Measurement of the decays B → η ℓ ν ℓ and B → η ′ ℓ ν ℓ in fully reconstructed events at Belle
We report branching fraction measurements of the decays B+→ηℓ+νℓ and B+→η′ℓ+νℓ based on 711 fb−1 of data collected near the Υ(4S) resonance with the Belle experiment at the KEKB asymmetric-energy e+e− collider. This data sample contains 772 million B¯B events. One of the two Bmesons is fully reconstructed in a hadronic decay mode. Among the remaining (“signal-B”) daughters, we search for the η meson in two decay channels, η→γγ and η→π+π−π0, and reconstruct the η′meson in η′→ηπ+π− with subsequent decay of the η into γγ. Combining the two η modes and using an extended maximum likelihood, the B+→ηℓ+νℓ branching fraction is measured to be (4.2±1.1(stat.)±0.3(syst.))×10−5. For B+→η′ℓ+νℓ, we observe no significant signal and set an upper limit of 0.72×10−4 at 90% confidence level.
Physical Review D
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