Measurement of the Parity-Violating Longitudinal Single-Spin Asymmetry for W± Boson Production in Polarized Proton-Proton Collisions at √s=500 GeV

Abstract

We report the first measurement of the parity-violating single-spin asymmetries for midrapidity decay positrons and electrons from W+ and W- boson production in longitudinally polarized proton-proton collisions at √s=500 GeV by the STAR experiment at RHIC. The measured asymmetries, ALW+=-0.27±0.10(stat.)±0.02(syst.)±0.03(norm.) and ALW-=0.14±0.19(stat.)±0.02(syst.)±0.01(norm.), are consistent with theory predictions, which are large and of opposite sign. These predictions are based on polarized quark and antiquark distribution functions constrained by polarized deep-inelastic scattering measurements.