Centrality fluctuations and decorrelations in heavy-ion collisions in a Glauber model
Centrality fluctuations and decorrelations in heavy-ion collisions in a Glauber model
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DOI：
10.1103/physrevresearch.2.023319
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发表时间：
2020-01
影响因子：
4.2
通讯作者：
J. Jia;Chunjian Zhang;Jun Xu
中科院分区：
文献类型：
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作者：
J. Jia;Chunjian Zhang;Jun Xu
重离子碰撞中产生的系统的中心性或初始态源V的数量是一个没有唯一定义的概念，并且受到很大的理论和实验不确定性的影响。我们认为，可以根据以伪快速度分隔的两个子事件 Na 与 Nb 之间的逐事件多重性相关性，在初始状态源与最终状态多重性之间建立更稳健的联系。这种相关性对两种主要类型的中心性波动 (CF) 敏感：(1) 每个源 p(n) 的粒子产生，它模糊了用于实验中心性的 V 和 Na 之间的关系，以及 (2) 两个子事件 Vb 和 Va 中的源之间的去相关性。CF 是根据 Vb 和 Nb 的累积量作为 Na 的函数进行分析的，即实验中心性是用 Na 定义的。我们发现，在中中心碰撞中，平均值 VbNa 和 NbNa 随 Na 线性增加，但在超中心碰撞中则趋于平缓。这种非线性行为对 Na 的中心性分辨率敏感。在存在中心性去相关的情况下，发现尺度方差 <(δVb)2>/Vb 和 <(δNb)2>/Nb 在中中心碰撞中随 Na 线性减小，而 p(n) 导致超中心区域再次急剧减小。 Vb 和 Nb 的高阶累积量表现出有趣但相当复杂的行为，值得进一步研究。我们的结果表明，可以利用二维多重相关性的累积量，特别是均值和方差，来约束粒子产生机制以及初始状态源的纵向波动。
The centrality or the number of initial-state sources V of the system produced in heavy ion collision is a concept that is not uniquely defined and subject to significant theoretical and experimental uncertainties. We argue that a more robust connection between the initial-state sources with final-state multiplicity could be established from the event-by-event multiplicity correlation between two subevents separated in pseudorapidity, Na vs Nb. This correlation is sensitive to two main types of centrality fluctuations (CF): (1) particle production for each source p(n) which smears the relation between V and Na used for experimental centrality and (2) decorrelations between the sources in the two subevents Vb and Va. The CF is analyzed in terms of cumulants of Vb and Nb as a function of Na, i.e., experimental centrality is defined with Na. We found that the mean values VbNa and NbNa increase linearly with Na in midcentral collisions but flatten out in ultracentral collisions. Such nonlinear behavior is sensitive to the centrality resolution of Na. In the presence of centrality decorrelations, the scaled variances 〈(δVb)2〉/Vb and 〈(δNb)2〉/Nb are found to decrease linearly with Na in midcentral collisions, while the p(n) leads to another sharp decrease in the ultracentral region. The higher-order cumulants of Vb and Nb show interesting but rather complex behaviors which deserve further studies. Our results suggest that one can use the cumulants of the two-dimensional multiplicity correlation, especially the mean and variance, to constrain the particle production mechanism as well as the longitudinal fluctuations of the initial-state sources.