Measurement of the ratio of the $B^0\to D^{\ast -}{\tau }^{+}{\nu }_{\tau }$ and $B^0\to D^{\ast -}{\mu }^{+}{\nu }_{\mu }$ branching fractions using three-prong $\tau$-lepton decays

LHCb collaboration, R. Aaij, B. Adeva +806

The ratio of branching fractions $\mathcal{R}(D^{\ast -})\equiv \mathcal{B}(B^0\to D^{\ast -}{\tau }^{+}{\nu }_{\tau })/\mathcal{B}(B^0\to D^{\ast -}{\mu }^{+}{\nu }_{\mu })$ is measured using a data sample of proton-proton colli…