T2K is a long-baseline neutrino oscillation experiment in which a νµ beam is produced at the J-PARC facility and detected 295 km away by the Super-Kamiokande, water Cherenkov detector. Up to May 2013, T2K has accumulated 6.57 × 10 20 protons on target, approximately 8% of the experimental goal. T2K has observed 120 νµ candidates, which show a clear disappearance oscillation pattern, and 28 νe candidates, with which νe appearance was established. The measurement of νe appearance is particularly

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... mportant because it enables us to determine δCP when θ23 and θ13 are known. Using values of θ23 determined by T2K disappearance measurements and θ13 measured by reactorνe experiments, T2K has obtained the first constraint on δCP from a νe appearance measurement. The Tokai to Kamioka experiment The Tokai to Kaimoka (T2K) experiment is a long-baseline neutrino oscillation experiment located in Japan. An intense, high purity ν µ beam is produced (at J-PARC) by colliding a 30 GeV proton beam with a stationary graphite target, resulting in a beam of secondary hadrons. Three magnetic horns are used to select π + , which decay to produce an almost pure beam of ν µ (approximately 1% ν e contamination). The neutrino beam is directed 2.5 • away from the axis between the target and the far detector 295 km away. This off-axis technique produces a narrow band beam with a peak energy around 0.6 GeV. This corresponds to the energy of the first ν µ → ν e oscillation maximum. The near detector complex is located 280 m downstream from the neutrino production point and consists of an on-axis Interactive Neutrino GRID (INGRID) detector and an off-axis near detector (ND280). INGRID is used to monitor the beam intensity and direction. ND280 is used to measure the neutrino flux and interaction cross-sections, which reduces systematic uncertainties on the oscillation analyses. The off-axis detector consists of several sub-detectors inside a 0.2 T magnet, namely a π 0 detector, two active fine grain detectors, three gaseous argon time projection chambers, an electromagnetic calorimeter and a side muon range detector. The far detector, located 295 km from the neutrino production point, is the Super-Kamiokande water Cherenkov detector. Super-Kamiokande is divided into an inner and outer detector. The inner detector has a 22.5 kton water fiducial volume that is surrounded by 11,129 photomultiplier tubes (PMTs). The inner detector and PMTs are surrounded by a 2 m wide outer detector. Neutrino interactions with water produce Cherenkov light which can be used to distinguish be- PANIC14 1 PANIC2014 303