Energy and centrality dependences of charged multiplicity density in relativistic nuclear collisions

Using a hadron and string cascade model, JPCIAE, the energy and centrality dependences of charged particle pseudorapidity density in relativistic nuclear collisions were studied. Within the framework of this model, both the relativistic p+p̄ experimental data and the PHOBOS and PHENIX Au+Au data at snn=130 GeV could be reproduced fairly well without retuning the model parameters. The predictions for full RHIC energy Au+Au collisions and for Pb+Pb collisions at the ALICE energy were also given. We computed participant nucleon distributions using different methods. It was found that the number of participant nucleons is not a well defined variable both experimentally and theoretically. Therefore, it may be inappropriate to use the charged particle pseudorapidity density per participant pair as a function of the number of participant nucleons for distinguishing various theoretical models.