Kamioka Observatory

The Mozumi mine is one of two adjacent mines owned by the Kamioka Mining and Smelting Co. (a subsidiary of the Mitsui Mining and Smelting Co. Mitsui Kinzoku ). The mine is famous as the site of one of the greatest mass-poisonings in Japanese history. From 1910 to 1945, the mine operators released cadmium from the processing plant into the local water. This cadmium caused what the locals called itai-itai disease. The disease caused weakening of the bones and extreme pain. Although mining operations have ceased, the smelting plant continues to process zinc, lead and silver from other mines and recycling. is also available. It is not quite as deep, but has stronger rock and is the planned site for the very large Hyper-KamiokaNDE caverns. == Past experiments ==

KamiokaNDE The first of the Kamioka experiments was named KamiokaNDE for Kamioka Nucleon Decay Experiment. It was a large water Cherenkov detector designed to search for proton decay. To observe the decay of a particle with a lifetime as long as a proton an experiment must run for a long time and observe an enormous number of protons. This can be done most cost effectively if the target (the source of the protons) and the detector itself are made of the same material. Water is an ideal candidate because it is inexpensive, easy to purify, stable, and can detect relativistic charged particles through their production of Cherenkov radiation. A proton decay detector must be buried deep underground or in a mountain because the background from cosmic ray muons in such a large detector located on the surface of the Earth would be far too large. The muon rate in the KamiokaNDE experiment was about 0.4 events per second, roughly five orders of magnitude smaller than what it would have been if the detector had been located at the surface. The distinct pattern produced by Cherenkov radiation allows for particle identification, an important tool for both understanding the potential proton decay signal and for rejecting backgrounds. The identification is possible because the sharpness of the edge of the ring depends on the particle producing the radiation or electrons (and therefore also gamma rays) produce fuzzy rings due to the multiple scattering of the low mass electrons. Minimum ionizing muons, in contrast, produce very sharp rings as their heavier mass allows them to propagate directly. Construction of the Kamioka Underground Observatory (the predecessor of the present Kamioka Observatory, Institute for Cosmic Ray Research, University of Tokyo) began in 1982 and was completed in April, 1983. The detector was a cylindrical tank which contained 3,000 tons of pure water and had about 1,000 50 cm diameter photomultiplier tubes (PMTs) attached to the inner surface. The size of the outer detector was 16.0 m in height and 15.6 m in diameter. The detector failed to observe proton decay, but set what was then the world's best limit on the lifetime of the proton. KamiokaNDE-I operated 1983–1985. KamiokaNDE-II The KamiokaNDE-II experiment was a major step forward from KamiokaNDE, and made a significant number of important observations. During this phase the NDE part of the name came to be called "Neutrino Detection Experiment". With the upgrades completed, the experiment was renamed KamiokaNDE-II, and started taking data in 1985. The experiment spent several years fighting the radon problem, and started taking "production data" in 1987. Once 450 days of data had been accumulated, the experiment was able to see a clear enhancement in the number of events which pointed away from the Sun over random directions. Raymond Davis Jr. and Riccardo Giacconi were co-winners of the prize. K2K The KEK To Kamioka experiment used accelerator neutrinos to verify the oscillations observed in the atmospheric neutrino signal with a well-controlled and understood beam. A neutrino beam was directed from the KEK accelerator to Super KamiokaNDE. The experiment found oscillation parameters which were consistent with those measured by Super-K. ==Current experiments==

Super Kamiokande By the 1990s particle physicists were starting to suspect that the solar neutrino problem and atmospheric neutrino deficit had something to do with neutrino oscillation. The Super Kamiokande detector was designed to test the oscillation hypothesis for both solar and atmospheric neutrinos. The Super-Kamiokande detector is massive, even by particle physics standards. It consists of 50,000 tons of pure water surrounded by about 11,200 photomultiplier tubes. The detector was again designed as a cylindrical structure, this time tall and across. The detector was surrounded with a considerably more sophisticated outer detector which could not only act as a veto for cosmic muons but actually help in their reconstruction. Super-Kamiokande started data taking in 1996 and has made several important measurements. These include precision measurement of the solar neutrino flux using the elastic scattering interaction, the first very strong evidence for atmospheric neutrino oscillation, and a considerably more stringent limit on proton decay. Nobel prize For his work with Super Kamiokande, Takaaki Kajita shared the 2015 Nobel prize with Arthur McDonald. Super Kamiokande-II On November 12, 2001, several thousand photomultiplier tubes in the Super-Kamiokande detector imploded, apparently in a chain reaction as the shock wave from the concussion of each imploding tube cracked its neighbours. The detector was partially restored by redistributing the photomultiplier tubes which did not implode, and by adding protective acrylic shells that it was hoped would prevent another chain reaction from recurring. The data taken after the implosion is referred to as the Super Kamiokande-II data. Super Kamiokande-III In July 2005, preparation began to restore the detector to its original form by reinstalling about 6,000 new PMTs. It was finished in June 2006. Data taken with the newly restored machine was called the SuperKamiokande-III dataset. Super Kamiokande-IV In September 2008, the detector finished its latest major upgrade with state-of-the-art electronics and improvements to water system dynamics, calibration and analysis techniques. This enabled SK to acquire its largest dataset yet (SuperKamiokande-IV), which continued until June 2018, when a new detector refurbishment involving a full water drain from the tank and replacement of electronics, PMTs, internal structures and other parts will take place. Tokai To Kamioka (T2K) The "Tokai To Kamioka" long baseline experiment started in 2009. It is making a precision measurement of the atmospheric neutrino oscillation parameters and is helping ascertain the value of . It uses a neutrino beam directed at the Super Kamiokande detector from the Japanese Hadron Facility's 50 GeV (currently 30 GeV) proton synchrotron in Tōkai such that the neutrinos travel a total distance of . In 2013 T2K observed for the first time the neutrino oscillations in the appearance channel: transformation of muon neutrinos to electron neutrinos. In 2014 the collaboration provided the first constraints on the value of CP violating phase, together with the most precise measurement of the mixing angle . KamLAND The KamLAND experiment is a liquid scintillator detector designed to detect reactor antineutrinos. KamLAND is a complementary experiment to the Sudbury Neutrino Observatory because while the SNO experiment has good sensitivity to the solar mixing angle but poor sensitivity to the squared mass difference, KamLAND has very good sensitivity to the squared mass difference with poor sensitivity to the mixing angle. The data from the two experiments may be combined as long as CPT is a valid symmetry of our universe. The KamLAND experiment is located in the original KamiokaNDE cavity. Cryogenic Laser Interferometer Observatory (CLIO) CLIO is a small gravity wave detector with arms which is not large enough to detect astronomical gravity waves, but is prototyping cryogenic mirror technologies for the larger KAGRA detector. KAGRA The KAmioka GRAvitational wave detector (formerly LCGT, the Large-scale Cryogenic Gravitational Wave Telescope) is an interferometric gravitational wave detector built inside the Kamioka mine. KAGRA was initially approved in 2010; construction was completed in 2019 and the detector first began observing in 2020 . KAGRA is a Michelson interferometer with 3km arm length. Uniquely among current gravitational wave detectors, it uses cryogenically cooled mirrors to decrease thermal noise; it is also the first and only underground gravitational wave detector. KAGRA is designed to eventually be able to observe gravitational waves from neutron star binaries at a distance of up to ∼150 Mpc . As of 2026 it had reached a maximum sensitivity of ~7 Mpc and with continuing upgrades is expected to reach a sensitivity of 50-90 Mpc by the early 2030s . XMASS XMASS is an underground liquid scintillator experiment in Kamioka. It has been searching for dark matter. NEWAGE NEWAGE is a direction-sensitive dark-matter-search experiment performed using a gaseous micro-time-projection chamber. == Future experiments ==

Hyper-Kamiokande There is a program to build a detector ten times larger than Super Kamiokande, and this project is known by the name Hyper-Kamiokande. First tank will be operable in the mid-2020s. At the time of 'inauguration' in 2017 the tank(s) is announced to be 20 times greater than the last one (1000 million liters in Hyper-Kamiokande against 50 million in Super-Kamiokande). ==See also==