出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：In 2003, NA60 collected data on dimuon production in indium-indium collisions at 158 GeV
per incident nucleon, to study several anomalies previously observed in high-energy heavy-ion
collisions at the CERN SPS. Among these anomalies stands the observation, by NA50, that the
production yield of J/y mesons is suppressed in central Pb-Pb collisions beyond the normal nuclear
absorption defined by proton-nucleus data. This behaviour was predicted to occur if the
matter produced in these extreme collisions goes through a phase of deconfined partonic matter,
where the charmonium states would be dissolved either due to the screening of their binding potential
when the medium temperature exceeds certain critical thresholds (thermal transition, QGP)
or when the density of interacting partons exceeds certain thresholds (geometrical transition, percolation).
Thanks to its exceptionally good vertexing capabilities, NA60 is able to accurately
study the centrality dependence of J/y production without using the Drell-Yan sample as reference.
Our data shows that the J/y is anomalously suppressed for In-In collisions with more than
90 participant nucleons. The comparison with three theoretical predictions shows that none of
them properly describes the observed suppression pattern.
