Physics Potential of a Long Baseline Neutrino Oscillation Experiment Using 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${}^7$ sec integrated proton beam power (corresponding to $1.56\times 10^{22}$ protons on target with a 30 GeV proton beam) to a $2.5$-degree off-axis neutrino beam, it is expected that the leptonic $CP$ phase $\hat{I}{´}_{CP}$ can be determined to better than 19 degrees for all possible values of $\hat{I}{´}_{CP}$, and $CP$ violation can be established with a statistical significance of more than $3\ddot{I}ƒ$ ($5\ddot{I}ƒ$) for $76\%$ ($58\%$) of the $\hat{I}{´}_{CP}$ parameter space. Using both $\hat{I}{½}_e$ appearance and $\hat{I}{½}_{\hat{I}}¼$ disappearance data, the expected 1$\ddot{I}ƒ$ uncertainty of ${\sin }^2\hat{I}{¸}_{23}$ is 0.015(0.006) for ${\sin }^2\hat{I}{¸}_{23}=0.5(0.45)$.

40 pages, 26 figures