PROCEEDINGS OF RIKEN BNL RESEARCH CENTER WORKSHOP: THEORY STUDIES FOR POLARIZED PP SCATTERING (VOLUME 53)

In the past two runs of RHIC, the first measurements with polarized proton beams have been performed. For many years to come, the RHIC spin program will offer exciting physics, exploring QCD and the nucleon in new ways. The aim of this small workshop was to attract several spin theorists to the center for about two weeks, in order to collaborate with both experimentalists and theorists at RBRC, and to initiate and/or complete studies of relevance to RHIC spin. A major focus of polarized-pp measurements at RHIC is on measuring the spin-dependent gluon density, Δg. A channel for accessing Δg is high-pT pion production. The unpolarized cross section for this reaction has been measured by PHENIX and was found in good agreement with a perturbative-QCD based (NLO) calculation. It was a remarkable and exciting coincidence that PHENIX presented also the first results for the spin asymmetry for (rvec p)(rvec p) → π0X during this workshop. This sparked a lot of additional activity and discussion. First steps toward the interpretation of the data were taken. Marco Stratmann and Barbara Jager (Regensburg University) presented recent work on the NLO calculation of the polarized cross section and the spin asymmetry, setting the stage for future full analysis of the data in terms of Δg. Applications to (rvec e)(rvec p) scattering, very relevant to eRHIC, were also worked out and published during this workshop. Stratmann also discussed the procedure of NLO calculations for the case of transverse polarization in pp scattering