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

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 as a function of $p_{\mathrm{T}}$, 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 $p_{\mathrm{T}}$ $>$ 9.6 GeV.

Replaced with the published version. Added the journal reference and the DOI. All the figures and tables, including additional supplementary figures, can be found at http://cms-results.web.cern.ch/cms-results/public-results/publications/HIN-25-014 (CMS Public Pages)

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