9-14 September 2018
University of Ferrara
Europe/Rome timezone
23RD INTERNATIONAL SPIN SYMPOSIUM

Overview of Gluon Helicity Measurements at STAR

12 Sep 2018, 17:20
20m
A10 (Polo degli Adelardi - Via Adelardi, 33)

A10

Polo degli Adelardi - Via Adelardi, 33

Parallel Sessions Nucleon Helicity Structure Nucleon helicity structure

Speaker

Christopher Dilks (Pennsylvania State University)

Description

The contribution to the spin of the proton from the gluon helicity is starting to come into focus: for gluons carrying a large fraction $x$ of the proton momentum, evidence of positive gluon polarization has been observed, via measurements of the longitudinal double-spin asymmetry $A_{LL}$ for inclusive jet and dijet production. $A_{LL}$ is sensitive to the polarized gluon distribution function, $\Delta g(x)$, and while it is positive at high $x$, it is not well constrained for $x<0.05$. Recent measurements at STAR of observables originating dominantly from quark-gluon and gluon-gluon subprocesses aim to improve the precision of $\Delta g(x)$ at high $x$, as well as for the first time provide insight into the low-$x$ contribution. $A_{LL}$ measurements of inclusive jets and dijets at midrapidity $(|\eta|<1)$ and intermediate rapidity $(0.8<\eta<2)$ at STAR at $\sqrt{s}=200$ and $510$ GeV will be shown, along with the statuses of ongoing analyses; these measurements will help improve the $\Delta g(x)$ precision for $x\gtrsim 0.01$. Recent $\pi^0$ $A_{LL}$ measurements in the forward region $(2.65<\eta<3.9)$ at $\sqrt{s}=510$ GeV will also be presented, which probe $\Delta g(x)$ down to $x \sim 10^{-3}$. Comparisons of these results to recent global analyses and extrapolations will be discussed.

Primary author

Christopher Dilks (Pennsylvania State University)

Presentation Materials