This book is based on the author's work in the T2K long-baseline neutrino oscillation
experiment in which neutrinos are generated by a proton beam and are detected by near and far
neutrino detectors. In order to achieve the precise measurement of the neutrino oscillation an
accurate understanding of the neutrino beam and the neutrino interaction is essential. Thus
the author measured the neutrino beam properties and the neutrino interaction cross sections
using a near neutrino detector called INGRID and promoted a better understanding of them. Then
the author performed a neutrino oscillation analysis using the neutrino beam and neutrino
interaction models verified by the INGRID measurements. As a result some values of the
neutrino CP phase are disfavored at the 90% confidence level. If the measurement precision is
further improved we may be able to discover the finite CP phase which involves the CP
violation. Thus this result is an important step towards the discovery of CP violation in the
lepton sector which may be the key to understanding the origin of the matter-antimatter
asymmetry in the universe.
