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

TL;DR

This paper measures branching fractions of specific B meson decays and uses these results to determine the CKM matrix element |Vub|, providing experimental data and comparison with theoretical form-factor predictions.

Contribution

It provides new precise measurements of B to pi and rho semileptonic decay branching fractions and a determination of |Vub| using combined experimental and lattice QCD data.

Findings

Branching fraction for B0 → pi- l+ nu: (1.41 ± 0.05 ± 0.07)×10^{-4}

Branching fraction for B0 → rho- l+ nu: (1.75 ± 0.15 ± 0.27)×10^{-4}

|Vub| = (2.95 ± 0.31)×10^{-3}

Abstract

We report a measurement of the branching fractions for $B^{0} \rightarrow \pi^- \ell^+\nu$ and $B^{0} \rightarrow \rho^-\ell^+\nu$ decays, using charged and neutral $B$ decays with isospin constraints. We find ${\cal B}(B^{0} \rightarrow \pi^- \ell^+\nu} = (1.41 \pm 0.05 \pm 0.07) \times 10^{-4}$, and ${\cal B}(B^{0} \rightarrow \rho^-\ell^+\nu} = (1.75 \pm 0.15 \pm 0.27) \times 10^{-4}$, where the first error is statistical and the second is systematic. We measure $\Delta{\cal B}/\Delta q^2$, with 6 $q^2$ bins for $B^{0} \rightarrow \pi^- \ell^+\nu$ and 3 \q2 bins for $B^{0} \rightarrow \rho^-\ell^+\nu$, 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 $|V_{ub}| = (2.95 \pm 0.31) \times 10^{-3}$.