Belle observes b → d

The Belle collaboration, with a detector operating at the KEKB facility, has recently reported that they have observed the rare b → d transitions. After analyzing 386 million B meson pairs, they have identified 35 events in which the B meson decays into either a ρ or an ω meson with an accompanying photon, implying a branching fraction

Br(B → (ρ, ω)γ) = 1.34 + 0.34 − 0.31 (stat) + 0.14 − 0.10 (syst) × 10⁻⁶ with a significance of 5.5σ. From this they derive the ratio of CKM matrix elements |V_td⁄V_ts| = 0.200 + 0.026 − 0.025 (exp) + 0.038 − 0.029 (theo). This is the first time that such B decays have been observed, due to the low branching fraction.

Belle has also reported evidence for signals in B⁺  → K⁰bar K⁺ and B⁰ → ⁰K⁰bar with significances of 3.0σ and 3.5σ respectively, albeit from a sample of 275 million BBbar pairs. These decay modes are examples of hadronic b → d transitions. The corresponding branching fractions are measured to be Br(B → K⁰bar K⁺) = 1.0 ± 0.4 ± 0.1 × 10⁻⁶ and Br(B⁰ → K⁰K⁰bar) = 0.8 ± 0.3 ± 0.1 × 10⁻⁶.