Charged-particle nuclear modification factors in XeXe collisions at $\sqrt{s_\mathrm{NN}}$ = 5.44 TeV

TL;DR

This study measures charged-particle yields in xenon-xenon collisions at 5.44 TeV, analyzing nuclear modification factors and comparing suppression patterns to lead-lead collisions, revealing differences in medium effects.

Contribution

First measurement of charged-particle nuclear modification factors in XeXe collisions at 5.44 TeV, providing new insights into system size dependence of parton energy loss.

Findings

$R_{AA}^*$ reaches 0.17 at 6-8 GeV, increasing to 0.7 at 100 GeV

XeXe shows less suppression than PbPb at similar centrality

Suppression in XeXe slightly greater than in PbPb for similar participant numbers

Abstract

The differential yields of charged particles having pseudorapidity within $|\eta|<$ 1 are measured using xenon-xenon (XeXe) collisions at $\sqrt{s_\mathrm{NN}}$ = 5.44 TeV. The data, corresponding to an integrated luminosity of 3.42 $\mu$b$^{-1}$, were collected in 2017 by the CMS experiment at the LHC. The yields are reported as functions of collision centrality and transverse momentum, $p_\mathrm{T}$, from 0.5 to 100 GeV. A previously reported $p_\mathrm{T}$ spectrum from proton-proton collisions at $\sqrt{s}$ = 5.02 TeV is used for comparison after correcting for the difference in center-of-mass energy. The nuclear modification factors using this reference, $R_\mathrm{AA}^*$, are constructed and compared to previous measurements and theoretical predictions. In head-on collisions, the $R_\mathrm{AA}^*$ has a value of 0.17 in the $p_\mathrm{T}$ range of 6-8 GeV, but increases to approximately 0.7 at 100 GeV. Above $\approx$ 6 GeV, the XeXe data show a notably smaller suppression than previous results for lead-lead (PbPb) collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV when compared at the same centrality (i.e., the same fraction of total cross section). However, the XeXe suppression is slightly greater than that for PbPb in events having a similar number of participating nucleons.