uc l - th / 0 10 70 56 v 1 2 0 Ju l 2 00 1 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 v 1 differs considerably from that of antikaons at SPS energy (E lab = 160 AGeV), while at RHIC energy (√ s = 130 AGeV) 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 t pass = 0.12 fm/c. As a function of transverse momentum the elliptic flow increases almost linearly with rising p t. It stops to rise at p t ≥ 1.5 GeV/c reaching the saturation value v K 2 (p t) ≈ 10%. 1 Introduction. The main aim of experiments on heavy-ion collisions at relativistic and ultra-relativistic energies is to study the properties of nuclear matter under extreme conditions and to search for distinct signals from the deconfined quark-gluon plasma (QGP) (see [1] and references herein). The transverse collective flow of particles is at present one of the most intensively studied characteristics of heavy-ion collisions [2–4], because the flow is directly linked to the equation of state (EOS) of the system. If even a small amount of the QGP is formed in the course of the collision, it would lead to a reduction of pressure [5–7] and a softening of the EOS [8,9] that can be detected experimentally. To study the properties of transverse particle flow the method of Fourier series expansion [10,11] has been proved to be very useful: