Jet Quenching With Detailed Balance And Dilepton Production In Strong Interacting Medium

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. 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 QED and QCD many theoretical studies focus on radiative energy loss induced by the multiple scattering. The radiative energy loss of a charged fast particle which undergoes successive scattering has been studied in the framework of QED by Landau, Pomeranchuk and Migdal long ago, the LPM destructive interference effect is demonstrated. To investigate the energy loss of a hard parton jet passing through QGP, 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 physics characters in QCD, the energy loss with non-abelian LPM effect is obtained easily. Now G-W model has been widely used to study the radiative energy loss in QCD and in QED. 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 paper we use opacity expansion and reaction operator approach developed by Gyulassy, Levai and Vitev(GLV) to investigate the effect of thermal absorption further and derive the gluon radiative probability distribution and energy loss to all orders in opacity. The numerical results and analysis are given. It turns out that the energy loss due to stimulated radiation increases logarithmically with increasing jet energy, the energy gain due to thermal absorption decreases reciprocally with increasing jet energy. Its contribution is important for small jet energy region. The higher order contribution in opacity is also important for small jet energy region.Electromagnetic signals, such as photon and dilepton production signals, are traditional signals for formation of QGP. Photon and dilepton have large mean free path and pass through collision region easily to reach the detectors, so they can be observed directly in experiment. In another part of this paper we focus on photon radiation and dilepton production induced by multiple parton rescattering. Recent studies on gluon radiation turns out. non-abelian energy loss depends quadratically on thickness of medium targets. While abelian energy loss due to photon radiation is likely to have different dependence on medium thickness. This investigation will help us to understand electromagnetic signal of QGP in high energy heavy ion collision. By using also the opacity expansion technique developed by GLV, it turns out that abelian energy loss depends linearly on thickness of medium targets. The transverse momentum spectrum for radiatied photon is presented. It is shown that the photon radiation decreases with increasing transverse momentum. We generalize the method to investigate dilepton production, theinvariant mass spectrum of dilepton is given, it is shown that the dilepton production decreases with increasing invariant mass.