Chemical equilibration of partons in high-energy heavy-ion collisions?

The chemical composition of the hot and dense parton matter formed in the central region of ultrarelativistic heavy-ion collisions is studied for the case of Au+Au collisions at energies reached at the BNL RHIC using the parton cascade model. It is shown that within this framework, which is based on current understanding of semihard and hard interactions in QCD including the emission and absorption of soft partons, a chemical equilibration between the gluons and the quarks cannot be achieved. The gluons and $u$, $d$, $s$, and $c$ quarks all rapidly approach kinetic equilibrium with a common temperature. The gluons subsequently also achieve chemical equilibrium, but the light quarks only reach about 60% of their ideal chemical equilibrium densities. It is demonstrated that the baryon density in the central region is small relative to the total parton density, with an associated ratio of baryon chemical potential to temperature of 0.35, slowly decreasing with time. The implications of the formation of such a hot, gluon-dominated plasma for strangeness, charm, and dilepton production are discussed.