Physicists have detected “ghost particles” in the Large Hadron Collider for the first time. An experiment called FASER picked up telltale signals of neutrinos being produced in particle collisions, which can help scientists better understand key physics.
Neutrinos are elementary particles that are electrically neutral, extremely light and rarely interact with particles of matter. That makes them tricky to detect, even though they’re very common – in fact, there are billions of neutrinos streaming through your body right now. Because of this, they’re often described as ghost particles.
Neutrinos are produced in stars, supernovae, quasars. radioactive decay and from cosmic rays interacting with atoms in the Earth’s atmosphere. It’s long been thought that particle accelerators like the LHC should be making them too, but without the right instruments they would just zip away undetected.
And now that “right instrument” has been installed and tested. During a pilot run of an experiment called FASER, installed in 2018, scientists picked up six neutrino interactions.
“Prior to this project, no sign of neutrinos has ever been seen at a particle collider,” says Jonathan Feng, co-author of a study describing the results. “This significant breakthrough is a step toward developing a deeper understanding of these elusive particles and the role they play in the universe.”
Located 480 m (1,575 ft) down the line from where the particle collisions occur, the FASER instrument works a little like film photography, the team says. The detector is made up of plates of lead and tungsten, separated by layers of an emulsion. Some of the neutrinos will strike the nuclei of atoms in the dense metals, which creates other particles that stream through the emulsion. The tracks they leave behind can then be seen when the emulsion layers are “developed” like film. And sure enough, six of these marks were spotted in the data.
“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,” says Feng.
This full version, named FASERnu, will weigh over 1,090 kg (2,400 lb), compared to the pilot’s 29 kg (64 lb). Its increased sensitivity will allow it to not only detect neutrinos more often, but differentiate between the three different “flavors” they come in, as well as antineutrinos.
“Given the power of our new detector and its prime location at CERN, we expect to be able to record more than 10,000 neutrino interactions in the next run of the LHC, beginning in 2022,” says David Casper, co-author of the study. “We will detect the highest-energy neutrinos that have ever been produced from a human-made source.”
The research was published in the journal Physical Review D.
Source: University of California, Irvine
