The Jiangmen underground neutrino observatory experiment

The Jiangmen Underground Neutrino Observatory (JUNO) is a multipurpose neutrino-oscillation experiment designed to determine the neutrino mass hierarchy as a primary physics goal, by detecting reactor antineutrinos from two power plants at 53-km distance. The detector is placed at 1800-m.w.e. deep underground and consists of a 20 kiloton liquid scintillator contained in a 34.5 m-diameter acrylic ball, instrumented by more than 17,000 20-in. PMTs ensuring a 77% photocatode coverage. To reach an unprecedented 3% energy resolution (at 1 MeV), the PMTs need a quantum efficiency of more than 30% and the attenuation length of the liquid has to be better than 20 m (at 430 nm). This precision on the energy is a key point to determine at the 3-4 σ significance level the neutrinos mass hierarchy with six years of running. The measurement of the antineutrino spectrum will also lead to the precise determination of three out of the six oscillation parameters to an accuracy of better than 1%. The experiment will also be able to observe neutrinos from terrestrial and extra-terrestrial sources. The international collaboration of JUNO was established in 2014, the civil construction started in 2015 and the R&D of the detectors is ongoing. JUNO is planning to start data taking in 2020.