Temperatures and densities in nuclear matter obtained in Au-Au collisions at RHIC-BNL energies

Ultrarelativistic heavy ion collisions are useful tools to investigate highly excited dense nuclear matter. At sufficiently high temperature, nuclear matter is expected to undergo a phase transition to quark-gluon plasma. Some predictions and experimental results on the rapidity and pseudorapidity distributions, as well as on hadron spectra are included in this paper. For predictions the UrQMD and HIJING codes have been used. The rapidity density and pseudorapidity density are used to estimate energy density. From transverse mass spectra and transverse momentum spectra pion, kaon, proton and antiproton temperatures are extracted. The mass dependence of the slope parameters provides evidence of collective transverse flow. Comparisons with the two codes predictions are included. Taking into account the fact that some information on the collision dynamics and the thermalization degree is obtained from the spectral shapes of the interesting physical quantities and their dependencies on rapidity, the dependencies of the average transverse momentum on the rapidity densities and on the pseudorapidity densities are studied in this paper. The values of the energy and baryon densities - over 10 normal values - as well as the agreement between the experimental values on participants and phenomenological model estimations, represent a support for the estimated thermodynamic parameters of the nuclear matter in Au-Au collisions at RHIC-BNL energies, as well as for the possibility to evidence phase transitions to the quark plasma and quark-gluon plasma in these collisions. (authors)