Dilepton Production In PP Collisions Within Pythia Model

The relativistic heavy ion collisions have been paid a lot of interest all over the world. By the study of collision, people mainly intend to know some properties of QCD at the finite temperature and finite density, the critical value of phase transition, and the boundary of the first order phase transition. LHC and RHIC have done a lot of work in this area, and many researchers around the world have made much analysis of the experimental data. It was found that a new kind of matter, which has a strong coupling effect, may be formed in the collisions at high energy. The new matter, which is very popular now, is called QGP. Those conclusions are mainly based on the measurement of the final-state hadrons. In high-energy nuclear collisions, the dileptons, which will be produced in each phase of system evolution, don’t participate in the strong interactions. As a good electromagnetic probe, the dileptons play an important role on the exploring the characteristic of the new matter created in the collisions.The production of dileptons can be divided into three stages:the leptons in the low mass region (Mee<1.1GeV/c2) are mainly produced by the mesons of hadronic gas and the virtual photons; The dileptons in the intermediate mass region (Mee<1.1GeV/c2) may be produced by the semileptonic decays of heavy quarks and QGP thermal radiation. Heavy quarkonium decays and Drell-Yan processes, which are at the early stage of the collision, dominate the dilepton spectrum in the high mass region (Mee>3.0GeV/c2).In this thesis, we use Pythia event generator software to simulate dilepton production via various processes in pp collisions at (?)=200GeV. This study can offer a background for the dilepton study in high energy nuclear collisions.The thesis is arranged as follows:The present status of high energy physics and the nature of dileptons are introduced in the first chapter. The second chapter covers a brief introduction of Pythia model and various processes of dilepton production in pp collisions. In the third chapter are presented our main simulation results.The contribution from different chains are presented and compared. Then Discussion and conclusions are made in the fouth chapter.We find that cc dominate the production of dileptons in the intermediate mass region, and bb give little contribution to the production of dileptons. Besides, the mass resonance peak of dileptons also reflects indirectly the nature of some resonances, such as using the resonance peak to get the production of ω and ρ.