Speaker
Description
Understanding the three-dimensional spin structure of the nucleon is one of the key questions in QCD. Among the transverse-momentum-dependent (TMD) PDFs, the TMD helicity distributions in particular are poorly constrained. Measurements of the longitudinal single-spin asymmetry ($A_L$) of $W^\pm$ bosons in polarized proton-proton collisions at RHIC provides a unique opportunity for accessing the flavor separated TMD helicity distributions of quarks and anti-quarks. The $W^\pm$ bosons can be identified through their leptonic decay channel ($W \rightarrow e + \nu$), and their full kinematics can be constructed by using a recoil-based method. In this talk, we will present the motivation, analysis procedures, and the status of the $A_L$ measurement as functions of $W^\pm$ transverse momentum and rapidity, based on the dataset collected by the STAR experiment in longitudinally polarized $p+p$ collisions at $\sqrt{s} = 510~\mathrm{GeV}$ in 2013.
