MINUTE GUIDE -Understand the Super-Kamiokande in 5 minutes-

Elucidate the mystery
of the universe
and matter through neutrino observation

The Super-Kamiokande is a large detector that mainly observes elementary particles called neutrinos.
In 2015, Professor Takaaki Kajita won the Nobel Prize for discovering neutrino oscillations in this Super-Kamiokande.
Also, for the predecessor Kamiokande, Professor Masatoshi Koshiba won the Nobel Prize in 2002.
Thus, Super-Kamiokande has continued to lead the world in neutrino research.


What are Neutrinos?

Where are Neutrinos?

Even at this moment, neutrinos are
going through our bodies.

Although each neutrino is extremely small, neutrinos are the second most abundant particles in the universe only after light. Many neutrinos are pouring down on the earth from the sun and stars. Neutrinos are also produced by the collision between radiation from space (cosmic rays) and the earth’s atmosphere. (Even bananas emit neutrinos!) Since a neutrino is so small and does not feel the electromagnetic force, it easily goes through even the earth. Therefore, neutrinos not only pour from the sky, but also come from the backside of the earth and go into the sky. Hundreds of trillions of neutrinos from the sun are passing through our bodies every second.

Supernova 1987A (right: before explosion, left: after explosion)
Neutrinos emitted from the supernova explosion 160,000 light years away reached the Earth.

(Anglo-Australian Observatory/Daved Malin)

Tell me about
Neutrinos briefly.

The smallest elements of matter, “elementary particles” and Invisible “ghost particles”.

Neutrinos are “elementary particles” that are smaller than atoms. As of 2021, 17 elementary particles have been found, such as electrons and quarks. The mass of neutrino is much smaller than that of the other elementary particles, and neutrino does not have an electric charge. Neutrinos are elementary particles that still have many mysteries.

What are Neutrinos?


How do you observe Neutrinos?

How do you observe elementary particles
smaller than atoms?

If the particle have electric charge,
you can observe the tracks.

An electron microscope can see an atom. However, it is difficult to observe elementary particles smaller than atoms directly. Instead, we generally see the tracks generated by charged particles or interaction with matter. On the other hand, since a neutrino is electrically neutral, it is even harder to see it. That is why neutrinos are called “ghost particles.”

How do you observe Neutrinos
without electric charge?

We observe the light emitted
when neutrinos very rarely collide with matter.

Although it is difficult to observe neutrinos themselves, we can detect charged particles generated by interactions with neutrinos. A neutrino can pass through anything, but in rare cases, it ejects charged particles by colliding with matter in its path. In the Super-Kamiokande, we observe weak ring-shaped “Cherenkov light” emitted by a charged particle ejected when a neutrino collides with water in the detector.

Let’s see the real-time data monitor
of Super-Kamiokande!

You can see the real-time data observed at the Super-Kamiokande on the web. About 30 neutrinos are observed per day. Most of the data are the interactions by cosmic ray muons (about two times per second). If you are lucky, you might be able to observe the interaction of a neutrino.


Where is the
Super-Kamiokande located?

Where is the
Super-Kamiokande located?

It is located at 1,000m underground
in the mountains of Kamioka Town, Hida City, Gifu Prefecture.

It is a large water tank of 39 m in diameter and 41 m in height located 1,000 m underground (about the height of a 10-story building.). That is the Super-Kamiokande detector. It is located underground to avoid the influence of other particles as much as possible. When primary cosmic rays collide with the earth’s atmosphere, elementary particles such as muons (cosmic ray muons), electrons, and neutrinos are generated. Most cosmic ray muons lose energy in the soil and stop, but neutrinos can pass through anything. That’s why the Super-Kamiokande is located underground to minimize the influence of cosmic ray muons.

What are those many spheres
on the wall of the Super-Kamiokande?

Those are the high-sensitivity photo sensors that would detect the light from a flashlight on the surface of the moon.

In order to increase the number of interactions between neutrinos and nucleons (protons and neutrons in a nucleus) or electrons in water, the water tank of the Super-Kamiokande contains 50,000 tons of water. The high-sensitive photo-sensors called photomultiplier tubes installed all over the wall detect the weak Cherenkov light emitted by the charged particles. The diameter of a photomultiplier tube is 50 cm, the largest in the world. Although a photomultiplier tube looks like a light bulb, it does not emit light but plays a role in looking at a light, just like “eyes.” The sensitivity of the photomultiplier tubes is so high that it would detect the light from a flashlight on the surface of the moon.

About detectors


Why are you doing research?

What we expect to know

The origin of the universe
The reason why we exist

The present universe is full of matter. However, equal amounts of matter and antimatter were created at the beginning of the universe. Since matter and antimatter annihilate when they are encountered, it could have been a universe where the stars and we didn’t exist. Why did only matter survive? By studying the differences and properties of neutrinos and antineutrinos, we expect to elucidate the evolution of the universe and the mysteries of matter.

New framework of elementary particles

So far, 17 elementary particles have been discovered, including neutrinos, and there is a hypothesis that “they consist of the identical particle, only they look different.” The discovery of the proton decay phenomenon will confirm this hypothesis. In fact, Kamiokande originally started to search for proton decay, but it has not yet been observed. Clarifying the mechanism of elementary particles is another important theme of Super-Kamiokande.

What we expect to see

Inside of stars

Neutrinos can also “see” inside stars and the whole universe. For example, neutrinos from the center of the sun and the process of supernova explosions provide information about those activities. Super-Kamiokande is also conducting a project to explore the history of the universe by capturing neutrinos from supernova explosions that have occurred since the beginning of the universe.

The Sun as seen by neutrinos.

(Based on Super-Kamiokande data from 1996 to 2018)


Hyper-Kamiokande project

And now, the Hyper-Kamiokande is under construction to start observation in 2027.
The huge and high-performance detector of Hyper-Kamiokande
will be able to obtain an amount of data corresponding
to 100 years of data collection time using Super-Kamiokande, in only 10 years.
We continues to lead the world in neutrino research.