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 leadlead 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 root s(NN) = 5.36 TeV. The neon-neon data correspond to an integrated luminosity of 0.76 nb(-1). The R-AA in all collision systems examined show similar qualitative trends as a function of p(T), 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.