China’s JUNO Detector Reports First Neutrino Measurements From Underground Lab

A huge detector built deep below ground in China has presented its first significant scientific results, offering new data on the elusive particles known as neutrinos.

The Jiangmen Underground Neutrino Observatory, or JUNO, began recording information in August. Its mission is to study neutrinos, extremely small particles from the early universe that have existed since the Big Bang. Trillions pass through the human body every second without causing harm, but their near-zero mass makes them very hard to detect.

In research released Wednesday in the journal Nature, the JUNO collaboration reported findings from its first two months of operation. The team said the data include among the most accurate measurements yet of the way neutrinos change among three types, known as flavours, while travelling through space.

"It really makes me look forward to more exciting results in the future," said Duke University physicist Kate Scholberg, who was not involved in the study.

JUNO’s round detector sits 2,297 feet, or 700 metres, beneath the surface. It studies antineutrinos produced by reactions at two nearby nuclear power plants. Antineutrinos are the mirror-like counterparts of neutrinos, and researchers use them to learn more about how neutrinos behave.

When antineutrinos strike particles inside the instrument, the interaction creates a burst of light that can be measured.

Researchers hope JUNO will help settle a major question in particle physics: how the three neutrino flavours compare in mass. Scientists believe two of the flavours are close in weight and the third is different, but they have not yet confirmed whether the pair is heavier or lighter than the outlier.

The first results do not solve that puzzle. However, they demonstrate the detector’s sensitivity and show that it "will be able to test the finer ripples" distinguishing the neutrino flavours and their masses, said Liangjian Wen, a study co-author and member of the JUNO collaboration.

Two other large neutrino projects, Japan’s Hyper-Kamiokande and the Deep Underground Neutrino Experiment in the United States, are expected to start gathering data within the next decade. Scientists plan to use those experiments to compare results with JUNO through separate methods.