Bulletin of the American Physical Society
2005 2nd Joint Meeting of the Nuclear Physics Divisions of the APS and The Physical Society of Japan
Sunday–Thursday, September 18–22, 2005; Maui, Hawaii
Session 2WC: Workshop 3B: Spin Structure Studies at RHIC |
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Sponsoring Units: DNP JPS Chair: Gerry Bunce, Brookhaven National Laboratory Room: Ritz-Carlton Hotel Salon 2 |
Sunday, September 18, 2005 2:00PM - 2:30PM |
2WC.00001: Physics of Transverse Spin Invited Speaker: In this talk, I present a theoretical overview on the novel features of the transverse spin phenomena in hard scatterings, in particular, single spin asymmetries (SSA). The large SSAs observed in pp collisions and semi-inclusive DIS reflects the chiral-symmetry breaking in QCD, and its understanding requires extention of the framework for hard processes: It requires formulating new concepts, such as intrinsic transverse momentum of quarks (``T-odd'' distribution and fragmentation functions), quark-gluon correlation in a hadron (twist-3 effects) and the transverse extention of hadrons (impact-parameter dependent parton distribution) etc. I discuss recent developments in our understanding on SSA in terms of these novel effects. [Preview Abstract] |
Sunday, September 18, 2005 2:30PM - 3:00PM |
2WC.00002: Exploration of Transverse Proton Structure with the PHENIX Experiment at RHIC Invited Speaker: Over the past 30 years large single spin asymmetries have been observed for inclusive hadron yields in polarized proton-proton collisions. The physics of the origin of these asymmetries remains unexplained and constitutes an important challenge to the understanding of the strong interaction: QCD itself predicts no sizeable asymmetries at hard scales. Novel mechanisms involving spin- or transverse momentum dependent effects in either the initial or final state were proposed. Recently, experimental information from semi inclusive deep inelastic scattering experiments at DESY and Jefferson Laboratory appear to suggest that the observed transverse spin effects originate from: (a) $k_T$-dependent quark distribution functions proposed by Sivers and (b) spin dependent quark distributions (transversity) in transversely polarized protons. The interpretation of the experimental results from semi inclusive deep inelastic scattering at soft scales is based on assuming the validity of a factorization ansatz in which higher order terms from the operator product expansion and perturbative QCD can be neglected. Experiments on transverse spin effects at RHIC are carried out at hard scales and an unambigous theoretical interpretation becomes available. This opens an exciting window to study transverse proton spin structure in polarized proton-proton collisions at RHIC. In this talk we present first results on $A_N$ for inclusive hadron production and discuss prospects for future measurements of Sivers and transversity distributions with the PHENIX detector. [Preview Abstract] |
Sunday, September 18, 2005 3:00PM - 3:30PM |
2WC.00003: Transverse Spin Results from STAR Invited Speaker: One of the main objectives of the Spin physics program at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory is to study transverse spin effects. Measurements of large Feynman x (xF) neutral pion production in polarized proton collisions at sqrt(s) = 200 GeV has been reported by STAR. Cross section measurements at eta = 3.3, 3.8, and 4.0 were found to be consistent with next-to-leading order perturbative QCD calculations. The analyzing power was found to be large and positive at xF$>$0.3, and consistent with phenomenological calculations based on the Collins effect, the Sivers effect, and initial-state higher twist contributions. This contribution will summarize these measurements, as well as give an outlook of future STAR semi-inclusive measurements to determine the Transversity and Sivers distribution functions. [Preview Abstract] |
Sunday, September 18, 2005 3:30PM - 4:00PM |
2WC.00004: Transverse Spin at HERMES Invited Speaker: |
Sunday, September 18, 2005 4:00PM - 4:30PM |
2WC.00005: Measurement of Spin Dependent Fragmentation Functions in e+e- Annihilation at Belle Invited Speaker: The so-called Collins fragmentation function connects the transverse quark spin with a measurable azimuthal dependence of the produced hadrons around the quark's momentum axis. Therefore, it can be used as a transverse spin analyzer in semi-inclusive DIS and proton-proton collisions. While in those measurements the Collins function appears convoluted with the so far unknown quark transversity distribution, it is directly accessible in e+e- collisions, where one measures a combination of a quark and an antiquark fragmentation function. We present measurements of azimuthal asymmetries for certain charge combinations of hadrons in which it is possible to minimize other systematic effects that could obscure the effect of spin-dependent fragmentation. [Preview Abstract] |
Sunday, September 18, 2005 4:30PM - 5:00PM |
2WC.00006: Lattice QCD and Spin Physics Invited Speaker: The computation of nucleon properties in lattice QCD is now progressing with steadily increasing accuracy. I review the current status of recent and ongoing lattice calculations relevant for spin physics. This talk also includes a brief introduction of lattice techniques intended for the non-expert. [Preview Abstract] |
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