Formation and evolution of the quark-gluon plasma

Imposing an equilibrium between the thermal pressure of deconfined quarks and gluons and the dynamical compression pressure exercised by in-flowing nuclear matter, we study the initial thermal conditions reached in a quark-gluon plasma fireball formed in a relativistic heavy ion collision. We show that entropy is produced primarily in the pre-equilibrium stage of the reaction. We test our approach, comparing our results with the S→W Pb collision results at 200 GeV A and find a surprising degree of agreement assuming about 50% stopping. We apply our method to a determination of the conditions in collisions of Au→Au at 11 GeV A and Pb→Pb at 157 GeV A, assuming full stopping of momentum, energy and baryon number. Our detailed results directly determine the spectral shape and abundance of (strange) hadrons and electromagnetic probes (photons, dileptons) produced in the collision, and we explore specific experimental consequences.