Measurement of Pion-Carbon Cross Sections at DUET and Measurement of Neutrino Oscillation Parameters at the T2K Experiment

The Tokai-to-Kamioka (T2K) experiment is a long baseline neutrino oscillation experiment. An intense muon neutrino (or antineutrino) beam is produced at the Japan Proton Accelerator Research Complex (J-PARC) by protons hitting a graphite target. The neutrinos are measured 280 m from the target, and again 295 km across Japan using the Super-Kamiokande detector. This allows for the study of the neutrino oscillations in four channels: the electron neutrino and antineutrino appearance, and muon neutrino and antineutrino disappearance.

In T2K, neutrinos are observed primarily via charged current quasi-elastic scattering (CCQE) interactions, as well as charged current single pion (CC1) production. The pion is free to interact inside and outside the nucleus primarily via absorption and charge exchange processes. Reducing the uncertainties on these cross sections reduces the systematic uncertainties for neutrino oscillation measurements. The Dual Use Experiment at TRIUMF (DUET) was conducted to address this issue. This thesis describes the recent results from DUET: the most precise measurements of absorption and charge exchange cross sections of pion on carbon for the momentum range of 201.6~295.1 MeV/c.

These DUET measurements, along with existing pion-nucleus scattering data for different atomic nuclei, are used to improve the cascade model that simulates pion-nucleus scattering in T2K, and to reduce the associated systematic uncertainties. These improvements are used in a Markov Chain Monte Carlo neutrino oscillation analysis of the T2K Run 1-8 data, corresponding to 14.7x10e20 protons-on-target in neutrino mode and 7.6x10e20 in antineutrino mode. As a result, the most precise measurement of the parameters that govern the neutrino oscillation phenomenon is obtained. In particular, the values indicative of no matter-antimatter asymmetry (CP-conservation) are excluded at the 95.4% (2-sigma) level. This constitutes the world-leading constraint for CP-violation in the leptonic sector.