Search for the decay B0→γγ

We report the result of a search for the rare decay B 0 → γ γ in 426 fb − 1 of data, corresponding to 226 × 10 6 B 0 ¯¯¯ B 0 pairs, collected on the Υ ( 4 S ) resonance at the PEP-II asymmetric-energy e + e − collider using the BABAR detector. We use a maximum likelihood fit to extract the signal yield and observe 21 + 13 − 12 signal events with a statistical significance of 1.8 σ . This corresponds to a branching fraction B ( B 0 → γ γ ) = ( 1.7 ± 1.1 ( stat . ) ± 0.2 ( syst . ) ) × 10 − 7 . Based on this result, we set a 90% confidence level upper limit of B ( B 0 → γ γ ) < 3.2 × 10 − 7