Probing Gluon Helicity with Dijets from $\sqrt s$ = 510 GeV Polarized Proton Collisions at STAR

TL;DR

This paper reports on measuring the dijet longitudinal double-spin asymmetry in polarized proton collisions at 510 GeV to better understand the gluon contribution to proton spin, extending previous measurements to lower momentum fractions.

Contribution

It presents the first measurement of dijet $A_{LL}$ at 510 GeV, providing new constraints on the gluon helicity distribution at lower momentum fractions.

Findings

Preliminary dijet $A_{LL}$ results at 510 GeV are consistent with previous data.

The measurement extends sensitivity to gluon momentum fractions below 0.05.

Results contribute to understanding gluon polarization in the proton.

Abstract

The production of jets in polarized proton collisions at STAR is dominated by quark-gluon and gluon-gluon scattering processes. The dijet longitudinal double-spin asymmetry $(A_{LL})$ is sensitive to the helicity distributions and may be used to extract information about the gluon helicity contribution $\Delta{g(x,Q^2)}$ to the spin of the proton. Previous STAR jet measurements at $\sqrt s$ = 200 GeV show evidence of polarized gluons for gluon momentum fractions above 0.05. The measurement of dijet $A_{LL}$ at $\sqrt s$ = 510 GeV will extend the current constraints on $\Delta{g(x,Q^2)}$ to lower gluon momentum fractions and allow for the reconstruction of the partonic kinematics at leading order. These proceedings present preliminary results from the dijet $A_{LL}$ measurement from $\sim50 pb^{-1}$ of $\sim50 \%$ polarized proton data taken during the 2012 RHIC run.