A Monte Carlo Study On The Identification Of Quark And Gluon Jets

Multiparticle production is the most charateristic feature of current high energy physics. Observed particle multiplicities are typically between ten and a hundred. One task of data analysis is to obtain useful information on interactions from the distribution of final state particles. In high energy electron-positron collision physics, some final state particles may have similar momentum direction and stay in a cone to form a "jet". It's believed that "jets" result from the hadronization of par-tons, and the better understanding of jets, the more we know about quarks and gluon. In addition, studying the properties of quark and gluon jets is a way to verify Quantum Chromodynam-ics(QCD) and investigate the parton hadronization mechanics. Monte Carlo simulation is a widely used method in high energy physics since the high energy interaction involved a lot of uncertain factors and random variables.In this thesis, firstly we briefly introduce the difference between quark and gluon jets predicted by QCD and the published experimental results on jet mean multiplicity ratio between quark jet and gulon jet. Secondly we present some basic knowledge about Monte Carlo event generator, focusing on the different hadronization models included in the widely used event generators HERWIG and JETSET. Thirdly we carry out a detailed study on quark and gluon jet identification by using the angles between jets of three-jet events in e+e~collisions from both parton and hadron levels, including theoretical background, efficiency and purity improvement by introducing an extra angular cut. Finally we give the result on quark and gluon jet multiplicity by using the angular method. The result is consistent with QCD prediction and the experimental results qualitatively.