JUNO Neutrino Observatory Releases First Results

China's giant underground neutrino observatory just released its first results – and they're promising.

TO Ginna Bryner edited by Claire Cameron

Trillions of neutrinos zip through our bodies every day, pulsing from the Sun, from space and deep beneath the Earth. However, these elusive subatomic particles have proven difficult to study. However, the situation may soon change. Buried 700 meters below the hills of southern China. a huge neutrino observatory called JUNO published its first results in just 59 days of work. And so far they are very promising, physicists say.

“The physics result is already world-leading in the areas it addresses,” says particle physicist Juan Pedro Ochoa-Ricu of the University of California, Irvine, who co-leads the JUNO team.

“In particular, we measured two parameters of neutrino oscillations, and this measurement is already the best in the world in both parameters,” he says. results were published in two separate preprints on arXiv.org.

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JUNO (short for Jiangmen Underground Neutrino Observatory) was given the difficult task of determining the order of mass of three types of neutrinos. In other words, do they follow “normal mass order,” in which the first neutrino mass state is the lightest and the third is the heaviest, or inverted, in which the third neutrino mass state is the lightest?

The answer to this question has many implications, from informing other experiments to discovering new physics and explaining some cosmological mysteries. This is because even though neutrinos are so light, they are so incredibly abundant that they can play a huge role in the distribution of matter in the universe.

JUNO's spherical, aquarium-like detector, 13 stories high, primarily measures so-called electron antineutrinos emitted by the nearby Yangjiang and Taishan nuclear plants. When the particles hit a proton inside the detector, the reaction causes two flashes of light, which send signals to photomultiplier tubes and are converted into electrical signals.

The new measurements of these neutrino-proton collisions are now considered the most accurate for two oscillation parameters that serve as an indicator of differences in their masses, Ochoa-Riku said.

“This is the first time we've included a scientific instrument like JUNO, which we've been working on for over a decade. It's just incredibly exciting,” says Ochoa-Riku. “And then to see that we can already make world-leading measurements with it, even with such a small amount of data, is also very exciting.”

However, physicists will need years of recording neutrinos to answer the mystery of mass ordering.

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