Analyzing new physics in the decays ${\bar{B}}^0\to D^{(\ast )}{\tau }^{-}{\bar{\nu }}_{\tau }$ with form factors obtained from the covariant quark model

Abstract

We study possible New Physics (NP) effects in the exclusive decays ${\bar{B}}^0\to D^{(\ast )}{\tau }^{-}{\bar{\nu }}_{\tau }$. We extend the Standard Model (SM) by taking into account right-handed vector (axial), left- and right-handed (pseudo)scalar, and tensor current contributions. The ${\bar{B}}^0\to D^{(\ast )}$ transition form factors are calculated in the full kinematic $q^2$ range by employing a covariant quark model developed by us. We provide constraints on NP operators based on measurements of the ratios of branching fractions $R(D^{(\ast )})\equiv \mathcal{B}({\bar{B}}^0\to D^{(\ast )}{\tau }^{-}{\bar{\nu }}_{\tau })/\mathcal{B}({\bar{B}}^0\to D^{(\ast )}{\mu }^{-}{\bar{\nu }}_{\mu })$ and consider the effects of these operators on physical observables in different NP scenarios. We also derive the four-fold angular distribution for the cascade decay ${\bar{B}}^0\to D^{\ast +}(\to D^0{\pi }^{+}){\tau }^{-}{\bar{\nu }}_{\tau }$ which allows one to analyze the polarization of the $D^{\ast }$ meson in the presence of NP effects. We discuss several strategies to distinguish between various NP contributions.

Comments: 31 pages, 10 figures, some corrections made, discussions extended, figures updated, references added; a version to appear in PRD