Medium information from anisotropic flow and jet quenching in relativistic heavy ion collisions

TL;DR

This study uses the AMPT model with updated initial conditions to analyze anisotropic flow and jet quenching in Pb+Pb collisions at the LHC, constraining medium properties and predicting flow coefficients.

Contribution

It introduces a constrained gluon shadowing parameter s_g based on LHC multiplicity data and demonstrates how adjusting the QCD coupling reproduces observed hadron suppression.

Findings

Final-state parton scatterings reduce hadron yield at midrapidity.

Model predictions for flow coefficients match RHIC data and provide LHC predictions.

Hadron suppression is overpredicted at LHC unless alpha_s is reduced by ~30%.

Abstract

Within a multiphase transport (AMPT) model, where the initial conditions are obtained from the recently updated HIJING 2.0 model, the recent anisotropic flow and suppression data for charged hadrons in Pb+Pb collisions at the LHC center of mass energy of 2.76 TeV are explored to constrain the properties of the partonic medium formed. In contrast to RHIC, the measured centrality dependence of charged hadron multiplicity dN_ch/deta at LHC provides severe constraint to the largely uncertain gluon shadowing parameter s_g. We find final-state parton scatterings reduce considerably hadron yield at midrapidity and enforces a smaller s_g to be consistent with dN_ch/deta data at LHC. With the parton shadowing so constrained, hadron production and flow over a wide transverse momenta range are investigated in AMPT. The model calculations for the elliptic and triangular flow are found to be in excellent agreement with the RHIC data, and predictions for the flow coefficients v_n(p_T, cent) at LHC are given. The magnitude and pattern of suppression of the hadrons in AMPT are found consistent with the measurements at RHIC. However, the suppression is distinctly overpredicted in Pb+Pb collisions at the LHC energy. Reduction of the QCD coupling constant alpha_s by ~30% in the higher temperature plasma formed at LHC reproduces the measured hadron suppression.