On the anomalous enhancement observed in $B \to D^{(*)} \, \tau \, {\bar \nu}_\tau $ decays

TL;DR

This paper investigates the anomalous enhancement in B meson decays involving tau leptons, exploring how an additional tensor operator could explain deviations from the Standard Model in certain decay ratios.

Contribution

It introduces a new physics scenario with a tensor operator to explain anomalies in B decay ratios and analyzes its effects on various semileptonic decay observables.

Findings

Tensor operator can account for observed anomalies in decay ratios.

Predictions for decay observables align with experimental deviations.

Provides constraints on new physics contributions in B decays.

Abstract

The BaBar measurements of the ratios ${\cal R}(D^{(*)})=\frac{{\cal B}(B \to D^{(*)} \tau {\bar \nu}_\tau)}{{\cal B}(B \to D^{(*)} \mu {\bar \nu}_\mu)}$ deviate from the standard model expectation, while new results on the purely leptonic $B \to \tau {\bar \nu}_\tau$ mode show a better consistency with the standard model, within the uncertainties. In a new physics scenario, one possibility to accomodate these two experimental facts consists in considering an additional tensor operator in the effective weak hamiltonian. We study the effects of such an operator in a set of observables, in semileptonic $B \to D^{(*)}$ modes as well as in semileptonic $B$ and $B_s$ decays to excited positive parity charmed mesons.