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_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_𝐴𝐴) measured by the CMS Collaboration at the CERN LHC. Previous CMS measurements of 𝘙_𝐴𝐴 in oxygen-oxygen, xenon-xenon, and lead-lead collisions are recast with identical ⁢𝑝_T intervals and are complemented by the first measurement of the charged-particle 𝘙_𝐴𝐴 in neon-neon collisions at √[b]𝑠_𝑁𝑁 = 5.36 TeV. The neon-neon data correspond to an integrated luminosity of 0.76nb⁻¹. The 𝘙_𝐴𝐴 in all collision systems examined show similar qualitative trends as a function of p <inf>T</inf>, but have a magnitude which is ordered with the nucleon number 𝐴. The 𝘙_𝐴𝐴 feature a downward slope at low p _T, a local minimum at around 5–7 GeV, and an upward slope with increasing 𝑝_T. The 𝘙_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_T 9.6 GeV.