Measurement of the ${B}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}{l}^{+}\ensuremath{\nu}$ Form-Factor Shape and Branching Fraction, and Determination of $|{V}_{ub}|$ with a Loose Neutrino Reconstruction Technique

Measurement of the $B^{0} \to π^{-} l^{+} ν$ Form-Factor Shape and Branching Fraction, and Determination of $| V_{u b} |$ with a Loose Neutrino Reconstruction Technique

B. Aubert et al. (The BABAR Collaboration)

Phys. Rev. Lett. 98, 091801 – Published 28 February 2007

Abstract

We report the results of a study of the exclusive charmless semileptonic decay, $B^{0} \to π^{-} ℓ^{+} ν$ , undertaken with approximately $227 \times 10^{6}$ $B \bar{B}$ 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 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 $B (B^{0} \to π^{-} ℓ^{+} ν) = (1.46 \pm {0.07}_{stat} \pm {0.08}_{syst}) \times 10^{- 4}$ . 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 $| V_{u b} |$ to be $(4.1 \pm {0.2}_{stat} \pm {0.2}_{syst} {\binom{+ 0.6}{- 0.4}}_{FF}) \times 10^{- 3}$ , where the last uncertainty is due to the normalization of the form factor.