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

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 $R(D^{(\ast )})$ 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 $R(D^{(\ast )})$, 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.

Comments: 19 pages, 4 figures