The Dynamics Of η And K Mesons Produced Near Threshold Energy In Heavy-ion Collisions

Heavy ion collision is a complex process of multi-body, experiments can be done from dozens Me V of low-energy to hundreds Ge V of extreme relativistic energy in heavy-ion collisions, the study of the theory for the heavy ion collisions of different energy is also different. Generally low energy(under nuclear Fermi energy) heavy ion collision can research such as gas-liquid phase change, nuclear fusion properties; In high energy heavy-ion collisions it can study high temperature and density properties of nuclear matter, such as the high density behavior of the symmetry energy, the in-medium effects of mesons, etc. The high temperature and density properties of nuclear matter is very important for studying the nature of the universe evolution, the quark-gluon plasma, supernova explosions and the physical properties of neutron star, etc. Mostly people use computer simulation method for the study of the theory of the heavy ion collision, based on people’s understanding of the reaction process is different, there are mainly two categories based on statistical equilibrium and non-equilibrium model. In recent years, the nonequilibrium statistical class model is developing rapidly, mainly includes the class of the QMD(quantum molecular dynamics) model and the class of BUU(the Boltzmann- Uehling- Uhlenbeck) model. Our work is largely based on the LQMD(lanzhou quantum molecular dynamics) model, LQMD model is developed by the personnel of Institute of Modern Physics, Chinese Academy of Sciences which is based on the early QMD version with continuous improvement and innovation.Because the in-medium effects of mesons can significantly affect the producing of mesons under-threshold, the investigating of the producing mechanism ofmesons near the threshold energy in heavy-ion collisions can be a good hlep to understand the in-medium effects of mesons. So in this thesis, we use LQMD model to studied the η and K mesons in-medium effects near the threshold energy in heavy ion collisions, and also studied the impact of the symmetry energy and the incompressible coefficient of nuclear matter, its main content is as follows:1. With adding η meson optical potential from the chiral perturbation theory at mean field level and the related reaction channels to the LQMD model,studied the influence of the symmetry energy and the η meson optical potential to the the dynamics of η meson produced in proton-induced nuclear reactions and heavy-ion collisions near the threshold energy, the influence to such as the multiplicity, collective flow, transverse momentum distribution, invariant cross sections distribution and rapidity distributions, etc. The main conclusion is that the symmetry energy hardly influence the producing of η, but the impact of theη meson optical potential is quite significant.2. Useing the K meson optical potential from the chiral perturbation theory at mean field level and the related reaction channels in the LQMD model, studied the influence of symmetry energy, the incompressible coefficient of nuclear matter and the K meson optical potential to the the dynamics of K meson produced in heavy-ion collisions near the threshold energy, the influence to such as the angular distribution, and rapidity distributions, etc. The main conclusion is that in some cases the angular distribution of K+meson is influenced by the symmetry energy and optical potential notably, through compared with the experimental data one can get that the high density behavior of the symmetry energy to be hard could be better. The rapidity distribution of K-/K+ratio not only can be influenced by the symmetry energy, but also by the incompressible coefficient of nuclear matter, and both show the opposite trend.Through the above research and comparison with the experimental data,one can get some knowledge of the behavior for the high density of the symmetry energy, η and K mesons in-medium effects and the effects of incompressible coefficient of nuclear matter in nuclear reaction.