Measurement of the Ratios of Branching Fractions R(D^{*}) and R(D^{0})

The ratios of branching fractions R(D^{})≡B(B[over ¯]→D^{}τ^{-}ν[over ¯]{τ})/B(B[over ¯]→D^{*}μ^{-}ν[over ¯]{μ}) and R(D^{0})≡B(B^{-}→D^{0}τ^{-}ν[over ¯]{τ})/B(B^{-}→D^{0}μ^{-}ν[over ¯]{μ}) are measured, assuming isospin symmetry, using a sample of proton-proton collision data corresponding to 3.0 fb^{-1} of integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The tau lepton is identified in the decay mode τ^{-}→μ^{-}ν_{τ}ν[over ¯]_{μ}. The measured values …