'Portal to physics beyond the Standard Model': World's largest neutrino detector starts up — with incredible results

By Rory Harris 

Published 8 hours ago

Deep underground in southern China, there is a 20,000-ton tank of liquid that can detect neutrinos. Named JUNO, the detector's first results are in — and they're very promising.

The first results from the world's largest neutrino detector have just been published, and they reveal the most precise measurements of neutrino parameters yet.

After running the detector — the Jiangmen Underground Neutrino Observatory (JUNO), in southern China — for just shy of two months, the researchers were able to measure the parameters of the different types, or "flavors," of neutrinos with unprecedented precision.

The results narrow down the value of two key neutrino parameters: the mixing angle describing how different neutrino mass states combine to form the neutrino flavors, and the difference between these mass states squared.

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"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," Gioacchino Ranucci, deputy spokesperson for JUNO, told Live Science. "In 59 days we have overcome 50 years of measurement. So this gives an idea of how powerful [JUNO] is."

The facility's first results were published to the preprint server arXiv and have been submitted to the journal Chinese Physics C for peer review.

The ghostly mystery of neutrinos

The JUNO detector seen from the outside. (Image credit: JUNO collaboration)

Neutrinos are perhaps the most mysterious of the known particles. Every second, trillions of them pass through your body. However, they very rarely interact with you or any other matter and weigh next to nothing, giving them the nickname "ghost particles." This makes the neutrino one of the hardest particles to study, as most will simply go through a detector without leaving a trace.

But physicists are eager to know more about neutrinos because they may be able to break the Standard Model of particle physics, which is our best explanation of the subatomic world. While it is an incredibly successful theory, it is not quite complete — and something that it did not predict was that neutrinos would have mass.

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The discovery that ghost particles do, in fact, have mass (for which the 2015 Nobel Prize in physics was awarded) is due to something called neutrino oscillation. Neutrinos come in three flavors (electron, muon and tau), and they switch between these identities as they move through time and space. The reason for this strange phenomenon is not yet fully understood, but it may hold the key to exciting new physics.

"The oscillation phenomenon means that neutrinos are so far the only particle for which there is a property that the Standard Model does not predict," Ranucci said. "So, neutrinos are the only portal to physics beyond the Standard Model."

To explore neutrino properties and probe beyond the Standard Model, scientists have built large detectors deep underground. Here, Earth's crust forms a natural shield from most other particles, while the ghost particles pass through and have the chance to make their presence known in the detector.