System size and energy dependence of the mean transverse momentum fluctuations at the LHC

Abstract

Event-by-event fluctuations of the event-wise mean transverse momentum, , of charged particles produced in proton-proton (pp) collisions at root s = 5.02 TeV, Xe-Xe collisions at root s(NN) = 5.44 TeV, and Pb-Pb collisions at root s(NN) = 5.02 TeV are studied using the ALICE detector based on the integral correlator <>. The correlator strength is found to decrease monotonically with increasing produced charged-particle multiplicity measured at midrapidity in all three systems. In Xe-Xe and Pb-Pb collisions, the multiplicity dependence of the correlator deviates significantly from a simple power-law scaling as well as from the predictions of the HIJING and AMPT models. The observed deviation from power-law scaling is expected from transverse radial flow in semicentral to central Xe-Xe and Pb-Pb collisions. In pp collisions, the correlation strength is also studied by classifying the events based on the transverse spherocity, S-0, of the particle production at midrapidity, used as a proxy for the presence of a pronounced back-to-back jet topology. Low-spherocity (jetty) events feature a larger correlation strength than those with high spherocity (isotropic). The strength and multiplicity dependence of jetty and isotropic events are well reproduced by calculations with the PYTHIA 8 and EPOS LHC models.