OBSERVATION OF A SIGNIFICANT EXCESS OF PI(0) PI(0) EVENTS IN B MESON DECAYS

We present an observation of the decay B0->π0π0 based on a sample of 124 million Bbar B pairs recorded by the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC. We observe 46+-13+-3 events, where the first error is statistical and the second is systematic, corresponding to a significance of 4.2 standard deviations including systematic uncertainties. We measure the branching fractionΒ(B0->π0π0) = (2.1+-0.6+-0.3) x 10-6, averaged over B0 and bar B0 decays