What is the Brightest Source for Dilepton Emissions at RHIC?

We calculate the dilepton emissions as the decay product of the charm and bottom quarks produced in heavy-ion collisions at RHIC energy. We take into account the next-to-leading-order radiative corrections in perturbative QCD to the heavy quark production from both an initial hard parton-parton scattering and an ideal quark-gluon plasma. We find that the thermal charm decay dominates the dilepton production in the low dilepton mass region ($<2$ GeV), while the heavy quark production from the initial scattering takes over the intermediate and high mass regions ($> 2$ GeV). Our result also indicates the importance of the bottom quark in the high mass region ($>4$ GeV ) due to its large mass and cascade decay. If the initial scattering produced charm suffers a significant energy loss due to the secondary interaction, the bottom decay constitutes the major background for the thermal dileptons.