Directed Flow of Identified Particles in Au+Au Collisions at √SNN=200 GeV at RHIC
STAR’s measurements of directed flow (v1) around midrapidity for π±, K±, K0S, p, and p¯ in Au+Au collisions at √sNN=200 GeV are presented. A negative v1(y) slope is observed for most of produced particles (π±, K±, K0S, and p¯). In 5%–30% central collisions, a sizable difference is present between the v1(y) slope of protons and antiprotons, with the former being consistent with zero within errors. The v1 excitation function is presented. Comparisons to model calculations (RQMD, UrQMD, AMPT, QGSM with parton recombination, and a hydrodynamics model with a tilted source) are made. For those models which have calculations of v1 for both pions and protons, none of them can describe v1(y) for pions and protons simultaneously. The hydrodynamics model with a tilted source as currently implemented cannot explain the centrality dependence of the difference between the v1(y) slopes of protons and antiprotons.