Prospects for $\tau$ Lepton Physics at Belle II

TL;DR

The Belle II experiment, an upgraded collider detector, aims to extensively study tau lepton physics, especially lepton flavor and number violations, to uncover potential signs of new physics beyond the Standard Model.

Contribution

This paper reviews Belle II's tau physics program and its potential to significantly improve limits on lepton flavor and number violation decays.

Findings

Expected to reduce upper limits on LFV and LNV tau decays by an order of magnitude.

Potential to discover signs of physics beyond the Standard Model through LFV and LNV observations.

Operational since 2019 with plans to collect 50 ab$^{-1}$ of data over 5 years.

Abstract

The Belle II experiment is a substantial upgrade of the Belle detector and will operate at the SuperKEKB energy-asymmetric $e^+e^-$ collider. The design luminosity of the machine is 8$\times10^{35}$ cm$^{-2}$s$^{-1}$ and the Belle II experiment aims to record 50 ab$^{-1}$ of data, a factor of 50 more than its predecessor. From February to July 2018, the machine has completed a commissioning run and main operation of SuperKEKB has started in March 2019. Belle II has a broad $\tau$ physics program, in particular in searches for lepton flavor and lepton number violations (LFV and LNV), benefiting from the large cross section of the pairwise $\tau$ lepton production in $e^+e^-$ collisions. We expect that after 5 years of data taking, Belle II will be able to reduce the upper limits on LFV and LNV $\tau$ decays by an order of magnitude. Any experimental observation of LFV or LNV in $\tau$ decays constitutes an unambiguous sign of physics beyond the Standard Model, offering the opportunity to probe the underlying New Physics. In this talk we will review the $\tau$ lepton physics program of Belle II.