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Neutrinos – the most elusive of known particles – are finally getting spotted at the most powerful particle accelerators in the world. The ghostly particles are extremely light and have no charge so they seldom interact. Studying the one produced in such a powerful accelerator will bring forth new insights into their nature.
The detection, presented in the journal Physical Review D, represents the first observations of such neutrinos at a particle accelerator. The detector called FASER detected just six of these particles during its pilot testing in 2018.
"Prior to this project, no sign of neutrinos has ever been seen at a particle collider," the paper’s co-author Jonathan Feng, UCI Distinguished Professor of physics & astronomy and co-leader of the FASER Collaboration, said in a statement. "This significant breakthrough is a step toward developing a deeper understanding of these elusive particles and the role they play in the universe."
The detector is located near the ATLAS experiment, one of the four main detectors of the Large Hadron Collider. It is housed in an older tunnel used to inject beams in the previous particle accelerators at the site, and it is where an intense and highly collimated beam of neutrons is sent. So finding these six neutrinos has taught the team two crucial things.
"First, it verified that the position forward of the ATLAS interaction point at the LHC is the right location for detecting collider neutrinos," Feng said. "Second, our efforts demonstrated the effectiveness of using an emulsion detector to observe these kinds of neutrino interactions."
The pilot detector was 29 kilograms (64 pounds) but the next one, called FASERnu will be almost 1,100 kilos (2,400 pounds). When it goes online in 2022, the team expects to detect 10,000 neutrinos. These will be all three versions – technically called flavors – electron neutrino, muon neutrino, and tau neutrino, as well as all their anti-matter counterparts.
"Having verified the effectiveness of the emulsion detector approach for observing the interactions of neutrinos produced at a particle collider, the FASER team is now preparing a new series of experiments with a full instrument that's much larger and significantly more sensitive," Feng said.
The team is particularly excited about the detection of tau neutrinos, which so far have only been detected about ten times. This instrument should add a few dozen more detections over the next three years. There is also the possibility that FASERnu would detect something that is not in our current understanding of physics, such as a dark photon. We’ll just have to wait and see.
