Optimal-observable analysis of possible new physics in $B\to D^{(\ast)}\tau\nu_{\tau}$

TL;DR

This paper explores how various observables in B meson decays to D(*) tau nu can reveal new physics, especially tensor, scalar, and vector interactions, by analyzing their sensitivity across different kinematic regions.

Contribution

It introduces an optimal observable framework to extract NP Wilson coefficients from B decay data, highlighting the differential sensitivity of various observables to different NP operators.

Findings

B→D τν observables are more sensitive to scalar interactions.

B→D* τν observables are more sensitive to tensor interactions.

Tau polarization asymmetry is highly sensitive to new physics.

Abstract

We study all possible observables in $B\to D^{(\ast)}\tau\nu_{\tau}$ with new physics (NP), including new vector, scalar and tensor interactions, and investigate the prospects of extracting NP Wilson coefficients with optimal observables. Analysis of the full $q^2$ integrated branching fractions of $B\to D^{(\ast)}\tau\nu_{\tau}$ show that the overall sensitivity of the observables of $B\to D \tau\nu_{\tau}$ is more towards the scalar current, whereas the bin-by-bin analysis of $q^2$ distribution of the differential branching fraction points to regions of $q^2$ sensitive to tensor interactions. Interestingly, the observables in $B\to D^{\ast}\tau\nu_{\tau}$ are more sensitive to tensor interactions, and bin-by-bin analysis of this mode shows the distinct regions of $q^2$ sensitive to vector or scalar interactions. In addition to that, the $\tau$ polarisation asymmetry is found to be more sensitive to NP compared to the other observables, in both decay modes.