Exploration Of Signal For Phase Transition From Hadron Matter To Parton Matter

The main purpose of heavy ion collision is, colliding two heavy nuclei which have been accelerated to extreme high energy to accumulate a mass of energy in the colliding area. In such high temperature environment, quarks in hadrons may be decomfined to form an amount of Quark Gluon Plasma (QGP). However, due to "color confinement", quark gluon plasma cannot exist for a long time, it will cool down and hadronize to hadrons in a very short time. We can only observe the distribution of final-state hadrons to determine what has happened in colliding process.Charge balance function is a widely-used signal of quark gluon plasma. Charge balance function is considered to be a signal of late hadronization. If quark gluon plasma has been created in the system, the hadronization will happen in a late time. The later the hadronization happed, the narrower the charge balance function of final-state hadrons will be. So it was proposed that, later hadronization will result in a narrower charged balance function. In order to examine this relationship, we calculate the dependence of charge balance function on hadronization time with a commonly-used multiphase transport model AMPT. In AMPT model, each parton has its own hadronization time, there is no unique hadronization time for the whole system. In our calculation, we use the average of all parton's hadronization time as the charactering hadronization time of the event. We found that, the dependence of charge balance function on multiplicity is much stronger than that on hadronization time. So we conclude that charge balance function cannot be a good signal for late hadronization, as well as for the appearance of quark gluon plasma.In order to search for the critical end point, the matching point of 1^st order phase transition and crossover from hadron gas to quark gluon plasma, predicted by lattice QCD, RHIC is performing an energy scanning. In the search of critical end point, constructing a good signal to indicate the occurrence of phase transition is very important. In this thesis, we propose that the 3^rd scaled moment of transverse momentum could be a good signal of phase transition. We construct a thermal percolation model to examine this signal. We found that transverse momentum suffers a rapid increase around the critical point. So we conclude that the 3^rd scaled moment of transverse momentum may be a good signal of phase transition.