Measurement of transverse single-spin asymmetries of π0 and electromagnetic jets at forward rapidity in 200 and 500 GeV transversely polarized proton-proton collisions
Measurement of transverse single-spin asymmetries of π0 and electromagnetic jets at forward rapidity in 200 and 500 GeV transversely polarized proton-proton collisions
复制标题
在 200 和 500 GeV 横向极化质子-质子碰撞中测量 α0 和电磁射流的横向单自旋不对称性
DOI：
10.1103/physrevd.103.092009
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发表时间：
2021
影响因子：
5
通讯作者：
Aparin, A.
中科院分区：
文献类型：
--
作者：
Adam, J.;Adamczyk, L.;Adams, J. R.;Adkins, J. K.;Agakishiev, G.;Aggarwal, M. M.;Ahammed, Z.;Alekseev, I.;Anderson, D. M.;Aparin, A.
STAR Collaboration 报告了在赝快度区域 2.7 至 4.0 的横向偏振质子-质子碰撞中对 200 GeV 和 500 GeV 质心能量 () 的横向单自旋不对称性 (TSSA) 的测量。两种不同能量下的结果表明，费曼能量下的 TSSA 持续增加，并且与之前的测量相比，没有发现 19.4 GeV 到 500 GeV 之间的依赖关系。为了研究导致如此大 TSSA 的基础物理原理，我们对不同的拓扑进行了研究。附近的粒子往往不会具有比包容性更高的 TSSA。包容性电磁射流的 TSSA 对初始状态下的 Sivers 效应敏感，要小得多，但表现出与作为费曼函数的包容性不对称性相同的行为。为了研究终态效应，测量了内部电磁射流的柯林斯不对称性。分析了柯林斯不对称性对横向于射流推力轴的动量的依赖性及其对所携带的射流能量分数的依赖性。发现两种质心能量的不对称性都很小。所有测量结果都与基于 QCD 的横向动量相关部分子分布函数和碎片函数的理论计算进行了比较。发现了一些差异，这表明可能涉及新的机制。
The STAR Collaboration reports measurements of the transverse single-spin asymmetry (TSSA) of inclusiveat center-of-mass energies () of 200 GeV and 500 GeV in transversely polarized proton-proton collisions in the pseudo-rapidity region 2.7 to 4.0. The results at the two different energies show a continuous increase of the TSSA with Feynman-, and, when compared to previous measurements, no dependence onfrom 19.4 GeV to 500 GeV is found. To investigate the underlying physics leading to this large TSSA, different topologies have been studied.with no nearby particles tend to have a higher TSSA than inclusive. The TSSA for inclusive electromagnetic jets, sensitive to the Sivers effect in the initial state, is substantially smaller, but shows the same behavior as the inclusiveasymmetry as a function of Feynman-. To investigate final-state effects, the Collins asymmetry ofinside electromagnetic jets has been measured. The Collins asymmetry is analyzed for its dependence on themomentum transverse to the jet thrust axis and its dependence on the fraction of jet energy carried by the. The asymmetry was found to be small in each case for both center-of-mass energies. All the measurements are compared to QCD-based theoretical calculations for transverse-momentum-dependent parton distribution functions and fragmentation functions. Some discrepancies are found, which indicates new mechanisms might be involved.