The study of neutrino oscillations has entered a precision era, driven by long-baseline experiments like T2K, which compare neutrino signals at near and far detectors to probe key parameters, including possible Charge-Parity Violation (CPV). Detecting CPV in neutrinos could help explain the Universe’s matter–antimatter asymmetry. T2K’s 2020 results gave first hints of CPV but remain limited by statistics. To improve sensitivity, T2K has undergone major upgrades: replacing the most upstream part of its near detector with a new target, increased accelerator power (up to 800 kW by 2025, aiming for 1.3 MW by 2030). The next-generation Hyper-Kamiokande (Hyper-K) experiment, starting in 2028, will reuse the T2K beam and near detector but with new far detector 8.4 times larger than Super-Kamiokande greatly boosting the statistics. The IRFU group has key role in the near detector upgrade and is now focusing on analysis, crucial for controlling systematic uncertainties crucial for the Hyper-K high statistics time. The proposed PhD work centers on analyzing the new near detector data: designing new sample selections taking into account for the low-momentum protons and neutrons from neutrinos, and refining neutrino–nucleus interaction models to improve energy reconstruction. The second goal is to propagate these improvements to Hyper-K, guiding future oscillation analyses. The student will also contribute to Hyper-K construction and calibration (electronics testing at CERN, installation in Japan).