On energy densities reached in heavy-ion collisions at the CERN SPS

We present a few estimates of energy densities reached in heavy-ion collisions at the CERN SPS. The estimates are based on data and models of proton-nucleus and nucleus-nucleus interactions. In all of these estimates the maximum energy density in central Pb+Pb interactions is larger than the critical energy density \(\varepsilon_c\approx 0.7 \)GeV/fm3 following from lattice gauge theory computations. In estimates which we consider as realistic the maximum energy density is about \(2\varepsilon_c\). In this way our analysis gives some support to claims that deconfined matter has been produced at the CERN SPS. Any definite statement requires a deeper understanding of formation times of partons and hadrons in nuclear collisions. We also compare our results with implicit energy estimates contained in earlier models of anomalous \(J/\psi\) suppression in nuclear collisions.