The authors review the search for the quark-gluon plasma using the signal of the suppression of J/[psi] production in high-energy heavy-ion collisions. Recent anomalous J/[psi] suppression in high-energy Pb-Pb collisions observed by the NA50 Collaboration are examined and compared with earlier results from pA and nucleus-nucleus collisions with heavy ions of smaller mass numbers. The anomalous suppression of J/[psi] production in Pb-Pb collisions can be explained as due to the occurrence of a new phase of strong J/[psi] absorption, which sets in when the number of nucleon-nucleon collisions at a spatial point exceeds about 4 and corresponds to a local energy density of about 3.4 GeV/fm3.

The anomalous suppression of J/[psi] production in Pb-Pb collisions at 158 GeV observed by the NA50 Collaboration can be explained as due to the occurrence of a new phase of strong J/[psi] absorption, which sets in when the local energy density exceeds about 3.4 GeV/fm[sup 3]. The peculiar behavior of the[psi][sup']/[psi] ratio in[ital p]-A and nucleus-nucleus collisions can be understood as due to approximately equal[psi]-N and[psi][sup']-N absorption cross sections, but greater absorption cross sections for[psi][sup'] than J/[psi] with regard to absorption by soft particles and matter in the new phase.

J/psi and psi' 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 psi' 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/psi production data in pA, O-Cu, O-U, and S-U collisions that the degree of J/psi absorption by produced soft particles is small and cannot account for the J/psi data in Pb-Pb collisions. The anomalous suppression of J/psi production in Pb-Pb collisions can be explained as due to the occurrence of a new phase of strong J/psi absorption, which sets in when the local energy density exceeds about 3.4 GeV/fm3. 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.

Yields of prompt and non-prompt J/psi, as well as Y(1S) mesons, are measured by the CMS experiment via their dimuon decays in PbPb and pp collisions at sqrt(sNN) = 2.76 TeV for quarkonium rapidity.