Measurement of the antineutrino flux and cross section at the near detector of the T2K experiment

T2K (Tokai to Kamioka) is a long-baseline neutrino oscillation experiment installed in Japan. It is designed to measure neutrino flavor oscillation using an off-axis neutrino beam produced at the J-PARC accelerator facility in Tokai. In 2014 T2K has switched its beam magnet polarities to run with an antineutrino beam to enhance its sensitivity to the charge-parity violation in the leptonic sector. The beam is dominated by muon antineutrinos and contains a sizable contamination of muon neutrinos. The analysis of both neutrino and antineutrino charged-current interactions in the off-axis near detector (ND280), provides a significant reduction of the flux and cross-section modeling uncertainties on the oscillation analysis. ND280 data also gives the opportunity to measure antineutrinos cross-sections at the energy around 600 MeV. This thesis is focused on three different arguments. First the selection of charged current interactions in the off-axis near detector of muon neutrinos in the antineutrino beam is shown. In a first iteration the selected sample has been divided into two sub-sample based on the track multiplicity, then with more statistic a separation into three sub-samples based on the pion content in each event was possible. The second argument is the simultaneous measurement of the double-differential muon neutrino and antineutrino charged-current cross-section without pions in the final state at ND280. The cross-sections will be simultaneously extracted as a function of muon kinematics, allowing the evaluation of the sum, difference and asymmetry between the two cross-sections. Sum and difference can shed light on the processes involved in neutrino interactions. The asymmetry is a direct estimation on any possible bias on the charge-parity violation measurement due to cross section mismodeling. The last topic concerns the proposal of the multi-PMT technology as detector for Hyper-Kamiokande, the upgrade of Super-Kamiokande, and the intermediate water Cherenkov proposed to study the neutrino flux at about 1-2 km from the beam production point. A multi-PMT is a plastic sphere filled with 26 photomultiplier tube that could improve the reconstruction efficiency and the granularity of such Cherenkov detectors.