Bulletin of the American Physical Society
2013 Fall Meeting of the APS Division of Nuclear Physics
Volume 58, Number 13
Wednesday–Saturday, October 23–26, 2013; Newport News, Virginia
Session PC: Helicity Structure and Orbital Angular Momentum |
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Chair: Oscar Rondon, University of Virginia Room: Grand Ballroom III |
Saturday, October 26, 2013 10:30AM - 10:42AM |
PC.00001: Accessing sea quark's angular momentum through polarized target Drell-Yan single-spin asymmetry measurements Xiaodong Jiang A Letter-Of-Intent (P-1039) has been submitted to the Fermilab's Program Advisory Committee in May 2013, for a measurement of transversely polarized proton target (NH$_3$) single-spin asymmetry (SSA) in Drell-Yan reaction with a 120 GeV/c unpolarized proton beam using a similar setup as in the ongoing unpolarized target experiment (E906). The goal of this LOI is to clearly pin down the $\bar{u}$-quark Sivers distribution in the $x$ range of 0.1-0.3, where a large sea flavor asymmetry ($\bar{d}/\bar{u}$) has been observed. A non-vanishing quark Sivers distribution arises from the imaginary piece of amplitudes interference between quark angular momentum $L=0$, and $L \neq 0$ wave functions. Existing semi-inclusive DIS Sivers-type SSA data from HERMES, COMPASS and JLab-Hall A, while sensitive to valence quarks' Sivers distributions, do not provide much constrains on sea quarks' Sivers distributions. In the case that $\bar{u}$-quark carries zero angular momentum, one expects $\bar{u}$-quark's Sivers distribution to vanish, therefore observing a zero target SSA in Drell-Yan reaction in P-1039. [Preview Abstract] |
Saturday, October 26, 2013 10:42AM - 10:54AM |
PC.00002: Probing Sea Quark Polarization in the Proton With A$_L$ in the $W \rightarrow \mu$ Decay Channel Michael Beaumier The Relativistic Heavy Ion Collider (RHIC) is the only polarized hadron collider in the world - it offers us a unique opportunity to study nucleon spin structure. In this talk, I will present a study how we constrain the contribution of sea-quark polarization to the proton spin in the context of PHENIX's W-Physics program. This year, the W-Physics program at PHENIX has accumulated $240 pb^{-1}$ of longitudinally polarized p+p data at $\sqrt{s}$ = 510 GeV. I will describe the analysis of this data set, focusing on PHENIX's forward muon detectors at $ 1.2 < |\eta| < 2.2 $ , and discuss how we exploit the kinematics of the $W \rightarrow \mu$ decay in order to learn about sea-quark polarization with $A_L$. [Preview Abstract] |
Saturday, October 26, 2013 10:54AM - 11:06AM |
PC.00003: First JAM results on the determination of polarized parton distributions Pedro Jimenez-Delgado The Jefferson Lab Angular Momentum (JAM) collaboration is a new initiative aimed at the study of the angular-momentum-dependent structure of the nucleon. First results on the determination of spin-dependent parton distribution functions from world data on polarized deep-inelastic scattering will be presented and compared with previous determinations from other groups. Different aspects of global QCD analysis will be discussed, including effects due to the nuclear structure of deuteron and Helium targets, target-mass corrections and higher twist contributions to the g1 structure function as well as the g2 structure function. [Preview Abstract] |
Saturday, October 26, 2013 11:06AM - 11:18AM |
PC.00004: Extracting W Single Spin Asymmetry in Longitudinally Polarized $pp$ Collisions at PHENIX Daniel Jumper The PHENIX experiment at RHIC has a goal of better constraining the sea quark contribution to the spin of the proton. This is accomplished by measuring the parity violating single helicity asymmetry in muons decayed from W bosons at forward rapidity in $\sqrt{s}=500 GeV$ longitudinally polarized pp collisions. Data toward this measurement has been accumulated over the past 3 years totaling about $310 pb^{-1}$ integrated luminosity over the full collision vertex range. The largest contribution of $240 pb^{-1}$ has come from this years dedicated pp run and analysis of this data is currently underway. A significant challenge of this analysis, however, is the dominance of background events over $\mu$ from W decay signal events of interest. To address this issue, a maximum likelihood technique is employed to select events with an increased signal to background fraction and obtain their asymmetry. This talk will present details of this technique as well as the progress of the 2013 data analysis work. [Preview Abstract] |
Saturday, October 26, 2013 11:18AM - 11:30AM |
PC.00005: The 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 matrix element $d_2^p $ (an integral of $g_2$ weighted by $x^2$) is most sensitive. The data was taken from $Q^2$ equal to $2.5 GeV^2$ up to $6.5 GeV^2$. In this polarized electron scattering off a polarized hydrogen target experiment, two double spin asymmetries, $A_\parallel$ and $A_\perp$ were measured using 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. We will present the results of the measured asymmetries in addition to the extraction of the virtual Compton scattering asymmetries and spin structure functions. [Preview Abstract] |
Saturday, October 26, 2013 11:30AM - 11:42AM |
PC.00006: Pair-Symmetric Background of the Spin Asymmetries of the Nucleon Experiment Luwani Ndukum The Spin Asymmetries of the Nucleon Experiment (SANE) at the Thomas Jefferson Lab National Accelerator Facility measured inclusive double spin asymmetries by scattering longitudinally polarized electrons on a longitudinally and transversely polarized NH3 target. The measurements were done at momentum transfer of 2.5 $\le $ Q$^{2} \le $ 6.5 GeV$^{2}$ and Bjorken x of 0.3 $\le $ x $\le $ 0.8. Data were also taken at 0.2 \textless\ x \textless\ 0.3. Analysis of the pair-symmetric background used to extract asymmetries from this low x data will be discussed. [Preview Abstract] |
Saturday, October 26, 2013 11:42AM - 11:54AM |
PC.00007: Measurements of the Neutron Longitudinal Spin Asymmetry $A_1$ and Structure Function $g_1$ in the Valence Quark Region David Flay The current data for the nucleon-virtual photon longitudinal spin asymmetry $A_1$ on the proton and neutron have shown that the ratio of the polarized-to-unpolarized down-quark parton distribution functions, $\Delta d/d$, tends towards -1/2 at large $x$, in disagreement with the perturbative QCD prediction that $\Delta d/d$ approaches 1. As a part of experiment E06-014 in Hall A of Jefferson Lab, double-spin asymmetries were measured in the scattering of a longitudinally polarized electron beam of energies 4.73 and 5.89 GeV from a longitudinally and transversely polarized $^3$He target in the deep inelastic scattering region, allowing for the extraction of the neutron asymmetry $A_1^n$ and the longitudinal spin structure function $g_1^n$. We will discuss our analysis of the data and present results for $A_1$ and $g_1$ on both $^{3}$He and the neutron in the kinematic range of $0.2 < x < 0.65$ and $2 < Q^2 < 5$ GeV$^2$ for the scattered electrons. Our measurements of $A_1$ and $g_1$ are compared to the world data and a new value of the second moment of $g_1$, namely $a_2$, is evaluated and compared to a lattice QCD calculation. The quantity $a_2$ is needed to extract the twist-4 matrix element known as $f_2$. [Preview Abstract] |
Saturday, October 26, 2013 11:54AM - 12:06PM |
PC.00008: The Proton Spin-Dependent Structure Function, $g_2$, at Low $Q^2$ Ryan Zielinski The Jefferson Laboratory accelerator has been used to great effect in the study of the polarized structure of nucleons. Measurements of the spin-dependent structure functions have proven to be powerful tools in testing the validity of a number of effective theories of Quantum Chromodynamics. While the neutron spin structure functions, $g^n_{1,2}$, and longitudinal proton spin structure function, $g^p_1$, have been measured over a wide kinematic range, the second proton spin structure function, $g^p_2$, has not. In this talk I will present the E08-027 (g2p) experiment, which was an inclusive measurement of the proton's spin structure function, $g_{2}^{p}$, in the resonance region at Jefferson Lab's Hall A. This is the first measurement of $g_{2}^{p}$ covering 0.02 GeV$^{2}$ $<$ $Q^{2}$ $<$ 0.2 GeV$^{2}$. The experiment will allow us to test the Burkhardt-Cottingham Sum Rule at low Q$^2$ as well as extract the longitudinal-transverse generalized spin polarizability and compare it to predictions made by Chiral Perturbation Theory. In addition, the data will reduce the systematic uncertainty of calculations of the hyperfine splitting of hydrogen and extractions of the proton charge radius. An update on the status of the analysis, along with preliminary results, will be presented. [Preview Abstract] |
Saturday, October 26, 2013 12:06PM - 12:18PM |
PC.00009: A study of quark energy loss via Drell-Yan process in p+A collisions at Fermilab Kun Liu E906/SeaQuest is a new fixed-target experiment being operated at Fermi National Accelerator Laboratory. Using the 120 GeV proton beam from the main injector, E906/SeaQuest measures the Drell-Yan productions in the dimuon mass range 4-8 GeV in p+p and p+A collisions over a wide xF range, with A =D, C, Fe, W. These new measurements will help us to clarify the nature of parton energy loss mechanisms in nuclear medium. Parton energy loss in QGP is considered the dominant contributor to the observed jet quenching phenomena at RHIC and LHC. Since the center of mass energy of p+A collisions at E906/SeaQuest is low and out of the nuclear shadowing region, the measurements will provide the clean determination of parton energy loss effect in cold nuclear medium. E906/SeaQuest conducted a short commissioning run in 2012 and will resume data taking in September 2013. I will present the current status and the prospect of the parton energy loss measurements with the E906/SeaQuest experiment at Fermilab. [Preview Abstract] |
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