Neutrino interaction event reconstruction and analysis in the Opera emulsion targets and charmed background rejection in the τ → 3h channel

OPERA (Gran-Sasso, Italy) is a long-baseline neutrino experiment dedicated to the tau neutrino detection in a pure muon neutrino beam, produced at CERN (730 km away). The main goal is to observe the νμ → ντ oscillation. The experiment uses a hybrid technology with electronic detectors and target blocks made of lead plates interleaved with nuclear emulsion sheets, in order to sign efficiently the ντ interactions. The fundamental features of OPERA are its particle reconstruction performances achieved in spatial and angular resolutions. The first studies done in this thesis concern the development of several analysis tools like the particle momentum determination using the multiple coulomb scattering in target, and a method of neutrino interaction reconstruction for multi-vertex events. Then it has been possible to develop a multivariable analysis in order to separate τ and charmed events in the τ decay channel into three charged hadrons. These tools have been tested with neutrino interactions observed first with the OPERA test-beam called PEANUT, then with the OPERA events accumulated during the first CNGS (CERN Neutrino to Gran Sasso) run in 2007. The combined analysis of these events has shown that both the analysis method and the OPERA detector behaviour are well understood. (author)