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

Abstract

We present a search for the lepton-flavor-violating decays $B{}_s^0\to {\ell }^{\mp }{\tau }^{\pm }$, where $\ell =e,\mu$, using the full data sample of $121{\mathrm{fb}}^{-1}$ collected at the ${\rm Y}(5S)$ 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 $B{}_s^0\to {\ell }^{\mp }{\tau }^{\pm }$ decays and set upper limits on their branching fractions at $90\%$ confidence level as $\mathcal{B}(B{}_s^0\to e^{\mp }{\tau }^{\pm })<14\times 10^{-4}$ and $\mathcal{B}(B{}_s^0\to {\mu }^{\mp }{\tau }^{\pm })<7.3\times 10^{-4}$. Our result represents the first upper limit on the $B{}_s^0\to e^{\mp }{\tau }^{\pm }$ decay rate.

arXiv comment14 pages, 5 figures

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Cited by in corpus (1)

• Constraining lepton flavor violating SMEFT $2q2\ell$ operators from low-energy cLFV processes