Situated 700 meters underground close to the town of Jiangmen in southern China, an enormous sphere—35 meters in diameter and stuffed with greater than 20,000 tons of liquid—has simply began a mission that can final for many years. That is Juno, the Jiangmen Underground Neutrino Observatory, a brand new, large-scale experiment finding out a number of the most mysterious and elusive particles recognized to science.
Neutrinos are the most abundant particles within the universe with mass. They’re elementary particles, which means they don’t break down into smaller constituent elements, which makes them very small and really mild. Additionally they have zero electrical cost; they’re impartial—therefore their identify. All of because of this they fairly often don’t work together with different matter they arrive into contact with, and might move proper by it with out affecting it, making them tough to look at. It’s because of this that they’re typically known as “ghost particles.”
Additionally they have the flexibility to shift (or “oscillate”) between three completely different types, also referred to as “flavors”: electron, mu, and tau. (Be aware that electron-flavored neutrinos are completely different from electrons; the latter are a special sort of elementary particle, with a destructive cost.)
The truth that neutrinos oscillate was confirmed by the physicists Takaaki Kajita and Arthur Bruce McDonald. In two separate experiments, they noticed that electron-flavored neutrinos oscillate into mu- and tau-flavored neutrinos. In consequence they demonstrated that these particles have mass, and that the mass of every taste is completely different. For this, they gained the Nobel Prize in Physics in 2015.
An explainer on neutrino oscillations from the Fermi Nationwide Accelerator Laboratory.
However an essential but nonetheless unknown truth is how these lots are ordered—which of the three flavors has the best mass, and which the least. If physicists had a greater understanding of neutrino mass, this might assist higher describe the habits and evolution of the universe. That is the place Juno is available in.
A Distinctive Experiment
Neutrinos can’t be seen with typical particle detectors. As a substitute, scientists need to search for the uncommon indicators of them interacting with different matter—and that is what Juno’s giant sphere is for. Known as a scintillator, it’s stuffed with a delicate inner liquid made up of a solvent and two fluorescent compounds. If a neutrino passing by this matter interacts with it, it would produce a flash of sunshine. Surrounding the liquid is an enormous stainless-steel lattice that helps an enormous array of extremely delicate mild sensors, referred to as photomultiplier tubes, able to detecting even a single photon produced by an interplay between a neutrino and the liquid, and changing it right into a measurable electrical sign.
“The Juno experiment picks up the legacy of its predecessors, with the distinction that it’s a lot bigger,” says Gioacchino Ranucci, deputy head of the experiment and the previous head of Borexino, one other neutrino-hunting experiment. One of many primary options of Juno, Ranucci explains, is that Juno can “see” each neutrinos and their antimatter counterpart: antineutrinos. The previous are usually produced in Earth’s environment or by the decay of radioactive supplies in Earth’s crust, or else arrive from outer space—coming from stars, black holes, supernovae, and even the Large Bang. Antineutrinos, nonetheless, are artificially produced, on this case by two nuclear energy vegetation positioned close to the detector.
“As they propagate, neutrinos and antineutrinos proceed to oscillate, remodeling into one another,” Ranucci says. Juno will be capable to seize all of those alerts, he explains, displaying how they oscillate, “with a precision by no means earlier than achieved.”
