Search for a Dark Photon in e+e− Collisions at BaBar

Dark sectors charged under a new Abelian interaction have recently received much attention in the context of dark matter models. These models introduce a light new mediator, the so-called dark photon (A′), connecting the dark sector to the standard model. We present a search for a dark photon in the reaction e+e−→γA′, A′→e+e−, μ+μ− using 514 fb−1 of data collected with the BABAR detector. We observe no statistically significant deviations from the standard model predictions, and we set 90% confidence level upper limits on the mixing strength between the photon and dark photon at the level of 10−4−10−3 for dark photon masses in the range 0.02–10.2 GeV. We further constrain the range of the parameter space favored by interpretations of the discrepancy between the calculated and measured anomalous magnetic moment of the muon