| Over the past twenty years, one of the most important aims in the field of high energy nuclear physics is to explore a new form of matter — quark gluon plasma (QGP), which has been predicted by the lattice Quantum Chromodynamics (QCD) at finite temperature. To answer whether there is QGP formation in relativistic high energy heavy ion collision, we should study the signatures of the QGP. A very interesting feature of the experiments at RHIC and LHC is that the hard processes will play an important role for the very high colliding energy. Therefore, the hard probe signal (in particular, the jet quenching) was proposed as a effective QGP signature and has been attracted a lot of attentions up to now. The concept of jet quenching interprets that the jet produced in hard scattering processes in the early stages of a relativistic heavy ion collision should pass through the nuclear medium and lose energy by induced gluon radiation due to multiple scattering in nuclei. It is predicted the energy loss of these propagating partons is sensitive to the medium through which they travel, and should be a direct method of investigating the features of strong interacting medium.Perturbative Quantum Chromodynamics (pQCD) is considered as a useful tool to study the jet quenching. However, in reality any physics processes are involved the long-distance behaviors because the initial states or final states in any experiments are hadrons, which are described by the hadron wave functions, a typical long-distance behavior. The asymptotical freedom shows that perturbative theory is no longer effective for any long-distance physics. Therefore, to make any perturbative calculation possible in QCD, one has to separate the long-distance from the short-distance behavior, which method is called as factorization. The nonperturbative part, such as parton distribution function (PDF) and parton fragmentation function (PFF), can only be measured from experiments, but it is universal and we can predict its scale evolution with pQCD, which is known as DGLAP QCD evolution equations.In this thesis, I would like to explore the parton energy loss in eA deeply inelastic scattering (DIS). Because the multiple scattering is always associated with the high twist processes, firstly I will review the case at twist-4 in eA DIS which has been studied recently by other authors. Furthermore, to extend the previous work to the higher twist case, I calculate the hadronic tensor at twist-6 and give a general analysis about the higher twist contributions. It is shown that when the radius of the nucleus (Rα) is not very large but the momentum transfer (Q2) is large, one can only consider double scattering because all higher twist contributions will be suppressed significantly. However, when Rα is very large but Q2 is not large, the higher twist terms will give considerable contributions and the resummation of all higher twist contributions should be needed. In the thesis, I introduce a new method to calculate the amplitude for gluon radiation on the base of helicity amplitude approximation (HAA). Using this new method, one can easily calculate the amplitude for gluon radiation of multiple scattering, which gives a road to resum all higher twist contributions.
|
PDF Full Text Request