Phase transitions in nuclear matter. Formation conditions and experimental signals

The nuclear collisions at different energies offer conditions to excite fundamental nuclear matter and some phase transitions could appear. The phase transition type is related to the collision energy, as well as to the collision geometry. The two aspects involve associated de Broglie wavelength and the mean free path. Depending on the relationships of the two quantities with the nuclear radius and the internucleonic distance different excitation mechanisms can be supposed. Diverse phase transition can be considered in connection with these excitation mechanisms. Therefore, a discussion on the correlation between phase transition type and excitation mechanisms is useful to establish formation conditions and experimental signatures. An important stage in this discussion is related to the energy range where different phase transitions are more or less probable. The energy dependencies for some interesting physical quantities could reflect such energy ranges for a few phase transitions. The aspects related to the influences of effectiveness of the nuclear structure are important, too. The present work discusses all these aspects of the phase transitions in nuclear matter. They are reviewed and analysed in the terms of the present experimental results. The formation conditions and experimental signals for four phase transitions - nuclear liquid-vapour, resonance matter, hadronic plasma and quark-gluon plasma - are presented in the paper. Some new aspects related to the quark-gluon plasma formation in Au-Au collisions at the energies available at RHIC-BNL(USA) are included, too. A special attention will be done to the antiproton regeneration mechanisms in highly excited nuclear matter as signals of a phase transition. These considerations include mainly the author results obtained in different collaborations (SKM 200 - JINR Dubna, MULTI - KEK Tsukuba, UB - RIKEN Tokyo, BRAHMS - BNL Upton, New York). (author)