Chemical equilibration in relativistic heavy ion collisions

In the hadronic sector of relativistic heavy ion physics, the p reversible arrow 2pi reaction is the strongest one, strong enough to equilibrate the p with the pions throughout the region from chemical freezeout to thermal freezeout when free-particle interactions (with no medium-dependent effects) are employed. Above the chiral restoration temperature, only rho's and pi's are present, in that the chirally restored A(1) is equivalent to the rho and the mesons have an SU(4) symmetry, with no dependence on isospin and negligible dependence on spin. In the same sense the sigma and pi are "equivalent" scalars. Thus the chirally restored rho reversible arrow 2pi exhaust the interspecies transitions. We evaluate this reaction at T-C and find it to be much larger than below T-C, certainly strong enough to equilibrate the chirally restored mesons just above T-C. When emitted just below T-C the mesons remain in the T-C + epsilon freezeout distribution, at least in the chiral limit because of the Harada-Yamawaki "vector manifestation" that requires that mesonic coupling constants go to zero (in the chiral limit) as T goes to T-C from below. Our estimates in the chiral limit give deviations in some particle ratios from the standard scenario (of equilibrium in the hadronic sector just below T-C) of about double those indicated experimentally. This may be due to the neglect of explicit chiral symmetry breaking in our estimates. We also show that the instanton molecules present above T-C are the giant multipole vibrations found by Asakawa, Hatsuda and Nakahara and of Wetzorke et al. in lattice gauge calculations. Thus, the matter formed by RHIC can equivalently be called: chirally restored mesons, instanton molecules, or giant collective vibrations. It is a strongly interacting liquid. (C) 2004 Elsevier B.V. All rights reserved.