Experimental results on charge fluctuations in heavy-ion collisions

TL;DR

This paper reports experimental measurements of charge fluctuations in heavy-ion collisions across various energies, aiming to identify signals of the QCD phase transition and critical point, and compares results with theoretical models.

Contribution

It provides new experimental data on charge fluctuation measures and higher moments, and explores their implications for the QCD phase diagram and freeze-out parameters.

Findings

Charge fluctuations increase from central to peripheral collisions.

Monotonic decrease of fluctuation measure with collision energy suggests QGP origin.

No significant non-monotonic behavior observed in higher moments of net-charge distributions.

Abstract

We present a subset of experimental results on charge fluctuation from the heavy-ion collisions to search for phase transition and location of critical point in the QCD phase diagram. Measurements from the heavy-ion experiments at the SPS and RHIC energies observe that total charge fluctuations increase from central to peripheral collisions. The net-charge fluctuations in terms of dynamical fluctuation measure $\nu_{(+-,dyn)}$ are studied as a function of collision energy (\sqsn) and centrality of the collisions. The product of $\nu_{(+-,dyn)}$ and $\langle N_{ch} \rangle$ shows a monotonic decrease with collision energies, which indicates that at LHC energy the fluctuations have their origin in the QGP phase. The fluctuations in terms of higher moments of net-proton, net-electric charge and net-kaon have been measured for various \sqsn. Deviations are observed in both $S\sigma$ and $\kappa\sigma^2$ for net-proton multiplicity distributions from the Skellam and hadron resonance gas model for \sqsn $<$ 39 GeV. Higher moment results of the net-electric charge and net-kaon do not observe any significant non-monotonic behavior as a function of collision energy. We also discuss the extraction of the freeze-out parameters using particle ratios and experimentally measured higher moments of net-charge fluctuations. The extracted freeze-out parameters from experimentally measured moments and lattice calculations, are found to be in agreement with the results obtained from the fit of particle ratios to the thermal model calculations.