Bulletin of the American Physical Society
4th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 59, Number 10
Tuesday–Saturday, October 7–11, 2014; Waikoloa, Hawaii
Session DF: Spin Structure and Parton Distributions |
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Chair: Jen-Chieh Peng, University of Illinois at Urbana-Champaign Room: King's 2 |
Thursday, October 9, 2014 9:00AM - 9:15AM |
DF.00001: Di-jet production constraining $\Delta g(x)$ at low $\mathbf{x}$ in polarized $\mathbf \vec{p}+\vec{p}$ collisions at RHIC Bernd Surrow Polarized $\vec{p}+\vec{p}$ collisions at $\sqrt{s}=200\,$GeV and at $\sqrt{s}=500\,$GeV at RHIC provide a unique way to probe the proton spin structure. Inclusive measurements, such as inclusive jet and hadron production, have so far been the prime focus of various results at $\sqrt{s}=200\,$GeV constraining $\Delta g(x)$. A recent global analysis provides for the first time evidence of a non-zero value of the gluon polarization $\int_{\tiny 0.05}^{\tiny 1}\Delta g (x)\, dx \,(Q^{2}=10\,{\rm GeV}^{2}) = 0.20^{+0.06}_{-0.07}$. First results of di-jet production at $\sqrt{s}=200\,$GeV by the STAR collaboration will allow a better constraint of the underlying event kinematics. Forward di-jet production at STAR beyond the current acceptance of $-1<\eta<+2$, in particular at $\sqrt{s}=500\,$GeV, provides access to low $x$ values at the level of $10^{-3}$ where current uncertainties of $\Delta g(x)$ remain very large. Recent STAR di-jet results constraining $\Delta g(x)$ will be briefly summarized followed by a detailed presentation of the physics case of forward di-jet production at $\sqrt{s}=500\,$GeV for $2.5<\eta<4$ requiring an upgrade of the STAR forward detection system, including a discussion of the kinematic coverage and projected uncertainties. [Preview Abstract] |
Thursday, October 9, 2014 9:15AM - 9:30AM |
DF.00002: Gluon Polarization and Inclusive Jet Measurements with STAR Carl Gagliardi The STAR Collaboration at RHIC has performed several measurements of the longitudinal double-spin asymmetry, $A_{LL}$, for mid-rapidity inclusive jet production in polarized $pp$ collisions at $\sqrt{s}=200$ GeV in order to determine the gluon polarization within the proton. The most recent study, using data that were recorded during 2009, profits from a 20-fold increase in event statistics compared to the previous measurements and improved analysis procedures that lead to reduced systematic uncertainties. The results provide evidence of positive gluon polarization in the Bjorken-$x$ region $x>0.05$. The data analysis and final results will be presented. In addition, a status report will be given on a similar analysis of data that were recorded by STAR at $\sqrt{s}=510$ GeV during 2012, and plans to extend the $\sqrt{s}=200$ GeV measurements at STAR during 2015 will be described. [Preview Abstract] |
Thursday, October 9, 2014 9:30AM - 9:45AM |
DF.00003: Transverse-spin gluon distribution function Kazuhiro Tanaka We define the novel polarized parton distribution function, the transverse-spin gluon distribution function $G_T(x)$, as the nucleon matrix element of the gauge-invariant bilocal light-cone operator in QCD, and discuss their properties. $G_T(x)$ is the gluonic analogue of the transverse-spin quark distribution function $g_T(x)$ that contributes to the transverse-spin structure function $g_2(x, Q^2)$ in the deep inelastic scattering of a longitudinally-polarized lepton off a transversely-polarized nucleon target. $g_T(x)$ and $G_T(x)$ are relevant to the ``angular momentum sum rule'' for the transversely-polarized nucleon, because their integral over $x$ gives, respectively, the quark and gluon spin contributions arising in the partonic decomposition of the transverse nucleon spin. We show that $G_T(x)$ can be expressed as the sum of the chromoelectric and chromomagnetic light-cone correlators; both of these are of twist-three and correspond to the helicity flip by one unit, similarly as the helicity-flip nature of $g_T(x)$. The relevance of the chromomagnetic correlator has not been noticed so far. We derive the moment sum rules for $G_T(x)$ and the corresponding operator product expansion, and demonstrate that $G_T(x)$ receives the three-gluon correlation effects. [Preview Abstract] |
Thursday, October 9, 2014 9:45AM - 10:00AM |
DF.00004: Transverse single-spin asymmetry of heavy-flavor production in $p+p$ collisions at $\sqrt{s}$ = 200 GeV Feng Wei Transverse single-spin asymmetries provide valuable information about the spin structure of the nucleon. At RHIC energies, heavy-flavor production is dominated by gluon-gluon fusion, and the subsequent decay into high $p_T$ electrons or muons is easily observed in a collider detector like PHENIX. The transverse single-spin asymmetry in heavy-flavor production originates from the initial state correlation between the internal transverse momentum of the parton and the transverse spin of the nucleon (similar with the known Sivers effect). The measurement of transverse single-spin asymmetry of single muons from heavy flavor decay at RHIC serves as a clean probe and would provide important information on the gluon Sivers function. In 2012, the PHENIX experiment collected 9.2 $pb^{-1}$ integrated luminosity in transversely polarized $p+p$ collisions at $\sqrt{s}$ = 200 GeV with a polarization of $60\%$. The signal-to-background ratio was improved by a factor of two compared to the previous RHIC 2006 and 2008 results in high transverse momentum region ($p_{T}>3$GeV). The status of the recent analysis of transverse single-spin asymmetries of single muons from heavy flavor decay at forward-rapidity will be presented. In addition, I would like to discuss possible improvement on this measur [Preview Abstract] |
Thursday, October 9, 2014 10:00AM - 10:15AM |
DF.00005: Measurement of Single Spin Asymmetries between $W$-Boson Yields in Polarized $pp$ Collisions at PHENIX Daniel Jumper The PHENIX experiment at RHIC has a goal of better constraining the quark and antiquark contributions to the spin of the proton. This is accomplished by measuring parity violating single helicity asymmetries between muon yields stemming from W boson decay at forward and backward rapidity, $1.2< |\eta| < 2.4$ at a center of mass energy of $\sqrt{s}=500 GeV$ with beams of longitudinally polarized proton colliding. Data toward this measurement has been accumulated over 3 years totaling about $310 pb^{-1}$ integrated luminosity over the full collision vertex range, with the largest contribution of $240 pb^{-1}$ taken in 2013 with an average polarization of 56\%. This talk will present the status of the ongoing analysis of the 2013 data. Discussion will focus on calculating and testing asymmetries after signal events are extracted from the data set. [Preview Abstract] |
Thursday, October 9, 2014 10:15AM - 10:30AM |
DF.00006: Efforts to Measure Drell-Yan Cross Section and Longitudinal? Double Spin Asymmetry in the PHENIX Experiment at RHIC Gonaduwage Perera Drell-Yan process in high energy polarized proton-proton collisions provides valuable and unique information concerning the proton spin structure. The longitudinal double spin asymmetry ($A_{LL}$) in the Drell-Yan production is sensitive to the sea-quark polarization and provides a clean access to the anti-quark helicity distributions without involving quark fragmentation functions. In the PHENIX experiment at RHIC, the Forward Silicon Vertex Detector (FVTX), together with barrel Silicon Vertex Tracker (VTX) and forward muon spectrometers, creates an opportunity for us to study the Drell-Yan process by detecting forward muon pairs ($1.2<|\eta|<2.4$). In this talk we present the status of the Drell-Yan measurement for the intermediate mass region (4 GeV $< M <$ 8 GeV) using the RHIC 2012 and 2013 data of proton-proton collisions at a center of mass energy of 510 GeV. [Preview Abstract] |
Thursday, October 9, 2014 10:30AM - 10:45AM |
DF.00007: fsPHENIX: Forward Jet and Drell-Yan Single Spin Asymmetries at RHIC Michael McCumber An opportunity exists to measure forward jet and Drell-Yan single spin asymmetries (SSA) at RHIC energies prior to the construction of an electron-ion collider detector. The PHENIX collaboration is currently pursuing a set of upgraded calorimeters built around the BaBar superconducting magnet under a proposal named sPHENIX. The open aperture of the sPHENIX design in the forward direction with the additional instrumentation of fsPHENIX would allow an exciting program of forward jet and Drell-Yan observables to be recorded in conjunction with the sPHENIX measurements. This talk will cover the proposed physics observables, the impact of the new measurements on the understanding of SSA, and details of the forward detector design. [Preview Abstract] |
Thursday, October 9, 2014 10:45AM - 11:00AM |
DF.00008: The E-906/SeaQuest experiment at Fermilab Kun Liu The Fermilab E906/SeaQuest experiment is successor of a series of fixed target Drell-Yan experiments designed to explore the quark and antiquark structure of nucleon and their nuclear modifications when nucleon is embedded in different nuclei. Using the 120 GeV proton beam extracted from Fermilab's main injector, E906/SeaQuest will measure the JPsi, Psi' and Drell-Yan productions in the dimuon mass from 4-9 GeV in p$+$p and p$+$A (A$=$D, C, Fe W) collisions over a wide kinematic range. With these new measurements, we will be able to extend the existing knowledge of down to up antiquark distributions to higher values of Bjorken-x and quantify the cold nuclear medium effects in partonic energy loss and quarkonia production. E906/SeaQuest experiment started its physics data taking in March 2014 to achieve high-precision measurements. This talk will include the status report of the ongoing experiment and preliminary physics results. [Preview Abstract] |
Thursday, October 9, 2014 11:00AM - 11:15AM |
DF.00009: New JAM global analysis of spin-dependent parton distributions W. Melnitchouk We present the results of a new global next-to-leading order analysis of spin-dependent parton distribution functions from the most recent world data on polarized deep-inelastic scattering (DIS) and $pp$ collisions, focusing in particular on the large-$x$ and low-$Q^2$ regions. By directly fitting DIS polarization asymmetries, we eliminate biases introduced by using polarized structure function data extracted under nonuniform assumptions for the unpolarized structure functions. For analysis of the large-$x$ data, we implement nuclear smearing corrections for deuterium and $^3$He nuclei, and systematically include target mass and higher twist corrections to the $g_1$ and $g_2$ structure functions at low $Q^2$. We also explore the effects of $Q^2$ and $W^2$ cuts in the data sets, and the potential impact of future data on the behavior of the spin-dependent parton distributions at intermediate and large $x$. [Preview Abstract] |
Thursday, October 9, 2014 11:15AM - 11:30AM |
DF.00010: New measurements of longitudinal spin asymmetries in pion electroproduction Peter Bosted We present new preliminary results for the longitudinal beam, target, and beam-target spin asymmetries in exclusive electro-production of charged and neutral pions. The measurements cover a wide range of four-momentum transfer squared (up to 4 GeV$^2$), and invariant final mass $W$ (up to 2.4 GeV). The results come from two experiments using the CLAS instrument in Hall B at Jefferson Lab. The first experiment used 1.6, 2.4, 4.2, and 5.7 GeV longitudinally polarized electrons with scattering angles ranging from 10 to 45 degrees. The second experiment used 6 GeV electrons scattering at angles form 16 to 45 degrees. Both experiments used a longitudinally polarized NH$_3$ target for $\pi^+$ and $\pi^0$ production from polarized protons, and an ND$_3$ target for $\pi^-$ production from polarized neutrons. The preliminary results indicate the possible presence of baryon resonance excitations at relatively high masses ($W>1.6$ GeV). The status of a simple empirical fit to the results will be presented. It is hoped that the new results will be used in global unitary isobar fits in order to improve the knowledge of baryon resonance structure. [Preview Abstract] |
(Author Not Attending)
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DF.00011: Spin Asymmetries of the Nucleon Experiment Whitney Armstrong The Spin Asymmetries of the Nucleon Experiment (SANE) measured the proton spin structure function $g_2$ in a range of Bjorken $x$, $0.3 < x < 0.8$, where extraction of the twist-3 matrix element, $d_2^p$, is most sensitive. The data were taken from $Q^2 = 2.5 GeV^2$ up to $6.5 GeV^2$. Using a polarized proton target and polarized electron beam, two double spin asymmetries, $A_\parallel$ and $A_\perp$, were measured at Jefferson Lab's Hall-C with the BETA (Big Electron Telescope Array) detector. BETA consists of a scintillator hodoscope, gas Cherenkov, lucite hodoscope and a large array of lead glass detectors. With a unique open geometry, a threshold gas Cherenkov detector allowed BETA to cleanly identify electrons for this inclusive experiment. In addition to presenting the latest results from SANE on the spin structure functions and virtual Compton scattering asymmetries, I will discuss the physics impact and extraction of the matrix element $d_2^p$. [Preview Abstract] |
Thursday, October 9, 2014 11:45AM - 12:00PM |
DF.00012: Extracting W Single Spin Asymmetry in Longitudinally Polarized pp Collisions at PHENIX forward arms Abraham Meles The parity-violating longitudinal single spin asymmetry $A_L$ in the production of $W$ bosons in $p+p$ collisions at $\sqrt{s}$ = 510 GeV is sensitive to the polarization of light quarks and anti-quarks in the proton. However, identifying the muons from the decay of the $W$ is challenging due to a great background of hadronic processes and other muon producing processes. In the forward and backward hemispheres of PHENIX at RHIC, the muon spectrometers have been recently upgraded in order to provide additional trigger and tracking information to suppress those backgrounds. One of those upgrades is the Forward Vertex (FVTX) detector, a silicon-strip tracker. In 2013, PHENIX collected approximately 240 pb$^{-1}$ of polarized $p+p$ collisions at $\sqrt{s}$ = 510 GeV with a beam polarization of 56$\%$. The ability of the FVTX to improve the $W$ signal will be reviewed, over view of the analysis techniques used to extract the signal from the data in RHIC 2013 run will be discussed. [Preview Abstract] |
Thursday, October 9, 2014 12:00PM - 12:15PM |
DF.00013: Medium modification of hadronic distributions in SIDIS Harut Avagyan Medium modifications of spin-orbit correlations in Semi-Inclusive Deep Inelastic Scattering (SIDIS) processes with polarized leptons and targets provide access to studies of partonic distributions in nucleons and nuclei. Measurements of multiplicities and different spin and azimuthal asymmetries can be used to extract the quark transverse momentum broadening $\Delta_{2F}$ and/or quark transport parameter $\hat q$ studied theoretically in the corresponding cases. We will present ongoing studies of medium modifications of SIDIS observables at Jefferson Lab, and proposed future measurement to study the transverse momentum broadening and some spin and azimuthal asymmetries in reactions using polarized lepton and polarized and unpolarized nuclei. Calculations have been preformed assuming factorized Gaussian dependence on intrinsic momenta for the TMD distributions and a Gaussian dilution from the fragmentation functions. [Preview Abstract] |
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