‘Portal to physics beyond the Standard Model’: World’s largest neutrino detector starts up — with incredible results
The first results of the largest neutrino detector have just been published and reveal the most precise measurements of neutrino parameters to date.
After operating the detector – the Jiangmen Underground Neutrino Observatory (JUNO) in southern China – for just under two months, the researchers were able to measure the parameters of different types, or “flavors,” of neutrinos with unprecedented precision.
“Before turning on JUNO, these parameters were derived from a long series of experiments… Half a century of effort is distilled into the numerical value of these two parameters,” Gioacchino Ranuccideputy spokesperson for JUNO, told Live Science. “In 59 days, we overcame 50 years of measurements. So this gives an idea of the power [JUNO] East.”
The ghostly mystery of neutrinos
Neutrinos are perhaps the most mysterious particles known. Every second, billions of them pass through your body. However, they very rarely interact with you or any other matters and weighs almost nothinggiving them the nickname “ghost particles”. This makes the neutrino one of the most difficult particles to study, because most simply pass through a detector without leaving a trace.
But physicists are eager to learn more about neutrinos, because they might be able to break the Standard model of particle physics, which is our best explanation of the subatomic world. While this is an incredibly successful theory, it’s not quite complete – and what it didn’t predict was that neutrinos would have mass.
The discovery that ghost particles actually have mass (for which the 2015 Nobel Prize in Physics was awarded) is due to what is called neutrino oscillation. Neutrinos come in three types (electron, muon, and tau) and alternate between these identities as they move through time and space. The reason for this strange phenomenon is not yet fully understood, but it could be 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. “Neutrinos are therefore the only portal to physics beyond the Standard Model.”
To explore the properties of neutrinos and go beyond the standard model, scientists have built large detectors at depth. Here, the Earth’s crust forms a natural shield against most other particles, while ghost particles pass through it and have the opportunity to make their presence known in the detector.
JUNO is the latest and largest of these neutrino detectors. It is a 35-meter-wide sphere that contains 19,700 tons (20,000 metric tons) of liquid scintillator. This liquid is specially formulated to interact with a neutrino and produce a flash of light. At the edge of the tank are sensors capable of locating the flash and providing useful information about the neutrino that caused it.
Previous neutrino detectors worked on the same principle; JUNO is simply much bigger. It contains 20 times more liquid scintillator than any previous experiment, making JUNO significantly more sensitive to neutrinos. This allowed physicists to measure the parameters that describe the oscillation between different flavors of neutrinos with unprecedented precision, according to the researchers.
In search of new physics
The JUNO team has big ambitions for the future and these initial results show that they are on track to achieve these goals. With more time and more data, the researchers hope to achieve even better precision on these oscillation parameters.
Over its lifetime, JUNO may be able to solve older physics mysteries. Physicists hope to be able to order the mass states of neutrinos from heaviest to lightest and perhaps even find clues as to why we don’t see as many of them. antimatter as matter in the universe.
For now, these ghostly particles have given rise to tantalizing whispers of physics beyond our current theories. Thanks to larger and more efficient neutrino detectors, our understanding of the universe is becoming more precise.
