Baksan Neutrino Observatory

The Baksan Neutrino Observatory (BNO, Baksan is sometimes spelled Baxan) is a scientific laboratory of INR RAS located in the Baksan River gorge in the Caucasus mountains in Russia. Cleared for building in 1967, it started operations in 1977, becoming the first such neutrino observatory in the USSR. It consists of the Baksan Underground Scintillation Telescope (BUST), located 300 m (980 ft) below the surface, the gallium–germanium neutrino telescope (Soviet–American Gallium Experiment, SAGE) located 4,700 m.w.e. deep (2, 100 meters) as well as a number of ground facilities. The Baksan Experiment on Sterile Transitions (BEST) is currently (2019) being conducted at Baksan with aims of understanding sterile neutrinos. The laboratory itself is located in a 4,000 meter long horizontal tunnel mined specifically for this purpose; this is in contrast to most underground physics laboratories which are placed in abandoned or still in-use mines. The entrance of the tunnel is at a valley at 1,700 meters high from sea level and the tunnel itself is located under the 4,000 meters tall mountain Mount Andyrchi. A small town named Neutrino was built in the valley, in conjunction with the construction of the laboratory, to house the scientists and their families. The first experiment undertaken at BNO was not underground; it was the Carpet air-shower cosmic ray experiment in 1973

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