"The Little Bang"

Ulrich Heinz

Department of Physics
The Ohio State University

Abstract

For the first few microseconds after the Big Bang, our universe existed in the form of a quark-gluon plasma, in which quarks were not yet confined inside hadrons. This state can be recreated in the laboratory in heavy-ion collisions at ultra-relativistic energies. Experiments at CERN and BNL have been searching for the quark-gluon plasma and the phase transition associated with its conversion back to normal hadrons. The data provide evidence for the "Three Pillars of the Little Bang": primordial hadrosynthesis at the quark-hadron phase transition, thermal hadron radiation, and strong Hubble-like collective expansion of the collision fireball. First data from the Relativistic Heavy-Ion Collider (RHIC) at BNL show that this fireball reaches thermodynamic equilibrium very quickly, at energy densities far above the critical value for quark-deconfinement. Does this mean that quark-gluon plasma has been made? I will dicuss some signatures which will soon settle this question.