Contraindre les modèles de flux et de section efficace des neutrinos à T2K pour la dernière analyse d’oscillation à l’aide du fitter GUNDAM et des données du détecteur proche ND280

Neutrinos are the most elusive particles of the Standard Model, yet they hold the key to fundamental open questions in phy­sics : the origin of their mass, the ordering of mass states, and the possible violation of CP symmetry in the lepton sector. Neutrino oscillations, established over the past two decades, have revealed that neutrinos mix and change flavor as they propagate, requiring physics beyond the Standard Model. This thesis presents an overview of neutrino properties and sources, followed by a focus on long-baseline accelerator expe­riment, called Tokai-to-Kamioka (T2K) project. The near detector ND280 plays a central role in reducing uncertainties on fluxes, cross sections, and detector effects, a crucial step to improve the measurement of neutrino oscillation parameters in T2K. 1 detail my contributions to the upgrade of ND280, that is now composed of new High-Angle TPCs, Time-of-Flight subdetectors, and the Su­perFGD. 1 also detail my constribution in the cotext of the T2K os­cillation analysis : by using a new statistical framework called GUN­DAM (Generalized and Unified Neutrino Data Analysis Methods), 1 was one of the main analysers of the ND280 data (pre-upgrade). This analysis implies the use of new event samples as well as a more consistent description of neutrino-nucleus interactions with the addition of new cross-section parameters responsible of the event suppression at low Q2 . The results of my work are used to provide updated measurement of neutrino oscillation parameters.