${D}^{*}$ polarization as a probe to discriminate new physics in $\overline{B}\ensuremath{\rightarrow}{D}^{*}\ensuremath{\tau}\overline{\ensuremath{\nu}}$

$D^{}$ polarization as a probe to discriminate new physics in $\bar{B} \to D^{} τ \bar{ν}$

Ashutosh Kumar Alok, Dinesh Kumar, Suman Kumbhakar, and S Uma Sankar

Phys. Rev. D 95, 115038 – Published 30 June 2017

Abstract

The confirmation of excess in $R_{D^{*}}$ at the LHCb is an indication of lepton flavor nonuniversality. Various different new physics operators and their coupling strengths, which provide a good fit to $R_{D}$ , $R_{D^{*}}$ , and $q^{2}$ spectra, were identified previously. In this work, we try to find angular observables in $\bar{B} \to D^{*} τ \bar{ν}$ which enable us to distinguish between these new physics operators. We find that the $D^{*}$ polarization fraction $f_{L} (q^{2})$ is a good discriminant of scalar and tensor new physics operators. The change in $⟨ f_{L} (q^{2}) ⟩$ , induced by scalar and tensor operators, is about 3 times larger than the expected uncertainty in the upcoming Belle measurement.