A neutrino of record-breaking energy — 220 PeV — has been detected by the underwater KM3NeT telescope, marking a pivotal moment in astrophysics. This tiny but powerful particle, born from the universe’s most extreme events, provides fresh clues about cosmic accelerators. While its exact origin remains unknown, scientists believe it could be the first detected cosmogenic neutrino. The discovery fuels new momentum for multi-messenger astronomy, with future observations expected to shed light on the deepest mysteries of the cosmos.
The KM3NeT collaboration, an international team operating a powerful underwater telescope in the Mediterranean, has announced the discovery of the highest-energy neutrino ever detected by such an experiment. Their findings, published on February 12 in Nature and featured on its cover, provide the first evidence that neutrinos of this extreme energy exist in the universe. However, their exact origin remains a mystery. Scientists from the University of Granada are among those contributing to the KM3NeT project.
On February 13, 2023, the ARCA detector — one of KM3NeT’s deep-sea instruments — recorded an extraordinary event linked to a neutrino with an estimated energy of approximately 220 PeV (220,000 trillion electron volts). This is far more energetic than the particles produced at CERN’s Large Hadron Collider (LHC). The event, named KM3-230213A, marks the most energetic neutrino ever observed, confirming that such high-energy neutrinos are indeed produced somewhere in the cosmos. After an extensive process of data analysis and verification, the KM3NeT team has now detailed their discovery in Nature.
Neutrinos are nearly invisible subatomic particles that travel through space at almost the speed of light, passing effortlessly through stars, planets, and even our own bodies without a trace. Known as “ghost particles,” they rarely interact with matter, making them incredibly difficult to detect. Despite their elusive nature, neutrinos hold the key to understanding some of the universe’s most extreme events, from exploding supernovae to the mysterious processes inside black holes. Scientists use massive underground or underwater detectors to catch these fleeting particles, helping to unlock the secrets of the cosmos.
Researchers identified the event as a muon — an elementary particle related to the electron — traveling through the detector. The muon’s steep trajectory and immense energy strongly indicate that it originated from a high-energy cosmic neutrino interacting near the detector.
“KM3NeT has begun to explore an energy and sensitivity range where the detected neutrinos can be produced in extreme astrophysical phenomena. This first detection of a neutrino of hundreds of PeV opens a new chapter in neutrino astronomy and a new window for observing the universe,” said Paschal Coyle, KM3NeT spokesperson at the time of the detection and researcher at the IN2P3/CNRS Particle Physics Center in Marseille (France).
Although they are the second most abundant particles in the universe after the photons that make up light, their extremely weak interaction with matter makes them very difficult to detect, and requires huge detectors. The KM3NeT neutrino telescope, currently under construction, is a gigantic infrastructure on the seabed consisting of two detectors, ARCA and ORCA. KM3NeT uses seawater as the interaction medium to detect neutrinos. Its high-tech optical modules detect Cherenkov light, a bluish glow generated by the propagation in water of ultra-relativistic particles resulting from interactions with neutrinos.
This ultra-high-energy neutrino could originate directly from a powerful cosmic accelerator. Alternatively, it could be the first detection of a cosmogenic neutrino. However, based on this single neutrino, it is difficult to draw conclusions about its origin, say the collaboration’s scientists. Future observations will focus on detecting more events of this type to build a clearer picture. The ongoing expansion of KM3NeT with additional detection units and the acquisition of new data will improve its sensitivity and increase its ability to identify sources of cosmic neutrinos, making KM3NeT a major player in multi-messenger astronomy.
The KM3NeT collaboration brings together more than 360 scientists, engineers, technicians, and students from 68 institutions in 22 countries around the world. On behalf of the University of Granada, researchers from the departments of Theoretical and Cosmos Physics and Computer Engineering, Automation, and Robotics have been participating in the KM3NeT Collaboration for a decade. Since then, their research has been funded through various programs of the Ministry of Science, Innovation and Universities, as well as regional programs funded by the Regional Government of Andalusia, and through Next Generation EU funds. The UGR works in coordination with researchers from the Institute of Corpuscular Physics (IFIC) in Valencia, the Polytechnic University of Valencia (UPV), the IGIC of the UPV and the Joint Unit of the Spanish Institute of Oceanography (IEO) in KM3NeT.
“The group from the University of Granada that is part of KM3NeT contributes to the experiment in two main aspects. On the one hand, based on the analysis of the data collected by the detector, we work on various physics analyses focused on the search for neutrino sources in the Universe, the detection of dark matter or the study of new physics effects through the measurement of neutrino properties,” explains Sergio Navas, one of the principal investigators of KM3NeT at the University of Granada.
“On the other hand, we are participating in the construction of telescope elements focused on the optimal measurement of the time of arrival of signals at optical sensors, which is a key aspect in reconstructing the direction of arrival of neutrinos. We have an infrastructure in the laboratory that allows us to design and apply protocols that ensure that the components we build and install in the experiment meet the required precision requirements (temporal accuracies of less than a billionth of a second),” adds Antonio Díaz García, co-leader of the project at the University of Granada.
“The detection of the KM3-230213A event has been a huge incentive for those of us working on the experiment,” says Sergio Navas, ”and it is acting as a magnet for new research centers to join the project. At the UGR we continue to work on unraveling the nature of this unique event, about which there are still so many unknowns to be deciphered.” The research team is confident that with the full installation of the two KM3NeT detectors, ARCA and ORCA, new light can be shed on the mystery of the origin of cosmic neutrinos.
