Centrality dependence of multiplicity fluctuations from a hydrodynamical approach

TL;DR

This study uses a hydrodynamical model to analyze multiplicity fluctuations in heavy-ion collisions, aiming to distinguish noncritical background effects from potential signals of the QCD critical point.

Contribution

It introduces a hydrodynamical approach focusing on noncritical factors affecting multiplicity fluctuations, enhancing the interpretation of experimental signals in heavy-ion collision studies.

Findings

Hydrodynamical expansion properties influence fluctuation patterns.

Finite volume and resonance decay effects are significant background factors.

Results help differentiate critical signals from noncritical background.

Abstract

As one of the possible signals for the whereabouts of the critical point on the QCD phase diagram, recently, the multiplicity fluctuations in heavy-ion collisions have aroused much attention. It is a crucial observable of the Beam Energy Scan program of the Relativistic Heavy Ion Collider. In this work, we investigate the centrality dependence of the multiplicity fluctuations regarding the recent measurements from STAR Collaboration. By employing a hydrodynamical approach, the present study is dedicated to the noncritical aspects of the phenomenon. To be specific, in addition to the thermal fluctuations, finite volume corrections, and resonance decay at the freeze-out surface, the model is focused on the properties of the hydrodynamic expansion of the system and the event-by-event initial fluctuations. It is understood that the real signal of the critical point can only be obtained after appropriately subtracting the background, the latter is investigated in the present work. Besides the experimental data, our results are also compared to those of the hadronic resonance gas, as well as transport models.