Branching fraction and form-factor shape measurements of exclusive charmless semileptonic B decays, and determination of vertical bar V-ub vertical bar

We report the results of a study of the exclusive charmless semileptonic decays, B0→π−ℓ+ν, B+→π0ℓ+ν, B+→ωℓ+ν, B+→ηℓ+ν, and B+→η′ℓ+ν (ℓ=e or μ) undertaken with approximately 462×106 BB⎯⎯⎯ 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 in several bins of q2, the square of the momentum transferred to the lepton-neutrino pair, for B0→π−ℓ+ν, B+→π0ℓ+ν, B+→ωℓ+ν, and B+→ηℓ+ν. From these distributions, we extract the form-factor shapes f+(q2) and the total branching fractions ℬ(B0→π−ℓ+ν)=(1.45±0.04stat±0.06syst)×10−4 (combined π− and π0 decay channels assuming isospin symmetry), ℬ(B+→ωℓ+ν)=(1.19±0.16stat±0.09syst)×10−4 and ℬ(B+→ηℓ+ν)=(0.38±0.05stat±0.05syst)×10−4. We also measure ℬ(B+→η′ℓ+ν)=(0.24±0.08stat±0.03syst)×10−4. We obtain values for the magnitude of the Cabibbo-Kobayashi-Maskawa (CKM) matrix element |Vub| by direct comparison with three different QCD calculations in restricted q2 ranges of B→πℓ+ν decays. From a simultaneous fit to the experimental data over the full q2 range and the FNAL/MILC lattice QCD predictions, we obtain |Vub|=(3.25±0.31)×10−3, where the error is the combined experimental and theoretical uncertainty.