Centrality Dependence of Multiplicity Fluctuations from a Hydrodynamical Approach

Abstract

As one of the possible signals for the whereabouts of the critical point on the QCD phase diagram, recently, the multiplicity fluctuations in heavy-ion collisions have aroused much attention. It is a crucial observable of the Beam Energy Scan program of the Relativistic Heavy Ion Collider. In this work, we investigate the centrality dependence of the multiplicity fluctuations regarding the recent measurements from STAR Collaboration. By employing a hydrodynamical approach, the present study is dedicated to the noncritical aspects of the phenomenon. To be specific, in addition to the thermal fluctuations, finite volume corrections, and resonance decay at the freezeout surface, the model is focused on the properties of the hydrodynamic expansion of the system and the event-by-event initial fluctuations. It is understood that the real signal of the critical point can only be obtained after appropriately subtracting the background, the latter is investigated in the present work. Besides the experimental data, our results are also compared to those of the hadronic resonance gas, as well as transport models.

Suppression of the Multiplicity Fluctuations in Particle Correlations

“…For a given centrality window, this is because that the multiplicity fluctuations are mainly of statistical origin. The latter can be attributed to the finite size of the centrality window or the finite multiplicity [37,61,126,127], which are largely irrelevant to the physics of interest. In this regard, the proposed method is inspired by the above observation and the analytic results encountered in [57].…”

Event-by-Event Particle Ratio Fluctuations at LHC Energies

“…This variable does not involve particle ratios directly but is related to σ dyn as σ 2 dyn ≈ ν dyn ½A, B [42,46]. ν dyn ½A, B is defined as [38,[43][44][45][46]…”

“…Particle ratio fluctuations in AA collisions have been addressed in a number of studies, e.g., NA49 experiment in Pb-Pb collisions at E lab = 20 -158 A GeV [40] [42], and several others [33,36,38]. At LHC energies, the particle ratio fluctuations have been investigated by the ALICE experiment at ffiffi s p NN = 2:76 TeV only [43][44][45]. It has been reported [43] that ν dyn for ½π, K and ½p, K combinations acquires positive values irrespective of the centrality class, whereas, for ½π, p combination, the variable changes sign from positive to negative toward more peripheral collisions, indicating the difference in the production mechanisms involved of these pairs.…”