| One of the focuses in investigating the high energy heavy-ion collisions is to explore the existence and the properties of Quark-Gluon-Plasraa (QGP) which is predicted by the strong interaction theory - quantum chromodynamics (QCD). From the SPS/CERN experiments at the end of last century and the RHIC/BNL experiments at the begining of this century we can see the complexity to explore QGP. Even if QGP is formed, it can just exist for a very short period of time and then decays into final state hadrons at the end of the expansion and the cooling of the system. The initial state information may be damaged by the final state interactions during the evolution process. So we can only explore the new phenomena related to the QGP phase transition through the properties of the finial state particles. Thus far, a variety of possible signatures have been proposed theoretically and experimentally. At the same time, we must study those new phenomena carefully and ask the question that whether similar phenomena may appear if there is not. QGP formation. To offer this "con" conclusion work is very arduous and numerous, but it is very necessary. Our work is of this kind. The main motivation of this thesis is to see the possibility of charge fluctuations as a signature of QGP phase transition.The first chapter is introduction. A lot of possible signatures of QGP formationpredicted by theorists are introduced in this part.The ultra-high energy heavy-ion experiments are the main ways to study QGP phase transition at the controlled condition. In the second chapter we give a simple introduction of the ultra-high energy heavy-ion experiments. From ACS energies to RHIC energies, heavier and heavier nucleus are accelerated and the beam energies become higher and higher. For the BNL/AGS fixed target experiments, baryon-rich region had been created but no direct evidences for QGP formation were found. The synthetical results from Pb+Pb collisions at CERN/SPS energies show some evidences of the deconfined phase but can not make a determination. With the running of Au+Au collisions at @@ = 58,130 and 200 GeV, each experimental collaboration gives the low px and high PT data. For the low pr hadrons, the bayon number density is very low and shows the evidence of early stage equilibrium. There exists elliptic flow character for the high PT hadrons. The jet quenching and energy density measurement directly for high density matter were also being taken into account extensively.Because of the non-Abelian feature of strong interaction theory, it can not describe non-perturbative effect, so phenomenological models provide the main study method for relativistic nucleon-nucleon collisions. Together with the rapid progress of relativistic nucleon-nucleon collisions, many phenomenological models were built up and hope that those models can give reasonable explanation of the existed experimental results and give reasonable prediction for the forthcoming experiments. The Lund string dynamical model FRIFIOF, LUCIAE model and JPCIAE model were introduced in the third chapter. LUCIAE model is based on FRIFIOF model,while JPCIAE model is based on PYTH1A. PACIAE model, a new model based on parton and hadron cascade is being improved and its physical ideas is introduced. The simplest form of the parton and hadron cascade model, PACIAE1.0, is employed to investigate the charge fluctuation of quark matter and the Pauli blocking at the partonic stage of ultra-relativistic nucleus-nucleus collisions and its effect on the hadronic final state.After the event-by-event charged particle ratio fluctuations were proposed by S. Jeori, V. Kock et al. as a signature of QGP formation, it had evoked extensive interesting theoretically and experimentally. Event-by-event fluctuations of charged particle ratios were measured by NA49 in Pb+Pb collisions at 40, 80 and 158A GeV/c and recently the charge fluctuations were also measured by PHENIX arid STAR in Au+Au collisions at @@=130 GeV.Charged multiplicity density is very important for the stud...
|
PDF Full Text Request