大だい規模きぼ 観測かんそく装置そうち「ハイパーカミオカンデ」の地下ちか空洞くうどうが公開こうかい

The massive underground cavity for the large-scale observation device Hyper-Kamiokande, which is being constructed in Hida City, Gifu Prefecture to observe neutrinos—elementary particles that pour down from space—and to explore the origins of stars and matter, was unveiled to the press on the 28th.

The large-scale observation devices Kamiokande and Super-Kamiokande, operated by the Institute for Cosmic Ray Research at the University of Tokyo in Kamioka Town, Hida City, succeeded in observing extremely small elementary particles called neutrinos that come from space and elsewhere, which contributed to two Japanese researchers receiving the Nobel Prize in Physics.

Since five years ago, construction has been underway 600 meters underground on Hyper-Kamiokande, which can observe about eight times as many neutrinos as Super-Kamiokande, in an effort to produce even more research results. On the 28th, the massive cavern at the construction site was opened to the press.

The excavation work for the hollow structure, which is 94 meters high and 69 meters in diameter, is expected to be completed next month. After that, a huge tank to hold water will be installed, and about 20,000 high-performance detectors for observing neutrinos are planned to be attached to the inside of the tank.

We are scheduled to begin observations in 2028, three years from now. Professor Masato Shiozawa, Director of the Kamioka Observatory, Institute for Cosmic Ray Research, University of Tokyo, said, I am relieved now that we can expect the completion of the cavity.

I want to achieve results that will surprise everyone, so I hope youll look forward to the outcome, he said.

Hyper-Kamiokande is a large-scale observation device being constructed to further advance research on neutrinos, a field in which Japan excels and which has led to two Nobel Prizes. The goal is to begin observations three years from now, in 2028.

What is a neutrino? A neutrino is one of the elementary particles that make up matter. An enormous number of them pour down on us from space and the atmosphere, and even if we limit it to just those coming from the sun onto our bodies, the number reaches several hundred trillion per second.

This neutrino has a mass about one millionth that of its counterpart, the electron, and since it carries no electric charge, it can even pass through the Earth, making it extremely difficult to observe.

The first-generation Kamiokande: In order to detect neutrinos, which are like ghosts, observations of neutrinos coming from space began in 1986 using the Kamiokande detector located underground in the Kamioka mine in Gifu Prefecture. For the first time in the world, neutrinos associated with a supernova explosion, which occurs when a star reaches the end of its life, were successfully observed.

With this achievement, Masatoshi Koshiba was awarded the Nobel Prize in Physics in 2002.

Second generation also wins Nobel Prize In 1996, the successor Super-Kamiokande began operation, and two years later in 1998, Takaki Kajita was awarded the Nobel Prize in Physics in 2015 for the achievement of being the first in the world to discover that neutrinos have mass.

The characteristic of the third generation—And in Japans neutrino research, which has led the world, the Hyper-Kamiokande is being constructed as the third-generation observation device.

In the future, a huge tank to be installed 600 meters underground will hold 190,000 tons of water, about eight times as much as Super-Kamiokande.

The plan is to line the inside of the tank with about 20,000 photomultiplier tubes, which are light detectors, to capture the extremely faint light produced when a neutrino passing through here very rarely collides with a water molecule.

The sensitivity of the detector is twice that of the one used in Super-Kamiokande, allowing it to detect even fainter light, and it is also said to be able to accurately determine the type of neutrino and the direction from which it came.

One of the objectives of Hyper-Kamiokande, which aims to enlarge and enhance the performance of the scientific apparatus pursued at Hyper-Kamiokande, is to achieve scientific results that approach the mysteries of the birth of the universe.

There is a possibility that there are differences in properties between neutrinos and their antimatter counterparts, antineutrinos, and Hyper-Kamiokande plans to investigate these differences in detail.

Right after the universe was born in the Big Bang, there was an equal amount of matter and antimatter, but it is believed that antimatter disappeared and only matter remained. Why matter became dominant in the universe remains a major mystery.

If the differences between neutrinos and antineutrinos become clear, it is expected that this will be a major step forward in solving this mystery, and attention is focused on whether Hyper-Kamiokande can achieve results that will lead to a third Nobel Prize.