Probing Sea Quark and Gluon Polarization at STAR

TL;DR

This paper reports measurements of spin asymmetries in W boson and jet production at RHIC, providing new insights into the polarization of sea quarks and gluons within the proton.

Contribution

It presents the first experimental constraints on antiquark helicity distributions and evidence for non-zero gluon polarization at RHIC energies.

Findings

Constraints on antiquark helicity distributions from W boson asymmetries

Evidence for non-zero gluon polarization from jet asymmetries

Enhanced understanding of proton spin structure

Abstract

One of the primary goals of the spin program at the Relativistic Heavy Ion Collider (RHIC) is to determine the polarization of the sea quarks and gluons in the proton. The polarization of the sea quarks is probed through the production of $W^{-(+)}$ bosons via the annihilation of $\bar{u}+d\,(\bar{d}+u)$, at leading order. In this proceedings we report measurements of the single-spin asymmetry, $A_{L}$, for $W$ boson production at $\sqrt{s} = 510$ GeV, and the new constraints these results place on the antiquark helicity distributions. Recent results on the longitudinal double-spin asymmetry, $A_{LL}$, for inclusive and di-jet production at $\sqrt{s} = 200$ GeV are also presented. The inclusive jet results provide the first experimental indication of non-zero gluon polarization in the $x$ range probed at RHIC.