SuperKamiokande

Super-Kamiokande, often called Super-K, is a large water Cherenkov neutrino observatory located in the Kamioka mine near Hida-Takayama, Gifu Prefecture, Japan. It is operated by the Institute for Cosmic Ray Research (ICRR) of the University of Tokyo. The detector observes Cherenkov light produced when neutrinos interact in ultra-pure water, enabling the study of neutrino properties and astronomy. The site provides substantial shielding from cosmic rays, with about 1,000 meters of rock overhead, roughly equivalent to 2,700 meters of water.

The main detector is a cylindrical tank housing about 50,000 tons of water. The inner detector contains around 11,000 large photomultiplier tubes that capture Cherenkov photons, while an outer detector provides a veto against remaining cosmic ray backgrounds. The water purification and calibration systems maintain high optical clarity essential for precise timing and reconstruction of events.

Operation and phases: Super-K began operation in 1996 as SK-I. In 2001 a PMT-related accident reduced the number of active PMTs, and SK-II operated with roughly half the original photomultipliers. Subsequent phases, SK-III and SK-IV, introduced upgraded electronics and improved calibration, with SK-IV continuing to operate in the 2010s and beyond. Over its history, the experiment has continually refined its performance and lowered energy thresholds to expand its physics reach.

Science program and impact: Super-K studies atmospheric and solar neutrinos, searches for proton decay, and observations of neutrinos from supernovae and other sources. It played a pivotal role in establishing atmospheric neutrino oscillations and has contributed to measurements of oscillation parameters, while providing global limits on nucleon decay. It remains one of the world’s leading neutrino detectors.