Search for Invisible Decays of a Dark Photon Produced in e^+e^− Collisions at BaBar

We search for single-photon events in 53 fb^(−1) of e^+e^− collision data collected with the BABAR detector at the PEP-II B-Factory. We look for events with a single high-energy photon and a large missing momentum and energy, consistent with production of a spin-1 particle A′ through the process e^+e^− → γA′; A′ → invisible. Such particles, referred to as “dark photons,” are motivated by theories applying a U(1) gauge symmetry to dark matter. We find no evidence for such processes and set 90% confidence level upper limits on the coupling strength of A′ to e^+e^− in the mass range m_A′≤8 GeV. In particular, our limits exclude the values of the A′ coupling suggested by the dark-photon interpretation of the muon (g−2)μ anomaly, as well as a broad range of parameters for the dark-sector models