This latter phase of matter in which quarks and gluons are deconfined existed for a short time after the Big Bang and may exist today in the cores of neutron stars. A large activity is devoted to the study of the nuclear response to induced collective motions of increasing amplitude. These collective excitations of the nucleus correspond to giant resonances built on top of other giant resonant states. Experimental evidence on the appearance of multifragmentation is now well established. For the first time a complete vaporization of highly excited nuclei into neutrons, protons and a particles has been observed.
Chiral symmetry appears to be restored during the same phase transition.
The early exploratory program with light ions up to 32S at Brookhaven and CERN have shown that high energy densities can indeed be obtained and produced evidence of the onset of new, collective phenomena. The recent experiments with heavy ions Au and Pb, both at Brookhaven and CERN should determine to what extent one can actually establish a regime of thermodynamic behavior. They should reach baryon densities larger than the ones in the core of neutron stars. The strangeness enhancement predicted by theory is found in several different channels. The large suppression of the Y observed recently at CERN is a possible indication that the onset of quark deconfinement has already been observed.