New method for non-standard invisible particle searches in tau lepton decays

TL;DR

This paper introduces a novel kinematic method to search for lepton flavor violating tau decays involving invisible particles, enhancing detection sensitivity and exploring new decay channels in upcoming Belle II data.

Contribution

The paper presents a new kinematic approach for detecting tau lepton decays to invisible particles, improving sensitivity and enabling analysis of previously unconsidered decay modes.

Findings

Expected upper limit on tau to lepton plus invisible particles improved by an order of magnitude.

Method allows for the first time the search in 1x1 prong tau decays.

Potential to discover new physics beyond the Standard Model.

Abstract

Motivated by models proposed to explain the Standard Model anomalies, and the unprecedented $\tau^{+}\tau^{-}$ data to be collected by the Belle~II experiment during the next years, we study the kinematics of tau pair decays and propose a new method to search for lepton flavor violating processes in tau lepton decays to invisible beyond Standard Model particles, such as $\tau \to \ell \alpha$, where $\ell$ is either an electron or a muon, and $\alpha$ is a massive particle that escapes undetected. The new method improves by one order of magnitude the expected upper limit on the $\tau \to \ell \alpha$ production in 3x1 prong tau decays and establishes the possibility of performing this search in 1x1 prong tau decays which has not been previously considered.