Beam-Energy and Centrality Dependence of Directed Flow of Identified Particles

Abstract

These proceedings present directed flow (v1) measurements in Au+Au collisions from STAR's Beam Energy Scan (BES) program at the Relativistic Heavy-Ion Collider, for p, p‾, Λ, Λ‾, K±, KS0 and π±. At intermediate centrality, protons show a minimum in directed flow slope, dv1/dy|y≤0.8, as a function of beam energy. Proton dv1/dy changes sign near 10 GeV, and the directed flow for Λ is consistent with the proton result. The directed flow slope for net protons shows a clear minimum at 14.5 GeV and becomes positive at beam energies below 10 GeV and above 30 GeV. New results for net-kaon directed flow slope resemble net protons from high energy down to 14.5 GeV, but remain negative at lower energies. The slope dv1/dy shows a strong centrality dependence, especially for p and Λ at the lower beam energies. Available model calculations are in poor agreement.