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

TL;DR

This paper discusses the analysis of rare B meson decays involving neutrinos and tau leptons using data from the Belle and Belle II experiments, highlighting their potential for new physics searches.

Contribution

It presents the first inclusive measurement of B→Xsνν̄ and reinterprets B+→K+νν̄ decays using Belle and Belle II data, emphasizing the clean environment for missing energy studies.

Findings

First inclusive measurement of B→Xsνν̄ with direct missing energy detection.

Reinterpretation of B+→K+νν̄ decays using combined Belle and Belle II data.

Studies of B decays involving tau leptons and missing energy.

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 $B^+\to K^{+}\tau^+\tau^-$.