2017/02/09 by Gunarathne, Devika
#FOS: Physical sciences #Nuclear Experiment (nucl-ex)
paper · doi:10.48550/arxiv.1702.02927
We present the preliminary results of measurements of single spin asymmetries, AL for W^± boson production in longitudinally polarized p+p collisions at √(s)=510 GeV and measurements of cross section ratios, σW+ / σW-, for W+,W- boson production in p+p collisions at √(s) = 500 and 510 GeV. The asymmetry measurements are based on 246.2 pb-1 of data taken in the RHIC 2013 run and the cross section ratio measurements are based on 102 pb-1 of data taken during RHIC 2011 and 2012 runs by the STAR experiment. While the asymmetry results are shown as a function of the decay lepton pseudorapidity, ηe, the cross section results are shown as a function of both ηe and W boson rapidity, yW in the mid-rapidity region (|ηe|<1). At this kinematics, W^± single spin asymmetries provide a theoretically clean probe of the proton's polarized quark and antiquark distributions and the W cross section ratio provides sensitivity to unpolarized sea quark distributions at the scale of the W mass. The asymmetry results are consistent with recently published STAR AW^±L results based on the data collected during RHIC 2011 and 2012 runs which showed a preference for a sizable, positive up antiquark polarization in the range 0.05 < x < 0.2. The new preliminary results can be considered as the most precise results of AW^±L in the world to date, with uncertainties reduced by 40% in comparison to the published results.