Kamioka Observatory

Kamioka Observatory is a Japanese neutrino observatory utilizing the underground rooms of an old mine. It has been the site of a number of Cherenkov detectors, beginning in the 1980s with KamiokaNDE (for Kamioka Nucleon Decay Experiment), consisting of a tank of 3,000 tons of pure water surrounded by photomultiplier tubes (PMTs), being a search for proton decay: it found none, providing evidence of how rare such decay is assuming it does occur. The equipment did detect other particle interactions, offering data for other physics. The subsequent experiment, Kamiokande-II was additionally focused on neutrino detections, and among its notable results were the collection of data revealing the solar neutrino problem, and the detection of a neutrino burst associated with SN 1987A, i.e., near in time and direction to the visible supernova. Subsequent experiments, built around larger tanks and more PMTs, focused on the neutrino observations (and NDE was redefined to mean neutrino detection experiment):

• KamLAND (for Kamioka Liquid Scintillator Antineutrino Detector) with 1,100 tons of a blend to serve as scintillator, to observe neutrinos from nearby nuclear reactors, and which in 2002 detected evidence of neutrino oscillation.
• Super-Kamiokande (Super-K, for Super-Kamioka Neutrino Detection Experiment) with 55,000 tons of water and 13,000 PMTs: it detected neutrino oscillation data that indicated a solution to the solar neutrino problem.
• Hyper-Kamiokande (Hyper-K) is yet another enlarged detector in development as of 2023.