| Modern physics believes that the basic components of protons and neutrons in the nucleus are quarks and gluons,but there are no free quarks and gluons in nature,which are bound to nucleon by strong interactions.This is the quark confinement described by Quantum Chromodynamics(QCD).At the same time,QCD theory also shows that the greater the momentum transferred between quarks through gluons,the smaller the strong interaction between quarks,and the more close the quark behavior is to the behavior of free particles,namely asymptotic freedom.In high-energy heavy-ion collisions at RHIC and the LHC,quarks are released from confinement in the nucleus,and a new form of matter——Quark-Gluon Plasma(QGP)is created.Due to its extremely short exsitence time,QGP could not be detected directly in experiments,so there have developed many probes to study the properties of QGP.Jet quenching effect,as hard probe,is an important means and method to study the formation and properties of the QGP.When large transverse momentum partons(quarks or gluons)produced in collision initial stage through the QGP medium,the gluon bremsstrahlung is caused by multiple scattering with the partons in the medium.And then the partons lost their energy.As one of the consequences of jet quenching and energy loss,the yield of high transverse momentum jets in nucleus-nucleus(A+A)collisions is suppressed as compared to that in proton-proton(p+p)collisions normalized by the number of binary nucleon-nucleon collisions.In this paper,the single inclusive cross section of hadron and jet in the final state under the framework of perturbation QCD theory are firstly introduced,and the calculation of the radiative energy loss of jets in the High-Twist theory is reviewed.Secondly,the parameterized form of the jet transverse momentum spectrum,in p+p collisions,is obtained by comparing with the experimental data,and the jet transverse momentum spectrum in the quenched nucleus-nucleus collisions is obtained by shifting ?pT to the left.We assume that the transverse momentum shift ?pT depends on the number of binary nucleon-nucleon collisions by Npart and depends on jet pT by exponential form.The parameterized form of the energy loss ?pT in the(?)and 2.76 Tev Pb+Pb collisions and 200 Gev Au+Au collisions is obtained by comparing the experimental data with that of the jet RAA.Then in the 5.02 TeV and 2.76 TeV Pb+Pb collisions and 200 GeV Au+Au collisions,the High-Twist theory calculation of the jet radiative energy loss AE is compared with the ?pT based on the shift of the jet transverse momentum spectrum.Our study shows that there is a great difference between the average radiative energy(?Ea)of the leading parton in QGP medium given by the High-Twist theory and ?pT based on the jet shift form.However,the average radiative energy loss<?Ejet>calculated by the High-Twist theory is close to ?pT in the large transverse momentum region after the jet with a certain cone size is defined with the leading parton as the axis.In peripheral collisions,the smaller Npart,the QGP medium volume is smaller,indicating that the path of the jet propagating through the medium is shorter,and the energy loss ofthe jet is smaller.By comparing the jet energy loss in different collision energies,we find that the higher the collision energy,(?Ejet)is closer to ?pT·We also calculated the radiative energy loss with different jet cone size R.The numerical calculation of the energy loss of the jet with different cone sizes given by the High-Twist theory and the shift of the jet transverse momentum spectrum shows that the smaller the cone size is,the greater the energy loss is,and the greater the gluon radiated from the jet is,indicating that the gluon radiation is mainly near the jet axis. |
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