Direct virtual photon production in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV

Abstract

We report the direct virtual photon invariant yields in the transverse momentum ranges $1<p_T<3$ GeV/$c$ and $5<p_T<10$ GeV/$c$ at mid-rapidity derived from the dielectron invariant mass continuum region $0.10<M_{ee}<0.28$ GeV/$c^2$ for 0-80\% minimum-bias Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV. A clear excess in the invariant yield compared to the number-of-binary-collisions ($N_{bin}$) scaled $p+p$ reference is observed in the $p_T$ range $1<p_T<3$ GeV/$c$. For $p_T>6$ GeV/$c$ the production follows $N_{bin}$ scaling. Model calculations with contributions from thermal radiation and initial hard parton scattering are consistent within uncertainties with the direct virtual photon invariant yield.

9 pages, 6 figures