Measurement of the ratio of the $B^0\to D^{\ast -}\ddot{I}{„}^{+}\hat{I}{½}_{\ddot{I}}„$ and $B^0\to D^{\ast -}\hat{I}{¼}^{+}\hat{I}{½}_{\hat{I}}¼$ branching fractions using three-prong $\ddot{I}„$-lepton decays

Abstract

The ratio of branching fractions $\mathcal{R}(D^{\ast -})\equiv \mathcal{B}(B^0\to D^{\ast -}\ddot{I}{„}^{+}\hat{I}{½}_{\ddot{I}}„)/\mathcal{B}(B^0\to D^{\ast -}\hat{I}{¼}^{+}\hat{I}{½}_{\hat{I}}¼)$ is measured using a data sample of proton-proton collisions collected with the LHCb detector at center-of-mass energies of 7 and 8 Tev, corresponding to an integrated luminosity of 3 fb${}^{-1}$. For the first time $\mathcal{R}(D^{\ast -})$ is determined using the $\ddot{I}„$ lepton decays with three charged pions in the final state. The $B^0\to D^{\ast -}\ddot{I}{„}^{+}\hat{I}{½}_{\ddot{I}}„$ yield is normalized to that of the $B^0\to D^{\ast -}\ddot{I}{€}^{+}\ddot{I}{€}^{-}\ddot{I}{€}^{+}$ mode, providing a measurement of $\mathcal{B}(B^0\to D^{\ast -}\ddot{I}{„}^{+}\hat{I}{½}_{\ddot{I}}„)/\mathcal{B}(B^0\to D^{\ast -}\ddot{I}{€}^{+}\ddot{I}{€}^{-}\ddot{I}{€}^{+})=1.97\pm 0.13\pm 0.18$, where the first uncertainty is statistical and the second systematic. The value of $\mathcal{B}(B^0\to D^{\ast -}\ddot{I}{„}^{+}\hat{I}{½}_{\ddot{I}}„)=(1.42\pm 0.094\pm 0.129\pm 0.054)\%$ is obtained, where the third uncertainty is due to the limited knowledge of the branching fraction of the normalization mode. Using the well-measured branching fraction of the $B^0\to D^{\ast -}\hat{I}{¼}^{+}\hat{I}{½}_{\hat{I}}¼$ decay, a value of $\mathcal{R}(D^{\ast -})=0.291\pm 0.019\pm 0.026\pm 0.013$ is established, where the third uncertainty is due to the limited knowledge of the branching fractions of the normalization and $B^0\to D^{\ast -}\hat{I}{¼}^{+}\hat{I}{½}_{\hat{I}}¼$ modes. This measurement is in agreement with the Standard Model prediction and with previous results.

All figures and tables, along with any supplementary material and additional information, are available at https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2017-017.html