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, $Δg(x)$, 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 $Δg(x)$ 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 $(|η|<1)$ and intermediate rapidity $(0.8<η<2)$ 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 $Δg(x)$ precision for $x\gtrsim 0.01$. Recent $π^0$ $A_{LL}$ measurements in the forward region $(2.65<η<3.9)$ at $\sqrt{s}=510$ GeV will also be presented, which probe $Δg(x)$ down to $x{\sim}10^{-3}$. Comparisons of these results to recent global analyses and extrapolations will be discussed.
Inclusive cross section and double helicity asymmetry for π^0 production in p+p collisions at sqrt(s)=200 GeV: Implications for the polarized gluon distribution in the proton
The gluon spin contribution to the proton spin from the double helicity asymmetry in inclusive pi^0 production in polarized p+p collisions at sqrt(s)=200 GeV
Two-gluon exchange contribution to elastic $γγ\to γγ$ scattering and production of two-photons in ultraperipheral ultrarelativistic heavy ion and proton-proton collisions
在高能近似下讨论了双胶子交换（形式上为三环）对弹性光子-光子散射的贡献。弹性$γγ\to γγ$振幅在所有螺旋度组态和有限夸克质量的冲击因子表示中给出。我们讨论的重要性，包括魅夸克，其中的贡献，由于干扰，可以大大提高截面。我们研究了软区对$γγ\to γγ$振幅的贡献，通过研究它对非微扰胶子质量的依赖。螺旋翻转的贡献被证明是远远小于螺旋守恒的。我们确定区域（S）的相空间中的两个胶子交换的贡献成为重要的成分相比，箱和非微扰的VDM-Regge机制在文献中考虑。讨论了$A A \to A A γγ$反应的后果。显示了几个微分分布。本文对双胶子交换效应进行了可行性研究。我们对$p p \to p p γγ$反应进行类似的分析。只有对$M_{γγ}$进行严格的削减，并对光子横动量进行窄窗处理，双胶子贡献才能与盒子贡献相媲美，但相应的截面相当小。
Helicity Dependent Distribution Functions of the Proton and $Λ$ and $Σ^0$ Baryons
East China Jiaotong University（华东交通大学）；Anhui Normal University（安徽师范大学）；Nanjing University（南京大学）；European Centre for Theoretical Studies in Nuclear Physics and Related Areas（核物理及相关领域欧洲理论研究中心）
