The OPERA experiment, designed to perform the first observation of $ u_mu rightarrow u_tau$ oscillations in appearance mode through the detection of the $tau$ leptons produced in $ u_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 mm from the neutrino interaction point, is described in detail. The results of its application to the search for charmed hadrons are then presented as a validation of the methods for $ u_tau$ appearance detection.
The OPERA experiment, designed to conclusively prove the existence of $rm u_mu to u_tau$ oscillations in the atmospheric sector, makes use of a massive lead-nuclear emulsion target to observe the appearance of $rm u_tau$s in the CNGS $rm u_mu$ be
am. The location and analysis of the neutrino interactions in quasi real-time required the development of fast computer-controlled microscopes able to reconstruct particle tracks with sub-micron precision and high efficiency at a speed of 20 cm^2 / h. This paper describes the performance in particle track reconstruction of the European Scanning System, a novel automatic microscope for the measurement of emulsion films developed for OPERA.
