Procedure for short-lived particle detection in the OPERA experiment and its application to charm decays

The OPERA experiment, designed to perform the first observation of \(\nu _\mu \rightarrow \nu _\tau \) oscillations in appearance mode through the detection of the \(\tau \) leptons produced in \(\nu _\tau \) charged current interactions, has collected data from 2008 to 2012. In the present paper, the procedure developed to detect \(\tau \) particle decays, occurring over distances of the order of \(1~\mathrm{mm}\) from the neutrino interaction point, is described in detail and applied to the search for charmed hadrons, showing similar decay topologies as the \(\tau \) lepton. In the analysed sample, 50 charm decay candidate events are observed while \(54\pm 4\) are expected, proving that the detector performance and the analysis chain applied to neutrino events are well reproduced by the OPERA simulation and thus validating the methods for \(\nu _\tau \) appearance detection.