Search for the lepton-flavour-violating decays $B_s^0\to \ddot{I}{„}^{\pm }\hat{I}{¼}^{\mp }$ and $B^0\to \ddot{I}{„}^{\pm }\hat{I}{¼}^{\mp }$

Abstract

A search for $B_s^0\to \ddot{I}{„}^{\pm }\hat{I}{¼}^{\mp }$ and $B^0\to \ddot{I}{„}^{\pm }\hat{I}{¼}^{\mp }$ decays is performed using data corresponding to an integrated luminosity of 3 fb${}^{-1}$ of proton-proton collisions, recorded with the LHCb detector in 2011 and 2012. For this search, the $\ddot{I}„$ lepton is reconstructed in the $\ddot{I}{„}^{-}\to \ddot{I}{€}^{-}\ddot{I}{€}^{+}\ddot{I}{€}^{-}\hat{I}{½}_{\ddot{I}}„$ channel. No significant signal is observed. Assuming no contribution from $B^0\to \ddot{I}{„}^{\pm }\hat{I}{¼}^{\mp }$ decays, an upper limit is set on the $B_s^0\to \ddot{I}{„}^{\pm }\hat{I}{¼}^{\mp }$ branching fraction of $\mathcal{B}\left(B_s^0\to \ddot{I}{„}^{\pm }\hat{I}{¼}^{\mp }\right)<4.2\times 10^{-5}$ at $95\%$ confidence level. If instead no contribution from $B_s^0\to \ddot{I}{„}^{\pm }\hat{I}{¼}^{\mp }$ decays is assumed, a limit of $\mathcal{B}\left(B^0\to \ddot{I}{„}^{\pm }\hat{I}{¼}^{\mp }\right)<1.4\times 10^{-5}$ is obtained at $95\%$ confidence level. These are the first limit on $\mathcal{B}\left(B_s^0\to \ddot{I}{„}^{\pm }\hat{I}{¼}^{\mp }\right)$ and the world's best limit on $\mathcal{B}\left(B^0\to \ddot{I}{„}^{\pm }\hat{I}{¼}^{\mp }\right)$.

15 pages, 5 figures. All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2019-016.html