Neutrinos are the most abundant particles in the cosmos, with trillions streaming through every person each second. Yet they rarely interact with matter, making them difficult to study. Scientists know neutrinos oscillate between three types and carry tiny but uncertain masses. Determining their precise properties has remained an open challenge for nearly a century.
JUNO tackles this challenge with a 35.4-meter-diameter transparent sphere filled with 20,000 tonnes of liquid scintillator, buried 700 meters underground between the Yangjian and Taishan nuclear plants. Neutrinos from the reactors occasionally interact with the medium, releasing flashes of light that 43,212 surrounding photomultipliers capture. The tank sits inside a water pool and beneath a Top Tracker system, which filters stray cosmic particles that might mimic neutrino signals.
The primary scientific goal is to measure neutrino oscillations with unprecedented precision, particularly their transformation frequencies. These results will help resolve the neutrino mass hierarchy - whether their ordering aligns with other fundamental particles or defies expectations.
Beyond particle physics, JUNO's data will deepen understanding of cosmological events such as inflation and matter-antimatter asymmetry, as well as astrophysical phenomena like supernovae. Neutrinos also hold keys to solar nuclear processes and even the radioactive dynamics of Earth's interior. JUNO is expected to deliver the most sensitive measurements of these signals ever achieved.
The collaboration involves 74 institutions across Asia, Europe, and the Americas, uniting 700 researchers. Led by the Chinese Academy of Sciences' Institute of High Energy Physics, the project benefits from longstanding CNRS involvement in design, construction, commissioning, and data exploitation.