[Paper Review] Hyper-Kamiokande Design Report

KE. Abe|Lancaster EPrints (Lancaster University)|May 9, 2018

Neutrino Physics ResearchPhysics and Astronomy10 references430 citations

TL;DR

Hyper-Kamiokande is a next-generation large water Cherenkov detector in Japan designed for long-baseline neutrino oscillations, proton decay searches, atmospheric and astrophysical neutrinos, with a second detector in Korea under consideration.

ABSTRACT

On the strength of a double Nobel prize winning experiment (Super)Kamiokande and an extremely successful long baseline neutrino programme, the third generation Water Cherenkov detector, Hyper-Kamiokande, is being developed by an international collaboration as a leading worldwide experiment based in Japan. The Hyper-Kamiokande detector will be hosted in the Tochibora mine, about 295 km away from the J-PARC proton accelerator research complex in Tokai, Japan. The currently existing accelerator will be steadily upgraded to reach a MW beam by the start of the experiment. A suite of near detectors will be vital to constrain the beam for neutrino oscillation measurements. A new cavern will be excavated at the Tochibora mine to host the detector. The experiment will be the largest underground water Cherenkov detector in the world and will be instrumented with new technology photosensors, faster and with higher quantum efficiency than the ones in Super-Kamiokande. The science that will be developed will be able to shape the future theoretical framework and generations of experiments. Hyper-Kamiokande will be able to measure with the highest precision the leptonic CP violation that could explain the baryon asymmetry in the Universe. The experiment also has a demonstrated excellent capability to search for proton decay, providing a significant improvement in discovery sensitivity over current searches for the proton lifetime. The atmospheric neutrinos will allow to determine the neutrino mass ordering and, together with the beam, able to precisely test the three-flavour neutrino oscillation paradigm and search for new phenomena. A strong astrophysical programme will be carried out at the experiment that will detect supernova neutrinos and will measure precisely solar neutrino oscillation.

Motivation & Objective

• Motivate the construction of a larger, more sensitive water Cherenkov detector building on Super-Kamiokande and T2K to address neutrino oscillations, CP violation, nucleon decay, and astrophysical neutrinos.
• Describe the experimental configuration including the J-PARC beam, near/ intermediate detectors, detector cavern, tank design, water system, and photosensors.
• Outline the software, calibration, background estimation, and computing needs for Hyper-Kamiokande.
• Present physics potential across accelerator-based, atmospheric, solar, and astrophysical neutrinos, plus a possible second detector in Korea and an optional second tank in Japan.

Proposed method

• Propose a design with two cylindrical tanks (60 m height, 74 m diameter) at 40% photocoverage.
• Integrate upgraded J-PARC beam (up to MW-class) with near detectors (ND280 suite, intermediate detectors) and off-axis beam configuration.
• Develop a full detector infrastructure including cavern, water purification/circulation, photosensors (inner/outer detectors), electronics, DAQ, calibration, and software (WCSim, FiTQun, BONSAI).
• Assess backgrounds (radon, muon spallation, neutrons) and computing needs for simulations and data handling.
• Provide physics reach assessments for neutrino oscillations (beam and atmospheric), nucleon decay, solar and astrophysical neutrinos, dark matter signals, and potential second detector.
• Discuss synergies with T2K, Super-K, and DUNE to maximize physics output.

Experimental results

Research questions

• RQ1 What sensitivity to leptonic CP violation can Hyper-Kamiokande achieve with a 1.3 MW beam and 2.5-degree off-axis configuration over 10 years?
• RQ2 Can Hyper-Kamiokande determine the neutrino mass hierarchy and refine θ23 and Δm^2_32 with combined beam and atmospheric data?
• RQ3 What are the projected proton decay lifetimes Hyper-Kamiokande can probe in key channels like p→e+π0 and p→ν̄K+?
• RQ4 How well can Hyper-Kamiokande observe solar, supernova, relic, and other astrophysical neutrino sources and constrain new physics?
• RQ5 What are the design and performance requirements for the second detector in Korea and potential additional tank(s) to enhance sensitivity?

Key findings

• Hyper-Kamiokande aims to determine δCP with better than 23 degrees precision for most δCP values given assumed parameters.
• The experiment anticipates >3σ evidence for CP violation in 76% of δCP space and >5σ in 57% of δCP space under specified conditions.
• Projected sensitivity to nucleon decay channels (e.g., p→e+π0, p→ν̄K+) reaches lifetimes around 10^34–10^35 years with 1.9 Mton·years exposure.
• Annualized sensitivities for atmospheric and beam-plus-atmospheric analyses indicate improved mass ordering determination and θ23 octant resolution over 10 years.
• Astrophysical neutrino programs include solar neutrinos, supernova neutrinos, relic supernova neutrinos, and WIMP-related signals, leveraging Hyper-Kamiokande’s low-energy threshold and large target mass.