Jet-medium Interaction In High Energy Heavy-ion Collisions

We have developed a Linear Boltzmann Transport（LBT）model which include the complete set of 2 → 2 elastic processes and induced gluon emission processes.Our Monte-Carlo simulation impose global energy momentum conservation of 2 → n processes,which will influence the energy spectrum of the radiated gluon.We first simulate the propagation of a single parton in an uniform medium to study the jet-medium interaction in detail.The leading parton energy loss is dominated by radiative energy loss and have a quadratic path length dependence at the beginning,this distance dependence will become much week due to the accumulated energy loss.We also look at the time evolution and spatial distribution of the medium excitation induced by a single jet parton,a mach cone like shock wave followed by the depletion wake is observed.Because of the recovery of the parton energy loss inside the jet cone,the reconstructed jet will have less energy loss compared to the leading jet.The energy flow inside and outside the jet cone will also lead to the modification of the jet profile.For the real calculation of jet modification inside the quark gluon plasma,we use Pythia to generate the initial parton shower and a 3+1D ideal hydrodynamic model to provide the information of the evolving bulk matter.We then calculate various observables in γ-jet events and dijet events in heavy ion collisions.Start with γ-jct asymmetry,we further exam the distance dependence of jet energy loss by looking at the shift of the peak of the pT distribution.Multiple jets are found to be suppressed according to the γ-jet azimuthal correlation.To look inside the jet cone,we investigate the modification of jet shape,jet fragmentation function and energy flow of γ-jet.For the dijet system,we carry the above calculation for the leading jet and subleading jet respectively and investigate the pT imbalance in particular.For the further study of the jet-medium interaction,We have combined the Linear Boltzmann Transport model with a event-by-event 3+1D hydrodynamic model in real time and developed the CoLBT-Hydro model（the coupled Linear Boltzmann Transport and hydro model）.In this hybrid approach,the energy momentum deposition from the high energy parton to the medium is treated as source term in hydrodynamic equation.Therefore we can simulate the evolution of both the jet and the bulk matter simultaneously.Within this CoLBT-Hydro model,we have calculated the-γ-hadron correlation in heavy ion collisions.We have found that the enhancement of the soft hadron in γ-jet events have a typical transverse momentum range pr<2GeV which is independent with the pT of theγ.The broadened azimuthal distribution of the final hadron in heavy ion collision has a depletion at the γ direction due to the jet-medium interaction.This two effects are the evidence of the jet-induced medium excitation inside quark gluon plasma.In addition,we have extended our Linear Boltzmann Transport model for the study of the heavy quark evolution.we first investigate the heavy quark energy loss and its mass dependence.As the energy losses suffered by the heavy quark from elastic scattering and induced gluon radiation are comparable at the early stage,radiative energy loss become the dominate source with the increasing of the path length.Due to the dead cone effect,energy loss of a b quark is considerably less than a c quark.For the study of the D meson in heavy ion collision,we use a hybrid model in which both the fragmentation and coalescence mechanisms are included to simulate the hadronization of the heavy quark.We have found that the heavy quark transport coefficient given by the leading order perturbative QCD calculation is incapable to describe the D meson R_AA and v₂.Therefore we have introduced a Kp factor for the modification of the momentum dependence of the transport coefficient at low p,and a KT factor for the modification of the temperature dependence of the transport coefficient near Tc.Our simulation can describe the experimental data of D meson R_AA and v₂ at both RHIC and LHC with this parametrization.