The Jiangmen Underground Neutrino Observatory (JUNO) in China's Guangdong province officially commenced operations on August 26, 2025. This marks a significant milestone in particle physics research, establishing JUNO as the world's largest and most precise facility dedicated to studying neutrinos.
The observatory's primary scientific objective is to definitively determine the mass ordering of neutrinos, a fundamental question in physics. This endeavor will also enable advanced studies of neutrinos from various cosmic and terrestrial sources, potentially illuminating new avenues for physics beyond the Standard Model, such as the search for sterile neutrinos and evidence of proton decay.
JUNO's detector is a colossal 35.4-meter diameter acrylic sphere, situated 700 meters underground within a 44-meter deep water pool. It contains 20,000 tons of liquid scintillator and is equipped with over 45,000 photomultiplier tubes to capture faint light signals produced by neutrino interactions. The observatory is projected to operate for at least 30 years, with provisions for future upgrades.
This pioneering facility is a testament to global scientific collaboration, involving over 700 researchers from 74 institutions across 17 countries and regions. The commencement of data taking signifies a new era in understanding these elusive particles, which have minuscule mass and no electric charge, and can pass through matter undetected. Current data show a slight preference for the normal ordering of neutrino masses, a phenomenon largely driven by neutrino oscillation measurements.