Études de sensibilité aux paramètres d'oscillation des neutrinos et système de synchronisation en temps pour l'expérience Hyper-Kamiokande

Despite intensive studies of their properties since the first experimental observation of neutrinos in the 1950s, these Standard Model particles remain a source of numerous questions for physicists. The next generation of neutrino detectors, like Hyper-Kamiokande (HK) currently in construction in Japan, aims at answering some of them like: what is the mass of the neutrinos? Is there an asymmetry between matter and anti-matter in neutrino flavour oscillation? Which one of the three neutrino mass states is the heaviest, or in other words, what is the neutrino Mass Ordering (MO)? HK will be the third generation of water Cherenkov detector in Japan and will have a fiducial volume 8 times larger than its predecessor Super-Kamiokande (SK). With the same physics program ranging from the monitoring of Supernovae explosion to the study of neutrino oscillation, it is expected to start operation in 2028. Neutrino oscillation will be studied both in the neutrinos produced in cosmic ray induced hadronic showers in the atmosphere and in a beam of muon (anti)neutrinos produced at the J-PARC accelerator facility, 295km away from HK, in the continuity of the currently running T2K experiment. The neutrino beam is produced via the collision of a 31GeV proton beam on a 90cm long graphite target that produces hadrons, mostly composed of charged pions that then decay into muons and muon (anti)neutrinos. As of today, with the measurement of electron flavour appearance in a muon neutrino and antineutrino beam, T2K has the best measurement of the δCP violation phase which quantifies the asymmetry between matter and anti-matter in neutrino flavour oscillation. This result, still limited by statistics, will be greatly improved with HK so-called long-baseline program. The work provided in this thesis participated to ensure the smooth running of the experiment and to maximise its physics potential with three different projects. First, a method of time synchronisation of the detector with the Universal Time Coordinated (UTC) was developed and optimised. We demonstrate a synchronisation down to the 10ns level, significantly better than the 100ns required by the collaboration, using a Rubidium atomic clock and a GNSS (Global Navigation Satellite System) antenna and receiver. Another requirement for HK to maximise its discovery potential is to reduce the systematic uncertainties for the long-baseline program coming from the detector modelling, the neutrino interaction modelling (cross section uncertainties) and the knowledge of the neutrino beam produced at J-PARC (flux uncertainties). These systematic uncertainties are constrained by measurements at near detectors like ND280, located 280m from the J-PARC neutrino beam production facility. However, systematic uncertainties can also be reduced using external measurements. For instance, the NA61/SHINE experiment at CERN Super Proton Synchrotron (SPS) can provide measurement of the hadron production in a replica of the T2K target in the same condition as the J-PARC neutrino beam production. These measurements will be used to tune the neutrino beam simulation in T2K hence reducing the flux uncertainties. New data were taken in summer 2022 with this T2K replica target. My contribution to the calibration and analysis of this dataset is presented here. Finally, the sensitivity of HK to measure neutrino oscillation parameters, using the J-PARC neutrino beam, was intensively studied using a frequentist framework originally developed for T2K oscillation analysis. The impact of systematic uncertainties on δCP measurement is presented and preliminary results including the atmospheric neutrinos samples to partially lift the degeneracy between δCP and the MO are also shown.