Bulletin of the American Physical Society
APS April Meeting 2015
Volume 60, Number 4
Saturday–Tuesday, April 11–14, 2015; Baltimore, Maryland
Session C4: Hadron Structure I |
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Sponsoring Units: GHP DNP DPF Chair: Howie Haber, University of California, Santa Cruz Room: Holiday 3 |
Saturday, April 11, 2015 1:30PM - 1:42PM |
C4.00001: Initial State Helicity Correlation in Wide Angle Compton Scattering Donal Day, Dustin Keller, Jixie Zhang Whether pQCD can describe exclusive reactions at medium energies remains an area of active study. Real Compton scattering (RCS) has the potential to provide insight to this unsettled issue. A pQCD description of RCS requires the participation of three quarks and two hard gluons. However its predictions for the RCS cross sections disagree with data while calculations based on the handbag mechanism, involving a single quark coupled to the spectator through generalized parton distributions (GPDs), match the data well. The measured longitudinal polarization transfer parameter $K_{LL}$ is inconsistent with predictions of pQCD yet consistent with calculations of the handbag mechanism. Furthermore, Miller's approach, which includes quark and hadron helicity flip, contradicts pQCD where $K_{LL} = A_{LL}$, the initial state helicity correlation asymmetry, by finding that $K_{LL} \neq A_{LL}$. The first ever measurement of $A_{LL}$ (E12-14-006) has been approved to run in Jefferson Lab's Hall C and will be able to discriminate between the various models. E12-14-006 will utilize an untagged bremsstrahlung photon beam and the longitudinally polarized UVA/JLAB proton target. After a brief introduction to the physics, the experiment will be described and the expected results presented. [Preview Abstract] |
Saturday, April 11, 2015 1:42PM - 1:54PM |
C4.00002: Neutron structure with (un)polarized deuterons and forward spectator tagging at the Electron-Ion Collider Kijun Park, Charles Hyde, Christian Weiss, Douglas Higinbotham, Pawel Nadel-Turonski An Electron-Ion Collider (EIC) would enable novel measurements of neutron structure through deep-inelastic electron-deuteron scattering with coincidence tagging of the forward-moving spectator proton. The free neutron structure functions can be obtained by extrapolating the measured recoil momentum distributions to the on-shell point. Such measurements provide essential information for the flavor separation of the nucleon parton densities, the nucleon spin decomposition, and precision studies of QCD evolution in the flavor-singlet and nonsinglet sectors. The EMC effect in light nuclei can be elucidated by measuring the recoil momentum dependence of the nuclear modification. A Jefferson Lab LDRD project has supported a study of neutron structure measurements with spectator tagging at an EIC, with Monte Carlo simulation of the physical processes and the accelerator and detector requirements. We present results of a model-independent extraction of the free neutron structure function $F_2^n$, as well as the spin structure function $g_1^n$, through on-shell extrapolation in the spectator momentum. [Preview Abstract] |
Saturday, April 11, 2015 1:54PM - 2:06PM |
C4.00003: Flavor dependence of the EMC effect John Arrington The 6 GeV program at Jefferson Lab has provided significant new insight into the EMC effect - the modification of quark distributions in nuclei compared to nucleons. These data have overturned the traditional assumptions of a density-dependent rescaling of the quark distributions, showing instead a connection to the detailed nuclear structure of the target nucleus. These results, as well as QCD-based calculations, also suggest significant flavor dependence to the EMC effect. I will show estimates of the potential size of such flavor dependence and discuss plans to isolate the up- and down-quark contributions to the EMC effect, in particular through the use of parity-violating electron scattering from nuclei. [Preview Abstract] |
Saturday, April 11, 2015 2:06PM - 2:18PM |
C4.00004: Exploring Sea Quark EMC Effect and Anti-Shadowing Through Drell-Yan at SeaQuest / Fermilab E906 Bryan Dannowitz Fermilab E906/SeaQuest is a fixed-target experiment that uses the 120 GeV Main Injector proton beam. SeaQuest will extract sea anti-quark structure of the proton by detecting dimuon pairs created by Drell-Yan and measuring the cross-section ratios for LH2, LD2, C, Fe, and W targets. The European Muon Collaboration (EMC) discovered that the momentum distribution of quarks in a free nucleon becomes modified when bound within a nucleus. In studying the EMC Effect, an anti-shadowing feature has been observed in DIS and pion-induced DY measurements in the $0.1 < x_B < 0.25$ region, but Fermilab E772's results suggest there to be no anti-shadowing in the proton-induced Drell-Yan case. SeaQuest will study these nuclear effects over the anti-shadowing $(0.1 < x_B < 0.25)$ region with higher precision than E772, and it will extend the measurement range well into the largely-unmeasured EMC region, up to $x_B=0.45$. Preliminary results from the analysis of our 2014 data set will be presented. [Preview Abstract] |
Saturday, April 11, 2015 2:18PM - 2:30PM |
C4.00005: Studies of Proton-Induced Dimuons with 120 GeV Protons and the Iron Beam Dump at E906/SeaQuest Randall McClellan E906/SeaQuest is a fixed-target dimuon experiment currently taking data using Fermilab's 120 GeV proton beam and hydrogen, deuterium, carbon, iron, and tungsten targets. The primary goal of SeaQuest is the measurement of nucleon antiquark structure via the Drell-Yan process on liquid hydrogen and deuterium targets. However, the use of a solid iron beam dump provides the opportunity to make high-statistics measurements of dimuon decays from proton-iron interactions. Analysis of the beam dump data will yield insights into a number of interesting topics. Drell-Yan decay angle distributions can be used to check the behavior of the Boer-Mulders function and the violation of the Lam-Tung relation in proton induced Drell-Yan. The polar decay angle distribution of $J/\Psi$ events is relevant for testing models of $c\bar{c}$ productions and hadronization. The intrinsic charm content of the proton could potentially be measured through the $x_F$-dependence of $J/\Psi$ decays and double-charmonium decays. The $p_T$ distributions of Drell-Yan and $J/\Psi$ decays can be measured for 120-GeV protons. Preliminary results from various analyses on proton-iron interactions from the 2014 dataset will be presented. [Preview Abstract] |
Saturday, April 11, 2015 2:30PM - 2:42PM |
C4.00006: Measuring the ratio of $\bar{d}/\bar{u}$ in the proton as a function of x at SeaQuest Bryan Kerns SeaQuest is a running fixed target experiment using Fermilab's 120 GeV Main Injector proton beam to study the structure of the proton. The comparison of the Drell-Yan cross section ratio for liquid hydrogen and liquid deuterium targets enables an extraction of the ratio of $\bar{d}/\bar{u}$ at Bjorken x ranging from around 0.1 to 0.45, measuring this quantity at much higher x than previous experiments. SeaQuest has already taken some data in pursuit of this goal but the majority of the data taking lies ahead. A preliminary analysis of this data with the purpose of extracting $\bar{d}/\bar{u}$ will be presented. [Preview Abstract] |
Saturday, April 11, 2015 2:42PM - 2:54PM |
C4.00007: Low mass Drell-Yan production at the CERN LHC within the dipole formalism M.Beatriz Gay Ducati, Mirian Griep, Magno Machado The low mass Drell-Yan production in proton-proton collisions at the LHC in the color dipole formalism is presented. The DY differential cross sections at center of mass energy of 7TeV as a function of dilepton rapidity, transverse momentum and invariant mass are analyzed. Kinematical cuts related to the low mass DY production investigated by ATLAS and LHCb collaborations are properly taken into account. [Preview Abstract] |
Saturday, April 11, 2015 2:54PM - 3:06PM |
C4.00008: Recent results from PHENIX on double helicity asymmetry ($A^{\pi^{0}}_{LL}$) measurement at center of mass energy ($\sqrt{s}$) = 510 GeV Hari Guragain One of the major objectives of the Relativistic Heavy Ion Collider (RHIC) spin program at Brookhaven National Laboratory is the measurement of the gluon helicity contribution to the proton spin via measuring the double longitudinal spin asymmetry ($A_{LL}$) in various channels. In PHENIX (Pioneering High Energy Nuclear Interaction eXperiment) we measure $A_{LL}$ in $\pi^{0}$ production. The $\pi^{0}$ is reconstructed through its diphoton decay channel. The photons are detected by the PHENIX Electromagnetic calorimeter, which consists of lead glass and lead scintillator detectors and covers rapidity of $\left| \eta \right|$ $<$ 0.35 and azimuthal angle of $180\,^{\circ}$. We present a preliminary results for $A_{LL}$ in $\pi^{0}$ production from the data collected in the year 2013 at center of mass energy ($\sqrt{s}$) = 510 GeV. In year 2013, the total integrated luminosity was 150 $pb^{-1}$ which is almost ten times the total luminosity recorded in the year 2009 at $\sqrt{s}$ = 200 GeV. Due to increase in the center of mass energy and integrated luminosity, the new measurements can cover the Bjorken x range down to 0.01. We found a non-zero $A_{LL}$ result which is consistent with positive gluon polarization at the probed kinematics. [Preview Abstract] |
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