Studies of dark sector & B decays involving $\tau$ at Belle and Belle II

TL;DR

The paper discusses how Belle II's high-luminosity data enables detailed studies of B decays involving tau leptons and dark sector particles, providing sensitive indirect searches for new physics like charged Higgs bosons and dark matter.

Contribution

It highlights the potential of Belle II to perform precise measurements and dark sector searches, advancing beyond previous capabilities with unprecedented data and dedicated triggers.

Findings

Expected high-precision measurements of B decay branching fractions.

Enhanced sensitivity to charged Higgs bosons beyond direct collider searches.

Potential to discover or constrain dark photon, dark Higgs, and low-mass dark matter.

Abstract

The Belle II experiment aims to record 50 ab$^{-1}$ data with the high luminosity to be provided by the SuperKEKB asymmetric-energy electron-positron collider. The anticipated high statistics data enables us to perform studies of $B$ decays involving $\tau$ leptons such as $B^+ \to \tau^+ \nu_\tau$ and $B \to D^{(*)} \tau^+ \nu_\tau$ modes. The precise measurements of branching fraction and of the $\tau$ lepton polarization in these $B$ decays provide a very sensitive indirect search for a charged Higgs boson. Belle II sensitivity for the charged Higgs is complementary to direct searches at ATLAS and CMS. With the large data sample and by using dedicated triggers the Belle II experiment is expected to explore dark sector by searching for visible and invisible decays of the dark photon and the dark Higgs boson, and by also searching for low mass dark matter with unprecedented precision.