Probing Chiral Symmetry Restoration with Heavy Ions

The goal of ultra-relativistic heavy-ion collisions is to create new states of hadronic matter that are believed to have existed until a few tens of microseconds after the ’big bang’. These efforts were largely stimulated by lattice QCD predictions that hadronic matter at high energy density undergoes a phase transition to a plasma of deconfined quarks and gluons. At present the lattice calculations with realistic light quark masses yield a transition temperature Tc = 150± 20 MeV [1] at which there is a rapid increase of the thermodynamic quantities such as energyand entropy density. The transition is accompanied by a restoration of chiral symmetry, signaled by a sharp decrease of the chiral condensate, 〈q̄q〉T , near Tc.