New Physics Scenarios in $b \to c \ell {\bar \nu}_\ell$ decays

TL;DR

This paper explores new physics scenarios involving tensor operators to explain deviations in B meson decay ratios observed by BaBar, analyzing their impact on various semileptonic decay modes and identifying key observables for discrimination.

Contribution

It introduces a tensor operator framework to account for anomalies in B decay ratios and evaluates its effects on multiple decay channels and observables.

Findings

Tensor operators can reconcile experimental ratios with theory.

Certain observables are highly sensitive to new physics effects.

The proposed scenarios do not affect other decay modes significantly.

Abstract

The latest BaBar measurements of the ratios ${\cal R}(D^{(*)})=\displaystyle{\frac{{\cal B}(B \to D^{(*)} \tau {\bar \nu}_\tau)}{{\cal B}(B \to D^{(*)} \mu {\bar \nu}_\mu)}}$ deviate from the Standard Model predictions at the global level of 3.4$\sigma$. A possibility to reproduce these experimental ratios without affecting other modes which do not show similar deviations is to consider new physics scenarios producing an additional tensor operator in the effective weak Hamiltonian. I describe the impact of such an operator in semileptonic $B \to D^{(*)}$ modes and in semileptonic $B$ and $B_s$ decays to excited positive parity charmed mesons. In particular, I discuss the most effective observables able to discriminate new physics from the Standard Model.