Measurements of the W boson rapidity, helicity, double-differential cross sections, and charge asymmetry in pp collisions at √s= 13 TeV
CMS-SMP-18-012
At LO (QCD), we have ud → W+, ud → W-
And Ws with large rapidity produced with momentum in same direction as quark (not antiquark) … since PDF of proton favors quark with large x.
V–A coupling of W to fermions : spin of boson aligned with that of quark (left-handed), aligned opposite to momenta of both W and quark. (Rates of left- and right- polarizations become equal at low |yW|.)
NLO processes contribute longitudinal polarization, and relative fraction of polarizations depend on relative size of three main production processes
ud → W+g , ug → W+d , and gd → W+ u