Tau and low multiplicity decays at Belle and Belle II

Abstract

We present recent measurements of $\tau$ physics at the Belle II experiment at SuperKEKB. Measurements include a test of $e-\mu$ lepton flavor universality in $\tau$ decays, a search for the lepton flavor violating $\tau \to \mu \mu \mu$ decay and a precision measurement of the $\tau$ lepton invariant mass. In addition, we present a measurement of the low multiplicity decay cross section $\sigma (e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}{\pi }^0)$, a key input in the theoretical prediction of the anomalous magnetic moment of the muon.