The Study Of The Distribution Functions Of The Particles In QGP In Quasi-equilibrium

One of the main objectives of the future high-energy experiments is to detect a new state of matter called the quark-gluon plasma (QGP). Considerable attention has been paid on the mechanism of the formation and the evolution of the QGP. It's generally believed that the QGP, if formed in the relativistic heavy ion collisions, be in a thermal non-equilibrium state during initial stage and then evaluates into equilibrium state. However, how to describe the non-equilibrium state of QGP is still an unsolved and important problem.The fundamental theoretic methods dealing with the phenomenon of the QGP in non-equilibrium are the finite-temperature field theory and the kinetic theory. The kinetic theory is a statistical theory that can describe the non-equilibrium phenomena in basic. The kinetic equations for the QGP have been formed under the general frame of the statistical theory and its dynamic basic is the quantum chromodynamics(QCD), which the component particles of the system obey. They are widely used in investigating the properties of the QGP.There are two basic forms of the QGP kinetic theory: quantum kinetic theory and (semi-)classical kinetic theory. Unfortunately, it is difficult to obtain the non-equilibrium distribution functions by strictly solving the QGP kinetic equations.Here based on the kinetic theory, we have mainly discussed the distribution function of the component particles in QGP which is in quasi-equilibrium. Our discussion can be divided into two aspects. The first aspect is about the distribution function for fermions in quasi-equilibrium QGP which is perturbed by the fluctuation of the color field. Neglecting the affect of the spin and the collision between the particles in QGP, the distribution function for fermions in quasi-equilibrium QGP has been obtained. Further more, the physical' basses that decide the departure factor are analyzed. And the characteristics of the departure factor in high-temperature-low-density and low-temperature-high-density are discussed. The second aspect: from QGP kinetic equations with collision integrals, by using the relaxation time approximation, we calculate the distribution functions to the second order correction. We obtain the distribution functions for quarks(and anti-quarks)and gluons under perturbation of the fluctuation of the color field. Then in the high-temperature-low-density area, we discuss the characteristics of the distribution functions, and use them to get the net baryon density and the energy density.