Testing the Standard Model in $B \to D \tau \bar \nu$ decay with minimal theory input

TL;DR

This paper assesses the consistency of the $B o D au ar u$ decay ratio with the Standard Model using minimal theoretical assumptions and discusses its potential to constrain new physics.

Contribution

It demonstrates that the measured decay ratio aligns with the Standard Model within $2\sigma$ and shows how these decays can effectively constrain new physics couplings with minimal theory input.

Findings

The decay ratio is consistent with the Standard Model within $2\sigma$.

These decay channels can provide strong constraints on new physics.

Minimal theoretical input suffices for experimental tests.

Abstract

Recent experimental results for the ratio of the branching fractions of $\bar B \to D^{(*)}\tau \nu_\tau$ and $B\to D^{(*)} \mu \nu_\mu$ decays came as a surprise and lead to a discussion of possibility to constraining new physics through these modes. Here we focus on $Br(B \to D \tau \bar\nu_\tau)/Br(B \to D \mu \bar\nu_\mu)$ and argue that the result is consistent with the Standard Model within $2\,\sigma$ and that the test of compatibility of this ratio with the Standard Model can be done experimentally with a minimal theory input. We also show that these two decay channels can provide us with quite good constraints of the new physics couplings.