Anomalous

Heavy ion production of J/ψ mesons has been studied at CERN for a decade, in search for the Quark-Gluon Plasma predicted by lattice-QCD. The suppression observed very early in O-Cu, O-U and S-U reactions has been shown to be eventually explained by nuclear absorption, and follow the same exponential behavior as the proton-nucleus reactions. The new Pb-Pb data deviate from this behavior very strongly, indicating the onset of a new regime in J/ψ suppression.