Antiflow 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 √sNN = 3.0 - 3.9 GeV. Using the transport model JAM, we investigate the directed flow of π±, 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 anti-flow of K⁰S 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 anti-flow of mesons at low pT in the high baryon density region.