B0→ωK∗0 and B0→ρ0ρ0 Decays at Belle

We report on a study of the charmless vector-vector decays B0→ωK∗0 and B0→ρ0ρ0 with pairs collected with the Belle detector at the KEKB e+e− collider. We find evidence for B0→ωK∗0 decays and measure the branching fraction to be with 3.0σ significance. A helicity analysis of the ω and K∗0 vector mesons is performed, and the longitudinal polarization fraction is measured to be . We also measure a large non-resonant branching fraction B(B0→ωK+π−;MKπ∈(0.755,1.250)GeV/c2)=[5.1±0.7(stat)±0.7(syst)]×10−6 with a significance of 9.5σ. We find a small signal for B0→ρ0ρ0 decays and set an upper limit of B(B0→ρ0ρ0)=1.0×10−6 at the 90% confidence level. From our B0→ρ0ρ0 measurement and an isospin analysis, we determine the Cabibbo-Kobayashi-Maskawa phase ϕ2 to be 91.7 ± 14.9 degrees. Additionally, we find excesses in B0→ρ0π+π− and non-resonant B0→4π± with 1.3σ and 2.5σ significance with branching fractions less than 12.0 × 10−6 and 19.3 × 10−6 at the 90% confidence level, respectively.