Simulation Analysis Of Elliptic Flow Splitting Between Particles And Corresponding Antiparticles At RHIC-bes Energies

In order to explore the QCD phase structure at higher baryon chemical potential,the beam energy scan（BES）experiment has been started at RHIC（Relativistic Heavy Ion Collider）.The beam energy dependence of the elliptic flow difference between particles and corresponding antiparticles is one of the main discoveries of the phase I of the beam energy scanning experiment（BES-I）.And this difference decreases with the increasing beam energy,indicating the violation of the number of constituent quark scaling of the elliptic flow at lower energies of the BES-I experiment,and the results of the dynamical mean-_Tfluctuations may indicate a change to a first order phase transition at corresponding energies.A multi-phase transport model（AMPT）contains the interaction of parton phase and the quark recombination process,which can be used to study the early dynamical evolution of heavy ion collisions.In this thesis,the AMPT model is used to study the elliptic flow and the dynamical mean-_Tfluctuations at RHIC-BES energy region.For the purpose of understanding the elliptic flow splitting between particles and corresponding antiparticles in the RHIC-BES energies,the effects of parton cascade,hadron cascade,and quark recombination processes on the elliptic flow of hadrons have been studied.The default reaction plane in the model is used to obtain the elliptic flow.We have calculated the elliptic flow ofπ⁺andπ^-,K⁺and K^-with the AMPT model,it is found that their elliptic flow difference between particles and corresponding antiparticles are not obvious.While for p and（?）,the elliptic flow of（?） is significantly larger than the elliptic flow of p,and their elliptic flow difference increases with the decreasing energy.The formation of the elliptic flow difference between particles and their corresponding antiparticles has been discussed,including parton cascade,hadronization mechanism and hadron cascade process.We then focus on the effect of the hadronization mechanism on the elliptic flow difference between p and（?）,and found that the hadronization mechanism is one of the reasons for the formation of elliptic flow splitting between p and（?）.By introducing the dynamical quark coalescence mechanism（DQCM）into the AMPT model,quarks are combined in phase space to form hadrons,and the corre-sponding results has been compared with the results from the original AMPT.The AMPT model has been used to calculate relative dynamical mean-_TfluctuationΦ_dynfor Au+Au collision at√（^SNN）=7.7–200 Ge V and Pb+Pb collision at√（^SNN）=2.76 Te V.The results show that at higher energies（200 Ge V and 2.76 Te V）,theΦ_dynof charged hadrons is not sensitive to the hadronization process;while at lower energy（19.6 Ge V）,the result ofΦ_dynis significantly different with these two coalescence scenarios.With the hadron information at different stages from the AMPT model,the direct affect of hadronization mechanism and the indirect effect caused by resonances production onΦ_dynare discussed.The results of the AMPT model are compared with the experimental results.It is found that the experimental results at higher energies can be well reproduced by the original AMPT which based on the coordinate coalescence scenario,and the DQCM AMPT based on the phase space coalescence scenario can explain most of the experimental data.DQCM AMPT is used to analyze the behavior of the elliptic flow and the transverse momentum spectrum.Firstly,we analyze transverse momentum spectrum of charged hadrons,and found that the transverse momentum spectrum of the antiproton is more sensitive to the hadronization mechanism.The dependence of the antiproton transverse momentum spectrum on the meson size parameter and baryon size parameter in the model has been discussed.The meson size parameter and baryon size parameter dependence of the elliptic flow has been studied,and the reason of the meson size parameter dependence of antiproton elliptic flow has been discussed.The behavior of elliptic flow splitting of proton and antiproton with these two coalescences has been studied,and the results show that the DQCM AMPT can partially explain the experimental data.Finally,a comparison has been made between the elliptic flow from these two coalescences and from the experiment.