The underwater observatory has discovered perhaps the most energetic neutrino ever

Cosmic Lottery: Despite being electrically neutral and possessing the smallest rest mass of the elementary particles (excluding massless photons), neutrinos are among the most abundant particles in the universe. Detecting neutrino interactions with traditional matter is extremely difficult, and identifying an ultrahigh-energy neutrino is akin to winning the lottery.

An underwater observatory known as the Abyssal Astroparticle Search (ARCA) has recorded unprecedented subatomic interactions, possibly as a result of an ultra-high-energy neutrino raining down from the sky. Neutrino physicist João Coelho announced the potential discovery at the Neutrino 2024 conference held in Milan, Italy, stating that he would detail the findings in a future paper.

ARCA consists of several Plexiglas spheres, each about half a meter wide, connected by strings attached to the Mediterranean seabed southeast of the Italian island of Sicily. The observatory, still being “assembled” 3,500 meters below sea level, is part of the large array of telescopes and detectors KM3NeT, designed as the next generation of neutrino telescopes.

ARCA’s spheres are designed to detect light radiation that can reach the seafloor, including high-energy cosmic rays and massless particles such as neutrinos. Neutrinos cannot be observed directly, but their presence can be inferred when a neutrino hits an atom of water, air, or rock. When this interaction occurs, the resulting cascade of subatomic particles is detected by ARCA’s instruments.

Ultra-energetic neutrinos have been known to exist for several years and are believed to be the result of some of the most violent events in the universe, such as the accretion of supermassive black holes or supernova remnants. These neutrinos can carry half a petaelectronvolt (PeV) or more of energy, while the potential high-energy neutrino announced by Coelho can have an energy level of many tens of petaelectronvolts.

If confirmed, University of Wisconsin-Madison physicist Francis Halzen said the discovery would be a “fantastic event” for particle physics researchers. Coelho described the discovery by ARCA – which has been collecting data since the mid-2010s, despite still being incomplete – as a phenomenon that is “far removed” from anything ever recorded in neutrinos.

Neutrinos are some of the most elusive particles known to exist in the universe and the least studied particles in the Standard Model, and numerous efforts are underway to unlock their secrets. CERN has been using the Large Hadron Collider for neutrino-related experiments, while more observatories designed to detect higher-energy neutrinos are under construction or proposed by researchers around the world.