PROBING THE STATES OF MATTER IN QCD

The ultimate aim of high energy heavy ion collisions is to study quark deconfinement and the quark–gluon plasma predicted by quantum chromodynamics. This requires the identification of observables calculable in QCD and measurable in heavy ion collisions. I concentrate on three such phenomena, related to specific features of strongly interacting matter. The observed pattern of hadrosynthesis corresponds to that of an ideal resonance gas in equilibrium at the pseudo-critical temperature determined in QCD. The critical behavior of QCD is encoded in the fluctuation patterns of conserved quantum numbers, which are presently being measured. The temperature of the quark–gluon plasma can be determined by the dissociation patterns of the different quarkonium states, now under study at the LHC for both charmonia and bottomonia.