New Physics solutions for $b\rightarrow c\,\tau\,\bar{\nu}$ anomalies after Moriond 2019

Abstract

At Moriond 2019, Belle collaboration has announced new measurements on the flavour ratios $R_D - R_{D^*}$ which are consistent with their Standard Model predictions within $1.2\sigma$. After inclusion of these measurements, the global tension in $R_D - R_{D^*}$ has reduced from $4.1\sigma$ to $3.1\sigma$ which is still significant. The measurements of these ratios indicate towards the violation of lepton flavor universality in $b\rightarrow c\,l\,\bar{\nu}$ decay. Assuming new physics in $b\rightarrow c\,\tau\,\bar{\nu}$ transition, we have done a global fit to all available data in this sector to identify the allowed new physics solutions. We find that there are seven allowed new physics solutions which can account for all measurements in $b\rightarrow c\,\tau\,\bar{\nu}$ transition. We show that a simultaneous measurement of the $\tau$ polarization fraction and forward-backward asymmetry in $B\rightarrow D\,\tau\,\bar{\nu}$, the zero crossing point of forward backward asymmetry in $B\rightarrow D^*\tau\bar{\nu}$ and the branching ratio of $B_c\rightarrow \tau\,\bar{\nu}$ decay can distinguish these seven new physics solutions if they can be measured with a required precision.