Difference in Elliptic Flow Between Particles and Antiparticles in Au+Au Collisions at √s_NN=7.7~62.4 GeV in UrQMD

Key words: 
• elliptic flow /
• heavy ion collision /
• UrQMD

Abstract: The elliptic flow for proton, π⁺, K⁺ and their corresponding antiparticles are investigated at mid-rapidity for Au+Au collisions at √s_NN =7.7, 11.5, 19.6, 27, 39, 62.4 GeV, utilizing ultrarelativistic quantum molecular dynamics (UrQMD-3.3p1). We analyze the difference in v2(pT) between the particles and the corresponding antiparticles as a function of the transverse momentum pT. We find that in UrQMD the v2 for K is larger than that for K⁺ at all BES energies. The v2(pT) values are almost identical for π⁺ and π^-􀀀at 7.7s62.4 GeV. While in experiments, at lower energies, 7.7, 11.5 and 19.6 GeV,v2(π^-) is larger than v2(π⁺) for all pT values. We can clearly see that in UrQMD the v2 for antiproton is larger than that for proton at all BES energies, which is in contradiction to the experimental result.The opposite trend observed in experiment is therefore an indication that the strong coupling in heavy ion collision and the non equilibrium in transport process may need further understanding.