[U-02_28PM2] Particle Geophysics

★ [U02-20] The Hyper-Kamiokande Project

*Masashi YOKOYAMA¹ (1.The University of Tokyo)

Keywords:neutrino, radiography

In this paper, we present the baseline design and expected performance of the Hyper-Kamiokande detector (Hyper-K)[1,2], a next generation underground water Cherenkov detector proposed in Japan. Hyper-Kamiokande is a successor of Super-Kamiokande (Super-K), which has been producing epoch-making results in particle physics and astrophysics, most notably the discovery of neutrino oscillation, since 1996. A water Cherenkov detector measures properties of elementary particles by detecting Cherenkov light, which is emitted when a charged particle travels faster than the velocity of light in water. Although neutrino itself does not emit Cherenkov light, it can be detected via particles produced in interaction with matter. Because the interaction probability is very small, a gigantic detector is necessary for the study of neutrinos. Water Cherenkov technique is the only solution to realize a Megaton scale detector with currently available technology. The design of Hyper-K is based on the highly successful Super-K, taking full advantage of a well-proven technology. The science goals of Hyper-K include not only the study of neutrino properties, but also broad topics in particle physics, astrophysics and geophysics. Hyper-K consists of two cylindrical tanks lying side-by-side, the outer dimensions of each tank being 48 (W) 54 (H) 250 (L) m³. The total (fiducial) mass of the detector is 0.99 (0.56) million metric tons, which is about 20 (25) times larger than that of Super-K. The inner detector region is viewed by 99,000 20-inch PMTs, corresponding to the PMT density of 20% photo-cathode coverage (one half of that of Super-K). In order to enhance the performance of the detector and to reduce the construction cost, new types of photosensors are under development. The design of critical components such as excavation of large caverns, mechanical structure of the tank, and water purification system is established. Further R&D towards detailed technical design, together with study of science cases, is ongoing by an international working group consisting of more than hundred scientists from eleven countries over the world.Hyper-K presents unprecedented potential for precision measurements of neutrino oscillation parameters and discovery reach for CP violation in the lepton sector. Hyper-K can extend the sensitivity to nucleon decays beyond what was achieved by Super-K by an order of magnitude or more. The scope of studies at Hyper-K also covers high precision measurements of solar neutrinos, observation of both supernova burst neutrinos and supernova relic neutrinos, and dark matter searches. Although the main motivation of the Hyper-K project arises from particle physics and astrophysics, thanks to its large volume and excellent performance, Hyper-K will be also able to contribute to geophysics by detection of neutrinos coming through the inside of the earth as discussed in [1]. The prospects for geophysics using Hyper-K will be discussed.References [1] K. Abe, T. Abe, H. Aihara, Y. Fukuda, Y. Hayato, K. Huang, A. K. Ichikawa and M. Ikeda et al., Letter of Intent: The Hyper-Kamiokande Experiment --- Detector Design and Physics Potential ---, arXiv:1109.3262 [hep-ex]. [2] Hyper-Kamiokande Working Group, Hyper-Kamiokande Physics Opportunities, arXiv:1309.0184 [hep-ex].