Multiplicity fluctuations in proton–proton and nucleus–nucleus collisions

Abstract We study the scaled variances of multiplicity fluctuations in nucleus–nucleus collisions at SPS and RHIC energies within the HSD transport model. The HSD results are compared with proton–proton data and with predictions of the hadron-resonance gas statistical model. We find that the HSD scaled variances ω i for negatively, positively, and all charged hadrons in central nucleus–nucleus collisions remain close to the ω i values in proton–proton collisions and increase with collision energy as the corresponding multiplicities per participating nucleon. The statistical model predicts very different behavior of ω i . However, a comparison with preliminary NA49 data for the most central Pb + Pb collisions at SPS energies does not permit to distinguish the HSD and statistical model results. New measurements of the multiplicity fluctuations in nucleus–nucleus collisions in a wide energy region with large acceptance are needed to allow for a proper determination of the underlying dynamics.