This Giant Sphere Just Joined the Hunt for ‘Ghost Particles’

The elusive neutrino—a near massless particle with no charge—tests the limits of physicists’ creativity, but sometimes the answer is just to go big. And the biggest detector of them all has finally joined the search for the so-called “ghost particles.”

After a decade of construction, China’s Jiangmen Underground Neutrino Observatory (JUNO) officially began taking data on August 26. The giant, spherical detector lies about 2,300 feet (700 meters) underground and collects antineutrino signals from two nuclear plants 33 miles (53 kilometers) away.

The sphere holds a whopping 20,000 tons of liquid scintillator that flickers whenever an antineutrino zips by. Surrounding the detector is a 144-foot-deep (44-meter-deep) water pool lined with tubes that capture these flashes and convert them into signals scientists can analyze.

As the neutrino’s antimatter counterpart, antineutrinos presumably have the same mass as neutrinos. Using this feature, JUNO scientists hope to better understand the nature of neutrino mass, which physicists theorize operates according to strange quantum mechanical principles.

Neutrinos are weird, period

Evidence suggests that trillions of neutrinos pass through us every second. But because they so rarely interact with anything, it’s excruciatingly difficult to confirm their existence—which, to be clear, we have done many times, but not without a lot of time and effort (and perhaps many physicist tears).

If that’s not enough of a hassle, neutrinos also come in three distinct flavors: electron, muon, and tau. Neutrinos flip between different flavors in a process known as oscillation. There are also three identified masses associated with neutrinos, unceremoniously named mass 1, mass 2, and mass 3.

But here’s the catch: physicists still don’t know which flavor corresponds to which mass number—if any. That’s because the annoying-yet-bewitching rules of quantum mechanics strongly suggest each neutrino flavor is a combination of different mass states.

So far, physicists believe some neutrino masses have a slightly higher chance of appearing as a certain flavor, but they’ve yet to find a conclusive answer. And this outstanding question regarding the order of neutrino masses represents one of JUNO’s primary goals.

The future is bright, er, sparkling

Even before JUNO’s official launch, the humongous detector preemptively caught antineutrino signals, and its key performance indicators “met or exceeded design expectations,” the JUNO Collaboration announced in a release.

“For the first time, we have in operation a detector of this scale and precision dedicated to neutrinos,” said Yifang Wang, JUNO’s spokesperson, in the release. “JUNO will allow us to answer fundamental questions about the nature of matter and the universe.”

Further down the line, JUNO’s extreme sensitivity could also probe tangentially related questions in particle physics, such as detecting sterile neutrinos or investigating proton decays. Currently, JUNO is planned to run for up to 30 years, during or after which it may receive upgrades to further boost its sensitivity. Either way, there’s no doubt that we’ll soon see phenomenal science coming from JUNO.