Search for the lepton-flavor-violating decay $B^{0}\to K^{\ast 0} \mu^{\pm} e^{\mp}$

TL;DR

This study searched for rare lepton-flavor-violating decays of B0 mesons into K*0, mu, and e, using a large data sample, but found no signals and set the most stringent upper limits to date.

Contribution

First search for lepton-flavor-violating B0 decays into K*0, mu, and e with the largest data sample to date, establishing new upper limits.

Findings

No signals observed for the decay modes.

Set upper limits on branching fractions at 1.2 and 1.6 times 10^{-7}.

Most stringent limits on these decays to date.

Abstract

We have searched for the lepton-flavor-violating decay $B^{0}\to K^{\ast 0} \mu^{\pm} e^{\mp}$ using a data sample of 711 $fb^{-1}$ that contains $772 \times 10^{6}$ $B\bar{B}$ pairs. The data were collected near the $\Upsilon (4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. No signals were observed, and we set 90% confidence level upper limits on the branching fractions of ${\cal B}(B^{0}\to K^{\ast 0} \mu^{+} e^{-})< 1.2\times 10^{-7}$, ${\cal B}(B^{0}\to K^{\ast 0} \mu^{-} e^{+})< 1.6\times 10^{-7}$, and, for both decays combined, ${\cal B}(B^{0}\to K^{\ast 0} \mu^{\pm} e^{\mp}) < 1.8\times 10^{-7}$. These are the most stringent limits on these decays to date.