Study of \(B→πlν\) and \(B→ρlν\) Decays and Determination of \(|V_{ub}|\)

Abstract

We present an analysis of exclusive charmless semileptonic B-meson decays based on (377×10^{6} B\overline{B}) pairs recorded with the BABAR detector at the (Υ(4S)) resonance. We select four event samples corresponding to the decay modes (B^{0}→π^{−}ℓ^{+}ν), (B^{+}→π^{0}ℓ^{+}ν), (B^{0}→ρ^{−}ℓ^{+}ν), and (B^{+}→ρ^{0}ℓ^{+}ν) and find the measured branching fractions to be consistent with isospin symmetry. Assuming isospin symmetry, we combine the two (B→πℓν) samples, and similarly the two (B→ρℓν) samples, and measure the branching fractions (ℬ(B^{0}→π^{−}ℓ^{+}ν)=(1.41±0.05±0.07)×10^{−4}) and (ℬ(B^{0}→ρ^{−}ℓ^{+}ν)=(1.75±0.15±0.27)×10^{−4}), where the errors are statistical and systematic. We compare the measured distribution in (q^2), the momentum transfer squared, with predictions for the form factors from QCD calculations and determine the Cabibbo-Kobayashi-Maskawa matrix element (|V_{ub}|). Based on the measured partial branching fraction for (B→πℓν) in the range (q^{2}<12 GeV^{2}) and the most recent QCD light-cone sum-rule calculations, we obtain (|V_{ub}|=(3.78±0.13^{+0.55}{−0.40})×10^{−3}), where the errors refer to the experimental and theoretical uncertainties. From a simultaneous fit to the data over the full (q^2) range and the FNAL/MILC lattice QCD results, we obtain (|V{ub}|=(2.95±0.31)×10^{−3}) from (B→πℓν), where the error is the combined experimental and theoretical uncertainty.