New type of detector enables deeper understanding of the universe
The underground “Jiangmen Underground Neutrino Observatory (JUNO)” near Jiangmen city in the Guangdong Province, which was prepared with the participation of researchers from the PRISMA+ Cluster of Excellence at Johannes Gutenberg University Mainz (JGU), has successfully completed the filling of its 20,000 tons of liquid scintillator and begun data taking. After more than a decade of preparation and construction, JUNO is the first of a new generation of very large neutrino experiments to reach this stage. Initial trial operation and data taking show that key performance indicators met or exceeded design expectations, enabling JUNO to tackle one of this decade’s major open questions in particle physics: the ordering of neutrino masses—whether the third mass state (ν₃) is heavier than the second (ν₂).
The liquid keeps it stable and absorbs movement, right?
The liquid is the detection media.
Neutrino detectors are basically just huge scintillators (systems that absorb ionizing radiation and re-emit that energy as light). The liquid inside of JUNO (Linear alkylbenzene) has especially attractive scintillating properties.
Ah ok, I was conceptualizing this as more akin to a large reflecting telescope.
Yeah, neutrino detectors don't work like conventional telescopes because neutrinos don't behave like light. Technically, neutrinos are actually a type of dark matter since they don't participate in the electromagnetic interaction, and that makes them very hard to detect.
When a beam of light shines on your body, some of that light is absorbed as heat and a lot of it is reflected off of you. Neutrinos don't do that. Tens of billions of neutrinos from the sun hit your body every second and just... don't do anything. They pass straight through you with zero interaction whatsoever. Very, very rarely they'll interact with something, and neutrino detectors are designed to both maximize the chances of such an interaction happening, and to make those interactions more easy to spot.
I'm not up to speed on all the technical details of JUNO in particular, but most neutrino detectors are searching for events that look something like this:
A neutrino enters the detection medium and directly collides with an electron. Enough energy is transferred into the electron that it is stripped free from its parent molecule and moves through the medium at very high speed. If it moves fast enough, it can even exceed the speed that light travels through the medium, creating something sort of like a sonic boom — only with light. We call this Cherenkov radiation. The scintillating properties of the medium boost this signal and photomultipliers at the perimeter of the detector gather this radiation so that the event can be reconstructed by computers.