[**Neutrino cross sections in T2K : from their measurements to the oscillation analysis*]
The T2K (Tokai to Kamioka) experiment is a long-baseline neutrino oscillation experiment based in Japan. A muon (anti-)neutrino beam is produced by the J-PARC accelerator complex in Tokai, it is characterized by a series of near detectors and travels then toward the far detector Super-Kamiokande, 295 km far from the neutrino production point. The main goal of T2K is the observation of the electron (anti-)neutrino appearance in a muon (anti-)neutrino beam, as well as the disappearance of muon (anti-)neutrinos. Thanks to these observations, T2K was able to provide the world leading measurements of some neutrino oscillation parameters, including the CP violation phase of the lepton sector, that could shed light on the origin of the matter/antimatter asymmetry in the current Universe.
Motivated by the already achieved results, T2K is planning a second phase of the experiment that is starting this year and will include a major upgrade of one of its near detectors.
During my HDR defense, I will guide you through the complexity of an oscillation analysis, focussing on the relevance of neutrino interaction uncertainties. I will start describing in details some T2K neutrino cross section analyses, showing the peculiarities of each of them, the evolution of our understanding of neutrino interaction models as well as of the required analysis techniques. I will then describe a recent developed parameterization of neutrino interaction related systematics. I will conclude showing the expected sensitivity of T2K upgraded near detectors in constraining this kind of systematics, thus ensuring improved oscillation parameter measurements in next years.