Hbt Radii And Character Of Emitting Source In Au+au Collisions At Rhic Energy

The goal of high energy heavy ion collision at RHIC is to study the propertiesof"color deconfined"nuclear matter with extremely high temperature and high den-sity. The system may come through the stages of pre-equilibrium, parton evolution,hadronization and hadron evolution. The final freeze-out source approximately reachthe local equilibrium. The extraction of the thermodynamical and geometrical param-eters(such as temperature, collective expansion velocity and size) is the issue whichpeople concern. The parton evolution dominate the system in the early stage when theenergy density is very high, so the interaction and the phase transition of partons areimportant to the final observables. The problem of phase transition between hadronsand partons becomes the focus for theorists and experimentalist. The HBT correlationis an important method to extract the space-time and dynamical information of theemitting source, and it also sensitive to the properties of the partonic stage. In mythesis, we use Blast-Wave parametrization and a multiphase transport model(AMPT)to discuss how to extract some physical parameters with two-particle HBT correlationand analyze the effects of different partonic phase transition mechanism on the HBTcorrelations.The Blast-Wave model is often used to fit the transverse mass(mt) spectra ofπ±,K±,p,pˉsimultaneously to extract the temperature and the transverse expan-sion velocity, which based on the assumption that these six species have the samefreeze-out temperature and expansion velocity. On the other hand, the pair transversemass(MT) dependence of HBT radius Rs is also restricted by the temperature andtransverse expansion velocity. In principle, we can use the mt spectra and the MTdependence of Rs of a single species to extract its own temperature and expansionvelocity. Within the Blast-Wave model, we combine the single-particle mt spectra ofπ? and MT dependence of two-pion HBT radius Rs to extract the thermal freeze-outtemperature and the surface radial ?ow rapidity for six centrality classes in Au+Aucollisions at√sNN = 200 GeV measured by the STAR Collaboration at RHIC. Wecompare the results to those obtained by simultaneous fitting the mt spectra of sixspecies, and find that they are consistent except for the peripheral collisions. This shows that the method of combining the mt spectra and Rs ofπto extract the tem-perature and expansion velocity is feasible and this also implies that it is not good toassume thatπ±,K±,p,pˉhave the same freeze-out condition for peripheral col-lisions. We combine the mt spectra and Rs of kaon to extract its temperature andexpansion velocity and found that kaon will induce larger errors than pion. We alsodiscuss the effect of inconsistent model assumption in single-particle spectrum andHBT correlation on the value of transverse size of the emitting source.AMPT model contain the partonic and hadronic evolution stage, and it can beused to investigate the effect of parton interaction and parton phase transition on thefinal observables. The AMPT model with string melting can reproduce the elliptic?ow and HBT correlation function by adjusting the parton cross section. However,it can not describe well the single-particle transverse mass spectra, rapidity spectraand transverse mass dependence of HBT radii. M. L. Yu et al. introduce the partoncollective phase transition by forcing parton collective hadronization at 5 fm/c andfind that this can improve the description of single-particle rapidity spectra. We studythe effect of collective phase transition of parton on the HBT correlation. We foundthat the collective hadronization ?attens the transverse mass dependence of HBT radii,and the results are more close to the experimental data. The rapidity dependence ofHBT radii is in?uenced by collective phase transition greatly, especially the increasedtrend of HBT radii Rol with rapidity is stronger.The azimuthally sensitive of HBT correlation can re?ect the space-time structureof the source more detailed. The non-central experiment at RHIC found that the oscil-lation amplitude of HBT radii with azimuthal angle is almost unchanged for differenttransverse momentum range. Presently, the Blast-Wave parametrization seem to havedifficult to reproduce this feature. We use AMPT model and RQMD model to inves-tigate the azimuthal angle dependence of HBT radii and found that the oscillation ofRo in transport model mainly comes from the xo ?t correlation term ?2Dxo,βot whilein Blast-Wave parametrization this mainly comes from Dxo,xo.