Measurements of B→{π,η,η′}lνl Branching Fractions and Determination of |Vub| with Semileptonically Tagged B Mesons

Abstract

We report measurements of branching fractions for the decays B → P ℓ ν ℓ , where P are the pseudoscalar charmless mesons π − , π 0 , η and η ′ , based on 348 fb − 1 of data collected with the BABAR detector, using B 0 and B + mesons found in the recoil of a second B meson decaying as B → D ( * ) ℓ ν ℓ . Assuming isospin symmetry, we combine pionic branching fractions to obtain B ( B 0 → π − ℓ + ν ℓ ) = ( 1.54 ± 0.17 ( stat ) ± 0.09 ( syst ) ) × 10 − 4 ; we find 3.2 σ evidence of the decay B + → η ℓ + ν ℓ and measure its branching fraction to be ( 0.64 ± 0.20 ( stat ) ± 0.03 ( syst ) ) × 10 − 4 , and determine B ( B + → η ′ ℓ + ν ℓ ) < 0.47 × 10 − 4 to 90% confidence level. Using partial branching fractions for the pionic decays in ranges of the momentum transfer and a variety of form factor calculation, we obtain values of the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element | V u b | in ranging from 3.6 × 10 − 3 to 4.1 × 10 − 3 .