Using 59 days of validated data collected between August 26 and November 2, 2025, the international JUNO Collaboration, led by the Institute of High Energy Physics of the Chinese Academy of Sciences, made highly precise measurements of two fundamental neutrino oscillation parameters. The analysis reduced the uncertainties in those measurements by a factor of 1.6 compared with the combined results from previous experiments conducted over several decades.

Why Neutrinos Matter

Neutrinos are among the most mysterious particles in the universe. They carry no electric charge, have extremely small masses, and interact only weakly with matter. As a result, vast numbers of neutrinos pass through Earth, and even through our bodies, without leaving a trace.

Because they are so difficult to detect, neutrinos remain the least understood of all known elementary particles.

JUNO began collecting data in August 2025. One of its primary scientific goals is to determine the mass ordering of neutrinos. The experiment is also designed to measure three of the six neutrino mixing parameters with better than 1% precision and to study neutrinos produced by supernovae, Earth's interior, the Sun, the atmosphere, and other sources.

Landmark Results for Neutrino Research

The study received strong praise during peer review.

The reviewer wrote: "These results not only validate the detector performance and analysis methodology but also 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 highlighted the work in a News & Views article, stating:

"Understanding the behavior of neutrinos is paramount to developing a complete description of matter and forces at the smallest scale. This first analysis builds confidence that the detector 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 will provide insights into the properties of these mysterious fundamental particles."

Earlier this year, in April, Chinese Physics C featured JUNO's detector performance on its cover.

Prof. Arthur McDonald, who received the 2015 Nobel Prize in Physics for the discovery of solar neutrino oscillation, commented on the publication:

"JUNO has met its design objectives, achieving exceptional radiopurity, energy resolution, and detector stability. The experiment is fully operational and ready to pursue its ambitious physics goals, including determining the neutrino mass ordering (NMO), studying neutrino oscillation parameters, detecting neutrinos from various sources, and exploring physics beyond the Standard Model for Elementary Particles."

Inside the Massive Underground Detector

At the center of the JUNO experiment, located 700 meters underground, is a giant liquid scintillator detector with an effective mass of 20,000 tons. The detector sits within a water pool that is 44 meters deep.

A stainless steel support structure measuring 41.1 meters in diameter holds a 35.4 meter acrylic sphere along with the liquid scintillator, 20,000 20-inch photomultiplier tubes (PMTs), 25,600 3-inch PMTs, front-end electronics, cabling, anti-magnetic compensation coils, and optical panels.

How JUNO Detects Neutrinos

The detector's PMTs operate simultaneously to capture tiny flashes of scintillation light produced when neutrinos interact inside the detector. These light signals are then converted into electrical signals that researchers can analyze.

By precisely measuring the energy of neutrinos during these interactions, JUNO can determine key oscillation parameters and investigate fundamental properties of these elusive particles.

More Discoveries Expected

JUNO has now been operating smoothly for nine months.

As the experiment continues to gather data, researchers expect to release a series of new scientific results beginning this summer. Those future findings could provide even deeper insights into the nature of neutrinos and help answer some of the most important questions in particle physics.