Super-Kamiokande is the world’s largest water Cherenkov detector. Construction began in 1991, and after a five-year construction period, the observation started on April 1st, 1996. The Super-Kamiokande is operated by an international collaboration of about 200 people and about 50 institutes from Japan, the United States, Poland, Korea, China, Spain, Canada, UK, Italy and France and Vietnam.
The Super-Kamiokande detector consists of a stainless-steel tank, 39.3m diameter and 41.4m tall, filled with 50,000 tons of water. About 13,000 photo-multipliers are installed on the tank wall. The detector is located at 1,000 meter underground in the Kamioka-mine, Hida-city, Gifu, Japan.
Elucidation of neutrino properties
One of the purposes of the Super-Kamiokande experiment is to reveal the neutrino properties through the observation of solar neutrinos, atmospheric neutrinos and man-made neutrinos. In 1998, from the observation of atmospheric neutrinos we discovered the neutrino oscillations which neutrinos are changing their types in flight. In 2001, solar neutrino oscillations were discovered by the observation of solar neutrinos. In 2011, the third neutrino oscillation mode was discovered by man-made neutrino observation.
Observations of the universe by neutrino
Super-Kamiokande can also use neutrinos to “see” inside stars and the universe as a whole. By observing solar neutrinos generated by the sun, it is possible to know the activities inside of the sun directly. By capturing neutrinos from supernova explosions, we can study the details of the explosion process of stars. We can also investigate the universe’s history by capturing neutrinos from the many supernova explosions since the beginning of the universe.
Search for proton decay
On the other hand, the Grand Unified Theories (GUTs), which can unify the fundamental forces of nature, predict that the proton can decay into lighter energetic charged particles. Super-Kamiokande searches for this unknown phenomenon. If the proton decay is observed, it may be possible to prove the GUTs.
Observation of supernova relic neutrino
Since August 2020, the rare earth element gadolinium has been introduced into the Super-Kamiokande detector, starting a new period of observations. The addition of gadolinium improves SK’s ability to observe neutrinos and enables the first-ever observation of supernova relic neutrinos.