Transition to meson-dominated matter at RHIC. Consequences for kaon flow

Anisotropic flow of kaons and antikaons is studied in heavy-ion collisions at CERN SPS and BNL RHIC energies within the microscopic quark–gluon string model. In the midrapidity range the directed flow of kaons v1 differs considerably from that of antikaons at SPS energy (Elab=160 A GeV), while at RHIC energy (s=130 A GeV) the excitation functions of both, kaon and antikaon, flows coincide within the statistical error bars. The change is attributed to formation of dense meson-dominated matter at RHIC, where the differences in interaction cross sections of kaons and antikaons become unimportant. The time evolution of the kaon anisotropic flow is also investigated. The elliptic flow of these hadrons is found to develop at midrapidity at times 3⩽t⩽10 fm/c, which is much larger than the nuclear passing time tpass=0.12 fm/c. As a function of transverse momentum the elliptic flow increases almost linearly with rising pt. It stops to rise at pt⩾1.5 GeV/c reaching the saturation value v2K(pt)≈10%.