JUNO achieves record neutrino measurements

Chinese scientists have released the first results from one of the world's most advanced underground physics experiments, reporting record-setting measurements of mysterious particles known as neutrinos.

The findings, published as a cover story on Wednesday in the journal Nature, come from the Jiangmen Underground Neutrino Observatory, or JUNO, a giant detector built deep beneath a hillside in South China's Guangdong province.

Neutrinos are tiny particles that are found throughout the universe. Trillions pass through the human body every second, but they almost never interact with matter, making them extremely difficult to detect. Because of their elusive nature, scientists often refer to them as "ghost particles".

Researchers said JUNO has already achieved the most precise measurements to date on how neutrinos change as they travel. The results are based on data collected during the detector's first 59 days of operation between Aug 26 and Nov 2, 2025.

Scientists have long established that neutrinos can switch between three different forms, or "flavors", as they move through space. Understanding exactly how this process works could help answer some of the biggest questions in physics, including how the universe evolved after the Big Bang.

According to the research team, JUNO measured two key properties governing these transformations with a level of precision that reduced previous uncertainties by about 40 percent.

Nature reviewers praised the achievement, saying the results confirm the detector is performing as designed and position JUNO as a leading facility for future neutrino research.

The experiment's main goal is to solve a long-standing mystery known as the neutrino mass ordering problem. Scientists know there are three types of neutrinos, but they still do not know the exact arrangement of their masses — in simple terms, which type is heavier and which is lighter. The answer could improve scientists' understanding of the fundamental building blocks of matter.

JUNO's massive detector is located about 700 meters underground to shield it from interference caused by cosmic radiation. At its core is a 20,000-metric-ton sphere filled with highly purified liquid.

When a neutrino occasionally collides with an atom inside the liquid, it produces a tiny flash of light. Thousands of sensitive light sensors surrounding the sphere capture these flashes, allowing scientists to study the particle's properties.

The project is an international collaboration involving more than 700 researchers from 75 institutions across 17 countries and regions.

Scientists said the detector has been operating smoothly since it began collecting data in August. As more observations are gathered, they expect to release additional findings later this year that could provide new clues about some of the universe's least understood particles.

JUNO follows China's earlier Daya Bay Reactor Neutrino Experiment, which operated from 2011 to 2020 and helped uncover an important property of neutrinos and established the country as a major contributor to particle physics research.

limenghan@chinadaily.com.cn