Review of CERN heavy-ion physics

The primary motivation for studying nucleus-nucleus collisions at very high energies is the possibility of forming a quark-gluon plasma (QGP). In these collisions energy and baryon densities are expected to increase and reach critical values where the quark constituents of the incident nucleons, bound in nuclei, form an extended volume of freely interacting quarks, antiquarks and gluons. Various signatures of the existence of a quark-gluon plasma in these collisions have been proposed: suppression of J/Psi production, an enhancement in strange particle production, event-by-event fluctuations in the rapidity distributions of produced particles, observation of direct photons from the plasma and other observables. The system is expected to evolve dynamically from a pure plasma or mixed phase through expansion, cooling, hadronization and freeze-out. To be able to determine that a new, transient state of matter has been formed it is necessary not only to identify QGP signatures but also to determine the space-time evolution of the collision process. This requires an understanding of the microscopic structure of hadronic interactions, at the level of quarks and gluons, at high temperatures and high densities. The physical observables important for understanding the dynamics of heavy-ion collisions at high energies and the present status of experimental results covering these observables are described. The various signatures of QGP formation, present experimental results and plausible interpretations of the results are also described. This talk is not meant to be a comprehensive review, it is rather a summary of important background information, current outstanding problems, observations of particular interest and recent results on dynamics and signatures.