Charged-particle multiplicity fluctuations in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV

TL;DR

This paper reports on measurements of charged-particle multiplicity fluctuations in Pb-Pb collisions at 2.76 TeV, analyzing their dependence on pseudorapidity, transverse momentum, and collision centrality, and comparing results with models and lower-energy data.

Contribution

It provides the first detailed analysis of multiplicity fluctuations at LHC energies, exploring their dependence on collision parameters and comparing with theoretical models.

Findings

Fluctuations decrease from peripheral to central collisions.

Results align with certain Monte Carlo models.

Fluctuations relate to the system's isothermal compressibility.

Abstract

Measurements of event-by-event fluctuations of charged-particle multiplicities in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV using the ALICE detector at the CERN Large Hadron Collider (LHC) are presented in the pseudorapidity range $|\eta|<0.8$ and transverse momentum $0.2 < p_{\rm T} < 2.0$ GeV/$c$. The amplitude of the fluctuations is expressed in terms of the variance normalized by the mean of the multiplicity distribution. The $\eta$ and $p_{\rm T}$ dependences of the fluctuations and their evolution with respect to collision centrality are investigated. The multiplicity fluctuations tend to decrease from peripheral to central collisions. The results are compared to those obtained from HIJING and AMPT Monte Carlo event generators as well as to experimental data at lower collision energies. Additionally, the measured multiplicity fluctuations are discussed in the context of the isothermal compressibility of the high-density strongly-interacting system formed in central Pb-Pb collisions.