In a groundbreaking achievement, an international team of physicists has achieved the first-ever detection of candidate neutrinos produced at CERN's Large Hadron Collider (LHC). Publishing their findings in Physical Review D, the researchers detail six interactions observed during a 2018 pilot experiment.
Neutrinos are elementary particles 100,000 times smaller than an electron, with virtually zero mass. Originating from stars, supernovae, and quasars, they rarely interact with matter, making detection challenging—hence their "ghost particles" moniker. Yet they are ubiquitous: billions pass through your body every second.
Over recent years, advanced facilities have enabled neutrino detection. These ultra-sensitive photomultipliers, often submerged in pure water, capture faint Cherenkov light flashes from neutrino-atom collisions. IceCube, the world's largest, is buried in Antarctic ice near the South Pole Station, with others in Japan and Russia's Lake Baikal.
For decades, experts hypothesized that accelerators like the LHC—straddling the France-Switzerland border—could produce and detect neutrinos, but suitable instruments were needed. That breakthrough has now arrived.
In the 2018 FASER pilot experiment, scientists detected six neutrino interactions.
“Before this project, no sign of neutrinos had ever been observed in a particle collider,” confirms Jonathan Feng, co-author of the study. “This significant breakthrough is a step towards developing a deeper understanding of these elusive particles and the role they play in the universe.”
Positioned 480 meters downstream from the LHC collision point, FASER features lead and tungsten plates interleaved with emulsion layers. Neutrinos striking atomic nuclei in these metals produce secondary particles that leave detectable tracks. Six such traces were identified.
Building on this success, the 76-physicist FASER collaboration from 21 institutions across nine countries is deploying FASERnu—a vastly upgraded detector weighing over 1,090 kg, compared to 29 kg for the pilot. Its enhanced sensitivity promises far more detections.
“Given the power of our new detector and its prime location at CERN, we expect to record over 10,000 neutrino interactions in the next LHC cycle, starting in 2022,” notes co-author David Casper. “We will detect the most energetic neutrinos ever produced from an artificial source.”
Ultimately, unraveling these "ghost particles" could resolve fundamental physics mysteries, like why the universe consists of matter rather than antimatter.
