论文标题
镜头机制遇到小$ x $物理：$ p^{\ uparrow}+p $和$ p $和$ p^{\ uparrow}+a $ collisision
Lensing Mechanism Meets Small-$x$ Physics: Single Transverse Spin Asymmetry in $p^{\uparrow}+p$ and $p^{\uparrow}+A$ Collisions
论文作者
论文摘要
我们计算了极化质子 - 蛋白质（$ p^{\ uparrow}+p $）和极化质子 - 核（$ p^{\ uparrow}+a $ a $）碰撞（$ a_n $）中的单个横向自旋不对称（STSA）。在夸克 - diquark模型中考虑了偏光质子，而其与非偏振目标的相互作用是使用小$ x $/饱和方法计算的，其中包括多个撤销和小$ x $演变。不对称性所需的相是由夸克和diquark之间的最终状态gluon交换引起的，这是布罗德斯基，黄和施密特的镜头机理中的标准配置。我们的计算将镜头机制与饱和框架中的小$ x $物理结合在一起。我们为生产夸克的不对称$ a_n $获得的表达具有以下属性：（i）不对称是由主导的弹性散射贡献和$ 1/n_c^2 $抑制的无弹性贡献（带有$ n_c $ $ n_c $ quark颜色的数量）而产生的； （ii）不对称的生长或振荡随产生的夸克的横向动量$ p_t $，直到动量达到饱和度量表$ q_s $，然后仅以$ 1/p_t $跌落，用于$ 1/p_t $； （iii）不对称的降低，随着原子数$ $ a $ a $的$ p_t $的增加或接近$ q_s $，但独立于$ a $ a $ $ a $ for $ p_t $显着高于$ q_s $。我们讨论了这些属性在定性上与Phanix Collaboration发布的$ A_N $的数据以及与Star Collaboration报告的$ A_N $的初步数据有关。
We calculate the single transverse spin asymmetry (STSA) in polarized proton-proton ($p^{\uparrow}+p$) and polarized proton-nucleus ($p^{\uparrow}+A$) collisions ($A_N$) generated by a partonic lensing mechanism. The polarized proton is considered in the quark-diquark model while its interaction with the unpolarized target is calculated using the small-$x$/saturation approach, which includes multiple rescatterings and small-$x$ evolution. The phase required for the asymmetry is caused by a final-state gluon exchange between the quark and diquark, as is standard in the lensing mechanism of Brodsky, Hwang and Schmidt. Our calculation combines the lensing mechanism with small-$x$ physics in the saturation framework. The expression we obtain for the asymmetry $A_N$ of the produced quarks has the following properties: (i) The asymmetry is generated by the dominant elastic scattering contribution and $1/N_c^2$ suppressed inelastic contribution (with $N_c$ the number of quark colors); (ii) The asymmetry grows or oscillates with the produced quark's transverse momentum $p_T$ until the momentum reaches the saturation scale $Q_s$, and then only falls off as $1/p_T$ for larger momenta; (iii) The asymmetry decreases with increasing atomic number $A$ of the target for $p_T$ below or near $Q_s$, but is independent of $A$ for $p_T$ significantly above $Q_s$. We discuss how these properties may be qualitatively consistent with the data on $A_N$ published by the PHENIX collaboration and with the preliminary data on $A_N$ reported by the STAR collaboration.
