Event-by-Event Particle Ratio Fluctuations at LHC Energies

Abstract

A Monte Carlo study of identified particle ratio fluctuations at LHC energies is carried out in the frame work of \hij model using the fluctuation variable $\nu_{dyn}$. The simulated events for Pb-Pb collisions at $\sqrt{s}_{NN}$ = 2.76 and 5.02 TeV and Xe-Xe collisions at $\sqrt{s}_{NN}$ = 5.44 TeV are analyzed. From this study, it is observed that the values of $[\pi,K]$, $[p,K]$ and $[\pi,p]$ follow the similar trends of energy dependence as observed in the most central collision data by NA49, STAR and ALICE experiments. It is also observed that $\nu_{dyn}$ for all the three combinations of particles for semi-central and central collisions, the model predicted values of $\nu_{dyn}[A,B]$ for Pb-Pb collisions at $\sqrt{s}_{NN}$ = 2.76 TeV agree fairly well with those observed in ALICE experiment. For peripheral collisions, however, the model predicted values of $\nu_{dyn}[\pi,K]$ are somewhat smaller, whereas for $[p,K]$ and $[\pi,p]$ it predicts larger values as compared to the corresponding experimental values. The possible reasons for the observed differences are discussed. The $\nu_{dyn}$ values scaled with charged particle density when plotted against $\langle$N$_{part}$$\rangle$, exhibit a flat behaviour, as expected from the independent particle emission sources. For $[p,K]$ and $[\pi,p]$ combinations, a departure from the flat trend is, however, observed in central collisions in the case of low p$_{T}$ window when effect of jet quenching or resonances are considered. Furthermore, the study of $\nu_{dyn}[A,B]$ dependence on particle density for various collision systems (including proton-proton collisions) suggests that at LHC energies $\nu_{dyn}$ values for a given particle pair is simply a function of charged particle density, irrespective of system size, beam energy and collision centrality.