Evidence for the Decay B⁰ → ωω and Search for B⁰ → ωφ

We describe searches for B meson decays to the charmless vector-vector final states ωω and ωφ with 471 x 10⁶ BB̅ pairs produced in e⁺e⁻ annihilation at √s̅ = 10.58 GeV using the BABAR detector at the PEP-II collider at the SLAC National Accelerator Laboratory. We measure the branching fraction ℬ(B⁰ → ωω) = (1.2 ± 0.3_{-0.2}^{+0.3}) x 10⁻⁶, where the first uncertainty is statistical and the second is systematic, corresponding to a significance of 4.4 standard deviations. We also determine the upper limit ℬ(B⁰ → ωφ) < 0.7 x 10⁻⁶ at 90% confidence level. These measurements provide the first evidence for the decay B⁰ → ωω, and an improvement of the upper limit for the decay B⁰ → ωφ.