A search for the quark-gluon plasma. Overview of J/ψ suppression

Anomalous J/ψ suppression found in Pb-Pb collisions at CERN-SPS is still an unsettled issue, although many theoretical efforts have been devoted intensively for the last years. Indeed, the coming experiments at BNL-RHIC and CERN-LHC accessible to higher energy by a factor 10 - 100 will supply more abundant data and any conclusive results to suggest evidence for the deconfinement transition. In such case also, however, we will still need detailed studies of hadronic scenarios, namely inelastic interaction of J/ψ with nucleons and co-movers, other possible contributions of gluon shadowing, enhanced charm production and the initial state energy loss. Before any real conclusions can be drawn, we now should make clear such various alternative mechanisms of the suppression to be excluded from the available data. Hence in this report, I first summarize various useful probes for the matter formed in high-energy nucleus-nucleus collisions and particularly give detailed explain about the J/ψ suppression. In the last of this report, I will introduce our recent study on the possibility of another J/ψ suppression mechanism from view of the hadronic scenario. It is based on a idea that the mass shift of the D-meson in nuclear matter could cause the level crossings of the charmonium states and the DD-bar threshold. (author)