Centrality Dependence of the Charged-Particle Multiplicity Density at Midrapidity in Pb-Pb Collisions at sNN=5.02TeV

Abstract

The pseudorapidity density of charged particles, dN ch /dη , at midrapidity in Pb-Pb collisions has been measured at a center-of-mass energy per nucleon pair of s NN − − − − √ =5.02 TeV . For the 5% most central collisions, we measure a value of 1943±54 . The rise in dN ch /dη as a function of s NN − − − − √ is steeper than that observed in proton-proton collisions and follows the trend established by measurements at lower energy. The increase of dN ch /dη as a function of the average number of participant nucleons, ⟨N part ⟩ , calculated in a Glauber model, is compared with the previous measurement at s NN − − − − √ =2.76 TeV . A constant factor of about 1.2 describes the increase in dN ch /dη from s NN − − − − √ =2.76 to 5.02 TeV for all centrality classes, within the measured range of 0%–80% centrality. The results are also compared to models based on different mechanisms for particle production in nuclear collisions.