The neutrino interaction analysis chain in OPERA

Th e aim of the OPERA experiment i s to provide a “smoking - gun” proof of neutrino oscillation s, through the detecti on of the appearance signal of ν τ ’s in an initially pure ν μ beam. The beam is produced at CERN, 732 Km fa r from the detector , which is located underground in t he Gran Sasso laboratory. The evidence of the appearance signal will be provided by the detection of the daughter particles produced in the decay of the τ lepton. A micro - metric spatial resolution is needed in order to measure a nd study the topology of the ν τ - induced events. With this goal, n uclear emulsions, the highest resolution tracking detector , were chosen to be the core of the OPERA apparatus. The analysis of the large amount of nuclear emulsions used in the OPERA experime n t has required the development of a new generation of fast automatic mi croscopes , featuring a scanning speed more than one order of magnitude hi g h er than in past emulsion - based experiments. The long R&D carried out by the Collaboration has given rise to t wo new systems: the European Scanning System (ESS) and the Japanese S - UTS. The work presented in this thesis has been carried out in o ne of the laboratories involved in the OPERA emulsion scanning , hosted at the University of Salerno , and during a 6 month’ s stay at the IPNL (Institut de Physique Nucleaire de Lyon) . As for emulsion data - taking, s everal bricks f ro m the 2008, 2009 and 2010 OPERA runs were scanned in Salerno and about 250 ν μ - induced events were located. For the events triggered in the 2008 run , a kinematical analysis was performed , by developing a new likelihood - based software, able to estimate the momentum of the particles tr aversing the emulsion sheets through m ultiple Coulomb s cattering. The algorithm was also tested on a set of Monte - Carlo data and a set of pion track s collected during the 2003, 2004 and 2007 test beam campaigns at CERN . The 2008 run sample was used also to perform the hadron interaction search and the data collected were merged with those from other laboratories to estimate the background to the hadronic decay channel. The kinematical analysis of the τ h decay channel is the subject of the second part of this thesis, developed while staying at the IPNL. The study on the quantities used to discriminate the signal and the background was accomplished by using simulated data . The kinematical cuts suggested by the OPERA P roposal were revi ewed and the efficiencies obtained by applying these cuts were re - computed. In addition , another set of discriminating variables a re suggested and their background suppression power is explored . Such estimators are proposed to be the subject of further work in the years to come.