Comparison of the Total Charged-Particle Multiplicity in High-Energy Heavy Ion Collisions with e+e- and pp/pbar-p Data

The PHOBOS experiment at RHIC has measured the total multiplicity of primary charged particles as a function of collision centrality in Au+Au collisions at sqrt(s_NN) = 19.6, 130 and 200 GeV. Above sqrt(s_NN) ~ 20 GeV, the total multiplicity per participating nucleon pair (<N_ch>/<N_part/2>) in central events scales with sqrt(s) in the same way as <N_ch> in e+e- data. This is suggestive of a universal mechanism of particle production in strongly-interacting systems, controlled mainly by the amount of energy available for particle production (per participant pair for heavy ion collisions). The same effect has been observed in pp/pbar-p data after correcting for the energy taken away by leading particles. An approximate independence of <N_ch>/<N_part/2> on the number of participating nucleons is also observed, reminiscent of ``wounded nucleon'' scaling (<N_ch> proportional to <N_part>), but with the constant of proportionality set by the multiplicity measured in e+e- data rather than by pp/pbar-p data.