Relativistic Nucleus-Nucleus Collisions without Hydrodynamics

TL;DR

This paper uses a nonequilibrium partition function within the maximum isotropization model to analyze experimental data on proton distributions, arguing that thermalization arises from parton degrees of freedom rather than nucleon collisions.

Contribution

It introduces a novel approach to analyze proton distributions without relying on hydrodynamics, emphasizing the role of parton thermalization in nucleus-nucleus collisions.

Findings

Nucleons are partitioned into ensembles based on collision number.

Large nucleon collision numbers do not lead to thermalization.

Thermalization is attributed to parton degrees of freedom.

Abstract

The partition function of nonequilibrium distribution which we recently obtained [arXiv:0802.0259] in the framework of the maximum isotropization model (MIM) is exploited to extract physical information from experimental data on the proton rapidity and transverse mass distributions. We propose to partition all interacting nucleons into ensembles in accordance with the number of collisions. We analyze experimental rapidity distribution and get the number of particles in every collision ensemble. We argue that even a large number of effective nucleon collisions cannot lead to thermalization of nucleon system; the thermal source which describes the proton distribution in central rapidity region arises as a result of fast thermalization of the parton degrees of freedom. The obtained number of nucleons which corresponds to the thermal contribution is treated as a ``nucleon power'' of the created quark-gluon plasma in a particular experiment.