A Long Baseline Neutrino Oscillation Experiment Using J-PARC Neutrino Beam and Hyper-Kamiokande

TL;DR

This paper discusses the physics potential of the Hyper-Kamiokande detector combined with the J-PARC neutrino beam for studying CP violation in neutrino oscillations, projecting significant sensitivity improvements over previous experiments.

Contribution

It updates the physics analysis for a long baseline neutrino experiment with Hyper-Kamiokande, based on T2K experience, and predicts its capability to measure CP violation with high significance.

Findings

CP phase $ heta_{CP}$ can be determined within 19 degrees for all values.

CP violation can be established with >3σ significance for 76% of $ heta_{CP}$ values.

The experiment can significantly improve sensitivity to neutrino CP violation.

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 document, 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 has been updated from the previous Letter of Intent [K. Abe et al., arXiv:1109.3262 [hep-ex]], based on the experience gained from the ongoing T2K experiment. With a total exposure of 7.5 MW $\times$ 10$^7$ sec integrated proton beam power (corresponding to $1.56\times10^{22}$ protons on target with a 30 GeV proton beam) to a $2.5$-degree off-axis neutrino beam produced by the J-PARC proton synchrotron, it is expected that the $CP$ 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.