Standard Model predictions for Lepton Flavour Universality ratios of inclusive semileptonic $B$ decays

TL;DR

This paper provides precise Standard Model predictions for lepton flavour universality ratios in inclusive semileptonic B decays, including tau modes with updated power corrections, serving as benchmarks to compare with exclusive decay measurements.

Contribution

It offers the first comprehensive SM predictions for inclusive B decay ratios, incorporating higher-order heavy-quark expansion corrections for tau modes.

Findings

Ratios for muon and electron modes are close to unity.

Updated SM predictions for tau mode branching ratios with power corrections.

Inclusive ratios serve as cross-checks for exclusive decay measurements.

Abstract

We present Standard Model predictions for lepton flavour universality ratios of inclusive $B\to X_{(c)} \ell \bar\nu_\ell$. For the $\ell=\mu,e$, these ratios are very close to unity as expected. For the $\tau$ mode, we update the SM prediction for the branching ratio including power-corrections in the heavy-quark expansion up to $1/m_b^3$. These inclusive ratios serve as an important cross-check of the exclusive $B\to D^{(*)}\ell\bar\nu_\ell$ modes, in which tensions exists between the predictions and measurements in those modes.