Phobos results on charged particle multiplicity and pseudorapidity distributions in Au+Au, Cu+Cu, d+Au, and p+p collisions at ultra-relativistic energies

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 |{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 dN{sub ch}/d{eta} and the total charged-particle multiplicity N{sub ch} are found to factorize into a product of independent functions of collision energy, {radical}(s{sub N{sub N}}), and centrality given in terms of the number of nucleons participating in the collision, N{sub part}. The total charged particle multiplicity, observed in these experiments and those at lower energies, assumes a linear dependence of (lns{sub N{sub N}}){sup 2} over the full range of collision energy of {radical}(s{sub N{sub N}})=2.7-200 GeV.