Superposition models and the multiplicity fluctuations in heavy ion collisions

TL;DR

This paper evaluates superposition models based on the Glauber approach against experimental data on multiplicity distributions in heavy ion collisions, highlighting limitations in modeling centrality dependence.

Contribution

It compares different superposition models and analyzes their assumptions, revealing their inability to fully explain the centrality dependence of multiplicity fluctuations.

Findings

Models fail to accurately reproduce the centrality dependence of scaled dispersion.

Assumptions about participant distributions significantly affect model outcomes.

None of the tested models satisfactorily match the experimental data.

Abstract

A class of simple superposition models based on the Glauber picture of multiple collisions is compared with the data on the centrality dependence of the multiplicity distributions in a central rapidity bin. We show how the results depend on the specific assumptions concerning the distributions in the number of participants and their relations to the distributions of the number of produced hadrons in various phase space bins. None of the versions of the model describes satisfactorily the centrality dependence of the scaled dispersion.