Flow And Evolution Effects On Jet Quenching And Thermalization In Strong Interacting Medium

In relativistic heavy ion collisions jet quenching has been proposed as a good probe of the hot and dense medium in high - energy nuclear collisions.Jet quenching is caused by gluon radiation induced by multiple scattering during jet propagates the hot QCD medium.As discovered in high-energy heavy-ion collisions at RHIC,jet quenching is manifested in both the suppression of single inclusive hadron spectrum at high transverse momentum PT region and the disappearance of the typical back-to-back jet structure in dihadron correlations.It is found that the analytic approximation of the energy loss by stimulated emission in a static medium is proportional to square of the propagation distance in a static medium.Later the detailed balance effect of jet energy loss in hot QGP medium is investigated.With partial cancellation by stimulated emission, the net result is an energy gain via absorption which reduces the effective patton energy loss. Such a reduction is found to be important for intermediate parton energy but can be neglected at very high energies.In this dissertation we studied parton equilibration effect on jet quenching with detailed balance.We first studied the parton evolution process from chemical non-equilibrium towards a fully equilibrated parton plasma.We derive a set of rate equations based on perturbative QCD to describe the chemical equilibration of gluons and quarks,and then put different initial conditions in to get the rapidity distribution of transverse energy dE_T/dy and particle multiplicites dN/dy. We compare the data with that from experiment and get that at the initial time 0.3fm/c,the initial temperature is 550MeV,gluon fugacity is 0.3.We also find that the parton gas cools faster than that predicted by Bjorken's scaling solution.With the parton equilibration,it is shown that the Debye screening mass and the inverse mean free path for a gluon reduce with the increasing proper time in the QGP medium.The parton equilibration has effect on patton energy loss with detailed balance,the patton energy loss from stimulated emission is linear dependence on the propagating distance rather than square dependence in the static medium. The energy gain is found to be important not only for intermediate parton energy,but also for the small propagating distance of the energetic parton.This will increase the energy dependence and propagating distance dependence of the parton energy loss and will affect the shape of suppression of moderately high PT hadron spectra.Moreover,we studied the flow effects on jet energy loss with detailed balance.We derived a new potential for the interaction of a hard jet with the parton target.It can be used to study the jet quenching phenomena in the presence of collective flow of the quark-gluon medium.With this new potential,we have investigated the effect of collective flow on jet energy loss with detailed balance.Collective flow along the jet direction,with the velocity V_z leads to a reduced opacity, (1 - v_z)² times that in static medium,and an increased LPM gluon formation factor,(1 + v_z) times that in static medium.The energy gain without rescattering is the same as in the static medium,but the total energy loss to the first order of opacity is(1 - v_z) times that in the static medium.Compared to calculations for a static medium,our results will affect the suppression of high p_T hadron spectrum and anisotropy parameter v₂ in high-energy heavy-ion collisions.At RHIC,one of the important signals of QGP is elliptic flow,which reflects the transverse anisotropy of the particle momentum distribution.Parton cascade model,which is proposed to provide a detailed description of the evolution of nuclear collisions at high energy from the onset of hard interactions among the partons,is used to study the elliptic flow.Recently,a new parton cascade model,BAMPS model(Boltzmann approach of multiparton scatterings),is developed with considering the important motivation for developing a consistent algorithm to handle inelastic process like gg←→ggg besides gg←→gg scatterings to study the QCD matter thermalization.In order to study thermalization of the Quark Gluon Plasma at RHIC and LHC in any kinetic approach,one needs suitable initial conditions for the parton production.Here,we use two different methods WN and CGC to study parton production and studied the difference of the rapidity distributions of parton number dN/dy and transverse energy dE_T/dy between the two methods.First,we present the lowest order minijet production from WN and find that the result is consistent with that from Eskola.We then study parton shower and multiple interaction and compare the parton production with that from CGC.It is shown that dN/dy and dE_T/dy from CGC at midrapidity at RHIC are larger than that from WN by using Pythia.We then put the two different parton production into BAMPS model to study QCD matter thermalization and get the same kinetic equilibration,but different chemical equilibration,the parton system stays in chemical equilibrium if using wounded nucleons,but if using CGC,chemical equilibrium is achieved at the same timesacle,1.5 fm/c.We also find the transverse energy dE_T/dy|_y=0 at time 4fm/c using the initial conditions from wounded nucleons is consistent with the experiment data 620±33GeV in central Au-Au collisions at RHIC,but the transverse energy using parton production from CGC is a bit larger.We also study the QCD matter thermalization at LHC and predict that the rapidity distribution of transverse energy dE_T/dy|_y=0 is from 1620 to 2150 GeV.