Bulletin of the American Physical Society
2015 Fall Meeting of the APS Division of Nuclear Physics
Volume 60, Number 13
Wednesday–Saturday, October 28–31, 2015; Santa Fe, New Mexico
Session PH: Hadron Physics II |
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Chair: Tanja Horn, Catholic University of America Room: General Kearny |
Saturday, October 31, 2015 10:30AM - 10:42AM |
PH.00001: The Beam-Helicity Asymmetry for $\gamma p \rightarrow p K^{+} K^{-}$ Rafael Badui, Jason Bono, Lei Guo, Brian Raue The first-time measurement of the angular dependence of the beam-helicity asymmetry is shown for $\gamma p \rightarrow p K^{+} K^{-}$ and is compared to $\gamma p \rightarrow p \pi^{+} \pi^{-}$. The data obtained were from the CLAS g12 experiment at Jefferson Lab. The experiment utilized a beam of circularly-polarized photons with energies between 1.1 and 5.4 GeV incident on an unpolarized liquid hydrogen target. An unprecedented number of hadrons with strange quarks in photoproduction were observed in g12. The production mechanism for these hadrons is not well understood. The beam-helicity asymmetry is a polarization observable that provides information on the competing production mechanisms in the reaction. It is shown that the asymmetry is sensitive to several kinematic variables (Mandelstam $t, \sqrt{s}, M(K^{+} K^{-}), M(p K^{-})$) that are key observables in modeling the reaction's dynamics. Furthermore, the comparison of the beam-helicity asymmetries between the kaon and pion channels serves as a platform for the investigation of its flavor dependence. Its significance to understanding the production mechanisms of the intermediate resonances is also discussed. [Preview Abstract] |
Saturday, October 31, 2015 10:42AM - 10:54AM |
PH.00002: Constraining nucleon strangeness Timothy Hobbs, Mary Alberg, Gerald Miller Determining the nonperturbative $s\bar{s}$ content of the nucleon has attracted considerable interest and been the subject of numerous experimental searches. These measurements used a variety of reactions and place important limits on the vector form factors observed in parity-violating (PV) elastic scattering and the parton distributions determined by deep inelastic scattering (DIS). In spite of this progress, attempts to relate information obtained from elastic and DIS experiments have been sparse. To ameliorate this situation, we develop an interpolating model using light-front wave functions capable of computing both DIS and elastic observables. This framework is used to show that existing knowledge of DIS places significant restrictions on our wave functions. The result is that the predicted effects of nucleon strangeness on elastic observables are much smaller than those tolerated by direct fits to PV elastic scattering data alone. Using our model, we find $-0.024 \le \mu_s \le 0.035$, and $-0.137 \le \rho^D_s \le 0.081$ for the strange contributions to the nucleon magnetic moment and charge radius. The model we develop also independently predicts the nucleon's strange spin content and scalar density, and for these we find agreement with previous determinations. [Preview Abstract] |
Saturday, October 31, 2015 10:54AM - 11:06AM |
PH.00003: Strangeness asymmetry in the proton sea Mary Alberg Meson cloud models describe the proton sea in terms of fluctuations of the proton into meson-baryon pairs. The leading contributions to proton strangeness are from states which contain a kaon and a Lambda or Sigma hyperon. We use a Fock state expansion of the proton in terms of these states to determine the strangeness distributions of the proton in a convolution model, in which the fluctuations are represented by meson-baryon splitting functions, which determine the total strangeness of the proton. Strangeness asymmetry, the difference between momentum distributions of the s and sbar quarks in the proton, arises because the quarks are constituents of different hadrons. For the parton distributions of the s(sbar) quarks in the bare baryons(mesons) of the Fock states, we use light cone wave functions or our statistical model, which expands the bare hadrons in terms of quark-gluon states. We show that strangeness asymmetry depends strongly on the parton distributions used for the hadrons in the cloud. We compare our results to NuTeV and to global parton distributions. [Preview Abstract] |
Saturday, October 31, 2015 11:06AM - 11:18AM |
PH.00004: Deeply Virtual Compton Scattering off $^4$He Sylvester Joosten The European Muon Collaboration (EMC) observed the first signs of a modification of the partonic structure of the nucleon when present in a nuclear medium. The precise nature of these effects, as well as their underlying cause, is yet to be determined. The generalized parton distribution (GPD) framework provides a powerful tool to study the partonic structure of nucleons inside a nucleus. Hard exclusive leptoproduction of a real photon off a nucleon, deeply virtual Compton scattering (DVCS), is presently considered the cleanest experimental access to the GPDs, through the Compton form factors (CFFs). This is especially the case for scattering off the spin-zero helium nucleus, where only a single CFF contributes to the process. The real and imaginary parts of this CFF can be constrained through the beam-spin asymmetry (BSA). We will present the first measurements of the DVCS process off $^4$He using the CEBAF 6 GeV polarized electron beam and the CLAS detector at JLab. The CLAS detector was supplemented with an inner electromagnetic calorimeter for photons produced at small angles, as well as a radial time projection chamber (RTPC) to detect low-energy recoil nuclei. This setup allowed for a clean measurement of the BSA in both the coherent and incoherent channels. [Preview Abstract] |
Saturday, October 31, 2015 11:18AM - 11:30AM |
PH.00005: DCA Separated Open Heavy Flavor Measurements with Forward Single Muons in Proton-Proton Collisions Matthew Snowball The PHENIX Forward Silicon Vertex (FVTX) detector was installed and commissioned in 2012 and has taken several runs of good data. Observations of the displaced vertices of long lived heavy flavor hadrons give the ability to measure the fractions of open charm and beauty production versus various kinematic observables. From these measurements, a baseline for Distance of Closest Approach (DCA) separated $R_{AA}$ in the forward and backward rapidities can be obtained for single muons from open heavy flavor production. I will present the latest status on DCA separated open heavy flavor production and B to J/$\psi$ over J/$\psi$ ratios in proton-proton collisions at 200 GeV and 510 GeV as measured with the PHENIX detector. [Preview Abstract] |
Saturday, October 31, 2015 11:30AM - 11:42AM |
PH.00006: The Hall C SIDIS program towards understanding the transverse momentum dependence of valence quarks E.R. Kinney, R. Ent, T. Horn, H. Mkrtchyan, V. Tadevosyan Semi-inclusive deep inelastic scattering (SIDIS) is an important tool for unveiling the inner structure of the core of the atom, the nucleons and their basic constituents. Azimuthal spin asymmetries in polarized SIDIS are directly related to transverse momentum dependent parton distributions (TMDs) and fragmentation functions. The TMDs allow one to probe the 3D dynamical structure of partons inside the nucleon. Understanding the nature of the SIDIS process is essential for TMD studies, in particular at modest energies where deviations from the leading order factorized picture may be a significant. Precise maps of the meson cross sections and their ratios at low transverse momentum provide a stringent test of the theoretical foundation of SIDIS in terms of factorized parton distributions convoluted with fragmentation functions. The magnetic spectrometers in Hall C at Jefferson Lab are well suited for such precision measurements of fully L/T separated cross sections and their ratios. The addition of neutral particle detection enables additional opportunities. Recent results and upcoming experiments that will investigate the potential for TMD studies at the 12 GeV Jefferson Lab will be presented. [Preview Abstract] |
Saturday, October 31, 2015 11:42AM - 11:54AM |
PH.00007: Measurement of nuclear dependence of pT at Fermilab SuYin Wang The suppression of JPsi and Psi\textquoteright{} production in the heavy ion collisions relative to their production in the p+p collisions has been proposed as one of the important signatures of the quark-gluon plasma (QGP) formation. The nuclear dependence of JPsi and Psi\textquoteright{} production in the p+A collisions is essential to characterize the important baseline of the cold nuclear matter effect in both the initial and final states of collisions. In addition the final-state effect can be further differentiated in comparison with the nuclear dependence of Drell-Yan process. Fermilab E906/SeaQuest is a fixed-target experiment where the JPsi, Psi\textquoteright{} and Drell-Yan productions from 120-GeV proton beam colliding with protons and various nuclear targets are measured simultaneously via the dimuon channel. In this talk we will report the recent progress of nuclear dependence of these productions as a function of the transverse momentum of dimuon from E906/SeaQuest\textquoteright{}s measurements. The results will be compared to those of E866 experiment obtained at higher beam energies. [Preview Abstract] |
Saturday, October 31, 2015 11:54AM - 12:06PM |
PH.00008: Measurement of Quark Energy Loss at Fermilab E906/Seaquest P.-J. Lin The measurement of initial state parton energy loss serves as one of the important tools to provide a thorough understanding of the properties of the quark-gluon plasma (QGP). Quantifying the energy loss in cold nuclear matter will help to set the baseline for the energy-loss effect relative to energy loss in the QGP. With the Drell-Yan process, the energy loss of incoming quarks in cold nuclear matter can be ideally investigated since the final state interaction is expected to be minimal. E906/SeaQuest is an on-going fixed-target experiment using the 120 GeV proton beam from the main injector and has been collecting data from p+p, p+d, p+C, p+Fe, and p+W collisions. Within the E906 kinematic coverage of Drell-Yan production via the dimuon channel, the quark energy loss can be studied in the regime where other nuclear effects are expected to be small. In this talk, the current analysis progress and preliminary results of the quark energy loss study will be presented. [Preview Abstract] |
Saturday, October 31, 2015 12:06PM - 12:18PM |
PH.00009: Angular Distributions of Drell-Yan Dimuons at Fermilab E-906/SeaQuest Bryan Ramson Transverse momentum dependent (TMD) parton distribution functions (PDF), fragmentation functions, and their necessary theoretical framework provide a rich foundation from which to build a more descriptive, quantitative understanding of QCD and hadron structure. Fortuitously, TMD sensitive analyses of leptonic angular distributions have been a fixture in Drell-Yan experiments since the $\pi$+W CERN NA-10 of the 1980's, with particular focus on the violation of the Lam-Tung relation through a non-zero $\cos(2\phi)$ modulation in the angular distributions of the final-state leptons. The $\cos(2\phi)$ modulation is sensitive to the correlation between the motion and spin of transversely polarized (anti)quarks within their encompassing unpolarized hadron, described by the Boer-Mulders TMD PDF. In the mid-1990's, Fermilab E-866/NuSea investigated angular distributions of p+p and p+d Drell-Yan and found that the relative strength of the $\cos(2\phi)$ modulation, as compared to pion-induced Drell-Yan, is reduced. Fermilab E-906/SeaQuest provides an ideal laboratory in which to measure the $\cos(2\phi)$ modulation at a higher target $x_{Bj}$ than possible with E-866. Recent progress in the analysis of the angular distributions from SeaQuest Drell-Yan dimuons will be shown. [Preview Abstract] |
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