The field of long-baseline neutrino oscillation physics is entering a precision era. Upcoming experiments such as Hyper-Kamiokande (HK) and the Deep Underground Neutrino Experiment (DUNE), both dominated by systematic uncertainties, aim to begin data-taking in the coming years. A primary goal of these experiments is the discovery of CP violation in the lepton sector, provided it is sufficiently large. Reducing systematic uncertainties—particularly those related to neutrino interactions and detector response—is therefore critical.

The Water Cherenkov Test Experiment (WCTE) and the Tokai-to-Kamioka (T2K) experiment are actively contributing to this effort. This thesis describes the methods developed by WCTE to identify particles and measure their momenta before they enter a water Cherenkov detector, which provide essential truth-level inputs for validating detector response and simulation models. It also presents the first characterisation of CERN’s T09 beamline in the sub-GeV momentum range, which was crucial in optimising WCTE's data-taking strategy.

This work also contains the first inclusive measurement of muon scattering on carbon in the 200 MeV/c to 4.5 GeV/c momentum range, using data from the T2K near detector ND280. The analysis is based on nearly one million negatively charged muons identified with over 98% purity. Comparisons with the Geant4 Bertini model reveal that it underestimates the total scattering cross section by (2.90 ± 0.03)%. Discrepancies are also found in differential distributions: the model underpredicts scattering in regions associated with correlated nucleon pairs by 10–20% and overpredicts single pion production by ~15%. Comparisons with an experimental version of the NEUT generator, adapted for muon scattering, also show poor agreement as expected. This work demonstrates the feasibility and value of further charged particle scattering measurements at T2K to constrain systematic uncertainties in future neutrino oscillation experiments.