Quenching of hadron spectra in XeXe and PbPb collisions at the LHC

TL;DR

This study analyzes the suppression of hadron spectra in XeXe and PbPb collisions at the LHC, showing a universal shape of the nuclear modification factor explained by an energy loss model, and finds a length-dependent energy loss consistent with theoretical expectations.

Contribution

It updates previous analyses by including recent CMS data and demonstrates a length dependence of parton energy loss in heavy-ion collisions.

Findings

The nuclear modification factor $R_{AA}$ has a universal shape well reproduced by a simple energy loss model.

Average parton energy loss in XeXe is about 20% less than in PbPb collisions.

The energy loss scales with the medium length as approximately $L^{1.3}$.

Abstract

The $p_\perp$ dependence of the nuclear modification factor $R_{\text{AA}}$ measured in PbPb collisions at the LHC exhibits a universal shape, which can be very well reproduced in a simple energy loss model based on the BDMPS medium-induced gluon spectrum. We update a former study by including in the analysis the recent CMS measurements on $J/\psi$ production in PbPb collisions at $\sqrt{s}=5.02$ TeV and charged hadron production in XeXe collisions at $\sqrt{s}=5.44$ TeV. The average parton energy loss extracted from minimum bias XeXe collisions is reduced typically by 20% compared to PbPb collisions, consistent with a length dependence $\langle\bar{\epsilon}\rangle \propto L^{1.3\pm0.5}$ with $L\propto A^{1/3}$.