Studies On The Mechanism Of Hadronization And The Correlations Of Final State Particles

The Standard Model of particle physics,as the main framework of the studying of particle physics,can provide accurate descriptions of a lot of experimental data and predict some new physical phenomena,although there exist some limitations.The theory of the strong interactions between quarks and gluons,QCD,is only valid when quarks or gluons are in the perturbative regime where the distances are small and momentum transfers are large.That conclusion has been proved by the experiments,such as deep inelastic scattering,electron-positron collision and hadron-hadron colli-sion.However,the QCD calculation faces difficulty when the involved regime is at large distances or small momentum transfers.Nevertheless,a large number of non-pert,urbative processes are involved during the production of particles in high energy collisions.The description of these processes needs various kinds of phenomenological models.The focus of this thesis is on the studies of the mechanism of hadronization and the correlations of final state particles.The theoretical background is briefly introduced in chapter two and three.Chap-ter two introduces the Standard Model and its limitations,and theories of high energy,heavy ion collisions within the framework of the standard model.Several Monte Carlo models are presented as important t,ools and references in chapter three,followed by the main part of the studies in the thesis.These studies are as follows.(1)The.discussion on the mechanism of hadronization based on color interac-tions between quarks.The hadronization process in high energy collisions is a typical non-perturbative process,which often relies on some models,e.g.the Lund string model used in PYTHIA,the cluster model used in HERWIG and the coalescence models used in AMPT and PACIAE,etc.However,the interactions are not taken into consideration in these models.Our purpose is to investigate the effects of such kind of interactions on the production,distributions and correlations of final state hadrons.This mechanism is a coalescence model based on molecular dynamics,with semi-relativistic motions of quarks and color interactions between quarks taken in-to account.In this model,a phenomenological potential of Cornell type is adopted to describe the interactions between quarks.The interactions drive the process of hadronization and finally make quarks form different clusters with neutral color.To investigate the effects of the interactions,PYTHIA is used to generate the initial s-tates of high energy pp collisions.Then different distributions and correlations of final state hadrons with different parameters are obtained.These results are compared with the results only calculated by PYTHIA to investigate the influence of this kind of interactions on hadronization.(2)The study on the two-particle azimuthal correlations.On the basis of the initial state geometrical symmetry of two colliding nuclei in the central rapidity region and non-central rapidity region during high energy collisions,general forms of one-and two-particle azimuthal distributions are derived.Some new coefficients about two-particle azimuthal correlations are suggested.These coefficients correspond to different patterns of interactions and thus could be applied to describe the collective behavior of final state particles.The relations between the coefficients and usual flow harmonics are discussed.For the reason that these correlation coefficients are derived on the basis of the initial state geometrical symmetry,they are independent of the details of models describing the interactions between partons or hadrons during the evolution process.Therefore,these coefficients could be widely applicable and help constrain the models describing high energy heavy ion collisions.The AMPT generator is applied to generate(?)=200 GeV Au + Au event samples within different centrality intervals.Some results in central and non-central rapidity region are calculated and analyzed.The main purpose of this study is to present the general forms of two-particle distributions in central rapidity region and non-central rapidity region.These numerical results are used to support the current theory,while the results rely on the details of interactions between particles in different models.