Evrim Yazgin
Cosmos science journalist
A detector sitting on the sea floor off the coast of Italy has made a remarkable discovery: the first observation of an ultra-high energy neutrino.
The kilometre cubic neutrino telescope (KM3NeT) spotted the neutrino in 2023. The event, dubbed KM3-230213A, was subject to meticulous analysis before being confirmed as the highest energy neutrino observed in a paper published today in Nature.
Researchers estimate that the neutrino had an energy of 220 petaelectronvolts.
An electronvolt (eV) is the amount of energy of a single electron which has been accelerated by 1 volt. A petaelectronvolt (PeV) is a million billion times that amount of energy (1 with 15 zeroes after it).
In other words, the neutrino had about 0.035 joules of energy – hundreds of times less than the amount of chemical energy in a single grain of rice.
Nevertheless, it is the most energetic neutrino ever observed.
The team was able to determine the neutrino had passed through the detector because it had caused the creation of a muon in the vicinity of the detector. The trajectory of the muon, which crossed the entire detector and induced signals in more than a third of its active sensors, suggested that it was created through an interaction event caused by a cosmic neutrino.
“KM3NeT has begun to probe a range of energy and sensitivity where detected neutrinos may originate from extreme astrophysical phenomena,” says Paschal Coyle, a researcher at Centre National de la Recherche Scientifique in France.
“This first ever detection of a neutrino of hundreds of PeV opens a new chapter in neutrino astronomy and a new observational window on the universe.”
High-energy cosmic neutrinos may come from such cataclysmic events as supermassive black holes, supernovae or gamma ray bursts. All of these phenomena are poorly understood, as are the neutrinos they generate.
“Neutrinos are one of the most mysterious of elementary particles,” explains Rosa Coniglione from the National Institute for Nuclear Physics, Italy. “They have no electric charge, almost no mass and interact only weakly with matter. They are special cosmic messengers, bringing us unique information on the mechanisms involved in the most energetic phenomena and allowing us to explore the farthest reaches of the universe.”
KM3NeT sits nearly 3.5km beneath the surface on the seafloor about 80km from the coast of Portopalo di Capo Passero, Sicily.
By the end of 2024, the Italian site (named ARCA) had 33 detection lines. A complimentary site off the French coast (called ORCA) has 24 detection lines.
Between the sites, scientists hope to obtain more observations of high-energy neutrinos to determine their origin and study the most mysterious and cataclysmic events in the cosmos.
