Revisiting the centrality definition and observable centrality dependence of relativistic heavy-ion collisions in PACIAE model

We improve the centrality definition in impact parameter in PACIAE model responding the fact reported by the ALICE, ATLAS, and CMS collaborations that the maximum impact parameter in heavy ion collisions should be extended to 20 fm. Meanwhile the PACIAE program is updated to a new version of PACIAE 2.2.2 with convenience of studying the elementary nuclear collisions, proton-nucleus collisions, and the nucleus-nucleus collisions in one unified program version. The new impact parameter definition together with the optical Glauber model calculated impact parameter bin, N_part, and N_coll in proton-nucleus and nucleus-nucleus collisions at relativistic energies are consistent with the improved MC-Glauber model ones within the error bar. The charged-particle pseudorapidity and the transverse momentum distributions in Pb-Pb collisions at $\sqrt{s_NN}$ = 5.02 TeV simulated by PACIAE 2.2.2 well reproduce the ALICE experimental data.

针对ALICE、ATLAS与CMS合作组报道的重离子碰撞最大碰撞参数（impact parameter）应拓展至20 fm的实验结果，我们改进了PACIAE模型（PACIAE model）中碰撞参数相关的中心度定义（centrality definition）。同时，我们将PACIAE程序升级至新版本PACIAE 2.2.2，该版本可在统一程序框架下便捷开展初等核碰撞、质子-核碰撞以及核-核碰撞的相关研究。在相对论性能量下的质子-核与核-核碰撞中，我们提出的新碰撞参数定义结合光学格劳伯模型（optical Glauber model）计算得到的碰撞参数区间、参与核子数（$N_{
m part}$）与碰撞核子数（$N_{
m coll}$），在误差范围内与改进后的蒙特卡洛格劳伯模型（MC-Glauber model）结果保持一致。利用PACIAE 2.2.2模拟得到的$sqrt{s_{
m NN}}$=5.02 TeV的Pb-Pb碰撞中带电粒子赝快度分布与横向动量分布，能够很好地复现ALICE合作组的实验测量数据。