Bulletin of the American Physical Society
2008 Annual Meeting of the Division of Nuclear Physics
Volume 53, Number 12
Thursday–Sunday, October 23–26, 2008; Oakland, California
Session FG: Mini-Symposium: 3D View of the Nucleon and Its Spin III |
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Chair: Jim Sowinski, Indiana University Room: Jewett Ballroom C |
Saturday, October 25, 2008 8:30AM - 9:06AM |
FG.00001: Exploring 3D Distributions at HERMES: Latest Results on Sivers Asymmetries and DVCS Amplitudes Invited Speaker: The HERMES experiment is able to study two different types of ``3D'' observables that are related to different aspects of the Wigner distribution describing the partonic structure of the proton: transverse momentum dependent distributions (TMDs), such as the Sivers distribution, and Generalized Parton Distributions (GPDs). The former is accessed by measurement of single-spin asymmetries in semi-inclusive production of charged hadrons on a transversely polarized hydrogen target, whereas the latter are accessed, {\it e.g.,} via the measurement of single-spin beam asymmetries in hard exclusive photon production. In both cases, interference between amplitudes results in an azimuthal dependence. For the case of TMDs, final results for the Sivers asymmetries for identified pions and charged kaons will be presented as well as that of the charged pion yield difference. For the exclusive case, new preliminary measurements of the charge asymmetry, beam spin asymmetry and the charge/beam spin interference asymmetry from hard exclusive photon production will be presented. The results are obtained from a combined analysis of polarized $e^+$ and $e^-$ beam spin asymmetries, arising from the interference of the Bethe-Heitler process with the Deeply Virtual Compton Scattering (DVCS) process. [Preview Abstract] |
Saturday, October 25, 2008 9:06AM - 9:18AM |
FG.00002: Recent HERMES Results in Exclusive $\rho$ and $\phi$ Transverse Target Spin Asymmetries Stephen Gliske, Wolfgang Lorenzon Recent results from HERMES on transversely polarized hydrogen include exclusive $\pi^+$ Transverse Target Spin Asymmetries (TTSAs), as well as two moments of the L/T separated TTSA for exclusive $\phi$ production. Fourier components of TTSAs provide access to mostly unknown Generalized Parton Distributions (GPDs), which extend our description of the nucleon structure beyond the standard parton distributions. GPDs also allow a model-dependent extraction of the orbital angular moment of quarks in the nucleon. Both the $\pi^+$ and $\phi$ results will be presented, along with recent NLO GPD model predictions. In addition, a new unbinned method for unfolding acceptance and smearing effects will be discussed that provides increased capabilities for future measurements, e.g. $p_T$-weighted TTSA moments and increased precision. [Preview Abstract] |
Saturday, October 25, 2008 9:18AM - 9:30AM |
FG.00003: Measurement of the Eta Meson Transverse Single Spin Asymmetry A$_{N}$ at large Feynman X$_{F }$with the STAR Forward Pion Detector. Len Eun The large values of the Transverse Single Spin Asymmetry, A$_{N}$, seen in forward $\pi ^{0}$ production from polarized proton collisions have stimulated important questions and have been studied in many QCD based transverse spin models.~ We report the first measurement of A$_{N}$ for forward Eta meson production. Eta mesons of energy greater than 50 GeV (X$_{F}>$0.5) were observed in the STAR Forward Pion Detectors, along with $\pi ^{0}$ mesons, at pseudorapidity of 3.65 in $\surd $s = 200 GeV pp collisions. The $\pi ^{0}$ transverse asymmetry, which has already been reported in detail by the STAR collaboration, is compared to the Eta transverse asymmetry. The current analysis suggests that in this kinematic region, the Eta asymmetry is larger than the already large $\pi ^{0}$ asymmetry. [Preview Abstract] |
Saturday, October 25, 2008 9:30AM - 9:42AM |
FG.00004: Measuring the Sivers Effect via Back-to-Back Di-Hadron Correlations in the PHENIX at RHIC Feng Wei The measurement of transverse single spin asymmetries at high energies gives us an opportunity to probe the parton structure of transversely polarized nucleons. We present here an analysis of single transverse spin asymmetries using di-hadron correlations in transversely polarized p+p collisions as measured by PHENIX. The Sivers effect can lead small azimuthal asymmetry for back-to-back di-jets events. Because the PHENIX detectors at mid-rapidity cover only half of the azimuthal angle it is not possible to fully reconstruct jets. Instead, we use leading hadrons in our analysis and measure the sum of two leading back-to-back hadrons' transverse momentum as qt. We present yields of the projection of qt on the perpendicular direction to spin orientation which is the most sensitive to the small asymmetry due to Sivers effect. We will also present plans to do the same analysis using correlations of higher rapidity hadrons in the PHENIX muon arms with data collected in RHIC Run-8 which will extend the sensitivity of the asymmetry analysis to smaller parton momentum fraction. [Preview Abstract] |
Saturday, October 25, 2008 9:42AM - 9:54AM |
FG.00005: Transverse Single Spin Asymmetries in Heavy Flavor production in Polarized p+p Collisions at RHIC Han Liu The measurement of transverse single spin asymmetries ($A_N$) at high energies gives us an opportunity to probe the quark and gluon structure of transversely polarized nucleons. At RHIC energy, heavy flavor production is dominated by gluon-gluon fusion, so the Collins effect has minimum impact on $A_N$ as the gluon's transversity is zero. The measurement of $A_N$ in heavy flavor production is uniquely sensitive to the gluon Sivers distribution which is related to the orbital angular momentum of gluons inside the polarized protons, thus allowing the first ever probe of the gluon's angular momentum contribution to the proton's spin. The PHENIX experiment has collected 2.7 pb$^{-1}$ data in transversely polarized p+p collisions at $\sqrt{s}$=200GeV in 2006 run. Results for J/$\psi$ and open heavy flavor $A_N$ at forward rapidity will be presented. [Preview Abstract] |
Saturday, October 25, 2008 9:54AM - 10:06AM |
FG.00006: Single transverse-spin asymmetry for $D$-meson production in semi-inclusive deep inelastic scattering Zhongbo Kang, Jianwei Qiu We study the single-transverse spin asymmetry for open charm production in the semi-inclusive lepton-hadron deep inelastic scattering. We calculate the asymmetry in terms of the QCD collinear factorization approach for $D$ mesons at high enough $P_{h\perp}$, and find that the asymmetry is proportional to the twist-three tri-gluon correlation function in the proton. With a simple model for the tri-gluon correlation function, we estimate the asymmetry for both COMPASS and eRHIC kinematics, and discuss the possibilities of extracting the tri-gluon correlation function in these experiments. The SSA for open charm production in pp collision at RHIC is also discussed. [Preview Abstract] |
Saturday, October 25, 2008 10:06AM - 10:18AM |
FG.00007: Beam-Spin Asymmetry Measurements at CLAS M. Aghasyan The single-spin asymmetries (SSA) that have been reported recently in semi-inclusive DIS by HERMES, COMPASS and CLAS, have emerged as a powerful tool to access the orbital motion of partons. SSAs could arise in the fragmentation of polarized quarks (Collins effect) and from the interference of wavefunctions with different orbital angular momentum (Sivers effect). The two mechanisms produce different kinematical dependences and their contributions could be separated in measurements of different beam and target single-spin asymmetries. This contribution presents recent results from Jefferson Lab's CLAS detector on beam SSAs in single neutral pion electroproduction off an unpolarized hydrogen targets in the DIS regime ($Q^2>1GeV^2,W^2>4GeV^2$). The measured kinematical dependences are compared with model predictions. [Preview Abstract] |
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