Search for $B{}_s^0\to {\ell }^{\mp }\ddot{I}{„}^{\pm }$ with the Semi-leptonic Tagging Method at Belle

Abstract

We present a search for the lepton-flavor-violating decays $B{}_s^0\to {\ell }^{\mp }\ddot{I}{„}^{\pm }$, where $\ell =e,\hat{I}¼$, using the full data sample of $121{\mathrm{fb}}^{-1}$ collected at the $\hat{I}\yen (5S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. We use $B{}_s^0\overline{B}{}_s^0$ events in which one $B{}_s^0$ meson is reconstructed in a semileptonic decay mode and the other in the signal mode. We find no evidence for $B{}_s^0\to {\ell }^{\mp }\ddot{I}{„}^{\pm }$ decays and set upper limits on their branching fractions at $90\%$ confidence level as $\mathcal{B}(B{}_s^0\to e^{\mp }\ddot{I}{„}^{\pm })<14\times 10^{-4}$ and $\mathcal{B}(B{}_s^0\to \hat{I}{¼}^{\mp }\ddot{I}{„}^{\pm })<7.3\times 10^{-4}$. Our result represents the first upper limit on the $B{}_s^0\to e^{\mp }\ddot{I}{„}^{\pm }$ decay rate.

14 pages, 5 figures