Super-Kamiokande

Coordinates: 36°25′32.6″N 137°18′37.1″E / 36.425722°N 137.310306°E / 36.425722; 137.310306 Super-Kamiokande (semi-abbreviation of full name: Super-Kamioka Neutrino Detection Experiment, also abbreviated to Super-K or SK; Japanese: スーパーカミオカンデ) is a neutrino observatory located under Mount Ikeno near the city of Hida, Gifu Prefecture, Japan. It is located 1,000 m (3,300 ft) underground in the Mozumi Mine in Hida's Kamioka area. The observatory was designed to detect high-energy neutrinos to search for proton decay, study solar and atmospheric neutrinos, and keep watch for supernovae in the Milky Way Galaxy. It consists of a cylindrical stainless steel tank about 40 m (131 ft) in height and diameter holding 50,000 tons of ultrapure water. Mounted on an inside superstructure are about 13,000 photomultiplier tubes that detect light from Cherenkov radiation. A neutrino interaction with the electrons of nuclei of water can produce an electron or positron that moves faster than the speed of light in water (not to be confused with exceeding the speed of light in a vacuum). This creates a cone of Cherenkov radiation light, which is the optical equivalent to a sonic boom. The Cherenkov light is recorded by the photomultiplier tube. Using the information recorded by each tube, the direction and 'flavor' (type) of the incoming neutrino is determined. The Super-K is located 1,000 m (3,300 ft) underground in the Mozumi Mine in Hida's Kamioka area. It consists of a cylindrical stainless steel tank that is 41.4 m (136 ft) tall and 39.3 m (129 ft) in diameter holding 50,000 tons of ultrapure water. The tank volume is divided by a stainless steel superstructure into an inner detector (ID) region, which is 36.2 m (119 ft) in height and 33.8 m (111 ft) in diameter, and outer detector (OD) which consists of the remaining tank volume. Mounted on the superstructure are 11,146 photomultiplier tubes (PMT) 50 cm (20 in) in diameter that face the ID and 1,885 20 cm (8 in) PMTs that face the OD. There is a Tyvek and blacksheet barrier attached to the superstructure that optically separates the ID and OD. A neutrino interaction with the electrons or nuclei of water can produce a charged particle that moves faster than the speed of light in water (not to be confused with exceeding the speed of light in a vacuum). This creates a cone of light known as Cherenkov radiation, which is the optical equivalent to a sonic boom. The Cherenkov light is projected as a ring on the wall of the detector and recorded by the PMTs. Using the timing and charge information recorded by each PMT, the interaction vertex, ring direction and flavor of the incoming neutrino is determined. From the sharpness of the edge of the ring the type of particle can be inferred. The multiple scattering of electrons is large, so electromagnetic showers produce fuzzy rings. Highly relativistic muons, in contrast, travel almost straight through the detector and produce rings with sharp edges. Construction of the predecessor of the present Kamioka Observatory, the Institute for Cosmic Ray Research, University of Tokyo began in 1982 and was completed in April 1983. The purpose of the observatory was to detect whether proton decay exists, one of the most fundamental questions of elementary particle physics. The detector, named KamiokaNDE for Kamioka Nucleon Decay Experiment, was a tank 16.0 m (52 ft) in height and 15.6 m (51.2 ft) in width, containing 3,048 metric tons (3,000 tons) of pure water and about 1,000 photomultiplier tubes (PMTs) attached to its inner surface. The detector was upgraded, starting in 1985, to allow it to observe solar neutrinos. As a result, the detector (KamiokaNDE-II) had become sensitive enough to detect neutrinos from SN 1987A, a supernova which was observed in the Large Magellanic Cloud in February 1987, and to observe solar neutrinos in 1988. The ability of the Kamiokande experiment to observe the direction of electrons produced in solar neutrino interactions allowed experimenters to directly demonstrate for the first time that the sun was a source of neutrinos. The Super-Kamiokande project was approved by the Japanese Ministry of Education, Science, Sports and Culture in 1991 for total funding of approximately $100 M. The US portion of the proposal, which was primarily to build the OD system, was approved by the US Department of Energy in 1993 for $3 M. In addition the US has also contributed about 2000 20 cm PMTs recycled from the IMB experiment.