Search for the Decay B0 →γγ

We present a limit on the branching fraction for the decay B0→γγ using data collected at the ϒ(4S) resonance with the BABAR detector at the PEP-II asymmetric energy e+e- collider. Based on the observation of one event in the signal region, out of a sample of 21.3×106 e+e-→ϒ(4S)→BB̅ decays, we establish an upper limit on the branching fraction of B(B0→γγ)<1.7×10-6 at the 90% confidence level. This result substantially improves upon existing limits.