Search for Rare or Forbidden Decays of the D0 Meson

We present a search for nine lepton-number-violating and three lepton-flavor-violating neutral charm decays of the type D0 → h'−h−ℓ'+ℓ+ and D0→h'−h+ℓ'±ℓ∓, where h and h0 represent a K or π meson and ℓ and ℓ′ an electron or muon. The analysis is based on 468 fb−1 of e+e− annihilation data collected at or close to the ϒ(4S) resonance with the BABAR detector at the SLAC National Accelerator Laboratory. No significant signal is observed for any of the twelve modes, and we establish 90% confidence level upper limits on the branching fractions in the range (1.0–30.6) × 10−7. The limits are between 1 and 3 orders of magnitude more stringent than previous measurements.