Measurement of Longitudinal Single-Spin Asymmetry for W$^\pm$ Production in Polarized Proton+Proton Collisions at STAR

TL;DR

This paper reports on measurements of the longitudinal single-spin asymmetry in W boson production in polarized proton-proton collisions at RHIC, providing insights into sea quark polarization and nucleon spin structure.

Contribution

It presents new preliminary results from 2013 data with higher luminosity, improving constraints on sea quark helicity distributions compared to previous STAR measurements.

Findings

Preliminary W boson $A_L$ results from 2013 data sample.

Enhanced dataset with 300 pb$^{-1}$ at $ oot s = 510$ GeV.

More than three times larger luminosity than previous measurements.

Abstract

The sea quark contribution to the nucleon spin is an important piece for a complete understanding of the nucleon spin structure. The production of W bosons in longitudinally polarized $p + p$ collisions at RHIC provides an unique probe for the sea quark polarization, through the parity-violating single-spin asymmetry, $A_L$. At the STAR experiment, W bosons through the leptonic decay channel $W \to e \nu $ can be effectively determined with the Electromagnetic Calorimeters and Time Projection Chamber at mid-rapidity. The previous STAR measurements of $A_L$ for W boson production from datasets taken in 2011 and 2012, have provided significant constraints on the helicity distribution functions of $\bar u$ and $\bar d$ quarks. In 2013 the STAR experiment collected $p+p$ data with an integrated luminosity of about 300 pb$^{-1}$ at $\sqrt s$ = 510 GeV with an average beam polarization of about $56\%$, which is more than three times larger than the total integrated luminosity of previous years. The preliminary results of W-boson $A_L$ from 2013 data sample will be presented.