Mass, quark-number, and VsNN dependence of the second and fourth flow harmonics in ultrarelativistic nucleus-nucleus collisions

Abstract

We present STAR measurements of the azimuthal anisotropy parameter v2 for pions, kaons, protons, Λ,Λ̅ ,Ξ+Ξ̅ , and Ω+Ω̅ , along with v4 for pions, kaons, protons, and Λ+Λ̅ at midrapidity for Au+Au collisions at √sNN=62.4 and 200 GeV. The v2(pT) values for all hadron species at 62.4 GeV are similar to those observed in 130 and 200 GeV collisions. For observed kinematic ranges, v2 values at 62.4, 130, and 200 GeV are as little as 10–15% larger than those in Pb+Pb collisions at √sNN=17.3 GeV. At intermediate transverse momentum (pT from 1.5–5 GeV/c), the 62.4 GeV v2(pT) and v4(pT) values are consistent with the quark-number scaling first observed at 200 GeV. A four-particle cumulant analysis is used to assess the nonflow contributions to pions and protons and some indications are found for a smaller nonflow contribution to protons than pions. Baryon v2 is larger than antibaryon v2 at 62.4 and 200 GeV, perhaps indicating either that the initial spatial net-baryon distribution is anisotropic, that the mechanism leading to transport of baryon number from beam- to midrapidity enhances v2 or that antibaryon and baryon annihilation is larger in the in-plane direction.