Physics potential of a long-baseline neutrino oscillation experiment using a J-PARC neutrino beam and Hyper-Kamiokande

Hyper-Kamiokande will be a next-generation underground water Cherenkov detector with a total (fiducial) mass of 0.99 (0.56) million metric tons, approximately 20 (25) times larger than that of Super-Kamiokande. One of the main goals of Hyper-Kamiokande is the study of CP asymmetry in the lepton sector using accelerator neutrino and anti-neutrino beams. In this paper, the physics potential of a long-baseline neutrino experiment using the Hyper- Kamiokande detector and a neutrino beam from the J-PARC proton synchrotron is presented. The analysis uses the framework and systematic uncertainties derived from the ongoing T2K experiment. With a total exposure of 7.5MW ×10⁷s integrated proton beam power (corresponding to 1.56 × 10²²protons on target with a 30 GeV proton beam) to a 2.5° off-axis neutrino beam, it is expected that the leptonic CP phase δ_CPcan be determined to better than 19 degrees for all possible values of δ_CP, and CP violation can be established with a statistical significance of more than 3 σ (5 σ) for 76% (58%) of the δ_CPparameter space. Using both ν_eappearance and νμ disappearance data, the expected 1 σ uncertainty of sin²Θ₂₃is 0.015(0.006) for sin²Θ₂₃= 0.5(0.45).