Multiplicity fluctuations in relativistic nuclear collisions

TL;DR

This paper analyzes multiplicity fluctuations in relativistic nuclear collisions using statistical models, comparing different ensembles and experimental data to understand the underlying conservation laws affecting particle production.

Contribution

It provides an analytical approach to multiplicity distributions in the hadron-resonance gas model, including resonance decays and energy conservation, and compares predictions with experimental results.

Findings

Micro-canonical ensemble predictions match experimental fluctuations.

Fluctuations are narrower than Poisson distribution.

Results favor micro-canonical over canonical ensemble.

Abstract

Multiplicity distributions of hadrons produced in central nucleus-nucleus collisions are studied within the hadron-resonance gas model in the large volume limit. In the canonical ensemble conservation of three charges (baryon number, electric charge, and strangeness) is enforced. In addition, in the micro-canonical ensemble energy conservation is included. An analytical method is used to account for resonance decays. Multiplicity distributions and scaled variances for negatively charged hadrons are presented along the chemical freeze-out line of central Pb+Pb (Au+Au) collisions from SIS to LHC energies. Predictions obtained within different statistical ensembles are compared with preliminary NA49 experimental results on central Pb+Pb collisions in the SPS energy range. The measured fluctuations are significantly narrower than a Poisson reference distribution, and clearly favor expectations for the micro-canonical ensemble.