Hadronic matter at high energy density and the search for the hadron–parton QCD phase transition

Recent progress is reviewed concerning the evidence for a phase change in strongly interacting matter, as predicted by Lattice QCD theory to occur at an energy density of about 2–3 GeV per cubic fermi. Experiments at the CERN SPS with Lead (208 Pb) beams show that such densities have been reached, and suggest a set of observable quantities to bear first evidence concerning the transition.