Measurement of the Branching Fraction Ratios R(D+) and R(D*+) Using Muonic τ Decays

The branching fraction ratios of B¯0→D+τ-ν¯τ and B¯0→D*+τ-ν¯τ decays are measured with respect to their muonic counterparts, using a data sample corresponding to an integrated luminosity of 2.0  fb-1 collected by the LHCb experiment in proton-proton collisions at s=13  TeV. The reconstructed final states are formed by combining D+ mesons with τ-→μ-ν¯μντ candidates, where the D+ is reconstructed via the D+→K-π+π+ decay. The results are R(D+)=0.249±0.043±0.047, R(D*+)=0.402±0.081±0.085, where the first uncertainties are statistical and the second systematic. The two measurements have a correlation coefficient of -0.39 and are compatible with the standard model.