Heavy-ion physics

A summary of the lecture on the current status of heavy-ion physics, given at the European School of High-Energy Physics, is presented. We introduce the main goal of this field, i.e. the study of the transition between ordinary hadronic matter and Quark-Gluon Plasma (QGP), the predicted new state of matter composed of deconfined quarks and gluons. As heavy-ion physics is more driven experimentally than by theory, the main part of the lecture is devoted to experimental signatures of a QGP formation, and to the recent results from the CERN SPS lead-ion programme. Among others, two main results are discussed: the more than order of magnitude enhancement in the production of Omega hyperons, and the observation of significant drops in the J/psi production as a function of energy density. Further, we describe the future experimental programme at heavy-ion colliders, at RHIC at Brookhaven and at LHC at CERN. We conclude that the present results give evidence for the formation of a new state of matter with characteristics compatible with those predicted for a QGP. Therefore, it is of utmost interest to study the properties of this new state of matter in much cleaner conditions at the higher collision energies provided by the new heavy-ion colliders.