$b\to s\ell^+\ell^- (\ell = e, μ, τ)$ and $b\to sν\barν$ 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 $Υ(4S)$ 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 $B^+\to K^+ν\barν$ and the first inclusive measurement of $B\to X_sν\barν$ with the missing energy directly from $B$ decays, as well as searches involving missing energy from $τ$ decays, such as $B^0\to K^{*0}τ^+τ^-$, $B^0\to K_S^{0}τ^+τ^-$, and $B^+\to K^{+}τ^+τ^-$.