2015/07/28 by Gunarathne, Devika
#FOS: Physical sciences #High Energy Physics - Experiment (hep-ex) #Nuclear Experiment (nucl-ex)
paper · doi:10.48550/arxiv.1507.07835
W^± boson production in longitudinally polarized p+p collisions provides unique and clean access to the individual helicity polarizations of u / d quarks and anti-quarks. Due to the maximal violation of parity in the coupling, W bosons couple to left-handed quarks and right-handed anti-quarks and hence offer direct probes of their respective helicity distributions in the nucleon. These can be extracted from measured parity-violating longitudinal single-spin asymmetries, AL, for W+(-) boson production as a function of the decay lepton (positron) pseudo-rapidity η. The STAR experiment is well equipped to measure AL for W^± boson production for |η|<1. The published STAR AL results (2011 and 2012 data combined) have been used by several theoretical analyses suggesting a significant impact in constraining the helicity distributions of anti-u and anti-d quarks. In 2013 the STAR experiment has collected a large data sample of ∼250 pb-1 which is more than 3 times larger than the total integrated luminosity in 2012, at √(s)=510 GeV with an average beam polarization of ∼54%, comparable to run 2012. The status of the 2013 AL analysis will be discussed along with an overview of future plans.