$B \to \rho l \bar \nu$ and $\omega l \bar \nu$ in and beyond the Standard Model: Improved predictions and $|V_{ub}|$

TL;DR

This paper refines predictions for B meson decays to rho and omega mesons, improving the extraction of |V_{ub}| and exploring potential new physics effects in decay observables.

Contribution

It provides a combined fit of experimental spectra with theoretical calculations, yielding more precise |V_{ub}| values and predictions for decay observables both within and beyond the Standard Model.

Findings

Smaller uncertainty in |V_{ub}| extraction.

Central |V_{ub}| values are lower than previous methods.

Enhanced predictions for lepton universality ratios and angular observables.

Abstract

We revisit the experimental and theoretical status of $B \to \rho l \bar{\nu}$ and $B \to \omega l \bar{\nu}$ decays. We perform a combined fit of averaged spectra from Belle and Babar measurements with prior light cone sum rule calculations, in order to obtain more precise predictions over the full $q^2$ range. The extracted values of $|V_{ub}|$ from these combined fits exhibit smaller uncertainty compared to previous extractions from $B \to \rho l \bar{\nu}$ and $B \to \omega l \bar{\nu}$ decays and the central values are found to be smaller than values extracted from $B \to \pi l \nu$ or inclusive measurements. We use our fit results to obtain more precise predictions in and beyond the Standard Model for the lepton universality ratios $R(\rho)$ and $R(\omega)$, as well as several angular observables that are sensitive to the full $q^2$ distribution, such as the longitudinal polarization of the vector meson, the $\tau$ polarization, and its forward-backward asymmetry.