 14, 2013 4:54PM - 5:06PM |
L9.00008: Transverse Single Spin Asymmetries in J/$\psi$ Production in Proton-Proton Collisions Oleg Eyser The PHENIX collaboration previously reported the first measurements of transverse single spin asymmetries in J/$\psi$ production in proton-proton collisions at center-of-mass energies of 200 GeV at the Relativistic Heavy Ion Collider [Phys. Rev. D 86, 099904(E), 2012]. The measurement was in part performed in the rapidity range of $1.2<|\eta|<2.2$ for transverse momenta up to 6 GeV/$c$. J/$\psi$ production at such energies is dominated by processes involving gluons inside the proton, and the observed transverse single spin asymmetries of the J/$\psi$ can therefore provide access to the dynamics of the intial-state gluons. We will present the latest and complementary results from the recent 2012 data set and discuss their possible implications for the underlying physics processes. [Preview Abstract] |
Sunday, April 14, 2013 5:06PM - 5:18PM |
L9.00009: Reduction of Background in Observation of W Decay Using the Forward Vertex (FVTX) detector at PHENIX Abraham Meles One of the major emphases of the RHIC spin program over the next few years is the observation of the parity-violating asymmetry $A_L$ in the production of $W$ bosons in $p+p$ collisions at $\sqrt{S}$ = 510 GeV. This asymmetry is sensitive to the polarization of light quarks and anti-quarks in the proton. Identifying the lepton ($e$ or $\mu$) from the decay of the $W$ is challenging due to a great background of hadronic processes. In PHENIX, in the forward and backward hemispheres, the muon spectrometers have been recently upgraded in order to provide additional tracking information to suppress those backgrounds. One of those upgrades is the Forward Vertex (FVTX) detector, a silicon-strip tracker. The FVTX will be especially useful in eliminating events where a low-momentum hadron decays in flight, and the decay muon is mis-reconstructed as a high momentum particle. In 2012, PHENIX collected an integrated luminosity of $\approx $30 pb$^{-1}$ of polarized $p+p$ collisions at $\sqrt{s}$ = 510 GeV with a beam polarization of $\approx $52$\%$. The ability of the FVTX to improve $W$ observation will be reviewed and progress on simulation and analysis of real data from the first use of the FVTX in the RHIC 2012 run will be discussed. [Preview Abstract] |
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