Formula omitted] and [formula omitted] Decays at Belle

Abstract

We report on a study of the charmless vector-vector decays B 0 → ω K ∗ 0 and B 0 → ρ 0 ρ 0 with 657 × 10 6 B B ¯ pairs collected with the Belle detector at the KEKB e + e − collider. We find evidence for B 0 → ω K ∗ 0 decays and measure the branching fraction to be B ( B 0 → ω K ∗ 0 ) = [ 1.8 ± 0.7 ( stat ) − 0.2 + 0.3 ( syst ) ] × 10 − 6 with 3.0 σ significance. A helicity analysis of the ω and K ∗ 0 vector mesons is performed, and the longitudinal polarization fraction is measured to be f L ( B 0 → ω K ∗ 0 ) = 0.56 ± 0.29 ( stat ) − 0.08 + 0.18 ( syst ) . We also measure a large non-resonant branching fraction B ( B 0 → ω K + π − ; M K π ∈ ( 0.755 , 1.250 ) GeV / c 2 ) = [ 5.1 ± 0.7 ( stat ) ± 0.7 ( syst ) ] × 10 − 6 with a significance of 9.5 σ . We find a small signal for B 0 → ρ 0 ρ 0 decays and set an upper limit of B ( B 0 → ρ 0 ρ 0 ) = 1.0 × 10 − 6 at the 90% confidence level. From our B 0 → ρ 0 ρ 0 measurement and an isospin analysis, we determine the Cabibbo-Kobayashi-Maskawa phase ϕ 2 to be 91.7 ± 14.9 degrees. Additionally, we find excesses in B 0 → ρ 0 π + π − and non-resonant B 0 → 4 π ± with 1.3 σ and 2.5 σ significance with branching fractions less than 12.0 × 10 −6 and 19.3 × 10 −6 at the 90% confidence level, respectively.