Jet-induced Medium Excitation In Heavy-ion Collision

The Relativistic Heavy Ion Collider(RHIC)at the Brookhaven National Laboratory and the Larger Hadron Collider(LHC)at the European Organization for Nuclear Research(CERN)attempt to produce a form of hot and dense matter called quark gluon plasma(QGP)and study its properties in these nuclear collsions.The quark-gluon plasma is a medium of very short space-time scales?The experiment can infer the properties of the hot and dense medium created in the early stages of the collision,by measuring the particles resulting from the collision.The experimental data used in trying to determine the properties of the hot medium can be divided into two categories:soft probes and hard probes.Soft probes involve the observation of the bulk of light hadrons with small transverse momentum produced in the collision?the hard probes are originated in the early stage of the collision,giving information about the QGP in a direct way.Energetic partons produced from hard parton scattering will lose energy while passing through the medium due to the interaction between partons and medium.Parton energy loss in dense medium was predicted to lead to jet quenching in heavy-ion collisions.Experimen-tal discovery of jet quenching at Relativistic Heavy-ion Collider(RHIC)provides important evidence for the formation of strongly coupled quark-gluon plasma(QGP).Recent theoreti-cal and experimental progress at both RHIC and LHC have advanced the jet tomography as a powerful tool for the study of QGP properties.Jet quenching leads to suppression of leading hadrons,dihadron and ?-hadron correla-tions,due to parton energy loss.It also modifies jet spectra,dijet and ?-jet correlations,jet profiles and jet fragmentation functions.Since jets are reconstructed from collimated clus-ter of hadrons within a jet cone,the final jet modification will be determined not only by energy loss of the leading jet shower partons but also how the lost energy is redistributed in the medium through induced radiation,rescattering and jet-induced medium excitation(j.i.m.e.).Similarly,dissipation of lost energy in medium can also influence soft hadron spectra associated with hard jet production.Tomography of QGP with jets and jet-hadron correlations therefore requires a complete understanding of both jet transport in a fluctuating and dynamically evolving QGP medium and j.i.m.e..Jet-induced medium excitation in heavy-ion collisions has been the subject of many re-cent studies.Theoretical tools used include parton transport,hydrodynamics and AdS/CFT.The Linear Boltzmann Transport(LBT)model has been developed for the study of both jet transport and j.i.m.e.in QGP.It simulates the propagation of not only jet shower partons and radiated gluons but also recoil and back reaction partons from jet-medium interaction within perturbative QCD(pQCD).We have recently developed the first Coupled Linear Boltzmann Transport and hydrody-namics(CoLBT-hydro)for simultaneous event-by-event simulations of jet propagation and hydrodynamic evolution of the bulk medium including j.i.m.e.In this coupled approach,LBT provides a source term for energy-momentum deposition by propagating partons in the hydrodynamics which in turn updates the bulk medium profile for LBT in the next time step.Hadron spectra in ?-jet events of A+A collisions at RHIC and LHC are calculated for the first time that include hadrons from both the modified jet and j.i.m.e.CoLBT-hydro de-scribes well experimental data on the suppression of leading hadrons due to parton energy loss.It also predicts the enhancement of soft hadrons from j.i.m.e.The onset of soft hadron enhancement occurs at a constant transverse momentum due to the thermal nature of soft hadrons from j.i.m.e.which also have a significantly broadened azimuthal distribution rela-tive to the jet direction.Soft hadrons in the ? direction are,on the other hand,depleted due to a diffusion wake behind the jet.