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

The OPERA experiment was designed to search for $\nu_{\mu} \rightarrow \nu_{\tau}$oscillationsinappearancemode,i\mathrm{.}e\mathrm{.}bydetectingthe$\tau$-leptonsproducedinchargedcurrent$\nu_{\tau}$ interactions. The experiment took data from 2008 to 2012 in the CERN Neutrinos to Gran Sasso beam. The observation of ${\nu }_{\mu }\to {\nu }_{\tau }$ 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 ${\nu }_{\mu }\to {\nu }_{\tau }$ oscillations in appearance mode with a significance larger than 5 $\sigma$.