Model Study Of Transverse Expansion And Anti-proton To Proton Ration From ～(197)Au+～(197) Au Collisions At RHIC Energies By RQMD

Transverse collective expansion, as an important kind of collective flow, characterizes particles that are emitted from source with a common velocity field independent of the azimuthal angel. By analyzing the transverse momentum or transverse energetic spectra of those particles from mid-rapidity in heavy-ion collisions, we can gain the information on transverse collective expansion in the center area of the collisions. Using RQMD to generate 80,000 Monte Carlo mini-bias events of 197Au +197 Au collisions at sNN = 200GeV, We study the transverse momentum distribution, particle ratios and the freeze-out time and transverse radius distributions of final state hadronic system, comparing them with the reported experimental results. We thus discuss an approach to study the early partonic collectivity in high energy nuclear collisions. It shows that in high energetic nuclear collisions at RHIC energies, there exists very strong transverse expansion, which becomes stronger with increasing colliding centrality. The transverse expansion origins in early stages, but mainly develops and finishes during the late stage of the colliding. For those heavier particles, such as J/ψ, E, and Ω etc.,becuase of their smaller hadronic cross section, they rarely participate the final state hadronic re-scattering, and depart the system much earlier. Their transverse expansion maybe is the result of the cumulative collective effect during the early partonic stage. This show us a very useful signal in studying the systematic property in the early stage of the evolutive colliding system, that's, a non-zero flow component of those particles observed by experiment could be interpreted as a signal for partonic flow.Particle ratios embody the chemical equilibrium driven by inelastic interaction during rapid expansion when the temperature decreases in the colliding system, The measured hadron ratios provide the chemical composition of the fireball at the chemical freeze-out point and access the baryon transporter stopping) for the initial conditions at early stage of the collisions. In this paper, we study the anti-proton to proton ratio from ig7Au +197 Au collisions, analyzing p/p ratio as functions of rapidity, transverse momentum and centrality at ^/SAW = 200GeV and the dependence on the center of mass energy of p/p ratio, compared with the experimental results. It shows that the p/p ratio hasn't obvious dependence on rapidity for mid-rapidity, but shows a slight increase trend with pt increasing in the range of pt < 1GeV/c for mini-bias or central collisions, and RQMD shows a more remarkable correlation between p/p ratio and centrality than experiments do at sNN=200GeV. Comparison of the results at various energies indicates that the mid-rapidity p/p ratio in heavy-ion collisions increases significantly with thecollision energy. And above all, at low energies, re-scattering RQMD predicts well p/p ratio, but predicts a smaller p/p ratio than experiments at RHIC energies. This indicates that hadronic re-scattering at final stage is suppressed at RHIC energies, compared to ACS, SPS energies.