Measurement of the parity-violating longitudinal single-spin asymmetry for W± boson production in polarized proton-proton collisions at √s=500GeV

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=500GeV 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. © 2011 American Physical Society.