Scaling Properties of Multiplicity Fluctuations in the AMPT Model

TL;DR

This study analyzes multiplicity fluctuations in Pb-Pb collisions at 2.76 TeV using the AMPT model, revealing scaling behaviors and exponents that do not indicate a phase transition, thus providing insights into the system's dynamical properties.

Contribution

It applies factorial moment analysis to AMPT simulation data, demonstrating the method's effectiveness in probing phase transition signatures in heavy-ion collisions.

Findings

Scaling behavior in factorial moments at small bin sizes in some regions.

Scaling exponents are independent of transverse momentum binning.

No signature of phase transition is observed in the AMPT model.

Abstract

From the events generated from the MC code of a multi-phase transport (AMPT) model with string melting, the properties of multiplicity fluctuations of charged particles in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=\rm{~2.76 \,TeV}$ are studied. Normalized factorial moments, $F_{q}$, of spatial distributions of the particles have been determined in the framework of intermittency. Those moments are found in some kinematic regions to exhibit scaling behavior at small bin sizes, but not in most regions. However, in relating $F_{q}$ to $F_{2}$ scaling behavior is found in nearly all regions. The corresponding scaling exponents, $\nu$, determined in the low transverse momentum ($p_{\rm{T}}$) region $\le$ 1.0 GeV/c are observed to be independent of the $p_{\rm{T}}$ bin position and width. The value of $\nu$ is found to be larger than 1.304, which is the value that characterizes the Ginzburg-Landau type second order phase transition. Thus there is no known signature for phase transition in the AMPT model. This study demonstrates that, for the system under investigation, the method of analysis is effective in extracting features that are relevant to the question of whether the dynamical processes leading phase transition are there or not.