Antiflow of kaons in relativistic heavy ion collisions

We compare relativistic transport model calculations to recent data on the sideward flow of neutral strange $K_s^0$ mesons for Au+Au collisions at $6A\mathrm{GeV}.$ A soft nuclear equation of state is found to describe very well the positive proton flow data measured in the same experiment. In the absence of the kaon potential, the $K^0$ flow pattern is similar to that of protons. The kaon flow becomes negative if a repulsive kaon potential determined from the impulse approximation is introduced. However, this potential underestimates the data which exhibit larger antiflow. An excellent agreement with the data is obtained when a relativistic scalar-vector kaon potential, that has stronger density dependence, is used. We further find that the transverse momentum dependence of directed and elliptic flow is quite sensitive to the kaon potential in dense matter.