JUNO's Breakthrough: World's Largest Neutrino Detector Delivers Unprecedented Precision

The Jiangmen Underground Neutrino Observatory (JUNO), now the world's largest neutrino detector, has released its first scientific results after a 59-day run — reporting the most precise measurements yet of key neutrino-oscillation parameters.

Operating for just under two months, the JUNO collaboration refined two critical quantities that describe how neutrinos change identity as they travel: the mixing angle that governs how neutrino mass states combine to form the observable flavors, and the squared mass difference between those states. These measurements were achieved with precision previously unattainable by earlier experiments.

"Before switching on JUNO, these parameters came from a long series of experiments… Half a century of effort is distilled in the numerical value of these two parameters," said Gioacchino Ranucci, deputy spokesperson for JUNO. "In 59 days we have overcome 50 years of measurement. So this gives an idea of how powerful JUNO is."

The initial results have been posted to the preprint server arXiv and submitted to the journal Chinese Physics C for peer review.

Neutrinos are among the most enigmatic known particles. Trillions pass through each person every second, yet they interact so rarely with ordinary matter and have such tiny masses that they are often called "ghost particles." Their weak interactions make detection challenging, but also make neutrinos valuable probes of fundamental physics.

Neutrino oscillation — the phenomenon by which neutrinos switch among three flavors (electron, muon and tau) — established that neutrinos have mass, a fact not predicted by the original Standard Model of particle physics. Because oscillations require physics beyond the model as originally formulated, precision measurements of oscillation parameters are a promising route to new discoveries.

JUNO is a 35-meter-wide (115-foot) spherical detector filled with about 19,700 tons (20,000 metric tons) of liquid scintillator designed to produce tiny flashes of light when a neutrino interacts. An array of light sensors surrounding the vessel records those flashes and reconstructs the interaction's energy and timing. JUNO holds roughly 20 times more scintillator than previous comparable detectors, greatly increasing its sensitivity to rare neutrino events.

Because of its size and precision, JUNO aims not only to refine oscillation parameters but eventually to determine the neutrino mass ordering (which mass state is heaviest and which is lightest) and to contribute to understanding why the universe contains far more matter than antimatter. Over its planned lifetime, JUNO's accumulating data could address these long-standing open questions.

For now, the collaboration's early results offer a striking demonstration of JUNO's capabilities: in just 59 days, the experiment has produced measurements that improve on decades of previous work and set the stage for deeper probes of physics beyond the Standard Model.