Comparison of the Total Charged-Particle Multiplicity in High-Energy Heavy Ion Collisions with e+e- and pp/pbar-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(sNN) = 19.6, 130 and 200 GeV. Above sqrt(sNN) ~ 20 GeV, the total multiplicity per participating nucleon pair (<Nch>/<Npart/2>) in central events scales with sqrt(s) in the same way as <Nch> 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 <Nch>/<Npart/2> on the number of participating nucleons is also observed, reminiscent of ``wounded nucleon'' scaling (<Nch> proportional to <Npart>), but with the constant of proportionality set by the multiplicity measured in e+e- data rather than by pp/pbar-p data.
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