In a groundbreaking discovery, scientists from the KM3NeT (Cubic Kilometre Neutrino Telescope) Collaboration have detected an ultra-high-energy neutrino with an estimated energy of approximately 220 petaelectronvolts (PeV), or 220 million billion electronvolts. This event, designated KM3-230213A, is the most energetic neutrino ever observed and provides the first evidence that such high-energy neutrinos are produced in the universe.
The detection occurred on February 13, 2023, using the ARCA (Astroparticle Research with Cosmics in the Abyss) detector, part of the KM3NeT observatory located 3,450 meters beneath the Mediterranean Sea near Sicily, Italy. The ARCA detector is specifically designed to observe high-energy neutrinos, while its counterpart, ORCA (Oscillation Research with Cosmics in the Abyss), situated near Toulon, France, focuses on low-energy neutrinos.
Neutrinos are subatomic particles with no electric charge and an incredibly small mass. They interact so weakly with matter that billions pass through us every second without a trace. This elusive nature makes their detection challenging, requiring massive detectors like KM3NeT, which utilizes seawater as the interaction medium. The high-tech optical modules of KM3NeT detect Cherenkov light—a bluish glow generated when charged particles produced by neutrino interactions move faster than light in the medium.
The KM3-230213A event was identified as a single muon traversing the entire detector, triggering signals in more than one-third of the active sensors. The muon's near-horizontal trajectory and immense energy suggest it originated from a cosmic neutrino interacting near the detector. This detection was achieved with only one-tenth of the detector's final configuration, highlighting the experiment's significant potential for advancing neutrino astronomy.
The origin of this ultra-high-energy neutrino remains uncertain. It may have been produced by a powerful cosmic accelerator, such as an active galactic nucleus or a gamma-ray burst, or it could be a cosmogenic neutrino resulting from interactions between ultra-high-energy cosmic rays and background photons in the universe. Further observations and detections of similar events are necessary to build a clearer picture of their origins.
The KM3NeT Collaboration comprises over 360 scientists, engineers, technicians, and students from 68 institutions across 21 countries. The ongoing expansion of KM3NeT, with additional detection units and increased data acquisition, will enhance its sensitivity and ability to pinpoint cosmic neutrino sources, solidifying its role as a leading contributor to multi-messenger astronomy.
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