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.

Highlights

  • Semileptonic decays offer a clean laboratory to search for physical phenomena beyond those predicted by the Standard Model (SM) of particle physics

  • If the same new physics (NP) were present in b → u semitauonic decays as in b → c semitauonic decays, one would naively expect lepton flavor universality violation (LFUV) deviations from the SM in the former to be enhanced by jVcbj2=jVubj2 ∼ 102 compared to the ∼10%–20% LFUV excess rates seen in b → cτν

  • Using our combined fit results, we provide improved SM predictions for the lepton universality ratio RðVÞ and several angular observables, such as the longitudinal polarization of the vector meson, the τ polarization, and its forward-backward asymmetry. [In doing so, we provide the explicit construction of the ω longitudinal polarization in terms of the B → ðω → πππÞτνfive-body differential rate.] We further briefly explore the potential to search for NP effects in B → ρτνand B → ωτνtransitions

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Summary

INTRODUCTION

Semileptonic decays offer a clean laboratory to search for physical phenomena beyond those predicted by the Standard Model (SM) of particle physics. This includes the explicit construction of the B → V form factors as well as their parametrization with respect to LCSR results [11], along with expressions for the B → Vlνdifferential decay rates. [11] quotes combined fits of LCSR predictions with LQCD results, which are available for those decays.) Importantly, the LCSR themselves generate correlated predictions between SM and NP form factors Fitting these predictions in combination with measurements of the q2 spectra for B → Vlν, in which only SM contributions.

BELLE AND BABAR SPECTRUM AVERAGES
COMBINED DATA AND THEORY FIT
PREDICTIONS IN THE STANDARD MODEL AND BEYOND
SUMMARY AND CONCLUSIONS
Findings
ApλffiVffiffisffilffisffiffiνffiAffiffiffiVλffiffiVffi λV 2mV ΓV ðA7Þ
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