The branching fraction ratios of $\overline{ B}^0\to D^+\tau^-\overline{ \nu}_{ \tau}$ and $\overline{ B}^0\to D^{ *+}\tau^-\overline{ \nu}_{ \tau}$ 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 $\sqrt{ s} = 13$ TeV. The reconstructed final states are formed by combining $D^+$ mesons with $\tau^-\to\mu^-\overline{ \nu}_{ \mu}\nu_{ \tau}$ candidates, where the $D^+$ is reconstructed via the $D^+\to K^-\pi^+\pi^+$ decay. The results are \begin{ align*} R(D^{ +}) &= 0.249 \pm 0.043 \pm 0.047, R(D^{ *+}) &= 0.402 \pm 0.081\pm 0.085, \end{ align*} 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.
Categories: hep-ex