Hadron production in nuclear collisions at RHIC and high-density QCD

We analyze the first results on charged particle multiplicity at RHIC in the conventional eikonal approach and in the framework of high-density QCD. We extract the fraction F of the hadron multiplicity originating from "hard" (i.e., proportional to the number of binary collisions) processes; we find a strong growth of this fraction with energy: F(√s = 56 GeV) ≃ 22%, while F(√s = 130 GeV) ≃ 37%. This indicates a rapid increase in the density of the produced particles. We outline the predictions of high-density QCD for the centrality, energy, and atomic number dependence of hadron production. Surprisingly, the predictions of the conventional eikonal approach and of high-density QCD for centrality dependence of hadron multiplicity at √s = 130 GeV appear very similar.