Measurement of Longitudinal Spin Asymmetries for Weak Boson Production at STAR

TL;DR

This paper reports measurements of the parity-violating single-spin asymmetry in W boson production at STAR, providing new insights into the proton's sea-quark spin-flavor structure through polarized proton-proton collisions.

Contribution

It presents the first measurements of W boson asymmetries at STAR with large datasets, constraining the helicity-dependent PDFs of sea quarks and advancing understanding of proton spin structure.

Findings

Significant constraints on $ar{u}$ and $ar{d}$ helicity PDFs.

First results from 2013 dataset with higher luminosity.

Implications for the sea-quark spin-flavor structure of the proton.

Abstract

The production of $W^\pm$ bosons in longitudinally polarized proton-proton collisions at RHIC provides a direct probe for the spin-flavor structure of the proton through the parity-violating single-spin asymmetry, $A_L$. At STAR, the leptonic decay channel $W \to e\nu$ can be effectively measured with the electromagnetic calorimeters and time projection chamber. STAR has measured the $A_L(W)$ as a function of the decay electrons pseudorapidity from datasets taken in 2011 and 2012, which has provided significant constraints on the helicity-dependent PDFs of $\bar{u}$ and $\bar{d}$ quarks. In 2013 the STAR experiment collected an integrated luminosity of $\sim$250 pb$^{-1}$ at $\sqrt{s}=510$ GeV with an average beam polarization of $\sim$56\%, which is more than three times larger than the total integrated luminosity of previous years. The final results from the 2013 dataset for $W$-boson $A_L$ will be reported. Also, the impacts of STAR data on our knowledge of the sea-quark spin-flavor structure of the proton will be discussed.