Pseudorapidity distributions of charged hadrons in xenon-xenon collisions at root S-NN=5.44 TeV

Measurements of the pseudorapidity distributions of charged hadronsproduced in xenon-xenon collisions at a nucleon-nucleon centre-of-massenergy of root S-NN = 5.44 TeV are presented. The measurements are basedon data collected by the CMS experiment at the LHC. The yield of primarycharged hadrons produced in xenon-xenon collisions in the pseudorapidityrange vertical bar eta vertical bar < 3.2 is determined using thesilicon pixel detector in the CMS tracking system. For the 5% mostcentral collisions, the chargedhadron pseudorapidity density in themidrapidity region vertical bar eta vertical bar < 0.5 is found to be 1187 +/- 36 (syst), with a negligible statistical uncertainty. Therapidity distribution of charged hadrons is also presented in the rangevertical bar y vertical bar < 3.2 and is found to be independent ofrapidity around y = 0. Existing Monte-Carlo event generators are unableto simultaneously describe both results. Comparisons of charged-hadronmultiplicities between xenon-xenon and lead-lead collisions at similarcollision energies show that particle production at midrapidity isstrongly dependent on the collision geometry in addition to the systemsize and collision energy. (C) 2019 The Author(s). Published by ElsevierB.V.