Work has started on a huge underground neutrino lab in China. The $330m Jiangmen Underground Neutrino Observatory (JUNO) is being built in Kaiping City, Guangdong Province, in the south of the country around 150 km west of Hong Kong. When complete in 2020, JUNO is expected to run for more than 20 years, studying the relationship between the three types of neutrino: electron, muon and tau.

The design concept for the detector was completed last year and it will be built by the Institute of High Energy Physics (IHEP), which is part of the Chinese Academy of Sciences (CAS). JUNO will require an 80 m high and 50 m diameter experimental hall located 700 m underground. Its detector – filled with 20,000 tonnes of liquid scintillator – will use more than 15,000 photomultiplier tubes to detect the scintillation light that is created when a neutrino hits a hydrogen atom.

Big challenge

Although JUNO will be able to detect neutrinos produced by supernovae as well as those from Earth, the observatory will mainly study neutrinos created at two nearby nuclear power plants being built around 50 km from the experiment. "We need to detect neutrinos from the nuclear reactors, from a proper distance," says Yifang Wang, IHEP director, who heads the JUNO project. "It will be a big challenge to build such a large underground lab and a detector in five years."

The detector is expected to have an energy resolution of around 3%, allowing JUNO to determine the relative masses of the three kinds of neutrinos, known as the neutrino-mass hierarchy. Several similar experiments around the world – including NOvA in the US, Hyper-Kamiokande in Japan and the planned Indian Neutrino Observatory – will also work towards this goal. "That is an important part – to solve the mystery of why matter dominated over antimatter in our universe," says Jun Cao, a particle physicist at IHEP.

Previous success

China's experience operating the Daya Bay neutrino experiment for the last three years will stand it in good stead for JUNO. "The success of Daya Bay has attracted more potential foreign partners for JUNO," adds Wang. Along with IHEP and 19 other Chinese institutions, interest in joining JUNO has also been expressed by more than 30 international institutions, including partners in Daya Bay from the Czech Republic, France, Germany, Italy, Russia and the US. "JUNO will help us build a leading research team, and make China one of the leaders in the field of particle physics," adds Wang.