在RHIC的STAR的低$\mathbf{x}$时限制$Δg(x)$的双射流生产的未来前景
Future prospects of di-jet production constraining $Δg(x)$ at low $\mathbf{x}$ at STAR at RHIC
摘要：
BNL RHIC高能自旋物理计划的主要目标之一是精确确定极化胶子分布函数$Δg(x)$。在RHIC的$\sqrt{s}=200\,$ GeV和$\sqrt{s}=500\,$ GeV的极化$\vec{p}+\vec{p}$碰撞为探测质子自旋结构提供了一种独特的方法。包容性测量，如包容性射流和强子的生产，迄今为止，在$\sqrt{s}=200\,$ GeV约束$Δg(x)$为$0.05<x<0.2$的各种结果的主要焦点。最近的一项全球分析首次提供了胶子极化$\int_{\tiny 0.05}^{\tiny 1}Δg (x)\, dx \,(Q^{2}=10\,{\rm GeV}^{2}) = 0.20^{+0.06}_{-0.07}$非零值的证据。由STAR合作在$\sqrt{s}=200\,$ GeV产生的第一批双喷流结果将允许对潜在事件运动学进行更好的约束。将目前的计划扩展到更小的$x$值是RHIC未来高能自旋物理计划的一个关键目标。从$-1<η<+2$到$+2.5<η<+4$，在STAR进行的超出当前接受范围的正向双喷流生产测量，特别是在$\sqrt{s}=500\,$ GeV进行的测量，提供了在$10^{-3}$水平上获得低$x$值的途径，其中$Δg(x)$的当前不确定性仍然非常大。这些测量最终将由未来的电子-离子对撞机设施补充，该设施将探测极化$\vec{e}+\vec{p}$碰撞中的$Δg(x)$。
英文摘要：
One of the main objectives of the high-energy spin physics program at RHIC at BNL is the precise determination of the polarized gluon distribution function, $Δg(x)$. Polarized $\vec{p}+\vec{p}$ collisions at $\sqrt{s}=200\,$GeV and at $\sqrt{s}=500\,$GeV at RHIC provide an unique way to probe the proton spin structure. Inclusive measurements, such as inclusive jet and hadron production, have so far been the prime focus of various results at $\sqrt{s}=200\,$GeV constraining $Δg(x)$ for $0.05<x<0.2$. A recent global analysis provides for the first time evidence of a non-zero value of the gluon polarization $\int_{\tiny 0.05}^{\tiny 1}Δg (x)\, dx \,(Q^{2}=10\,{\rm GeV}^{2}) = 0.20^{+0.06}_{-0.07}$. First results of di-jet production at $\sqrt{s}=200\,$GeV by the STAR collaboration will allow a better constraint of the underlying event kinematics. Extending the current program to smaller values of $x$ is a key goal for the future high-energy spin physics program at RHIC. Forward di-jet production measurements at STAR beyond the current acceptance from $-1<η<+2$ to $+2.5<η<+4$, in particular those carried out at $\sqrt{s}=500\,$GeV, provides access to low $x$ values at the level of $10^{-3}$ where current uncertainties of $Δg(x)$ remain very large. Those measurements will eventually be complemented by a future Electron-Ion Collider facility probing $Δg(x)$ in polarized $\vec{e}+\vec{p}$ collisions.
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