The KM3NeT Collaboration announces the detection from the abyss of the Mediterranean Sea of a cosmic neutrino with a record-breaking energy of about 220 PeV
An extraordinary event consistent with a neutrino with an estimated energy of about 220 PeV (220 x 1015 electron volts or 220 million billion electron volts), was detected on February 13, 2023, by the ARCA detector of the kilometre cubic neutrino telescope (KM3NeT) in the deep sea. This event, named KM3-230213A, is the most energetic neutrino ever observed and provides the first evidence that neutrinos of such high energies are produced in the Universe. After long and meticulous work to analyse and interpret the experimental data, today, February 12, 2025, the international scientific collaboration of KM3NeT reports the details of this amazing discovery in an article published in Nature.
The detected event was identified as a single muon which crossed the entire detector, inducing signals in more than one third of the active sensors. The inclination of its trajectory combined with its enormous energy provides compelling evidence that the muon originated from a cosmic neutrino interacting in the vicinity of the detector.
“KM3NeT has begun to probe a range of energy and sensitivity where detected neutrinos may originate from extreme astrophysical phenomena. 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”, comments Paschal Coyle, KM3NeTSpokesperson at the time of the detection, and researcher at CNRS Centre National de la Recherche Scientifique – Centre de Physique des Particules de Marseille, France.
Ultra-high energy
The high-energy universe is the realm of cataclysmic events such as accreting supermassive black holes at the centre of galaxies, supernova explosions, gamma ray bursts, all as yet not fully understood. These powerful cosmic accelerators, generate streams of particles called cosmic rays. Some cosmic rays may interact with matter or photons around the source, to produce neutrinos and photons. During the travel of the most energetic cosmic rays across the Universe, some may also interact with photons of the cosmic microwave background radiation, to produce extremely energetic “cosmogenic” neutrinos.
This ultra-high energy neutrino may 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 conclude on its origin. Future observations will focus on detecting more such events to build a clearer picture. The ongoing expansion of KM3NeT with additional detection units and the acquisition of additional data will improve its sensitivity and enhance its ability to pinpoint cosmic neutrino sources, making it a leading contributor to multi-messenger astronomy.
“Neutrinos are one of the most mysterious of elementary particles. 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”, explains Rosa Coniglione, KM3NeT Deputy-Spokesperson at the time of the detection, researcher at the INFN National Institute for Nuclear Physics, Italy.
Detecting neutrinos with KM3NeT
Although neutrinos are the second most abundant particle in the Universe after photons, their weak interaction with matter makes them very hard to detect and requires enormous detectors. The KM3NeT neutrino telescope, currently under construction, is a giant deep-sea infrastructure distributed across two detectors ARCA and ORCA. In its final configuration, KM3NeT will occupy a volume of more than one cubic kilometre. KM3NeT uses sea water as the interaction medium for neutrinos. Its high-tech optical modules detect the Cherenkov light, a bluish glow that is generated during the propagation through the water of the ultra-relativistic particles produced in neutrino interactions.
“To determine the direction and energy of this neutrino required a precise calibration of the telescope and sophisticated track reconstruction algorithms. Furthermore, this remarkable detection was achieved with only one tenth of the final configuration of the detector, demonstrating the great potential of our experiment for the study of neutrinos and for neutrino astronomy”, comments Aart Heijboer, KM3NeT Physics and Software Manager at the time of the detection, and researcher at Nikhef National Institute for Subatomic Physics, The Netherlands.
Dutch researchers and engineers play an important role
Dutch scientists and engineers are closely involved in this extraordinary discovery. From the Netherlands, Nikhef, NWO-I, the University of Amsterdam, Leiden University, NIOZ and TNO are members of the KM3NeT collaboration. They hold various leadership positions within the collaboration, collaborating on the design, construction and deployment of the detector, system engineering, software development and the final analysis of the data.
“What a very wonderful observation. This is promising for the future of this research field. I look forward to the next few years of expanding KM3NeT. That our researchers and technicians are involved in so many parts of this undersea telescope shows the strength of the Nikhef partnership in which theory, experiment and instrumentation come together,” says Jorgen D’Hondt, director of Nikhef.
Dorothea Samtleben, programme leader of the Nikhef neutrino group and affiliated with Leiden University, added: “The excellent diverse expertise and years of experience of the Nikhef neutrino group together with the excellence of the Nikhef workshop form a unique, fruitful combination. This allows us to make an important contribution to the KM3NeT collaboration in many different areas – from detector construction to complex reconstruction algorithms – and also provide inspiration to many young researchers, engineers and technicians.”
“Building a neutrino telescope at the bottom of the Mediterranean Sea is only possible through close international cooperation. You need the groundbreaking knowledge of many different experts, building together towards a shared vision. I am enormously proud of our consortium and the result published today,” said Paul de Jong, KM3NeT spokesperson, vice programme leader of the Nikhef neutrino group and professor at the University of Amsterdam.
The KM3NeT detectors
The KM3NeT/ARCA (Astroparticle Research with Cosmics in the Abyss) detector is mainly dedicated to the study of the highest energy neutrinos and their sources in the Universe. It is located at 3450 m depth, about 80 km from the coast of Portopalo di Capo Passero, Sicily. Its 700 m high detection units (DUs) are anchored to the seabed and positioned about 100 m apart. Every DU is equipped with 18 Digital Optical Modules (DOM) each containing 31 photomultipliers (PMTs). In its final configuration, ARCA will comprise 230 DUs. The data collected are transmitted via a submarine cable to the shore station at the INFN Laboratori Nazionali del Sud.
The KM3NeT/ORCA (Oscillation Research with Cosmics in the Abyss) detector is optimised to study the fundamental properties of the neutrino itself. It is located at a depth of 2450 m, about 40 km from the coast of Toulon, France. It will comprise 115 DUs, each 200 m high and spaced by 20 m. The data collected by ORCA are sent to the shore station at La Seyne Sur Mer.
The KM3NeT Collaboration
The KM3NeT Collaboration brings together more than 360 scientists, engineers, technicians and students of 68 institutions from 21 countries all over the world, including from the Netherlands Nikhef, NWO-I, University of Amsterdam, Leiden University, NIOZ and TNO.
Dutch contributions
Nikhef was one of the driving forces in KM3NeT from its inception, including in various leadership positions. Dutch scientists and engineers contributed from the initial design to the actual implementation and operation. The Digital Optical Modules (DOMs) and parts of the electronics were developed at Nikhef. It is one of the largest detector production sites within KM3NeT. The procedure of how the detector lines are put in the water is also a Dutch design. Nikhef is also a major contributor to the KM3NeT electronics, mechanics and optical network, and developed the software for in-situ selection, calibration, reconstruction and final analysis. Dutch scientists are closely involved in the final analyses of the data to detect cosmic neutrino point sources and to study the properties of the neutrinos.
About Nikhef
The National Institute for Subatomic Physics Nikhef conducts research in the fields of particle and astroparticle physics. Nikhef is a partnership between NWO-I and six universities: Radboud University, the University of Groningen, the University of Amsterdam, Maastricht University, Utrecht University and the Free University Amsterdam.
More information and contact
For more information, visit:
- The Nature publication about this detection (page opens in new tab)
- Background information about this detection
- The webpage about Nikhef’s KM3NeT programme
You can get in touch with:
Nikhef communication, Vanessa Mexner, v.mexner@nikhef.nl, +31 6 4681 2075
KM3NeT is included in the roadmap of the European Strategy Forum on Research Infrastructures, which recognises KM3NeT as a priority research infrastructure for Europe. KM3NeT receives funding from the European Union as well as national research agencies in several countries, KM3NeT has benefitted from various fundings through the European research and innovation programmes as well as the European Regional Development Fund.