Observation of B0 decay to two charmless mesons

We report results from a search for the decays B0→π+π-, B0→K+π-, and B0→K+K-. We find 90% confidence level upper limits on the branching fractions, Bππ<2.9×10-5, BKπ<2.6×10-5, and BKK<0.7×10-5. While there is no statistically significant signal in the individual modes, the sum of Bππ and BKπ exceeds zero with a significance of more than 4 standard deviations, indicating that we have observed charmless hadronic B decays. © 1993 The American Physical Society.