Centrality Dependence of the Charged-Particle Multiplicity Density at Midrapidity in Pb-Pb Collisions at root(NN)-N-S=5.02 TeV

The pseudorapidity density of charged particles, dN(ch)=d eta, at midrapidity in Pb-Pb collisions has been measured at a center-of-mass energy per nucleon pair of root(NN)-N-s p = 5.02 TeV. For the 5% most central collisions, we measure a value of 1943 +/- 54. The rise in dNch= d. as a function of root(NN)-N-s p is steeper than that observed in proton-proton collisions and follows the trend established by measurements at lower energy. The increase of dNch= d. as a function of the average number of participant nucleons, hNparti, calculated in a Glauber model, is compared with the previous measurement at root(NN)-N-s p = 2.76 TeV. A constant factor of about 1.2 describes the increase in dNch= d. from root(NN)-N-s p = 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.