OPERA tau neutrino candidate event 11113019758

No muon was identified by the reconstruction of the data provided by electronic detectors.</p><p>It occurred in the lead plate between the 22$^{nd}$ and 23$^{rd}$ emulsion films, 6.1 radiation lengths far from the downstream edge of the brick. The primary vertex lies close to the downstream emulsion film, at a depth in lead of only 120~${\mu}$m, and consists of two tracks: the ${\tau}$ lepton candidate and another track, which was classified as an hadron by combining the information from its momentum and range and exploiting their correlation.

A nuclear fragment going forward was also detected at a large angle and it was associated to the primary vertex, with an impact parameter of 15~${\mu}$m.</p><p>The ${\tau}$ lepton decay occurred in the plastic base, showing a trident topology after a flight length of ${(1466\pm 10)}$~${\mu}$m. The kink angle, evaluated as the mean kink angle for each daughter track, is $(87.4\pm 1.5)$~mrad. Having found the decay vertex in the plastic base allowed to exclude the emission of highly ionising nuclear fragments with an efficiency above 99.8${\%}$ at ${90\%}$~C.L.~up to ${\tan\theta=3}$.