Search for the lepton flavour violating decays $B^{+}\to K^{+}{\tau }^{\pm }{\ell }^{\mp }$ ($\ell =e,\mu$) at Belle

Abstract

We present a search for the lepton-flavour-violating decays $B^{+}\to K^{+}{\tau }^{\pm }{\ell }^{\mp }$, with $\ell =(e,\mu )$, using the full data sample of $772\times 10^6$ $B\overline{B}$ pairs recorded by the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. We use events in which one $B$ meson is fully reconstructed in a hadronic decay mode. We find no evidence for $B^{\pm }\to K^{\pm }\tau \ell$ decays and set upper limits on their branching fractions at the 90% confidence level in the $(1$-$3)\times 10^{-5}$ range. The obtained limits are the world's best results.

arXiv comment14 pages, 6 figures

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• Search for the lepton-flavor violating decay $B_s^0\to \varphi {\mu }^{\pm }{\tau }^{\mp }$
• Constraining lepton flavor violating SMEFT $2q2\ell$ operators from low-energy cLFV processes