Scaling of elliptic flow in heavy-ion collisions with the number of constituent quarks in a transport model

TL;DR

This study investigates the behavior of constituent quark scaling of elliptic flow in heavy-ion collisions at RHIC and LHC energies using the AMPT model, revealing energy-dependent scaling properties and their possible causes.

Contribution

It demonstrates that NCQ scaling holds at RHIC energies but breaks at LHC energies in Pb+Pb collisions, and explores the factors influencing this breaking.

Findings

NCQ scaling holds at top-RHIC energy with AMPT string melting.

NCQ scaling breaks in Pb+Pb collisions at LHC energy.

Scaling remains in small collision systems like Si+Si at LHC.

Abstract

We studied the number of constituent quark scaling (NCQ) behaviour of elliptic flow ($v_{2}$) under the framework of A Multi-Phase Transport model (AMPT) at both top-RHIC and LHC energies. The NCQ-scaling in $v_{2}$ holds at top-RHIC energy with AMPT string melting version, while it breaks in Pb+Pb collisions at LHC energy using the same framework. The breaking of NCQ-scaling at LHC energy has been studied by varying the magnitude of parton-parton scattering cross-section and lifetime of hadronic cascade as implemented in AMPT. We find that the breaking of NCQ scaling in Pb+Pb collisions at $\sqrt{s_{NN}}$ =2.76 TeV is independent of the magnitude of parton-parton cross-section and the later stage hadronic interactions. Further we observed that scaling holds in a small collision system like Si+Si at $\sqrt{s_{NN}}$ = 2.76 TeV. We discussed that the breaking of NCQ scaling is possibly due to high phase-space density of constituents quarks in Pb+Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV.