Fluctuations as a test of chemical non-equilibrium at the LHC

TL;DR

This paper investigates how large chemical potentials affect multiplicity fluctuations in bosons at the LHC, providing a method to distinguish between chemical equilibrium and non-equilibrium models through fluctuation analysis.

Contribution

It demonstrates that multiplicity fluctuations can serve as a test for chemical non-equilibrium in heavy-ion collisions, considering various experimental factors.

Findings

Large fluctuations indicate chemical non-equilibrium or pion condensation.

Normalized kurtosis of pion multiplicity increases significantly in non-equilibrium scenarios.

Results are applicable with current experimental data to identify non-equilibrium effects.

Abstract

It is shown that large chemical potential leads to the significant increase of multiplicity fluctuations for bosons, and makes the fluctuations infinite in the case of Bose-Einstein condensation. It allows to distinguish between the models that explain the anomalous proton to pion ratio and the low transverse momentum enhancement of pion spectra in Pb+Pb collisions at the LHC within chemical equilibrium or non-equilibrium models. The effects of resonance decays, finite size of the system, requirements to the event statistics, different momentum cuts, and limited detector acceptance are considered. The obtained results show the possibility to observe a substantial increase of the normalized kurtosis for positively or negatively charged pions in the case of non-equilibrium or partial pion condensation using currently measured data.