Angular distributions of $\bar B \to D^{(\ast)}\ell\bar \nu_\ell$ decays and search of New Physics

TL;DR

This paper derives comprehensive angular distribution formulas for B meson decays to D and D* mesons with leptons, proposing observables to detect New Physics and addressing background contamination issues.

Contribution

It provides general expressions for angular distributions in semileptonic B decays, enabling new physics searches and background discrimination.

Findings

Derived full angular distribution formulas for B decays.

Identified observables sensitive to non-Standard Model interactions.

Discussed methods to distinguish D* and D0* contributions in decay samples.

Abstract

We derive the expressions for the full angular distributions of $\bar B\to D\ell\bar \nu_\ell$ and $\bar B\to D^{\ast }\ell\bar \nu_\ell$ decays and discuss the spectra on each angle separately. The coefficient functions, depending on helicity amplitudes, can then be combined in an ensemble of observables which can then be used to check for the presence of New Physics. We examine the sensitivity of each of these observables on the presence of non-Standard Model interaction terms at low energies. The expressions presented here are general and can be used for studying any other semileptonic pseudoscalar to pseudoscalar/vector meson decay. We also examine the problem of pollution of the $\bar B\to D^{\ast}(\to D\pi)_S\ell\bar \nu_\ell$ decay sample by the $\bar B\to D_0^{\ast}(\to D\pi)\ell\bar \nu_\ell$ events, and point out that a measurement of two particular quantities could clarify whether or not the $(D\pi)_{S-\rm wave}$ in the vicinity of $D^\ast$-peak is (approximately) described by the Breit-Wigner formula.