Measurement of the B0→π−ℓ+ν and B+→η(')ℓ+ν branching fractions, the B0→π−ℓ+ν and B+→ηℓ+ν form-factor shapes, and determination of |Vub|

Abstract

We report the results of a study of the exclusive charmless semileptonic decays, B + → η ( ' ) ℓ + ν and B 0 → π − ℓ + ν , undertaken with approximately 464 × 10 6 B ¯¯¯ B pairs collected at the Υ ( 4 S ) resonance with the BABAR detector. The analysis uses events in which the signal B decays are reconstructed with a loose neutrino reconstruction technique. We obtain partial branching fractions for B + → η ℓ + ν and B 0 → π − ℓ + ν decays in three and 12 bins of q 2 , respectively, from which we extract the f + ( q 2 ) form-factor shapes and the total branching fractions B ( B + → η ℓ + ν ) = ( 0.36 ± 0.05 stat ± 0.04 syst ) × 10 − 4 and B ( B 0 → π − ℓ + ν ) = ( 1.42 ± 0.05 stat ± 0.07 syst ) × 10 − 4 . We also measure B ( B + → η ′ ℓ + ν ) = ( 0.24 ± 0.08 stat ± 0.03 syst ) × 10 − 4 . We obtain values for the magnitude of the CKM matrix element | V u b | using three different QCD calculations.