Scaling of charged particle multiplicity in Pb–Pb collisions at SPS energies

Abreu, M. C.; Alessandro, B.; Alexa, C.; Arnaldi, R.; Atayan, M.; Baglin, C.; Baldit, A.; Bedjidian, M.; Beole', Stefania; Boldea, V.; Bordalo, P.; Borges, G.; Bussière, A.; Capelli, L.; Castanier, C.; Castor, J.; Chaurand, B.; Chevrot, I.; Cheynis, B.; Chiavassa, Emilio Luciano; Cicalò, C.; Claudino, T.; Comets, M. P.; Constans, N.; Constantinescu, S.; Cortese, P.; De Falco, A.; De Marco, N.; Dellacasa, G.; Devaux, A.; Dita, S.; Drapier, O.; Ducroux, L.; Espagnon, B.; Fargeix, J.; Force, P.; Gallio, Mauro; Gavrilov, Y. K.; Gerschel, C.; Giubellino, P.; Golubeva, M. B.; Gonin, M.; Grigorian, A. A.; Grigorian, S.; Grossiord, J. Y.; Guber, F. F.; Guichard, A.; Gulkanyan, H.; Hakobyan, R.; Haroutunian, R.; Idzik, M.; Jouan, D.; Karavitcheva, T. L.; Kluberg, L.; Kurepin, A. B.; Le Bornec, Y.; Lourenço, C.; Macciotta, P.; Mac Cormick, M.; Marzari Chiesa, A.; Masera, Massimo; Masoni, A.; Monteno, M.; Musso, A.; Petiau, P.; Piccotti, A.; Pizzi, J. R.; Prado da silva, W. L.; Prino, F.; Puddu, G.; Quintans, C.; Ramello, L.; Ramos, S.; Rato mendes, P.; Riccati, L.; Romana, A.; Santos, H.; Saturnini, P.; Scalas, E.; Scomparin, E.; Serci, S.; Shahoyan, R.; Sigaudo, F.; Silva, S.; Sitta, M.; Sonderegger, P.; Tarrago, X.; Topilskaya, N. S.; Usai, G. L.; Vercellin, Ermanno; Villatte, L.; Willis, N.

doi:10.1016/S0370-2693(02)01353-9

The charged particle multiplicity distribution dNch/dη has been measured by the NA50 experiment in Pb–Pb collisions at the CERN SPS. Measurements were done at incident energies of 40 and 158 GeV per nucleon over a broad impact parameter range. The multiplicity distributions are studied as a function of centrality using the number of participating nucleons (Npart), or the number of binary nucleon–nucleon collisions (Ncoll). Their values at midrapidity exhibit a power law scaling behaviour given by Npart1.00 and Ncoll0.75 at 158 GeV. Compatible results are found for the scaling behaviour at 40 GeV. The width of the dNch/dη distributions is larger at 158 than at 40 GeV/nucleon and decreases slightly with centrality at both energies. Our results are compared to similar studies performed by other experiments both at the CERN SPS and at RHIC.