Direct Photons, Vector Mesons and Heavy Flavor Production at RHIC

Abstract

Recent results concerning the production of direct photons, vector mesons, charmonium, and open heavy flavor in p+p, d+Au, and Au+Au collisions at √s _NN = 200 GeV at RHIC are discussed. The production of direct photons in Au+Au collisions does not exhibit a centrality-dependent suppression at higher transverse momentum such as that observed for hadrons at RHIC. Rather, it is well-described by predictions based on NLO pQCD scaled by the number of binary nucleon-nucleon collisions. Measurements of φ production do exhibit a suppression in central Au+Au collisions relative to scaled peripheral collisions and scaled p+p collisions consistent with expectations of recombination models. Measurements of J/ψ production using dielectrons and dimuons exhibit a suppression rather than an enhancement in central Au+Au collisions as predicted by some recent models. Open heavy flavor production has been measured via semileptonic decays of heavy quarks as well as direct reconstruction of charmed mesons. In Au+Au collisions, although the total yield does scale by the number of binary collisions, the spectrum exhibits a strong modification relative to scaled results based on p+p collisions. Measurements of the azimuthal anisotropy parameter v₂ for electrons resulting from charm meson decay in Au+Au collisions are consistent with calculations in which charm quarks participate in the collective flow of the produced medium.