Effects of electric and magnetic fields on the event reconstruction in the ICARUS T600 detector

In recent years, a number of anomalies in neutrino oscillation scenario were observed, that point out to possible non-standard oscillations which could imply the existence of a fourth (or more) sterile neutrino. Its existence, or absence, calls for a definitive clarification with new data. In particular, the Short Baseline Neutrino program at FNAL, will exploit three Liquid Argon Time Projection Chamber (LAr TPC) detectors along the Booster Neutrino Beamline. Each detector has different mass and a different position: the near detector SBND is the smallest, the intermediate detector MicroBooNE is the medium sized while the biggest one is the far detector, the ICARUS T600. This Ph.D. thesis is focused on the ICARUS T600 detector, the largest LAr TPC ever built, which concluded successfully the operation at LNGS in Italy. Here it was exposed at underground conditions to the CNGS beam to study oscillations. After the CNGS shut down, the detector continued taking data with cosmic rays until it was de-commissioned and transported to CERN, where it is now under refurbishment, before moving to FNAL. In a LAr TPC, when a charged particle crosses the detector, ionizing electrons are drifted towards the wire anode planes, where they are collected providing two spatial coordinates of the track; arrays of PMTs detect scintillation light, providing the measurement of the absolute time of occurrence that, combined with the knowledge of the drift velocity, permits the determination of the third coordinate of the track, that along the drift direction. The goal of the ICARUS reconstruction procedure is to extract, in an accurate way, all the physical information contained in the wire and PMT output signals, to build a complete 3D spatial and calorimetric picture of the event. To have this faithful event reconstruction, it is mandatory to determine wire and drift coordinates accurately and so it is essential to understand everything that could distort the information. The uniformity of electric field is essential in order to ensure a uniform drift velocity and thus the proportionality between drift time and drift coordinate. Electric field distortions may arise by a local accumulation, along the drift path, of positive ions, which are drifted towards the cathode more slowly than the electrons. This accumulation is emphasised by high interaction rate, given for example by high cosmic ray flux. This problem, called space charge, could be present at FNAL, where the ICARUS detector will be placed at shallow depths. In order to understand the influence of this effect in track reconstruction, a data sample is analysed, collected when the detector was at surface condition for a test run in Pavia. In the thesis are described the parameters used to study space charge effects in the ICARUS detector and the obtained results are illustrated. As stated before, the drift coordinate precision is derived by the electrons drifted towards the wire planes and it is affected by several factors, such as the diffusion. To evaluate the diffusion parameter, a dedicated run with different electric field values was performed collecting cosmic rays at the end of LNGS run. The analysis of these data samples is pointed out, considering the dependence of the width of the signal registered by the TPC. The ICARUS Collaboration is also involved in a long time project, called DUNE (Deep Underground Neutrino Experiment): it will be a long baseline experiment, with modular kiloton LAr-TPCs, to be built in the next 20 years. The T600 could be used as Near Detector, once provided with a magnetic field for particle momentum measurements and charged particle identification. The presence of a magnetic field introduces new parameters and possibilities for the reconstruction procedure. In this framework, an algorithm is developed, in order to discriminate between electron neutrino and electron antineutrino, considering their interaction products.