Suppression of high transverse momenta hadrons in Pb+Pb collisions at LHC

TL;DR

This study uses a multiphase transport model to analyze hadron suppression in Pb+Pb collisions at LHC, revealing the importance of gluon shadowing and medium opacity in particle yield suppression.

Contribution

It introduces a constrained gluon shadowing parameter in the AMPT model to better match LHC hadron production data, highlighting medium properties at high energies.

Findings

Final-state scatterings reduce hadron yields at LHC.

Suppression patterns are consistent with RHIC at lower energies.

Reduced QCD coupling reproduces LHC suppression data.

Abstract

Hadron production and their suppression in Pb+Pb collisions at LHC at a center-of-mass energy of s_NN = 2.76 TeV are studied within a multiphase transport (AMPT) model whose initial conditions are obtained from the recently updated HIJING 2.0 model. The centrality dependence of charged hadron multiplicity dN_ch/deta at midrapidity was found quite sensitive to the largely uncertain gluon shadowing parameter s_g that determines the nuclear modification of the gluon distribution. We find final-state parton scatterings reduce considerably hadron yield at midrapidity and enforces a smaller gluon shadowing to be consistent with dN_ch/deta data at LHC. With such a constrained parton shadowing, charged hadron and neutral pion production over a wide transverse momenta range are investigated in AMPT. Relative to nucleon-nucleon collisions, the particle yield in central heavy ion collisions is suppressed due to parton energy loss. While the calculated magnitude and pattern of suppression is found consistent with that measured in Au+Au collisions at s_NN = 0.2 TeV at RHIC, at the LHC energy the suppression is overpredicted which may imply the medium formed at LHC is less opaque than expected from simple RHIC extrapolations. Reduction of the QCD coupling constant alpha_s by ~30% in the higher temperature plasma formed at LHC as compared to that at RHIC was found to reproduce the measured suppression at LHC.