"Figure 1 JP2" of "Longitudinal double-spin asymmetry for inclusive jet and dijet production in polarized proton collisions at $\sqrt{s}=200$ GeV"

We report high-precision measurements of the longitudinal double-spin asymmetry, $A_{LL}$, for midrapidity inclusive jet and dijet production in polarized $pp$ collisions at a center-of-mass energy of $\sqrt{s}=200\,\mathrm{GeV}$. The new inclusive jet data are sensitive to the gluon helicity distribution, $\Delta g(x,Q^2)$, for gluon momentum fractions in the range from $x \simeq 0.05$ to $x \simeq 0.5$, while the new dijet data provide further constraints on the $x$ dependence of $\Delta g(x,Q^2)$. The results are in good agreement with previous measurements at $\sqrt{s}=200\,\mathrm{GeV}$ and with recent theoretical evaluations of prior world data. Our new results have better precision and thus strengthen the evidence that $\Delta g(x,Q^2)$ is positive for $x > 0.05$.

本工作报道了质心系能量$sqrt{s}=200,mathrm{GeV}$的极化质子-质子（$pp$）碰撞中，中等快度区间内单举喷注与双喷注产生过程的高精度纵向双自旋不对称度$A_{LL}$（longitudinal double-spin asymmetry）。此次测得的单举喷注数据对胶子动量份额$x$介于$0.05simeq xsimeq0.5$区间内的胶子螺旋度分布$Delta g(x,Q^2)$（gluon helicity distribution）具有敏感性，而双喷注数据则为$Delta g(x,Q^2)$随$x$的依赖关系提供了额外约束。本结果与此前在$sqrt{s}=200,mathrm{GeV}$能量下的测量结果，以及近期基于全球已有实验数据的理论评估结果均符合良好。本次新结果具备更高的测量精度，因此进一步强化了当$x>0.05$时$Delta g(x,Q^2)$为正的实验证据。