An international Forward Search Experiment team has, for the first time, detected neutrino candidates at the Large Hadron Collider (LHC). The team has observed six neutrino interactions during a pilot run of a compact emulsion detector installed at the LHC in 2018.
The team made this discovery when the pilot gave two crucial pieces of information.
To study some of the most elusive particles, physicists have built detectors. However, no signs of neutrinos have ever been observed at a particle collider.
This new study acts as a significant breakthrough towards developing a deeper understanding of these elusive particles and their role in the universe.
Co-author Jonathan Feng, UCI Distinguished Professor of physics & astronomy and co-leader of the FASER Collaboration, said, “The pilot- at first- verified that the position forward of the ATLAS interaction point at the LHC is the right location for detecting collider neutrinos. Second, our efforts demonstrated the effectiveness of using an emulsion detector to observe these kinds of neutrino interactions.”
The pilot instrument is made from lead and tungsten plates. These plates are alternated with emulsion layers.
At LHC, when particles collide, the collision produces some neutrinos that then smash into nuclei in the dense metals, creating particles that travel through the emulsion layers. These particles also create marks that are visible following processing. These etchings provide clues about the energies of the particles, their flavors – tau, muon, or electron – and whether they’re neutrinos or antineutrinos.
The emulsion works similar to photography in the pre-digital camera. When the 35-millimeter film is exposed to light, photons leave tracks revealed as patterns when the film is developed. Physicists were able to observe neutrino interactions after removing and developing the detector’s emulsion layers.
Feng said, “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.”
Co-author David Casper, FASER project co-leader and associate professor of physics & astronomy at UCI, said, “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. We will detect the highest-energy neutrinos that have ever been produced from a human-made source.”
“What makes FASER unique is that while other experiments have been able to distinguish between one or two kinds of neutrinos, it will be able to observe all three flavors plus their antineutrino counterparts. There have only been about ten observations of tau neutrinos in all of human history, but that he expects his team will be able to double or triple that number over the next three years.”
Feng said, “This is an incredibly nice tie-in to the tradition at the physics department here at UCI because it’s continuing with the legacy of Frederick Reines, a UCI founding faculty member who won the Nobel Prize in physics for being the first to discover neutrinos.”
“We’ve produced a world-class experiment at the world’s premier particle physics laboratory in record time and with very untraditional sources. We owe an enormous debt of gratitude to the Heising-Simons Foundation and the Simons Foundation, as well as the Japan Society for the Promotion of Science and CERN, which supported us generously.”
- Henso Abreu et al. (FASER Collaboration). First neutrino interaction candidates at the LHC. DOI: 10.1103/PhysRevD.104.L091101