Measurement of $\mathcal{R}(D^{\ast })$ with Three-Prong $\tau$ Decays at LHCb

Abstract

The observable $\mathcal{R}(D^{(\ast )})=\mathcal{B}\left(B^0\to D^{(\ast )-}{\tau }^{+}{\nu }_{\tau }\right)/\mathcal{B}\left(B^0\to D^{(\ast )-}{\mu }^{+}{\nu }_{\mu }\right)$ is a probe for Lepton Universality violation, so it is sensitive to New Physics processes. The current combination of the measurements of $\mathcal{R}(D^{(\ast )})$ differs from Standard Model predictions with a $4\sigma$ significance. A measurement of $\mathcal{R}(D^{\ast })$ using three-prong $\tau$ decays is currently ongoing at LHCb. The statistical precision of this analysis is 6.7%, i.e. the smallest statistical uncertainty for a single measurement of this observable. Therefore this measurement will be important to confirm or disprove the current discrepancy from the theoretical expectations.

arXiv commentProceeding of the 52nd Rencontres de Moriond EW 2017, La Thuile, Italy, March 18-25, 2017

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