Neutrino Charge-Parity (CP) Symmetry Violation Search at the T2K Experiment

T2K is a long-baseline accelerator neutrino oscillation experiment using the high-intensity muon-neutrino beam produced at Japan Proton Accelerator Research Complex (JPARC). Sitting 295 km away, at an off-axis angle of 2.5 degrees, the giant Super-Kamiokande detector, a 50-kt water tank instrumented with 11,000 photosensitive detectors, sees a narrow band beam peaked at 600 MeV. The baseline to energy ratio is finely tuned for studying neutrino oscillations at the so-called atmospheric neutrino squared-mass splitting. The beam is also sampled 280 m downstream of the neutrino production target by a series of finely segmented solid scintillator and time projection chamber detectors. Observing changes in the neutrino beam between the two detectors allows oscillation parameters to be accurately extracted. World-leading results were obtained by T2K using an initial exposure of around 1E+21 protons on target, mainly in neutrino mode. These results include the first ever observation of electron-neutrino appearance in a muon-neutrino beam, the first experimental constraints on the neutrino CP-invariance violating phase (dCP) and high-precision measurements of the atmospheric neutrino squared-mass splitting and atmospheric mixing angle using both muon-neutrino and muon-antineutrino disappearance. The VALOR fitting group played a very important role in the T2K physics exploitation: It led numerous analyses within T2K, and it had a substantial contribution in most published oscillation physics papers. T2K is now well into a new phase of high-statistics running in anti-neutrino mode and numerous new oscillation results are expected in the near future, including the first measurement of electron-antineutrino appearance, the first strong evidence for CP violating effects (sin(dCP) not equal to zero) in neutrino mixing, an improvement in the precision of disappearance measurements and determination of the atmospheric mixing angle octant, and stringent tests of the 3-flavour paradigm.

Bench will join VALOR and, using the very high statistics runs expected in the next 4 years, he will lead the effort towards all above-mentioned physics goals simultaneously, using the unifying framework of the VALOR multi-sample 3-flavour analysis. In addition, Bench will investigate alternative methods to perform the near to far detector extrapolation and, should this option become available through inter-collaboration agreements, he will contribute substantially in efforts to perform a global analyses by combining T2K and NOvA results.