Introduction.- Overview of the T2K experiment.- The Fine-Grained Detector.- Pion Interaction measurement at TRIUMF M11 Beamline.- Extraction of Pion Absorption and Charge Exchange Cross Section.- Improvement of pion interaction model.- Monte Carlo Simulation for the Oscillation Analysis.- Near Detector Measurement.- Far Detector Measurement.- Oscillation Analysis and Results.- Conclusion.

<p>In this thesis the

author contributes to the analysis of neutrino beam data collected between 2010

and 2013 to identify ν_μ→ν_e events at the Super-Kamiokande detector. In particular,

the author improves the pion–nucleus interaction uncertainty, which is one of

the dominant systematic error sources in T2K neutrino oscillation measurement.

In the thesis, the measurement of ν_μ→ν_e oscillation in the T2K (Tokai to

Kamioka) experiment is presented and a new constraint on δ_CP is obtained. This

measurement and the analysis establish, at greater than 5σ significance, the

observation of ν_μ→ν_e oscillation for the first time in the world. Combining

the T2K ν_μ→ν_e oscillation measurement with the latest findings on oscillation

parameters including the world average value of θ13 from reactor experiments,

the constraint on the value of δ_CP at the 90% confidence level is obtained.