$b\to s\ell^+\ell^- (\ell = e, \mu, \tau)$ and $b\to s\nu\bar\nu$ at Belle and Belle II

Abstract

The Belle and Belle~II experiments have accumulated a combined 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 the well-constrained initial-state kinematics, these data are particularly well suited for studying channels involving missing energy from neutrinos. This includes the reinterpretation of $B^+\to K^+\nu\bar{\nu}$ and the first inclusive measurement of $B\to X_s\nu\bar{\nu}$ with the missing energy directly from $B$ decays, as well as searches involving missing energy from $\tau$ decays, such as $B^0\to K^{*0}\tau^+\tau^-$, $B^0\to K_S^{0}\tau^+\tau^-$, and $B^+\to K^{+}\tau^+\tau^-$.