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The Jiangmen Underground Neutrino Observatory (JUNO) is a medium baseline reactor neutrino experiment under construction at Kaiping, Jiangmen in Southern China. It aims to determine the neutrino mass hierarchy and perform precision measurements of the Pontecorvo–Maki–Nakagawa–Sakata matrix elements. It will build on the mixing parameter results of many previous experiments. The collaboration was formed in July 2014 and construction began January 10, 2015. Funding is provided by the Chinese Academy of Sciences, but the collaboration is international.
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Planned as a follow-on to the Daya Bay Reactor Neutrino Experiment, it was originally planned for the same location, but the construction of a third nuclear reactor (the planned Lufeng nuclear power plant) in that area would disrupt the experiment, which depends on maintaining a fixed distance to nearby nuclear reactors. Instead it was moved to a loation 53 km from both of the planned Yangjiang and Taishan nuclear power plants.
Detector
The main detector consists of a 35.4 m (116 ft) diameter transparent sphere containing 20,000 tons of linear alkylbenzene liquid scintillator, surrounded by approximately 17,000 photomultiplier tubes, a water pool, and a muon veto. Deploying this 700 m (2,300 ft) underground will detect neutrinos with excellent energy resolution. The overburden includes 270 m of granite mountain, which will reduce cosmic muon background.
The much larger distance to the reactors (compared to less than 2 km for the Daya Bay far detector) makes the experiment better able to distinguish neutrino oscillations, but requires a much larger, and better-shielded, detector to detect a sufficient number of reactor neutrinos.
Physics
The main approach of the JUNO Detector in measuring neutrino oscillations is the observation of electron-antineutrinos (
ν
e) coming from two future nuclear power plants at approximately 53 km distance. Since the expected rate of neutrinos reaching the detector is known from processes in the power plants, the absence of a certain neutrino flavor can give an indication of transition processes.
Although not the primary goal, the detector is sensitive to atmospheric neutrinos, geoneutrinos and neutrinos from supernovae as well.
Expected Sensitivity
Daya Bay and RENO measured θ13 and determined it has a large non-zero value. Daya Bay will be able to measure the value to ≈4% precision and RENO ≈7% after several years. JUNO is designed to improve uncertainty in several neutrino parameters to less than 1%.