Time dependence of partition into spectators and participants in relativistic heavy-ion collisions

TL;DR

This paper models the time evolution of participant and spectator nucleons in relativistic heavy-ion collisions using a simplified Glauber-like approach based on the relativistic Boltzmann transport equation, revealing the formation time of the participant system.

Contribution

It introduces a natural energy-dependent temporal scale to analyze the formation process of participants in heavy-ion collisions, independent of collision energy except for nucleon-nucleon cross-section.

Findings

Participant system formation completes around 1.5 times the scale t_c.

Time evolution of angular momentum and vorticity indicates the emergence of rotation.

Model provides insights into the timing and dynamics of participant-spectator partitioning.

Abstract

The process of formation of the participant system in heavy-ion collisions is investigated in the framework of a simplified analytic Glauber-like model, which is based on the relativistic Boltzmann transport equation. The key point lies in the time-dependent partition of the nucleon system into two groups: nucleons, which did not take part in any interaction before a given time and nucleons, which already have interacted. In the framework of the proposed model we introduce a natural energy-dependent temporal scale $t_c$, which allows us to remove all dependencies of the model on the collision energy except for the energy dependence of the nucleon-nucleon cross-section. By investigating the time dependence of the total number of participants we conclude that the formation process of the participant system becomes complete at $t\simeq1.5 t_c$. Time dependencies of participant total angular momentum and vorticity are also considered and used to describe the emergence of rotation in the reaction plane.