Discovery of tau neutrino appearance in the CNGS neutrino beam with the OPERA experiment

TL;DR

The OPERA experiment observed five tau neutrino appearance events in a long-baseline neutrino beam, providing strong evidence (>5 sigma) for muon to tau neutrino oscillations, confirming a key neutrino physics phenomenon.

Contribution

This paper reports the discovery of tau neutrino appearance in the CNGS beam, with the observation of five candidate events and improved background reduction, confirming neutrino oscillations in appearance mode.

Findings

Five tau neutrino candidate events observed.

Oscillation significance exceeds 5 sigma.

Confirmation of muon to tau neutrino oscillations.

Abstract

The OPERA experiment was designed to search for $\nu_{\mu} \rightarrow \nu_{\tau}$ oscillations in appearance mode, i.e. by detecting the $\tau$-leptons produced in charged current $\nu_{\tau}$ interactions. The experiment took data from 2008 to 2012 in the CERN Neutrinos to Gran Sasso beam. The observation of $\nu_{\mu} \rightarrow \nu_{\tau}$ appearance, achieved with four candidate events in a sub-sample of the data, was previously reported. In this paper, a fifth $\nu_{\tau}$ candidate event, found in an enlarged data sample, is described. Together with a further reduction of the expected background, the candidate events detected so far allow assessing the discovery of $\nu_{\mu}\rightarrow \nu_{\tau}$ oscillations in appearance mode with a significance larger than 5 $\sigma$.