Measurements of electroweak penguin and lepton-flavour violating $B$ decays to final states with missing energy at Belle and Belle~II

TL;DR

This paper reports on searches for rare electroweak penguin and lepton-flavour violating $B$ decays with missing energy using data from Belle and Belle~II, providing insights into potential new physics beyond the Standard Model.

Contribution

It presents the first results on $b o s uar{ u}$ processes and searches for specific LFV $B$ decays with missing energy, utilizing a large dataset from Belle and Belle~II.

Findings

Results set new upper limits on rare $B$ decay branching fractions.

No significant deviations from Standard Model predictions observed.

Provides constraints on new physics models involving lepton flavor violation.

Abstract

The Belle and Belle~II experiments have accumulated a data set of $1.2~\mathrm{ab}^{-1}$ of $e^+e^- \to B\bar{B}$ collisions at the $\Upsilon(4S)$ resonance. Owing to the clean event environment and well-constrained initial-state kinematics, these data are ideally suited for searches for rare electroweak penguin and lepton-flavour violating $B$ decays with missing energy from neutrinos. We report results on $b\to s\nu\bar{\nu}$ processes and the interpretation, together with searches for $B\to K^{*0}\tau^+\tau^-$ and for the LFV decays $B^0\to K_S^0\tau^\pm\ell^\mp$ and $B^0\to K^{*0}\tau^\pm\ell^\mp$ ($\ell=e,\mu$).