Directed flow of identified particles in Au+Au collisions at √s NN=200GeV at RHIC

Abstract

STAR's measurements of directed flow (v 1) around midrapidity for π ±, K ±, KS0, p, and p in Au+Au collisions at √s NN=200GeV are presented. A negative v 1(y) slope is observed for most of produced particles (π ±, K ±, KS0, and p̄). In 5%-30% central collisions, a sizable difference is present between the v 1(y) slope of protons and antiprotons, with the former being consistent with zero within errors. The v 1 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 v 1 for both pions and protons, none of them can describe v 1(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 v 1(y) slopes of protons and antiprotons. © 2012 American Physical Society.