Measurement of the branching fractions of the B + → η ℓ + ν ℓ and B + → η ′ ℓ + ν ℓ decays with signal-side only reconstruction in the full q 2 range

Abstract

The branching fractions of the decays B + → η ℓ + ν ℓ and B + → η ′ ℓ + ν ℓ are measured, where ℓ is either an electron or a muon, using a data sample of 711

fb − 1 containing 772 × 10 6 B ¯ B pairs collected at the Υ ( 4 S ) resonance with the Belle detector at the KEKB asymmetric-energy e + e − collider. To reduce the dependence of the result on the form factor model, the measurement is performed over the entire q 2 range. The resulting branching fractions are B ( B + → η ℓ + ν ℓ ) = ( 2.83 ± 0.5 5 ( stat . ) ± 0.3 4 ( syst . ) ) × 10 − 5 and B ( B + → η ′ ℓ + ν ℓ ) = ( 2.79 ± 1.2 9 ( stat . ) ± 0.3 0 ( syst . ) ) × 10 − 5 .