Intensity Interferometry Of Granular Source In High Energy Heavy-Ion Reaction

The aim of experiment in high energy heavy ion collisions is to probe a newstate of hadronic matter, the Quark-Gluon Plasma (QGP), with extreme energy densi-ties, temperatures and pressure. In terms of the Quantum Chromo-Dynamics (QCD),the collision system may occur the first-order phase transition between the QGP andhadronic state, when the QGP is created. One important sign of this transition isthe occurrence of granular structure in the particle-emitting source. The further in-vestigation indicate that the occurrence of a granular structure may not be limited tofirst-order phase transition. Many effects, such as the large ?uctuations of the initialtransverse energy density, the surface tension effect, and the longitudinal expansion,may lead to the fragmentation of the system and the formation of many droplets ofthe QGP. The pions interferometry (Hanbury-Brown-Twiss interferometry) is a pow-erful tool for studying the space-time structure and the dynamics of particle-emittingsource produced in high energy heavy ion collisions. Therefore, the elaborate analysisof pions interferometry with various methods on granular source may help in detect-ing the granular structure of particle-emitting source by interferometry, which is themotivation and purpose of studies in this thesis.The chaotic sources were assumed in the previously research on the granularsource, which can not explain the partially coherent (partially chaotic) source in ex-periment. It is necessary to investigate the chaoticity of the granular source. Based onthe chaotic granular source model, we examine the two-pion and three-pion correla-tion functions for a granular source model of coherent droplets under the assumptionthat the pions emitted from the same droplet are coherent. It is difficult to distinguishthe granular source and the partially coherent Gaussian source from the correlationfunctions due to the similar form. By comparing the normalized pure three-pion cor-relations of the granular source and a partially coherent Gaussian source, we findthat the difference of the normalized pure three-pion correlations between the twosources is distinct in small relative momentum region , when the chaoticity parameterof two-pion correlation is smaller than 0.8. It may be an approach for analysis on thegranularity of partially coherent source by pion interferometry. By means of the imaging technique introduced by Brown and Danielewicz, onecan reconstruct the two-pion source function from the measured two-pion correlations,this method is model-independent. We expect the imaging technique can be used todetect the granular structure of pion-emitting source in heavy ion collision, so theanalysis on granular source by imaging technique is the main research contents of thisthesis. We investigate the two-pion source function of a static granular source modeland find the"two-tiered"structure. By the examination on the evolving sources, wefind that the two-tiered structure of two-pion source functions are more obvious thanstatic case. Using a parametrized formula of granular source function, we examine thetwo-tiered structure of the source functions for the imaging data of Au+Au collisionsat AGS (2, 4, 6, 8 A GeV) and RHIC (√sNN = 200 GeV). Our analysis resultsindicate that there are not visible granularity for the sources produced in the collisionsat the AGS energies. However, the data for the RHIC collisions with the selections40% < centrality < 90% and 0.20 GeV/c < kT < 0.36 GeV/c are better described bythe model with granular emission than from that of one Gaussian.Based on the imaging technique, we propose new methods to describe the space-time structure of pion-emitting source by the characteristic quantities of the relative-distance of two particles. This method is model-independent. By the calculation ofmoments of the relative-distance, one can obtain more information about the space-time structure of sources. We discussed this method on the Gaussian model and in-troduce"the relative-distance radius"to characterize the spatial size of pion-emittingregion. By the examination on the granular source and the Core-Halo source andcompare the results with that of Gaussian fitting, the results indicate that the char-acteristic quantities of relative-distance can re?ect the contribution to the source sizeand chaoticity from the effects of dynamical expansion and long-lived resonance de-cays. This method may help us to understand correctly the space-time structure anddynamics of source.