Comparison of the total charged particle multiplicity in high-energy heavy ion collisions with e+ e- and p p / anti-p p data

Abstract

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 ( / ) in central events scales with sqrt(s) in the same way as 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 / on the number of participating nucleons is also observed, reminiscent of ``wounded nucleon'' scaling ( proportional to ), but with the constant of proportionality set by the multiplicity measured in e+e- data rather than by pp/pbar-p data.