Scientific first at the CERN facility a preview of the upcoming 3-year research campaign.
The International Forward Search Experiment team, led by physicists at the University of California, Irvine, has obtained the first ever detection of neutrino candidates produced by Large Hadron Collider on CERN plant near Geneva, Switzerland.
In a paper published on November 24, 2021 in the journal Physical review D, the researchers describe how they observed six neutrino interactions during a pilot run of a compact emulsion detector installed at the LHC in 2018.
“Before this project, no sign of neutrinos has been seen in a particle collision,” said co-author Jonathan Feng, UCI Distinguished Professor of Physics and Astronomy and co-chair of the PHASE Collaboration. “This significant breakthrough is a step towards developing a deeper understanding of these elusive particles and the role they play in the universe.”
He said the discovery made during the pilot gave his team two crucial pieces of information.
The FASER particle detector, which received CERN approval to be installed at the Large Hadron Collider in 2019, has recently been expanded with an instrument to detect neutrinos. The UCI-led FASER team used a smaller detector of the same type in 2018 to make the first observations of the evasive particles generated by a collision. The new instrument will be able to detect thousands of neutrino interactions over the next three years, the researchers say. Credit: Photo lent by CERN
“First, it confirmed that the position in front of the ATLAS interaction point at the LHC is the right place to detect colliding neutrinos,” Feng said. “Second, our efforts demonstrated the effectiveness of using an emulsion detector to observe these types of neutrino interactions.”
The pilot instrument consisted of lead and tungsten plates alternated with layers of emulsion. During particle collisions at the LHC, some of the neutrinos melt into nuclei in the dense metals, creating particles that travel through the emulsion layers and creating marks that are visible after treatment. These etchings give clues about the energy of the particles, their taste – tau, muon or electron – and whether they are neutrinos or antineutrinos.
According to Feng, the emulsion works in a way similar to photography in the pre-digital camera era. When 35-millimeter film is exposed to light, photons leave traces that are revealed as patterns when the film is developed. The PHASE researchers were also able to see neutrino interactions after removing and developing the detector’s emulsion layer.
“After verifying the efficiency of the emulsion detector approach to observe the interactions between neutrinos produced by a particle collider, the FASER team is now preparing a new series of experiments with a complete instrument that is much larger and significantly more sensitive,” Feng said.
The FASER experiment is located 480 meters from the ATLAS interaction point at the Large Hadron Collider. According to Jonathan Feng, UCI Distinguished Professor of Physics and Astronomy and co-chair of the PHASE Collaboration, this is a great place to detect neutrinos that are the result of particle collisions at the plant. Credit: Photo lent by CERN
Since 2019, he and his colleagues have been getting ready to conduct an experiment with FASER instruments to study dark matter at the LHC. They hope to detect dark photons, which would give scientists a first insight into how dark matter interacts with normal atoms and the second matter in the universe through non-gravitational forces.
With the success of their neutrino work over the last few years, the FASER team – consisting of 76 physicists from 21 institutions in nine countries – is combining a new emulsion detector with the FASER device. While the pilot detector weighed around 64 pounds, the FASERnu instrument will be more than 2,400 pounds and it will be much more reactive and able to distinguish between neutrino variants.
“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,” said co-author David Casper, FASER project co. -lead and associate professor of physics & astronomy at UCI. “We will discover the highest energy neutrinos that have ever been produced from a man-made source.”
What makes FASERnu unique, he said, 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. Casper said there have only been about 10 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.
“This is an incredibly good connection to the tradition of the physics department here at the UCI,” Feng said, “because it continues 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 have produced a world-class experiment at the world’s leading particle physics laboratory in record time and with very untraditional sources,” said Casper. “We owe a huge gratitude to the Heising-Simons Foundation and the Simons Foundation, as well as the Japan Society for the Promotion of Science and CERN, who generously supported us.”
Reference: “First neutrino interaction candidates at the LHC” by Henso Abreu et al. (FASER Collaboration), November 24, 2021, Physical review D.
DOI: 10.1103 / PhysRevD.104.L091101
Savannah Shively and Jason Arakawa, UCI Ph.D. students in physics & astronomy, also contributed to the paper.
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