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

In this thesis theauthor contributes to the analysis of neutrino beam data collected between 2010and 2013 to identify ? ??e  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 ? ??e  oscillation in the T2K (Tokai toKamioka) experiment is presented and a new constraint on dCP is obtained. Thismeasurement and the analysis establish, at greater than 5s significance, theobservation of ? ??e  oscillation for the first time in the world. Combiningthe T2K ? ??e  oscillation measurement with the latest findings on oscillationparameters including the world average value of ?13 from reactor experiments,the constraint on the value of dCP at the 90% confidence level is obtained. This constraint on dCP is an important step towards the discovery of CPviolation in the lepton sector.