Model Study Of Global Effect In Heavy Ion Collisions At Intermediate And High Energie

At present, through a large number of experimental data and theoretical model analyses, properties of the ground state of nuclear matter have been well known. But the nature of hot and dense nuclear matter is still poorly understood, it is mainly because the information about equation of state of nuclear matter cannot be directly obtained from the experiment. To explore the signals of quark-gluon plasma (QGP) phase transitions and the properties of heated and compressed nuclear matter transiently appeared in relativistic nucleus-nucleus collisions is the hot topic in the field of particle physics and nuclear physics. In particular, the study of transport phenomena in nuclear reactions is of major importance in the understanding of many fundamental properties. And, more interest is focused on the extracting the equation of state (EoS) of nuclear matter from the comparison of microscopic transport models with experimental measurements.The main purpose of this thesis is to try to extract the information about equation of state of nuclear matter by studying the rapidity distributions of final state particles at the intermediate and high energies in the framework of the statistical model——multi-source ideal gas model and the microscopic model——Ultra-relativistic quantum molecular dynamics (UrQMD) model with the mean field potentials taken into account.Firstly, we show the calculation results of the (pseudo)rapidity distributions, multiplicity distributions, transverse momentum spectra and azimuthal distributions of final-state particles produced in nucleus-nucleus collisions in intermediate and high energy regions from multi-source ideal gas model simulation and the comparison with data. This model can give some statistical properties of final state particles from low to ultra-high energy regions. It also provides the guidance for searching the causes of these statistical properties in the microscopic transport-model simulation.Secondly, we study nuclear stopping in the heavy ion collisions over a beam energy range from SIS, AGS up to SPS in the framework of the UrQMD transport model with the mean field potentials taken into account. It is found that the nuclear stopping is influenced by both the stiffness of the equation of state and the medium modifications of nucleon-nucleon cross sections at SIS energies. At the SPS energies, the two-bump structure is shown in the experimental rapidity distribution of free protons, which can be partly understood with the consideration of the "pre-formed" hadron potentials.In a word, the UrQMD model with the mean field potentials can describe the nuclear stopping for central nucleus-nucleus collisions from SIS to SPS energies. The modification about collision terms still need to research further, so that we can use the more perfect modified UrQMD model to study more physical quantities such as collective flow of final state particles and so on.