Tau and low multiplicity decays at Belle and Belle II

TL;DR

This paper reports recent tau physics measurements at Belle II, including tests of lepton flavor universality, searches for lepton flavor violation, and precise mass measurements, contributing to understanding fundamental particle interactions.

Contribution

It provides new experimental results on tau decays and low multiplicity cross sections using Belle II data, enhancing tests of the Standard Model and muon g-2 predictions.

Findings

Test of e–μ lepton flavor universality in tau decays

Search for tau → μμμ lepton flavor violation

Precise measurement of tau invariant mass

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 $\tau \rightarrow \mu \mu \mu$ decay and a precision measurement of the $\tau$ lepton invariant mass. In addition, we present a measurement of the low multiplicity decay cross section $\sigma(e^+ e^- \rightarrow \pi^+ \pi^- \pi^0)$, a key input in the theoretical prediction of the anomalous magnetic moment of the muon.