Evolution Effects On Parton Energy Loss With Detailed Balance

The experiments of heavy ion collisions In BNL relativistic heavy ion collider(RHIC)and Europe large hadron collider(LHC)found that there might have produced a new substance called the quark gluon plasma(QGP).Research on the physical properties of high temperature and high density QGP has become a hot issue in high energy nuclear physics.Because it can help us to understand the basic structure of matter and their inter-action,and can help us to understand the early universe evolution and the formation of galaxies.Relativistic heavy ion collision experiments are the most effective way to form the high temperature dense substance.In the early stages of a nuclear-nuclear collision,when the large transverse momentum jet pass through the QGP medium,it loses energy due to multiple scattering and gluon radiation.This phenomenon is known as Jet quench-ing,which is an important probe in reseaching QGP.The early research of jet quenching suggested that due to the multiple scattering and gluons radiation effect of non-Abelian LPM process,the jet energy loss in QGP medium was proportional to the square of the propagation distance.It was later found that the ef-fect of absorption reduced the effective energy loss.The study showed that the effect of this absorption was obvious in the intermediate energy region,and the influence in the high jet energy could be neglected.These studies considered the jet energy loss caused by the changing medium density when the medium expanded,but ignored the evolution of temperature and fugacity in high energy heavy-ion collisions.In fact,these effects will be reflected in the Debye screening mass,mean free path,which in turn affect the jet scatter-ing frequency(opacity)in the strong interaction,thus the jet energy loss will be changed.This paper is based on perturbation QCD and fluid mechanics model to research the evolution effect on jet quenching.First,we assume that the parton distribution function can be approximately equal to the phase space distribution with non-equilibrium quark and gluon fugacity.Secondly,by using perturbation QCD,we deduced a set of rate equations to study early high-energy collisions of quarks and gluons in chemical non-equilibrium evolution process.At the same time,using the method of the transverse energy method and particle multiplicities method,we identified the initial conditions in Au-Au collisions at RHIC:the initial temperature is 550 MeV,initial gluons fugacity is 0.3.Finally,using the initial conditions in rate equation,we obtained the time evolution of temperature and fugacity,and we also obtained the time evolution of Debye screening mass,mean free path and mean free path through a set of computation,then we obtain the propagating distance dependence of the opacity(medium thickness).When calculating the energy loss under the detailed balance,we also consider the gluon radiation and absorption process,by using the method of high twist,we respectively obtained energy loss through stimulated emission,energy gain through thermal absorption,the effective energy loss and their evolution with propagation distance and jet energy.We found that radiation energy loss,thermal absorption and total energy loss increased with increasing propagation distance.As the jet energy increases,radiation energy loss and total energy loss increase,while thermal absorption decreases.On the analysis of the heat absorption effects on total energy loss,we found that with the propagation distance increasing,the thermal absorption effect is more and more not obvious,and thermal absorption effect is obvious in the intermediate energy jet,and the influence of jet in the high energy region can be neglected.