Recent results on heavy-ion physics from the SPS

Abstract

The CERN SPS heavy-ion physics program was recently given an important and fresh impetus with the running of the NA60 dimuon experiment, which probed indium-indium collisions at 158 GeV per incident nucleon (in 2003), as well as proton-nucleus collisions at 158 and 400 GeV (essentially in 2004). Several interesting physics results have been obtained and were recently presented by NA60. They address such varied physics topics as the search for in-medium modifications on the ρ short-lived vector meson (which could be related to the restoration of chiral symmetry, spontaneously broken in the hadronic world), the understanding of the “anomalous” J/ψ suppression (expected to be a signature of quark-gluon deconfinement), the search for thermal dimuons (presumably radiated from a thermal system, maybe composed of deconfined quarks and gluons — the “quark-gluon plasma”), the understanding of the enhancement of θ production in heavy-ion collisions, etc. These topics were previously studied by other SPS experiments, and very interesting observations were made, but serious doubts remained concerning the interpretation of those earlier results. It is remarkable that one single experiment, NA60, is able to provide high-quality information on each of these many topics, potentially triggering a very significant step forward in our understanding of “quark-matter physics”.