Evolution of the moments of multiplicity distributions

TL;DR

This paper investigates how the moments of multiplicity distributions evolve during the cooling of hot QCD matter, highlighting potential deviations from equilibrium that affect temperature measurements.

Contribution

It introduces a master equation approach to model the non-equilibrium evolution of multiplicity moments in heavy-ion collisions.

Findings

Moments deviate from equilibrium during hadronic phase cooling.

Different moments suggest different apparent temperatures if interpreted as equilibrium.

Non-equilibrium effects can bias phase transition parameter extraction.

Abstract

Measured moments of the multiplicity distribution for a given sort of particles are used in the literature for the determination of the phase transition parameters of hot QCD matter in ultrarelativistic heavy-ion collisions. We argue that the subsequent cooling in the hadronic phase, however, may drive the multiplicity distribution out of equilibrium. We use a master equation for the description of the evolution of the multiplicity distribution to demonstrate how the different moments depart away from their equilibrium values. If such moments were measured and interpreted as if they were equilibrated, one would obtain different apparent temperatures from different moments.