Impact of Recent RHIC Data on Helicity-Dependent Parton Distribution Functions
Abstract
I study the impact of recent measurements performed at the Relativistic Heavy Ion Collider on the determination of helicity-dependent parton distribution functions of the proton. Specifically, I consider: preliminary data on longitudinally single-spin asymmetries for W-boson production recorded by the STAR experiment during the 2013 run at a center-of-mass energy s=510 GeV; data on longitudinally double-spin asymmetries for di-jet production recorded by the STAR experiment during the 2009 run at s=200 GeV; and data on longitudinally double-spin asymmetries for neutral pion production recorded by the PHENIX experiment during a series of runs between 2006 and 2013 at s=200 GeV and s=510 GeV. The impact of the new data is studied by applying Bayesian reweighting to NNPDFpol1.1, the most recent global analysis of helicity-dependent parton distribution functions based on the NNDPF methodology. In comparsion to NNDPFpol1.1, a slightly more positive polarized gluon PDF, extended to somewhat smaller values of momentum fractions with narrower uncertainties, as well as a slightly more marked and more precise asymmetry between polarized up and down sea quarks are found in this study.