Jet Transport And Medium-induced Photon And Gluon Bremsstrahlung In Dense Nuclear Matter

Quantum chromodynamics(QCD)is a quantum field theory based on the non-abelian S U(3)gauge symmetry and describes the strong interaction of quarks and gluons.There are two significant features in QCD:color confinement and asymptotic freedom.Due to color con-finement,quarks and gluons are confined within the hadrons.The asymptotic freedom indicates that under the extreme conditions of high temperature and density the quarks and gluon in the hadrons may be deconfined to a new state of matter—quark gluon plasma(QGP).Experimen-tally,high-energy heavy ion collisions may create a region with extreme high temperature and density,which provide conditions for the existence of QGP.Currently,there have been many experimental evidences for QGP for mation at the Relativistic Heavy-Ion Collider(RHIC)at Brookhaven National Laboratory(BNL)and the Large Hadron Collider(LHC)at European Or-ganization for Nuclear Research(CERN).But the deconfined QGP olny exists in a very short life time in high-energy heavy ion collisions.Quarks and gluons can not be observed directly,instead we measure the hadron of the final state.In order to find QGP and study its property at the relativistic heavy ion collider,we need to establish clear and unambiguous links between the created QGP and the final state measurement.By studying a large number of experimental data,many significant features of QGP can be determined.Jet quenching is an important signal of QGP and has been widely studied in high-energy nuclear physics.Jet quenching demonstrates that the interaction between the hard propagating partons produced in the early stages of rel-ativistic heavy ion collisions and the QGP medium results in a loss of energy of the original partons.The investigation of parton energy loss may be used to explore the property of QGP via the interaction with the hard jet.The parton energy loss may be divided into collisional energy loss and radiative energy loss.Collisions energy loss is usually considered to be smaller than radiative energy loss.Now there have been several theoretical schemes that study the radiative energy loss,such as Gyulassy-Wang model,BDMPS-Z,GLV and DGLV,ASW,AMY and HT(higher twist).However,only transverse scattering is considered for radiative energy loss in all these formalisms,and the con-tribution of longitudinal scattering is neglected.In fact,when a hard jet propagating through the medium interact with the constituents of the nuclear medium,both transverse and longitudinal momentum are exchanged.In this thesis we will study the influences of both transverse and longitudinal scatterings on medium-induced photon and gluon radiation.We first calculate the medium-induced photon bremsstrahlung spectrum via transverse and longitudinal scatterings in the dense nuclear matter within the framework of deep-inelastic s-cattering(DIS),for single scattering and multiple scatterings.With single scattering,we have used two methods to calculate the medium-induced photon radiation spectrum:(1)with Yukawa potential to model the correlation function of scattering gluon field.Using Yukawa potential,the photon emission spectra is expressed as the integration over three-dimensional momentum distribution of the exchanged gluon.(2)applying a gradient expansion up to the second order for the scattering three-dimensional momentum.By applying gradient expansion,we deduce the photon emission spectra including transverse momentum diffusion,longitudinal energy loss and momentum diffusion for both single and multiple scatterings.Compared to the results for single scattering and from the resummation of multiple scatterings,it can be found for small longitudinal scattering momentum,the leading contribution from the drag and diffusions to the photon bremLsstrahlung spectrum remain the same for single and multiple scatterings.We also find that the transverse momentum diffusion usually induces additional photon radiation,while the longitudinal momentum drag tends to suppress medium-induced gluon radiation in dense nuclear medium.Then,we compute the medium-induced gluon radiation spectrum with single scattering in dense nuclear matter within the framework of DIS for light quark and heavy quark.In particular,we extend the higher twist radiative energy loss formalism and include the contributions form both transverse and longitudinal scattering to the medium-induced gluon emission spectrum.Compared to the gluon radiation from heavy quark and light quark,we find the formation for gluon radiation from a heavy quark is shorter than that off a light quark due to the mass quark.In addition,we discuss the medium-induced gluon emission spectrum with only transverse mo-mentum exchange.Both the results from the light quark and the heavy quark reduce to the GLV result in the limit of soft gluon emission.This work makes a significant progress in our under-standing of the radiative process in the interaction between the hard jet and the dense nuclear medium.