J/ψ suppression in the threshold model and QGP formation time

In the QGP motivated threshold model, in addition to the normal nuclear absorption, J/ψ's are subjected to an additional 'anomalous' suppression. We have analysed the recently published PHENIX data on the participant number dependence of the nuclear modification factor for J/ψ's in Au + Au collisions and extracted the anomalous suppression required to explain the data. At mid rapidity J/ψ's are anomalously suppressed only above a threshold density nc=3.73fm-2. The forward rapidity data on the other hand require that J/ψ's are continuously 'anomalously' suppressed. The analysis strongly indicate that in mid rapidity J/ψ's are suppressed in a deconfined medium. Using the PHENIX data on the participant number dependence of the Bjorken energy density, we have also estimated the QGP formation time. For critical temperature Tc=192MeV, estimated QGP formation time ranges between 0.06-0.08 fm/c