Hyper-Kamiokande Underground Neutrino Observatory in Japan Unveils 94-Meter Cavern in Gifu Pref., Ahead of 2028 Opening

The Yomiuri Shimbun

15:28 JST, June 29, 2025

HIDA, Gifu — The underground cavern for the next-generation neutrino observatory Hyper-Kamiokande in Hida, Gifu Prefecture, was opened the press for the first time on Saturday.

The cavern — 94 meters high and 69 meters in diameter — is in the process of being excavated. The University of Tokyo’s Institute for Cosmic Ray Research (ICRR) plans to begin observation in 2028 at the facility, which is expected to deliver Nobel-level insights into the origin of matter.

Hyper-Kamiokande is being built 600 meters beneath a mountain. The detector will capture the faint flashes of light that appear when neutrinos occasionally collide with electrons in water and other particles. Inside the cavern, engineers will erect a gigantic cylindrical tank 71 meters high and 68 meters in diameter, line its walls with tens of thousands of ultra-sensitive photodetectors, and fill it with 260,000 tons of ultra-pure water — about eight times the volume used in its predecessor, Super-Kamiokande. This scale will enable observations with far higher precision.

First observations were originally slated for 2027, but rising material costs forced design changes, delaying the schedule by one year. Excavation is set to finish in July, after which the tank’s construction will begin. “We aim to produce results that will fundamentally change our understanding of elementary particles,” said Prof. Masato Shiozawa of the ICRR.