Research History


The operation of the Kamiokande experiment started. Four years later, Kamiokande detected the neutrinos emitted by the supernova explosion at 160,000 light-years away. The neutrinos flew in for only 10 seconds. This result would not have been obtained if the detector modification had been delayed for months or the maintenance had been delayed for a few minutes.

Jul. 1983

Kamiokande experiment started

The Kamiokande experiment was started to verify the Grand Unified Theory of particle physics by searching for proton decay. The Kamioka Underground Observatory (presently Kamioka Observatory), Institute for Cosmic Ray Research, The University of Tokyo, was founded in 1983 to promote the Kamiokande experiment. The detector filled with 3,000 tons of pure water in a cylindrical water tank with a 16 m diameter and a 16 m height was installed 1,000 m underground in the Kamioka mine in Kamioka Town, Gifu Prefecture. The Kamiokande was named after the first letters of “KAMIOKA Nucleon Decay Experiment.”

Dec. 1986

Kamiokande modified its detector to observe solar neutrinos. The modifications were completed, and observations resumed at the end of 1986.

Feb. 1987

Success in observing supernova explosion neutrinos

After the refurbishing work, the detector sensitivity dramatically increased. Thereby, Kamiokande achieved great results, i.e., succeeded in observing neutrinos from the supernova explosion in the Large Magellanic Cloud. In addition, neutrinos from the sun were observed in 1988, which researchers highly evaluated worldwide.

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The operation of the second generation detector, Super-Kamiokande, has started. Super-Kamiokande discovered the evidence of neutrino oscillations that went beyond the conventional wisdom of neutrinos, which had been thought to have zero mass. This discovery brought the second Nobel Prize in Physics to Kamioka. Furthermore, the K2K experiment, the world’s first using artificial neutrino beams, confirmed this discovery.

Dec. 1991

The cavity excavation for the construction of the Super-Kamiokande detector started. Hard rock of Hida gneiss was dug up.

Jun. 1994

The cavity excavation was completed. The construction of the detector was started. Stainless steel plates were attached to the wall of the huge cavity, and modularized photomultiplier tubes were attached to the inner wall.

Jan. 1996

The water supply to the detectors started. It took two months to fill the tank with a volume of 50,000 tons.

Apr. 1996

The operation of the Super-Kamiokande started.

The operation of the Super-Kamiokande started at midnight on April 1, 1996, while many researchers were watching in the mine. The person who pushed the operation starting button was Professor Yoji Totsuka, the first spokesperson of Super-Kamiokande.

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Jun. 1998

Discovery of atmospheric neutrino oscillation

It was revealed that the number of neutrinos coming from the other side of the earth was smaller, and solid evidence of neutrino oscillations was shown to the world.

Jan. 1999

The Super-Kamiokande Collaboration (Representative: Professor Yoji Totsuka) was awarded the Asahi Prize for “Discovery of Neutrino Mass.”

Jun. 1999

The K2K experiment started.

The world’s first long-baseline neutrino oscillation experiment, K2K, started. In this experiment, neutrinos artificially produced in the accelerator at KEK (High Energy Accelerator Research Organization) in Tsukuba City, Ibaraki Prefecture, were injected into the Super-Kamiokande about 250 km away. The K2K succeeded in confirming the neutrino oscillations discovered in atmospheric neutrinos.


The 30-year-old solar neutrino problem has been solved. There was an accident where about half of the photomultiplier tubes were broken, but they managed to be rebuilt. There was also the good news that Professor Koshiba was awarded the Nobel Prize in Physics. In addition, the T2K experiments, which are a further refinement of the K2K experiments, started.

Jun. 2001

Discovery of solar neutrino oscillation

Super-Kamiokande’s discoveries continued: in 2001, in conjunction with the results of the SNO experiment in Canada, solar neutrino oscillation was discovered.

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Nov. 2001

The photomultiplier tubes breakage accident

In July 2001, the number of defective photomultiplier tubes increased, so the photomultiplier tubes were replaced after being drained. In November 2001, during water injection after the replacement, an accident occurred wherein the photomultiplier tubes on the bottom were broken. Since the inside of the photomultiplier tubes was a vacuum, large shock waves were generated. These shock waves traveled through the water and damaged the other photomultiplier tubes in a chain reaction. More than 6,777 photomultiplier tubes, representing more than half of those in the inner water tank, were broken. In the outer water tank, 1,100 photomultiplier tubes were broken. Although the researchers were disappointed by the accident, they undertook an experiment to prevent the recurrence of the accident under the command of Professor Totsuka, spokesperson (at that time), who said, “We will rebuild the detector. There is no question.”

Oct. 2002

Restoration work from the accident

The 5,182 undamaged inner water tank photomultiplier tubes, encased in covers made of FRP and acrylic to prevent shock waves, were rearranged in every other position. The observations restarted in October 2002 with half the original density of photosensors.

Dec. 2002

The 2002 Nobel Prize in Physics awarded to Prof. Masatoshi Koshiba.

The 2002 Nobel Prize in Physics awarded to Prof. Masatoshi Koshiba for pioneering contributions to astrophysics, in particular for the detection of cosmic neutrinos.

Jun. 2004

The K2K experiment confirmed the atmospheric neutrino oscillation discovered by Super-Kamiokande.

Jul. 2004

Direct observation of an oscillatory signature in the atmospheric neutrino samples

Nov. 2004

The K2K experiment completed

Jun. 2006

Full reconstruction of Super-Kamiokande

The glass of the photomultiplier tubes was handmade one by one. While continuing observations after the partial reconstruction in 2002, we had steadily prepared to restore the original number of photomultiplier tubes. From October 2005 to June 2006, the tank was reopened, and complete reconstruction was carried out. As a result, the number of photomultiplier tubes in the inner tank is now 11,129, almost the same as before the accident.

Sep. 2008

Replacement of front-end electronics and data acquisition system (DAQ)

Apr. 2009

The T2K experiment started

The T2K experiment, using a neutrino beam about 50 times stronger than that of the K2K experiment, was started. A more precise study of neutrino oscillations began.

Nov. 2009

The lifetime of proton decay observed in the Super-Kamiokande exceeded 1034 years.

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All three types of neutrino oscillations have been experimentally confirmed. The T2K experiment has shown that neutrinos are likely to have “CP violation.” Why did matter not disappear through the pair annihilation with antimatter? Why do substances like the human body exist in the universe? We are gradually approaching the answers to these questions.

Jun. 2011

The T2K discovered electron neutrino appearance.

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July 2013

The T2K measured electron neutrino appearance.

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Nov. 2015

2016 Breakthrough Prize in Fundamental Physics awarded to Prof. Yoichiro Suzuki, Prof. Takaaki Kajita and SK Collaborators, and Prof. Koichiro Nishikawa and K2K/T2K Collaborators.

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Dec. 2015

The 2015 Nobel Prize in Physics awarded to Prof. Takaaki Kajita.

The Nobel Prize in Physics 2015 was awarded to Prof. Takaaki Kajita for the discovery of neutrino oscillations, which shows that neutrinos have mass.

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Jul. 2016

The T2K experiment represented the first CP violation search result.

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Aug. 2017

T2K presents hint of CP violation by neutrinos

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Jun. 2018

Work to refurbish Super-Kamiokande has started

It has been 12 years since the detector was last opened. Work to refurbish the detector was conducted in stages, draining the water a little at a time as the work progresses.

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Jan. 2019

Super-Kamiokande restarted the observation.

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Since the Kamiokande observed neutrinos emitted from the supernova explosion in 1987, no supernova explosion neutrinos have been observed. Therefore, the SK-Gd project started to perceive the “supernova relic neutrinos” that have been produced by the supernova explosion from the birth of the universe to the present. In addition, the construction of the Hyper-Kamiokande was also started to promote the further development of neutrino research.

Feb. 2020

The Hyper-Kamiokande project officially started.

The third-generation experiment in Kamioka, the Hyper-Kamiokande project, has started. It was designed to be able to obtain a huge amount of data more efficiently than the Super-Kamiokande, and new discoveries are expected.

Aug. 2020

The SK-Gd project started.

With the addition of gadolinium, the new Super-Kamiokande(SK-Gd) has started. The addition of gadolinium is expected to increase the sensitivity to observe neutrinos. In particular, we expect the world’s first observation of “supernova relic neutrinos (SRN).” Observing SRN will allow for the study of general features of supernova explosions. Understanding supernova explosions will advance our understanding on production of elements in the university.

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May. 2021

The access tunnel excavation for Hyper-Kamiokande started.

Hyper-Kamiokande website