Measurement of $W^{\pm}$ boson single-spin asymmetry in transversely polarized pp collisions at STAR

TMeasurement of $W^{\pm}$ boson single-spin asymmetry in transversely polarized pp collisions at STARhe Sivers function $f_{1T}^{\perp}$ describes the correlation of parton transverse momentum with the transverse spin of the nucleon. There is evidence of a quark Sivers effect in semi-inclusive DIS (SIDIS) measurements. Important aspects of the Sivers effect include its process dependence and the color gauge invariance. As a consequence, the quark Sivers functions are of opposite sign in SIDIS and in Drell-Yan and this non-universality is a fundamental prediction from the gauge invariance of QCD. The experimental test of this sign change is one of the open questions in hadronic physics, and can provide a direct verification of QCD factorization. While luminosities required for a meaningful measurement of asymmetries in Drell-Yan production are challenging, $W^{\pm}$ production with a comparable sensitivity to the predicted sign change can be measured at the STAR experiment. At these large $Q^2$ the result can also provide essential input for the evolution effects of the Sivers function. We report on the first attempt to measure the transverse single spin asymmetry, $A_N$, of the $W^{\pm}$ boson at RHIC. The $W$ kinematics is reconstructed by employing MC-based corrections dictated