QGP Evolution And Its Influence On Jet Quenching

It is expected that relativistic heavy ion collision forms an extreme environment with high temperature and high density, hadronic matter undergoes a phase transition to become a quark gluon plasma(QGP). One of main objects of ultra-relativistic heavy ion collisions experiments at RHIC and LHC is to discover this kind of new state of matter-quark gluon plasma. This dissertation included two parts,the first part is focused on the phase transition scenario from the hadronic phase to the QGP phase,and the second part is about the jet-quenching with the detailed balance in 1+1 dimension expanding system with chemical nonequilibrium.In the Ref.' 1, the author has used the state equations of the bag model and the hydrodynamics model to investigate the entropy density, energy density and temperature evolution with the proper time in the zero chemical potential and finite temperature when first-order phase transition occures. We will use the relevant hydrodynamics model and the state equations at finite densities to investigate the QGP phase transition in the zero temperature and finite density. It turns out that the remaining ratio of hadrons decreases from 1(the QGP phase) to 0(the hadrons phase)with the proper time evolution, and the energy density, decrease with it. If the first-order phase transition really happens, the chemical potential will diminished fastly with the proper time running up, and remains constant in the condition thatthe QGP and hadrons coexist, then it will decreases slowly. That is quite different from the scenario without phase changing.Secondly, the study on the signal of QGP is an intensive project in heavy ion physics. The energy loss of the fast parton jet produced at the initial stage of heavy ion collision(jet quenching) is a possible important probe for formation of QGP. In the framework of QCD many theoretical studies focus on radiative energy loss induced by the multiple scattering. M. Gyulassy and Xin-Nian Wang proposed a model(G-W model) which describes the multiple scattering of a high energy parton in the medium as static Debye screened potentials. This model keeps the main characters in QCD, the energy loss with non-abelian LPM effect is obtained easily. Moreover it has been used to study the relative researches about the QGP hard probes. Because of the presence of thermal gluons in the hot strong interacting medium, the stimulated gluon emission and absorption should be taken into account simultaneously. Such investigation on energy loss with detailed balance has been in important progress. In this dissertation, we studied that QGP should be in the chemical system which expands with the time the temperature of QGP will decreases steadly, at last, the QGP freeze out and fragment into the final hadrons. Thus, we will investigate the jet quenching with the detailed balance in 1+1 dimension expanding medium with chemical nonequilibium. Furthermore, the result is compared to the jet quenching in the static system at the initial time. It turns out that the energy loss in the static system is much more than that in the expanding system. The ratio between the energy loss in the static system to that in the expanding system depends on the energy for the jet with moderate energy. The thermal absorption gives important contribution for the jet with small energy, and the thermal absorption can be neglected for the jet with very high energy.