A global fit to $b\to c\tau \bar{\nu }$ anomalies after Moriond 2019

Abstract

At Moriond 2019, Belle collaboration announced their new measurements on $R_D$ and $R_{D^{\ast }}$ which are in agreement with their Standard Model (SM) predictions within $1.2\sigma$. After inclusion of these measurements, the discrepancy between the world averages and the SM predictions of $R_D$-$R_{D^{\ast }}$ comes down from $4.1\sigma$ to $3.1\sigma$. Here we do a global fit by taking all measurements in $b\to c\tau \bar{\nu }$ transition. We find that there are seven allowed new physics solutions, each with different Lorentz structure. Further we show that it is possible to distinguish between them by means of the five observables: the $\tau$ polarization fraction in the decay $B\to D\tau \bar{\nu }$, the precision measurement of $R_D$, the forward-backward asymmetries in the decays $B\to (D,D^{\ast })\tau \bar{\nu }$ and the branching ratio of $B_c\to \tau \bar{\nu }$.

Comments: 5 pages, Based on arXiv:1903.10486, Contribution to proceedings of EPS-HEP 2019, July 10-17, 2019, Ghent, Belgium