Researches On Particle Correlation And Hadronization Mechanism In QGP Phase Transition

Quark-gluon plasma (QGP) is a new form of matter predicted by lattice QCD. It is believed that QGP may exist instantly after high-energy nucleus-nucleus collisions and at the early time of universe. The research on its properties can help us understanding the deep microscopic structure of matter and the origin of universe, and hence it has become an important issue in the realm of high energy physics in nearly two decades. During a high-energy heavy-ion collision, the matter undergoes complex evolution, from the initial nuclear matter to various kinds of hadrons, leptons and photos, etc, finally. Instantly after a collision, a great deal of energy lost by ions is concentrated in a tiny space, which leads to a condition of high temperature and high density that may create QGP. After that, with the expansion and cooling of system, a transition from QGP occurs, and the produced hadrons fly to detectors.Since in experiment, only final particles are observable, while the intermediate process is undetectable. There is still no definite conclusion on the research about the properties of QGP. Additionally, the theory describing hadronization is far from perfect. Thus, people are trying to analysize the information carried by final particles and build various models on it, for the purpose of describing the intermediate process and predicting some possible phenomena, So far, however, there isn’t any single character that can be used as a definite proof of the existence of QGP. Whereas indirect evidences rely on concrete models that have been used. Some signals that indicating the existence of QGP, can also been deduced by models which don’t include QGP. In conclusion, we need synthesize different kinds of data and signals to judge whether QGP exists and to research on its properties.The distribution of multiplicity is a significant observable physical quantity, which contains dynamical information of evolution. And fluctuation is an important phenomenon in statistical physics. It may have some information on phase transition. During high-energy heavy-ion collision, there exists fluctuation in the distribution of density of one particular kind of particle. If the statistical fluctuation caused by the limit of number of particles can be subtracted, then the dynamical fluctuation part that containing the information of evolution of the system can be used as the basis to judge whether the phase transition from QGP to hadrons exists.In statistical physics, Ginzburg-Landau model, as a successful model that describing phase transition, has been used to describe the processes of multi-particle production in relativistic heavy-ion collisions. Based on the G-L phenomenological method, fluctuation of multiplicity can be regarded as a kind of behavior of QGP-hadron phase transition, and a possible signal of formation of QGP. Factorial moment could well remove the statistical fluctuation, and acquire information about dynamical fluctuation. This thesis calculated one kind of factorial moment, the correlator of first-order phase transition. After some studies, it is found that this kind of correlator shows the scaling behavior that is independent of concrete parameters. And as a result, the problems of observing and controlling parameters are solved. Therefore, it is expected this kind of scaling behavior can be regarded as one of the signs of QGP phase transition.The last chapter is a simple dynamical simulation on the hadronization process of a quark system, which can be regarded as a tentative trial on the research of hadronization mechanism.