Measuring CP violation in $b\to c\tau^-\bar{\nu}_\tau$ using excited charm mesons

TL;DR

This paper proposes a method to measure CP violation in semi-tauonic B decays using interference effects with excited charm mesons, which could reveal new physics beyond the standard model.

Contribution

It introduces a novel approach to detect CP violation in B decays by exploiting interference with excited charm mesons, potentially observing effects up to 10%.

Findings

CP violation observable could reach about 10%

Method feasible at Belle II and LHCb

Provides a new probe for new physics in B decays

Abstract

There is growing evidence for deviation from the standard model predictions in the ratios between semi-tauonic and semi-leptonic $B$ decays, known as the $R(D^{(*)})$ puzzle. If the source of this non-universality is new physics, it is natural to assume that it also breaks CP symmetry. In this paper we study the possibility of measuring CP violation in semi-tauonic $B$ decays, exploiting interference between excited charm mesons. Given the current values of $R(D^{(*)})$, we find that our proposed CP-violation observable could be as large as about 10%. We discuss the experimental advantages of our method and propose carrying it out at Belle II and LHCb.