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 framework of HIJING model using the fluctuation variable ${\nu }_{\text{dyn}}$ . The simulated events for Pb-Pb collisions at ${\sqrt{s}}_{NN}=2.76$ and 5.02 TeV and Xe-Xe collisions at ${\sqrt{s}}_{NN}=5.44\text{TeV}$ are analyzed. From this study, it is observed that the values of $\left[\pi ,K\right]$ , $\left[p,K\right]$ , and $\left[\pi ,p\right]$ 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 ${\nu }_{\text{dyn}}$ for all the three combinations of particles for semicentral and central collisions, the model predicted values of ${\nu }_{\text{dyn}}\left[A,B\right]$ for Pb-Pb collisions at ${\sqrt{s}}_{NN}=2.76\text{TeV}$ agree fairly well with those observed in the ALICE experiment. For peripheral collisions, however, the model predicted values of ${\nu }_{\text{dyn}}\left[\pi ,K\right]$ are somewhat smaller, whereas for $\left[p,K\right]$ and $\left[\pi ,p\right]$ it predicts larger values as compared to the corresponding experimental values. The possible reasons for the observed differences are discussed. The ${\nu }_{\text{dyn}}$ values scaled with charged particle density when plotted against $〈N_{\text{part}}〉$ exhibit a flat behaviour, as expected from the independent particle emission sources. For $\left[p,K\right]$ and $\left[\pi ,p\right]$ combinations, a departure from the flat trend is, however, observed in central collisions in the case of low $p_T$ window when the effect of jet quenching or resonances is considered. Furthermore, the study of ${\nu }_{\text{dyn}}\left[A,B\right]$ dependence on particle density for various collision systems (including proton-proton collisions) suggests that at LHC energies ${\nu }_{\text{dyn}}$ values for a given particle pair are simply a function of charged particle density, irrespective of system size, beam energy, and collision centrality.