Measurement of the ratios of branching fractions $\mathcal{R}(D^{\ast })$ and $\mathcal{R}(D^0)$

LHCb Collaboration

The ratios of branching fractions $\mathcal{R}(D^{\ast })\equiv \mathcal{B}(\bar{B}\to D^{\ast }{\tau }^{-}{\bar{\nu }}_{\tau })/\mathcal{B}(\bar{B}\to D^{\ast }{\mu }^{-}{\bar{\nu }}_{\mu })$ and $\mathcal{R}(D^{0})\equiv\mathca…