Anti-flow of Mesons in the High Baryon Density Region

The E895 and STAR experiments demonstrate that the slopes of directed flow with respect to rapidity (dv1/dy|y=0) of mesons are negative in the low transverse momentum (pT ) region, pT <0.8 GeV/c, in Au + Au collisions at root sNN = 3.0-3.9 GeV. Using the transport model JAM, we investigate the directed flow of pi +/-, K +/-, and K0 as functions of rapidity, pT, and collision energy in Au + Au collisions at the same energies as those in the E895 and STAR experiments. We find that the JAM model can qualitatively reproduce the antiflow of KS0 observed in the E895 experiment. The v1 slopes of pions and kaons are analyzed as functions of the pT window, revealing a strong pT dependence of the v1 slopes. Negative v1 slopes are observed in the low pT region, pT <0.8 GeV/c, while positive slopes are shown in the higher pT region. We find that the shadowing effect from spectators is crucial in generating the antiflow of mesons at low pT in the high baryon density region.