Observation of $B_s^0\to {\overline{D}}^{\ast 0}\ddot{I}•$ and search for $B^0\to {\overline{D}}^0\ddot{I}•$ decays

Abstract

The first observation of the $B_s^0\to {\overline{D}}^{\ast 0}\ddot{I}•$ decay is reported, with a significance of more than seven standard deviations, from an analysis of $pp$ collision data corresponding to an integrated luminosity of 3 fb${}^{-1}$, collected with the LHCb detector at centre-of-mass energies of $7$ and $8$ TeV. The branching fraction is measured relative to that of the topologically similar decay $B^0\to {\overline{D}}^0\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ and is found to be $\mathcal{B}(B_s^0\to {\overline{D}}^{\ast 0}\ddot{I}•)=(3.7\pm 0.5\pm 0.3\pm 0.2)\times 10^{-5}$, where the first uncertainty is statistical, the second systematic, and the third from the branching fraction of the $B^0\to {\overline{D}}^0\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ decay. The fraction of longitudinal polarisation in this decay is measured to be $f_{\mathrm{L}}=(73\pm 15\pm 3)\%$. The most precise determination of the branching fraction for the $B_s^0\to {\overline{D}}^0\ddot{I}•$ decay is also obtained, $\mathcal{B}(B_s^0\to {\overline{D}}^0\ddot{I}•)=(3.0\pm 0.3\pm 0.2\pm 0.2)\times 10^{-5}$. An upper limit, $\mathcal{B}(B^0\to {\overline{D}}^0\ddot{I}•)<2.0(2.2)\times 10^{-6}$ at $90\%$ (95\%) confidence level is set. A constraint on the $\ddot{I}‰-\ddot{I}•$ mixing angle $\hat{I}´$ is set at $|\hat{I}´|<5.2^{\circ }(5.5^{\circ })$ at $90\%$ ($95\%$) confidence level.

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-2018-015.html