Lepton Flavor Universality tests through angular observables of $\overline{B}\to D^{(\ast)}\ell\overline{\nu}$ decay modes

TL;DR

This paper explores how angular observables in B meson decays can be used to test lepton flavor universality violation and distinguish potential new physics effects, even if current ratios align with the Standard Model.

Contribution

It introduces a method to use angular distribution measurements in B decays to identify the Lorentz structure of new physics contributions, complementing existing ratio measurements.

Findings

Angular observables can differentiate Lorentz structures of new physics.

Even with Standard Model compatible ratios, significant new physics effects can be detected.

Proposed observables enhance sensitivity to new physics beyond ratio measurements.

Abstract

We discuss the possibility of using the observables deduced from the angular distribution of the $B\to D^{(\ast)} \ell\bar{\nu}$ decays to test the effects of lepton flavor universality violation (LFUV). We show that the measurement of even a subset of these observables could be very helpful in distinguishing the Lorentz structure of the New Physics contributions to these decays. To do so we use the low energy effective theory in which besides the Standard Model contribution we add all possible Lorentz structures with the couplings (Wilson coefficients) that are determined by matching theory with the measured ratios $R{(D^{(\ast)})}^\mathrm{exp}$. We argue that even in the situation in which the measured $R{(D^{(\ast)})}^\mathrm{exp}$ becomes fully compatible with the Standard Model, one can still have significant New Physics contributions the size of which could be probed by measuring the observables discussed in this paper and comparing them with their Standard Model predictions.