Signatures of Absorption Mechanisms for J/ψ and ψ′ Production in High-Energy Heavy-Ion Collisions

J/ψ and ψ produced in high-energy heavy-ion collisions are absorbed by their collisions with nucleons and produced soft particles, leading to two distinct absorption mechanisms. The signature of absorption by produced soft particles, as revealed by ψ production data, consists of a gap and a change of the slope in going from the pA line to the nucleus-nucleus line when we make a semi-log plot of the survival probability as a function of the path length. Using this signature, we find from the J/ψ production data in pA, O-Cu, O-U, and S-U collisions that the degree of J/ψ absorption by produced soft particles is small and cannot account for the J/ψ data in Pb-Pb collisions. The anomalous suppression of J/ψ production in Pb-Pb collisions can be explained as due to the occurrence of a new phase of strong J/ψ absorption, which sets in when the local energy density exceeds about 3.4 GeV/fm. To probe the chemical content of the new phase, we propose to study the abundance of open-charm mesons and charm hyperons which depends sensitively on the quark chemical potential.