J/psi suppression in Pb-Pb collisions at CERN SPS

The NA38 and NA50 experiments at the CERN SPS have measured charmonium production in different colliding systems with the aim of observing a phase transition from ordinary hadronic matter towards a state in which quarks and gluons are deconfined (Quark Gluon Plasma, QGP). In fact it was predicted that the J/psi yield should be suppressed in deconfined matter. The analysis of the data collected by the NA50 experiment with Pb-Pb collisions at 158 GeV/c per nucleon shows that the J/psi is anomalously suppressed in central collisions and the observed pattern can be considered as a strong indication for QGP production.