Shedding New Light on ${\cal R} (D_{(s)}^{(\ast)} )$ and $|V_{cb}|$ from Semileptonic $\bar B_{(s)} \to D_{(s)}^{(\ast)} \ell \bar {\nu}_{\ell}$ Decays

TL;DR

This paper calculates next-to-leading-order QCD corrections to form factors in semileptonic B decays, combining theory and lattice results to refine the determination of ${ m R}(D^{(*)})$ ratios and improve understanding of $|V_{cb}|$.

Contribution

It provides the first NLO QCD corrections to $ar B_{(s)} o D_{(s)}^{( ext{*)})}$ form factors at large recoil, enhancing precision in ${ m R}(D^{(*)})$ and $|V_{cb}|$ determinations.

Findings

Improved theoretical predictions for form factors at large recoil.

Significant refinement of lepton-flavour-universality ratios ${ m R}(D^{(*)})$.

Enhanced combined fits using theory and lattice QCD data.

Abstract

We compute for the first time the next-to-leading-order QCD corrections to the $\bar B_{(s)} \to D_{(s)}^{(\ast)}$ form factors at large hadronic recoil. Both the charm-quark-mass and the strange-quark-mass dependent pieces can generate the leading-power contributions to these form factors. Including further various power-suppressed contributions, we perform the combined fits of the considered form factors to both our large-recoil theory predictions and the lattice QCD results, thus improving upon the previous determinations of the lepton-flavour-universality ratios ${\cal R} (D^{(\ast)})$ significantly.