Charged-particle multiplicity and pseudorapidity distributions measured with the PHOBOS detector in Au+Au, Cu+Cu, d+Au, and p+p collisions at ultrarelativistic energies

Abstract

Pseudorapidity distributions of charged particles emitted in Au+Au, Cu+Cu, d+Au, and p+p collisions over a wide energy range have been measured using the PHOBOS detector at the BNL Relativistic Heavy-Ion Collider (RHIC). The centrality dependence of both the charged particle distributions and the multiplicity at midrapidity were measured. Pseudorapidity distributions of charged particles emitted with |η|<5.4 [|eta|<5.4], which account for between 95% and 99% of the total charged-particle emission associated with collision participants, are presented for different collision centralities. Both the midrapidity density dNch/dη [dN subscript ch / d eta] and the total charged-particle multiplicity Nch [N subscript ch] are found to factorize into a product of independent functions of collision energy, √sNN [square root of s subscript N N prime], and centrality given in terms of the number of nucleons participating in the collision, Npart [N subscript part]. The total charged particle multiplicity, observed in these experiments and those at lower energies, assumes a linear dependence of (lnsNN)2 [(1n s subscript NN) superscript 2] over the full range of collision energy of √sNN=2.7–200 [square root of S subscript NN + 2.7-200] GeV.