Abstract

New measurements of directed flow for charged hadrons, characterized by the Fourier coefficient v(1), are presented for transverse momenta p(T), and centrality intervals in Au+Au collisions recorded by the STAR experiment for the center-of-mass energy range root s(NN) = 7.7-200 GeV. The measurements underscore the importance of momentum conservation, and the characteristic dependencies on root s(NN), centrality and p(T) are consistent with the expectations of geometric fluctuations generated in the initial stages of the collision, acting in concert with a hydrodynamic-like expansion. The centrality and p(T) dependencies of v(1)(even)W, as well as an observed similarity between its excitation function and that for v(3), could serve as constraints for initial-state models. The v(1)(even) excitation function could also provide an important supplement to the flow measurements employed for precision extraction of the temperature dependence of the specific shear viscosity. (c) 2018 Published by Elsevier B.V.