Model Study On Non-thermal Phase Transition And Antiproton To Proton Ratio

We carry on model study on non-thermal phase transition and antiproton to proton ratio at RHIC energies.The local large fluctuation observed in the final phase space of cosmic rays experiment and high energy collisions cause intermittency and fractal to be the focus. Moreover, the different behavior (a large number of small fluctuations and a few large fluctuations) of local large fluctuation has called up people's attention. A variable is expected to explain the two behaviors. Making analogy with the '"spin-glass" phase in polymers, Peschanski put forward the idea that there exists non-thermal phase transition in multiparticle systems. A parameter Xq has been introduced to characterize the non-thermal phase transition. The parameter A, is studied in many experiments of hadron-hadron collisions and heavy ion collisions after it was introduced. But in the present available hadron-hadron collision experiments, due to the restriction of energy, the average multiplicity is very low. and the rank of the factorial moments could not be high. So, no clear evidence of non-thermal phase transition has been seen. Among the heavy ion experiments. the minimum value is observed in C-Cu collision. But the low multiplicity of this experiment and the vague intermittency in nuclear-nuclear collisions result in large error when the analysed rank of A, is high. So the results need to be checked. Dueto the not ideal results of present experiments, we study the non-thermal phase transition in self-similar cascading model.In the second part of the thesis, the non-thermal phase transition in high energy collisions is studied in detail in the framework of random cascade model. The relation between the characteristic parameter Xq of phase transition and the rank q of moment is obtained using Monte Carlo simulation, and the existence of two phases in self-similar cascading multiparticle systems is shown. The relation between the critical point qc of phase transition on the fluctuation parameter Q is obtained and compared with the experimental results from NA22. The same study is carried out also by analytical calculation under central limit approximation. The range of validity of the central limit approximation is discussed.Heavy ion collisions provide more ideal environment for studying into the deeper level structure of particles. The following phenomenon is desired to seen: with the increase of colliding energy, the net baryon number tends to be zero in the mid-rapidity region. The experimental results become close to entire baryon number transport step by step, from the entire baryon number stopping at low-energy to baryon transport with energy increasing. The primary goal of heavy ion experiment is to create environment for the formation of quark-gluon plasma. The formation of this state depends on the initial conditions of the matter created at the early stage of heavy ion collisions. Baryon number transport and stopping provide entirely different initial condition for the probably produced QGP. The information on baryon transporter stopping) may be accessed by the measure-merit of antiproton to proton ratio yield. Since RHIC has run at a center-of-mass energy SNN = 130 GeV, and STAR collaboration analysed antiproton to proton ratio in mid-rapidity region using the first batch of data. We do model study on antiproton to proton ratio here. And we expect to see whether HIJING can successfully describe Au-l-Au collisions at 130 AGeV and give a prediction to the results at 200 AGeV at the same time.In the third part of the thesis, the HIJING 2.0 is used to generate Monte Carlo events for Au+Au minimum bias collisions at RHIC energies-y/sjvN = 130 and 200 GeV. It is shown using the Monte Carlo event sample that impact parameter has approximately linear dependence on multiplicity. Both of them can be used as characteristic quantity for centrality. The results on the p/p ratio show that this ratio does not change remarkably with centrality. transverse momentum and rapidity, and is independent of the reaction p...