Measurement of the B~0 →π~- l~+v Form-Factor Shape and Branching Fraction, and Determination of |V_(ub)| with a Loose Neutrino Reconstruction Technique

摘要

We report the results of a study of the exclusive charmless semileptonic decay, B~0→ π~- l~+ v, undertaken with approximately 227 X 10~6 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 an innovative loose neutrino reconstruction technique. We obtain partial branching fractions in 12 bins of q~2, the momentum transfer squared, from which we extract the f_+(q~2) form-factor shape and the total branching fraction B(B~0 → π~- l~+v) = (1.46 ± 0.07_(stat) ± 0.08_(syst)) X 10~(-4). Based on a recent unquenched lattice QCD calculation of the form factor in the range q~2 > 16 GeV~2, we find the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element |V_(ub)| to be (4.1 ± 0.2_(stat) ± 0.2_(syst_(-0.4FF))~(+0.6) X 10~(-3), where the last uncertainty is due to the normalization of the form factor.