Measurement of the B^0 → π^-ℓ^+ ν and B^+ → η^((′))ℓ^+ν branching fractions, the B^0 → π^- ℓ^+ ν and B^+ → ηℓ^+ ν form-factor shapes, and determination of |V_(ub)|

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 BB̅ pairs collected at the Υ(4S) 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^+ → ηℓ^+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^+ → ηℓ^+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_(ub)| using three different QCD calculations.

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