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

Abstract

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, Npart, and Ncoll 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 sNN=5.02 TeV simulated by PACIAE 2.2.2 well reproduce the ALICE experimental data. New version program summaryProgram Title: PACIAE version 2.2.2CPC Library link to program files:https://doi.org/10.17632/w3g68dj4d9.4Licensing provisions: CC By 4.0Programming language: FORTRANJournal reference of previous version: Comput. Phys. Commun. 224 (2018) 417Does the new version supersede the previous version?: YesReasons for the new version: Recently ALICE, ATLAS and CMS collaborations reported that the maximum impact parameter bmax should be extended to 20 fm in the nuclear-nuclear collisions at relativistic energies. The impact parameter formula in PACIAE model has to be improved correspondingly. Meanwhile the PACIAE model is updated to PACIAE 2.2.2 with the convenience of studying the elementary nuclear collisions, proton-nucleus collisions, and the nucleus-nucleus collisions in one unified program version.Summary of revisions: The impact parameter b in PACIAE model is calculated by geometrical model ofb=c×bmax, where c refers to the centrality percentile and bmax is assumed to bebmax=RA+RB+f×d. In above equation RA (RB) is the radius of nuclear A (B), d=0.546 fm describes the tail of the nuclear density profile. Originally, the coefficient f is set to be equal to 2 and 1 for nucleus-nucleus and proton-nucleus collisions, respectively. Now they are assumed to be equal to 4 and 2, respectively. Meanwhile, the PACIAE model is updated to the version of PACIAE 2.2.2 with the convenience of studying the elementary nuclear collisions, proton-nucleus collisions, and the nucleus-nucleus collisions in a unified program version.Nature of problem: The ALICE, ATLAS and CMS collaborations reported that the maximum impact parameter, bmax, in heavy-ion collisions at relativistic energies should be extended to 20 fm where the interaction is really approaching to zero. The impact parameter centrality determination in heavy-ion collisions at relativistic energies has to be revised accordingly in the PACIAE model.Solution method: A new f coefficient sets in the impact parameter formula in PACIAE model, sequentially the new b bin corresponding to a given centrality percentile bin is introduced in the new version of PACIAE 2.2.2.