Chinese scientists report first physics results from Jiangmen Underground Neutrino Observatory

Chinese scientists have reported the first physics result from the Jiangmen Underground Neutrino Observatory, or JUNO, a massive underground detector that has achieved the most precise measurements of neutrino oscillation parameters to date, according to a study published as a cover article in the journal Nature on Wednesday.

The research team, led by the Institute of High Energy Physics of the Chinese Academy of Sciences, measured two key parameters governing how neutrinos — elusive subatomic particles that rarely interact with matter — change their identities as they travel, a phenomenon known as neutrino oscillation. The measurements improved on the combined experimental results of the past decades by a factor of 1.6.

Neutrinos are the most abundant matter particles in the universe, yet they carry no electrical charge, have very little mass and pass through ordinary matter virtually unimpeded — earning them the nickname "ghost particles". Among all elementary particles, they remain the least understood.

By analyzing data collected between Aug 26 and Nov 2, 2025, the team measured two oscillation parameters that describe how electron neutrinos transform as they travel to the detector.

Reviewers at Nature praised the achievement, noting that the results "validate the detector performance and analysis methodology" and "establish JUNO as a key player in the emerging precision era of neutrino oscillation physics, with direct implications for tests of the three-flavor paradigm, global oscillation fits, and future determinations of the neutrino mass ordering."

Nature also published an accompanying article, noting that JUNO's first measurements "demonstrate unprecedented precision and promise exciting results" and that the facility "will be able to determine the mass ordering."

"This first result from JUNO marks the dawn of the next era of precise neutrino oscillation measurements, and it promises fresh insights into the properties of these mysterious fundamental particles," Nature said.

The precision of the results relied heavily on the detector's capabilities. In April, the journal Chinese Physics C published a paper on JUNO's performance. Arthur McDonald, a Canadian physicist who shared the 2015 Nobel Prize in Physics for the discovery of solar neutrino oscillation, commented on that paper, recognizing JUNO's capabilities.

"JUNO has successfully met its design objectives, achieving exceptional radiopurity, energy resolution, and detector stability," McDonald said.

"The experiment is fully operational and ready to pursue its ambitious physics goals, including determining the neutrino mass ordering, studying neutrino oscillation parameters, detecting neutrinos from various sources, and exploring physics beyond the standard model for elementary particles," he added.

The detector's primary scientific goal is to determine the mass ordering of neutrinos — whether the third type of neutrino is heavier or lighter than the other two — a long-standing question in particle physics with implications for understanding how matter formed in the universe. JUNO will also measure three of the six neutrino mixing parameters to better than 1 percent precision and study neutrinos from supernovae, Earth's interior, the Sun and the atmosphere.

To detect these elusive particles, JUNO houses a 20,000-metric-ton spherical target of ultrapure liquid scintillator buried 700 meters underground in Jiangmen, Guangdong province. When a neutrino interacts with an atom in the liquid via the weak force, it produces a charged particle that excites the surrounding molecules, emitting tiny flashes of light as signals.

The JUNO project is a major international effort involving more than 700 scientists from 75 institutions across 17 countries and regions. The detector has been running smoothly for nine months, and as data continue to accumulate, new results will be released starting this summer, offering new insights into the mysteries of neutrinos.

JUNO follows China's first-generation neutrino detector, the Daya Bay Reactor Neutrino Experiment, which operated from 2011 to 2020 and discovered the last unknown neutrino mixing angle, theta-13.