Observation of ?_µ??_e Oscillation in the T2K Experiment

In this thesis theauthor contributes to the analysis of neutrino beam data collected between 2010and 2013 to identify νμ→νe  events at the Super-Kamiokande detector. In particular,the author improves the pion–nucleus interaction uncertainty, which is one ofthe dominant systematic error sources inT2K neutrino oscillation measurement.In the thesis, the measurement of νμ→νe  oscillation in the T2K (Tokai toKamioka) experiment is presented and a new constraint on δCP is obtained. Thismeasurement and the analysis establish, at greater than 5σ significance, theobservation of νμ→νe  oscillation for the first time in the world. Combiningthe T2K νμ→νe  oscillation measurement with the latest findings on oscillationparameters including the world average value of θ13 from reactor experiments,the constraint on the value of δCP at the 90% confidence level is obtained.This constraint on δCP is an important step towards the discovery of CPviolation in the lepton sector.