Study of B --> pi l nu and B --> rho l nu decays and determination of |Vub| at BaBar

Abstract

We report a measurement of the branching fractions for $B^0\to {\pi }^{-}{\ell }^{+}\nu$ and $B^0\to {\rho }^{-}{\ell }^{+}\nu$ decays, using charged and neutral $B$ decays with isospin constraints. We find ${\cal B}(B^{0} \rightarrow π^- \ell^+ν} = (1.41 \pm 0.05 \pm 0.07) \times 10^{-4}$, and ${\cal B}(B^{0} \rightarrow ρ^-\ell^+ν} = (1.75 \pm 0.15 \pm 0.27) \times 10^{-4}$, where the first error is statistical and the second is systematic. We measure $\Delta \mathcal{B}/\Delta q^2$, with 6 $q^2$ bins for $B^0\to {\pi }^{-}{\ell }^{+}\nu$ and 3 \q2 bins for $B^0\to {\rho }^{-}{\ell }^{+}\nu$, and compare the distributions in data with theoretical predictions for the form factors. We use these branching fractions and form-factor calculations to determine $|V_{ub}|$. Based on a combined fit to the FNAL/MILC lattice QCD calculation and data over the full $q^2$ range, we find $|V_{ub}|=(2.95\pm 0.31)\times 10^{-3}$.

arXiv comment5 pages, 2 figures. To be published in the proceedings of the 35th International Conference of High Energy Physics, July 22-28, 2010, Paris, France