Hyper-Kamiokande: The Future of Neutrino Research

The Hyper-Kamiokande (Hyper-K) is a next generation underground water Cherenkov detector, based on the double Nobel prize winning Super-Kamiokande experiment and Japan’s extremely successful long baseline neutrino programme. It will serve as a far detector of a long baseline neutrino experiment for the J-PARC neutrino beam, focusing on a precise study of CP asymmetry in the lepton sector. This existence of CP violation is one of the necessary conditions to explain the matter-antimatter asymmetry of the Universe. It is the future of astroparticle research, as a detector capable of observing proton decay, atmospheric neutrinos, and neutrinos from astronomical sources at a sensitivity far beyond that of the Super-Kamiokande. It will be completely open to the international community, with groups all over the world currently working with it.

The neutrino beam for Hyper-Kamiokande is produced at J-PARC located in Tokai Village, Ibaraki prefecture. The 30-GeV (kinetic energy) proton beam is extracted from the J-PARC Main Ring (MR) by single-turn fast extraction and transported to the production target after being deflected about 90◦ by superconducting combined function magnets to direct the beam towards Kamiokande. About 80% of incoming protons interact in the target. The secondary pions (and kaons) from the target are focused by three consecutive electromagnetic horns, entering a length decay volume (DV) filled with helium gas and decaying in flight into neutrinos. The beam dump, which consists of graphite blocks followed by iron plates, is placed at the end of the DV to absorb remnant hadrons with muon monitors (MUMONs) placed just behind the beam dump to monitor on a spill-by-spill basis the intensity and the profile of muons > 5 GeV which pass through the beam dump.

Hyper-K, itself, consists of two cylindrical tanks lying side-by-side, with outer dimensions each of 48(W) × 54(H) × 250(L) m³. The total (fiducial, i.e. reliable) mass of the detector is 0.99 (0.56) million metric tons, which is about 20 times larger than that of Super-Kamiokande. A proposed location for Hyper-K is about 8 km south of Super-Kamiokande (which would be 295 km away from J-PARC) at an underground depth of 1,750 meters water equivalent (m.w.e.). The inner detector region of the Hyper-K detector is viewed by 99,000 20-inch PMTs, corresponding to the PMT density of 20% photo-cathode coverage (one half of that of Super-Kamiokande). (1)

(Taken from https://warwick.ac.uk/fac/sci/physics/research/epp/exp/hyperk/)

The variety of applications of this detector cannot be overstated. It is already expected to improve supernovae models by a substantial degree, by distinguishing between five with high accuracy up to 100kpc, allowing for new and important insight into core collapse supernovae. (2) The future of neutrino astrophysics is wonderfully exciting and the Hyper-K will pioneer the field, shaping generations of experiments.

1. Lodovico, Francesca. (2017). The Hyper-Kamiokande Experiment. Journal of Physics: Conference Series. 888. 012020. 10.1088/1742-6596/888/1/012020.
2. Jost Migenda. Supernova Model Discrimination with Hyper-Kamiokande. 2020. arXiv: 2002.01649 [astro-ph.IM].