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

Abstract

The OPERA experiment was designed to search for $\hat{I}{½}_{\hat{I}}¼\to \hat{I}{½}_{\ddot{I}}„$ oscillations in appearance mode, i.e. by detecting the $\ddot{I}„$-leptons produced in charged current $\hat{I}{½}_{\ddot{I}}„$ interactions. The experiment took data from 2008 to 2012 in the CERN Neutrinos to Gran Sasso beam. The observation of $\hat{I}{½}_{\hat{I}}¼\to \hat{I}{½}_{\ddot{I}}„$ appearance, achieved with four candidate events in a sub-sample of the data, was previously reported. In this paper, a fifth $\hat{I}{½}_{\ddot{I}}„$ 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 $\hat{I}{½}_{\hat{I}}¼\to \hat{I}{½}_{\ddot{I}}„$ oscillations in appearance mode with a significance larger than 5 $\ddot{I}ƒ$.

7 pages, 3 figures