Nuclear modification factors of phi mesons in d+Au, Cu+Cu and Au+Au collisions at sqrt(SNN)=200 GeV
Abstract
The PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) has performed systematic measurements of phi meson production in the K+K- decay channel at midrapidity in p+p, d+Au, Cu+Cu and Au+Au collisions at sqrt(SNN)=200 GeV. Results are presented on the phi invariant yield and the nuclear modification factor RAA for Au+Au and Cu+Cu, and RdA for d+Au collisions, studied as a function of transverse momentum (1<pT<7 GeV/c) and centrality. In central and mid-central Au+Au collisions, the RAA of phi exhibits a suppression relative to expectations from binary scaled p+p results. The amount of suppression is smaller than that of the neutral pion and the eta meson in the intermediate pT range (2--5 GeV/c); whereas at higher pT the phi, pi0, and eta show similar suppression. The baryon (protons and anti-protons) excess observed in central Au+Au collisions at intermediate pT is not observed for the phi meson despite the similar mass of the proton and the phi. This suggests that the excess is linked to the number of constituent quarks rather than the hadron mass. The difference gradually disappears with decreasing centrality and for peripheral collisions the RAA values for both particles are consistent with binary scaling. Cu+Cu collisions show the same yield and suppression as Au+Au collisions for the same number of Npart. The RdA of phi shows no evidence for cold nuclear effects within uncertainties.