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

Abstract

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 7.5 MW |$\times 10^7$|s integrated proton beam power (corresponding to |$1.56 \times 10^{22}$| protons on target with a 30 GeV proton beam) to a |$2.5^\circ$| off-axis neutrino beam, it is expected that the leptonic |$CP$| phase |$\delta _{CP}$| can be determined to better than 19 degrees for all possible values of |$\delta _{CP}$|⁠, and |$CP$| violation can be established with a statistical significance of more than |$3\,\sigma$| (⁠|$5\,\sigma$|⁠) for |$76{\%}$| (⁠|$58{\%}$|⁠) of the |${\delta _{CP}}$| parameter space. Using both |$\nu _e$| appearance and |$\nu _\mu$| disappearance data, the expected 1|$\sigma$| uncertainty of |$\sin ^2\theta _{23}$| is 0.015(0.006) for |$\sin ^2\theta _{23}=0.5(0.45)$|⁠.