Measurement of the ratio of branching fractions $\mathcal{B}({\overline{B}}^0\to D^{\ast +}\ddot{I}{„}^{-}\overline{\hat{I}}{½}_{\ddot{I}}„)/\mathcal{B}({\overline{B}}^0\to D^{\ast +}\hat{I}{¼}^{-}\overline{\hat{I}}{½}_{\hat{I}}¼)$

Abstract

The branching fraction ratio $\mathcal{R}(D^{\ast })\equiv \mathcal{B}({\overline{B}}^0\to D^{\ast +}\ddot{I}{„}^{-}\overline{\hat{I}}{½}_{\ddot{I}}„)/\mathcal{B}({\overline{B}}^0\to D^{\ast +}\hat{I}{¼}^{-}\overline{\hat{I}}{½}_{\hat{I}}¼)$ is measured using a sample of proton-proton collision data corresponding to 3.0\invfb of integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The tau lepton is identified in the decay mode $\ddot{I}{„}^{-}\to \hat{I}{¼}^{-}\overline{\hat{I}}{½}_{\hat{I}}¼\hat{I}{½}_{\ddot{I}}„$. The semitauonic decay is sensitive to contributions from non-Standard-Model particles that preferentially couple to the third generation of fermions, in particular Higgs-like charged scalars. A multidimensional fit to kinematic distributions of the candidate ${\overline{B}}^0$ decays gives $\mathcal{R}(D^{\ast })=0.336\pm 0.027(stat)\pm 0.030(syst)$. This result, which is the first measurement of this quantity at a hadron collider, is 2.1 standard deviations larger than the value expected from lepton universality in the Standard Model.

17 pages, 1 figure. v2 after referees' comments