Limit on the B0→ρ0ρ0 Branching Fraction and Implications for the Cabibbo-Kobayashi-Maskawa Angle α

We search for the decay B0 → ρ0ρ 0 in a data sample of about 227 × 106 Γ(4S) → B B decays collected with the BABAR detector at the PEP-II asymmetric-energy e+ e- collider at SLAC. We find no significant signal and set an upper limit of 1.1 × 10-6 at 90% C.L. on the branching fraction. As a result, the uncertainty due to penguin contributions on the Cabibbo-Kobayashi-Maskawa unitarity angle α measured in B → ρρ decays is decreased to 11° at 68% C.L. © 2005 The American Physical Society.