System-size dependence of charged-particle suppression in ultrarelativistic nucleus-nucleus collisions

TL;DR

This study systematically examines how charged-particle suppression varies with system size in ultrarelativistic nucleus-nucleus collisions, revealing that energy loss effects depend on the size of the colliding nuclei and are consistent with energy loss models at high transverse momentum.

Contribution

It provides the first measurement of charged-particle nuclear modification factors in neon-neon collisions and compares suppression across four different nuclear systems using a consistent methodology.

Findings

Suppression magnitude scales with nucleon number A.

Energy loss models match data for $p_T$ > 9.6 GeV.

All systems show similar qualitative $R_{AA}$ trends.

Abstract

High-energy partons lose energy while propagating through the hot, strongly interacting medium produced in ultrarelativistic nucleus-nucleus collisions, leading to a suppression of particle production at high transverse momentum ($p_\mathrm{T}$). The dependence of this energy loss on the size of the colliding nuclear system has yet to be firmly established experimentally. This Letter presents a systematic study of charged-particle suppression across four different nucleus-nucleus collision systems using nuclear modification factors ($R_\mathrm{AA}$) measured by the CMS Collaboration at the CERN LHC. Previous CMS measurements of $R_\mathrm{AA}$ in oxygen-oxygen, xenon-xenon, and lead-lead collisions are recast with identical $p_\mathrm{T}$ intervals and are complemented by the first measurement of the charged-particle $R_\mathrm{AA}$ in neon-neon collisions at $\sqrt{s_\mathrm{NN}}$ = 5.36 TeV. The neon-neon data correspond to an integrated luminosity of 0.76 nb$^{-1}$. The $R_\mathrm{AA}$ in all collision systems examined show similar qualitative trends, but have a magnitude which is ordered with the nucleon number A. The $R_\mathrm{AA}$ feature a downward slope at low $p_\mathrm{T}$, a local minimum at around 5$-$7 GeV, and an upward slope with increasing $p_\mathrm{T}$. The $R_\mathrm{AA}$ are also compared in terms of A$^{1/3}$, which is proportional to the nuclear radius. Models including only initial-state nuclear effects fail to reproduce the observed trends, whereas energy loss models reproduce the trends in the region $p_\mathrm{T}$ $\gt$ 9.6 GeV.