论文标题
比较向前$π^{0} $的横向单旋差异不对称，$ pp $，$ p \ rm {al} $和$ p \ rm {au} $ collisions c.m.能量$ \ sqrt {s _ {\ mathrm {nn}}}} = 200 $ gev
Comparison of transverse single-spin asymmetries for forward $π^{0}$ production in polarized $pp$, $p\rm{Al}$ and $p\rm{Au}$ collisions at nucleon pair c.m. energy $\sqrt{s_{\mathrm{NN}}}= 200$ GeV
论文作者
论文摘要
该星团的合作报告了横向单旋旋转不对称的测量，$ a_ {n} $，用于与质子（$ pp $）的偏光质子碰撞中产生的中性亲，带有铝核（$ p \ rm {al} $）和带有金nuclei（$ p \ p \ rm rm {au} au nuc的nucen nuce的铝（$ p \ rm {al} $），相对于横向极化质子束，在伪宽度区域$ 2.7 <η<3.8 $，在向前方向上观察到中性乳头。结果以$π^0 $ s的形式显示在窄Feynman X（$ X_F $）和横向动量（$ P_T $）垃圾箱中的Star FMS电磁量热仪中，涵盖了0.17 <x_f <x_f <0.81 $和$ 1.7 <p_ {t} <6.0 $ GEV/$ gev/$ c $。对于固定的$ x_f <0.47 $，发现不对称会随着横向动量的增加而上升。对于较大的$ x_f $，不对称或跌落为$ {p_t} $增加。参数比率$ r（a）\ equiv a_n（pa）/a_n（pp）= a^p $在运动范围内，比率$ r（a）$仅微弱地依赖于$ a $ a $ a $ a $ a $ a $ {\ langle} p {\ rangle} = -0.027 = -0.027 \ pm pm pm 0.005 \ pm pm pm pm 0.005 \ pm pm pm pm pm pm pm pm pm pm pm pm 0.005 \ pm pm pm 0.005 \ pm pm pm pm pm 0.005 \。低-$ p_t $区域，$ p_t <2.5 $ gev/$ c $之间没有观察到$ p $的显着差异，其中gluon饱和效果可能扮演角色，而高$ p_t $ region，$ p_t> 2.5 $ gev/$ gev/$ c $。进一步观察到，对于具有$ a_n $的$ a_n $的价值要大于$ p_t $隔离$π^0 $的事件，而对于未分离的$π^0 $伴随着附加类似喷射的片段的事件。对于隔离和非隔离$π^0 $事件而言，核依赖$ r（a）$相似。
The STAR Collaboration reports a measurement of the transverse single-spin asymmetries, $A_{N}$, for neutral pions produced in polarized proton collisions with protons ($pp$), with aluminum nuclei ($p\rm{Al}$) and with gold nuclei ($p\rm{Au}$) at a nucleon-nucleon center-of-mass energy of 200 GeV. Neutral pions are observed in the forward direction relative to the transversely polarized proton beam, in the pseudo-rapidity region $2.7<η<3.8$. Results are presented for $π^0$s observed in the STAR FMS electromagnetic calorimeter in narrow Feynman x ($x_F$) and transverse momentum ($p_T$) bins, spanning the range $0.17<x_F<0.81$ and $1.7<p_{T}<6.0$ GeV/$c$. For fixed $x_F<0.47$, the asymmetries are found to rise with increasing transverse momentum. For larger $x_F$, the asymmetry flattens or falls as ${p_T}$ increases. Parametrizing the ratio $r(A) \equiv A_N(pA)/A_N(pp)=A^P$ over the kinematic range, the ratio $r(A)$ is found to depend only weakly on $A$, with ${\langle}P{\rangle} = -0.027 \pm 0.005$. No significant difference in $P$ is observed between the low-$p_T$ region, $p_T<2.5$ GeV/$c$, where gluon saturation effects may play a role, and the high-$p_T$ region, $p_T>2.5$ GeV/$c$. It is further observed that the value of $A_N$ is significantly larger for events with a large-$p_T$ isolated $π^0$ than for events with a non-isolated $π^0$ accompanied by additional jet-like fragments. The nuclear dependence $r(A)$ is similar for isolated and non-isolated $π^0$ events.
