Observation of ?_???_e Oscillation in the T2K Experiment e-bog

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