Semileptonic $B_{(s)}$ decays to excited charmed mesons with $e,\mu,\tau$ and searching for new physics with $R(D^{**})$

TL;DR

This paper provides detailed predictions for semileptonic $B_{(s)}$ decays into excited charmed mesons, including lepton mass effects, and explores their potential to reveal new physics beyond the Standard Model through $R(D^{**})$ ratios.

Contribution

It offers comprehensive Standard Model predictions for these decays and analyzes their sensitivity to new physics in two-Higgs-doublet models.

Findings

Predicted differential branching fractions for $B_{(s)}$ decays to excited charmed mesons.

Identified how $R(D^{**})$ ratios depend on two-Higgs-doublet model parameters.

Showed potential for future measurements to improve theoretical predictions.

Abstract

Semileptonic $B$ meson decays into the four lightest excited charmed meson states ($D_0^*$, $D_1^*$, $D_1$, and $D_2^*$) and their counterparts with $s$ quarks are investigated, including the full lepton mass dependence. We derive the standard model predictions for the differential branching fractions, as well as predictions for the ratios of the semi-tauonic and light lepton semileptonic branching fractions. These can be systematically improved using future measurements of the total or differential semileptonic rates to $e$ and $\mu$, as well as the two-body hadronic branching fractions with a pion, related by factorization to the semileptonic rate at maximal recoil. To illustrate the different sensitivities to new physics, we explore the dependence of the ratio of semi-tauonic and light-lepton branching fractions on the type-II and type-III two-Higgs-doublet model parameters, $\tan\beta$ and $m_{H}^\pm$, for all four states.