Bulletin of the American Physical Society
2008 APS April Meeting and HEDP/HEDLA Meeting
Volume 53, Number 5
Friday–Tuesday, April 11–15, 2008; St. Louis, Missouri
Session M3: New Results on the Polarized Glue in the Nucleon |
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Sponsoring Units: DNP Chair: Abhay Deshpande, Stony Brook University and RIKEN-BNL Research Center Room: Hyatt Regency St. Louis Riverfront (formerly Adam's Mark Hotel), St. Louis E |
Sunday, April 13, 2008 3:30PM - 4:06PM |
M3.00001: Review of results on polarized glue from fixed target DIS experiments Invited Speaker: The question of how the spin of the nucleon is made up from the spins and orbital angular momenta of its constituents is now in the front line since two decades. Due to the smallness of the contribution from the quark spins the focus is on the gluon polarization $\Delta g/g$. Our present knowledge of this quantity as obtained from deep-inelastic lepton--nucleon scattering experiments is mainly based on the recent results from COMPASS at CERN and HERMES at DESY. The main tools to study $\Delta g/g$ in DIS are scaling violations of the $g_1$ structure function and---in a more direct way---longitudinal double spin asymmetries in hadron production. For the latter the information on the gluon polarization enters the asymmetries via the photon--gluon fusion part of the cross-section. The relative contribution of this part must be determined using Monte Carlo simulations before the gluon polarisation can be determined. Results are shown from hadron pairs produced with $Q^2<1~\textrm{GeV}^2$ and $Q^2>1~\textrm{ GeV}^2$ as well as from single hadrons. In the case of charmed mesons basically only the photon--gluon fusion process contributes and thus the analysis is almost independent of MC simulations. Recent results from COMPASS obtained from $D$ meson asymmetries are presented and an outlook is given. All data indicate that the gluon polarization is small compared to earlier expectations, but still can make a major contribution to the nucleon spin. [Preview Abstract] |
Sunday, April 13, 2008 4:06PM - 4:42PM |
M3.00002: Review of recent results from RHIC on the polarized gluon distribution Invited Speaker: RHIC provides a unique laboratory to study the spin structure of the proton, using strongly interacting probes. Through remarkable control of the proton acceleration process, RHIC has achieved collisions with 55 to 60\% polarized proton beams, at root(s)=200 GeV, with high luminosity. Two experiments, PHENIX and STAR, feature measurements of inclusive production of jets, jet fragmentation products (with emphasis on pi$^0$), and direct photons, which probe the gluon polarization in the polarized protons. I will discuss how we connect the measurements to the underlying physics and the present (sensitive) and future constraints on the gluon spin contribution from RHIC. [Preview Abstract] |
Sunday, April 13, 2008 4:42PM - 5:18PM |
M3.00003: Beller Lectureship Talk: Theoretical status and advances in understanding the role of polarized gluons Invited Speaker: The contribution of quarks and gluons to the spin of the proton has been a puzzle since the first precise polarized measurements performed 20 years ago. In this talk, after summarizing the current knowledge on spin dependent parton distributions, I will present the results of a global QCD (NLO) analysis of all available polarized data. The inclusion of the recent proton-proton RHIC data, plus the DIS inclusive and semi- inclusive measurements allows attempting for a more precise determination of the gluon polarization. I will put special emphasis on the value obtained for the first moment of the gluonic distribution, the actual contribution of gluons to the spin of the nucleon. [Preview Abstract] |
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