Learning from tau appearance

TL;DR

This paper reviews the current experimental evidence for direct tau neutrino appearance from muon neutrino oscillations, discusses future prospects, and explores implications for standard and exotic neutrino physics scenarios.

Contribution

It provides a comprehensive overview of empirical evidence and future perspectives on tau neutrino appearance, including implications for standard and beyond-standard neutrino models.

Findings

Current evidence supports muon to tau neutrino oscillation.

Future experiments aim to improve detection and understanding.

Potential to explore sterile neutrinos and non-standard interactions.

Abstract

The study of numu->nutau oscillation and the explicit observation of the nutau through the identification of the final-state tau lepton ("direct appearance search") represent the most straightforward test of the oscillation phenomenon. It is, nonetheless, the most challenging from the experimental point of view. In this paper we discuss the current empirical evidence for direct appearance of tau neutrinos at the atmospheric scale and the perspectives for the next few years, up to the completion of the CNGS physics programme. We investigate the relevance of this specific oscillation channel to gain insight into neutrino physics within the standard three-family framework. Finally, we discuss the opportunities offered by precision studies of numu->nutau transitions in the occurrence of more exotic scenarios emerging from additional sterile neutrinos or non-standard interactions.