KM3NeT - neutrino

KM3NeT detects the highest energy neutrino ever observed

KM3NeT PRESS RELEASE – 12/02/2025

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, KM3NeT Spokesperson at the time of the detection, and researcher at CNRS Centre National de la Recherche Scientifique – Centre de Physique des Particules de Marseille, France.

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.

“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.

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.

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 scale of KM3NeT, eventually encompassing a volume of about one cubic kilometre with a total of about 200 000 photomultipliers, along with its extreme location in the abyss of the Mediterranean Sea, demonstrates the extraordinary efforts required to advance neutrino astronomy and particle physics. The detection of this event is the result of a tremendous collaborative effort between many international teams of engineers, technicians and scientists”, comments Miles Lindsey Clark, KM3NeT Technical Project Manager at the time of the detection, and research engineer at the CNRS – Astroparticle and Cosmology laboratory, France.

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.

The KM3NeT Collaboration brings together more than 360 scientists, engineers, technicians and students of 68 institutions from 21 countries all over the world.

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.

Press kit

Press contact

CNRS Press Office

presse@cnrs.fr | +33 1 44 96 51 51

INFN Press Office

Antonella Varaschin | antonella.varaschin@presid.infn.it | +39 349 5384481

Nikhef Press Office

Vanessa Mexner | v.mexner@nikhef.nl | +31 6 4681 2075

Contact person in Belgium

Gwenhael Wilberts Dewasseige | gwenhael.dewasseige@uclouvain.be

Contact person in Czech Republic

Jan Machonin | machonin@seznam.cz

Contact person in Greece

Aikaterini Tzamarioudaki | katerina@inp.demokritos.gr 

Contact person in Poland

Anna Żmuda-Muszyńska | rzecznik@agh.edu.pl

Contact person in Slovakia

Otakar Horák | otakar.horak@dennikn.sk

Contact person in South Africa

Markus Boettcher | Markus.Bottcher@nwu.ac.za

Contact person in Spain

Juande Zornoza | zornoza@ific.uv.es

Contact person in the United Arab Emirates

Satyendra Thoudam | satyendra.thoudam@ku.ac.ae

Contact person in the United Kingdom

David Benoit | d.benoit@hull.ac.uk

For contacts in all other countries

km3net-oc@km3net.de

The observation of an ultra-high-energy cosmic neutrino at the bottom of the sea

KM3NeT Popular Information – 12/02/2025

Unveiling the Universe Through Ultra-High-Energy Neutrinos

When we think of the universe, images of stars, galaxies, and vast expanses of darkness come to mind. Yet, hidden within this cosmic expanse are invisible messengers—neutrinos— tiny particles that can travel unimpeded from the furthest reaches of the universe.

On the 12th of February, 2025, scientists working on the Kilometre cube Neutrino Telescope (KM3NeT) in the Mediterranean Sea have published in Nature the observation of an extraordinary event: the evidence of an ultra-high-energy cosmic neutrino, shedding new light on some of the Universe’s most energetic processes.

What are neutrinos?

Neutrinos are subatomic particles with no electric charge and an incredibly small mass. They are elusive, interacting so weakly with matter that billions of them pass through us every second without a trace. Produced in a huge range of energies, and in many different processes – from large amount of low energy neutrinos produced in nuclear fusion processes in our Sun, to small amount of high energy neutrinos coming from particle collisions in cataclysmic cosmic events such as exploding stars or black hole activity – neutrinos are unique because their path remains undisturbed . This allows them to act as cosmic messengers, carrying information directly from their astrophysical source to detectors on Earth.

One module of KM3NeT with 31 light sensitive ‘eyes’ (called photomultiplier tubes) in the deep sea. The observatory which detected the ultra-high energy event (called KM3NeT/ARCA) had 378 of such modules installed at the time of the detection, on a total of 21 vertical detection lines attached to the sea bottom. The lines are at almost 100 meters distance from one another, and are almost 700 meters long. Altogether being a huge network of light sensitive ‘eyes’. Courtesy KM3NeT.

Detecting neutrinos requires giant observatories for example located deep underwater or in ice. These observatories look for faint flashes of Cherenkov light—a luminous glow created when charged particles produced by neutrino interactions move faster than light in the medium. The KM3NeT telescope located deep in the Mediterranean Sea is one such observatory, designed to catch high-energy neutrino events via these flashes of light.

A record-breaking discovery

On February 13, 2023, the KM3NeT team recorded a neutrino event unlike any other. Named KM3-230213A, the neutrino’s energy was estimated to be an astonishing 220 peta- electronvolts (PeV) – roughly a billion times 100 million times the energy of visible light photons and about 30 times the highest neutrino energy previously detected.

The event occurred in KM3NeT’s ARCA detector, located 3450 meters underwater near Sicily in Italy. KM3NeT/ARCA is designed to study high-energy neutrinos, while its sister detector KM3NeT/ORCA, located near Toulon in France, focuses on lower-energy neutrinos. During this event, the detector’s photomultiplier tubes recorded over 28 000 photons of light produced while the charged particle coming from the neutrino interaction crossed the entire detector.

What makes this event special?

The detection of KM3-230213A is ground-breaking for several reasons:

  1. Unprecedented Energy: Such high-energy neutrinos are extremely rare, making this a monumental discovery.
  2. Precision Detection: The advanced design of the ARCA detector, featuring multi- photomultiplier optical modules with nanosecond timing precision, enabled precise reconstruction of the neutrino’s trajectory and energy. Its near-horizontal path through the detector indicates a cosmic origin, as atmospheric muons cannot travel such long distances through the seawater without being absorbed.
  3. Cosmic Origins: This neutrino might originate from a powerful cosmic accelerator, such as an active galactic nucleus or a gamma-ray burst. Alternatively, it could be a cosmogenic neutrino, produced in the interaction between an ultra-high-energy cosmic ray with the background radiation in the universe.

Searching for the source

After detecting KM3-230213A, the KM3NeT scientists analysed its direction and energy to identify its possible astrophysical origin. Researchers cross-referenced data from gamma-ray, X-ray, and radio telescopes to look for potential counterparts, such as blazars or transient events. While its arrival direction aligns with regions containing active cosmic phenomena, no definitive source could be significantly identified.

Visual impression of the ultra-high energy neutrino event observed in KM3NeT/ARCA. The colours indicate the light seen by the ‘eyes’ on each module, where the different colours represent different observation times. The almost horizontally reconstructed track of the particle is shown as a line from right to left. Courtesy KM3NeT.

 Even though an extragalactic origin is most likely, the event’s position near the Galactic plane does not exclude the possibility it originated in our Milky Way.

This highlights the challenge of linking single neutrino detections to specific astrophysical sources.

Its importance for neutrino astronomy

This discovery marks a milestone in neutrino astronomy, a field still in its infancy compared to traditional optical or radio astronomy. High-energy neutrino observations like KM3- 230213A offer unique insights into the most extreme environments in the universe. They may help answer long-standing questions about the origins of cosmic rays and how they can be accelerated to such enormous energies.

Furthermore, KM3-230213A provides valuable data to refine models of cosmic neutrino production and propagation. It also demonstrates the capabilities of next-generation observatories like KM3NeT, which continue to push the boundaries of our understanding.

The road ahead

While KM3-230213A raises many questions, it also opens new doors. Future observations will focus on detecting more such events to build a clearer picture of their origins. The ongoing expansion of KM3NeT with additional detection lines and increasing data taking time will improve its sensitivity and enhance its ability to pinpoint neutrino sources.

The evidence of this ultra-high-energy cosmic neutrino is a testament to human ingenuity and the enduring quest to understand the universe. Each neutrino captured is like a piece of a jigsaw puzzle, revealing a bit more about the cosmos. As technology advances, we are poised to discover even more extraordinary phenomena in the vast expanse of space.

Observation of an ultra-high-energy cosmic neutrino with KM3NeT

On February 12, 2025, The KM3NeT Collaboration has announced the detection from the abyss of the Mediterranean Sea of a cosmic neutrino with a record-breaking energy of about 220 PeV.

More information can be found in the:

Additionally, 4 companion papers have been published on arXiv:

A fruitful Collaboration Meeting in Louvain-la-Neuve!

4 February 2025 – Last week, KM3NeT has met, both in person and online, for its winter Collaboration Meeting , in Louvain-la-Neuve, Belgium, hosted by UCLouvain.

Various discussions and presentations highlighted progresses and activities related to the ARCA and ORCA detectors, including updates on construction, simulation, calibration and data analysis efforts. The meeting also featured talks on the latest scientific results, including…plans for very exciting results to be announced soon!

Beyond the scientific sessions, the event fostered community engagement through social activities and networking opportunities.

It was also the occasion to welcome our new Management Team: Paul De Jong (Nikhef and University of Amsterdam, The Netherlands) serves as Spokesperson, Damien Dornic (CPPM/CNRS, France) as Deputy Spokesperson, Rosa Coniglione (INFN-LNS, Italy) as the Physics and Software Manager, and Antonio D’Amico (Nikhef, The Netherlands) holds the position of Technical Project Manager. The entire Collaboration extends its congratulations to the outgoing Management Team and wishes the best of luck to its newly elected members.

The KM3Net Collaboration is pleased to welcome a new team, from INFN and University of Florence, Italy, coordinated by Nicola Mori: we are happy to have you as part of our Collaboration and look forward to your valuable contributions.

Thanks a lot to the whole local team for the wonderful organization.

The next Collaboration Meeting is scheduled for the coming summer, in France, at Caen.

The KM3NeT Management team (from left to right): Damien Dornic, Paul De Jong, Rosa Coniglione and Antonio D’Amico.

 

 

 

 

Update of gSeaGen simulation software

23 November 2024 – In a new paper with the title ‘gSeaGen code by KM3NeT: an efficient tool to propagate muons simulated with CORSIKA’ we describe an open source solution for efficient simulation of cosmic-ray induced muons in neutrino telescopes.

For this, we adapted the gSeaGen code, which generates high statistic samples of simulated neutrino-induced events, detectable by neutrino telescopes.

Updated gSeaGen can now also process muons from cosmic-ray induced particle showers in the atmosphere, which are generated by the Monte Carlo simulation code CORSIKA.

The tracking of muons towards the simulated detector offers efficient re-use of the particle shower when a muon misses the detector. We added several other new functionalities for computational efficiency and user control.

We updated gSeaGen with KM3NeT in mind, but other under-ground, under-water, or under-ice experiments may profit from it as well.

The paper is submitted to Computer Physics Communications
A preprint is available at: https://arxiv.org/abs/2410.24115

In the image:
Sketch of the projection of the side area of the detector (the ‘can’) onto the sea surface.

KM3NeT gathered online for its fall collaboration meeting

13 November 2024 – Last week , the KM3NeT Collaboration has met online for its fall meeting.

During the meeting, we reviewed the current status of data taking for both ARCA and ORCA detectors, discussed the advancements in their construction, the progresses in MC simulation and detector calibration, and outlined the plans for the ongoing data analyses.

It was also the occasion to celebrate our two last sea campaigns and thus the expanded configurations of the detectors, ARCA 33 and ORCA24. The deployment of new instrumentation on the ORCA site will allow for a precise monitoring of the detector position and water properties.

During the meeting Antoine Kouchner started his mandate as chairperson of the Institute Board, taking over from Uli Katz: with many thanks to Uli for all the work done in the past years, and good luck to Antoine for his new duty.

Also during the meeting, the process to elect the new Management Team of the Collaboration was started.

Finally, KM3NeT gave a heartfelt greeting to its new members. Juan Antonio Aguilar Sánchez of the Université Libre de Bruxelles, Belgium, and Elisa Bernardini of Padova University, Italy,  joined as Observers, while the team led by Arthur Ukleja from the University of Krakow, Poland, was endorsed as Full Member. 

A warm welcome to everyone!

It was great to see the advancements in the physics analyses as well as the simulation and calibration works, to discuss recent scientific advancements and to see the Collaboration continue to grow.

The next Collaboration Meeting is scheduled for January, in Belgium, at Louvain-la-Neuve.

Quantum decoherence with ORCA6

30 October 2024 – Search for quantum decoherence in neutrino oscillations with six detection units of KM3NeT/ORCA

(KM3NeT paper, submitted to JCAP, arXiv: 2410.01388)

In a new paper we search for quantum decoherence in neutrino oscillations by looking for deviations of the standard neutrino oscillation pattern. We report upper limits on the decoherence parameters using data from ORCA6.

Usually, neutrino oscillations are studied in the framework of quantum mechanics assuming that the neutrino system is isolated. In this paper we study neutrino oscillations in the framework of open quantum systems, where the neutrino is coupled to a larger environment.

Several theories of quantum gravity postulate fluctuations in spacetime as a stochastic environment. A neutrino that propagates in such an environment will experience changes to its quantum phase. This will lead to a loss of coherence of the neutrino mass eigenstates during propagation. The phenomenon is referred to as decoherence in neutrino oscillations.

The search for decoherence in neutrino oscillations provides a rare opportunity to investigate quantum gravitational effects which are usually beyond the reach of current experiments.

The ORCA detector of KM3NeT is particularly designed to detect neutrinos generated in collision of cosmic ray particles with the Earth’s atmosphere. The atmospheric neutrinos are good probes to study oscillations and hence to search for quantum decoherence effects.

We used the neutrino data collected by the ORCA6 detector – an early detector configuration with six detection units –  in the period January 2020 to November 2021. In the analysis we focused on atmospheric neutrinos with energies of a few GeV to 100 GeV. We measured the parameters Γ21 and Γ31, that describe decoherence, assuming a power-law dependency on the neutrino energy Γij ∝ (E/E0)n and  explored two cases: with n = -2 and with n = -1.

Results

No significant deviation with respect to the standard oscillation hypothesis is observed. Therefore, 90% CL upper limits for the two cases are estimated as

The decoherence sensitivity of ORCA depends on the neutrino mass ordering. Therefore, we report upper limits for both normal and inverted ordering.

The results are comparable to bounds reported for IceCube/DeepCore and display the same dependency on the mass ordering.

In the figure below the 90% confidence level contours for Γ21 and Γ31 are shown for a decoherence model fitting both normal (NO) and inverted (IO) neutrino mass orderings.

 

KM3NeT on display at the “Des abysses au cosmos” exhibition

From the 15th of September to the 8th of October, KM3NeT is represented at the exhibition “Des abysses au cosmos” (From the abyss to the cosmos), at the Fort Napoléon cultural centre in La Seyne-sur-Mer, France, operating quarters of the ANTARES and KM3NeT experiments.

The exhibition presents 20 years of underwater exploration of the cosmos, as well as the scientific and technological challenges and innovations involved in studying neutrinos and the deep marine environment. Organised by the CPPM and the City Hall of la Seyne-sur-Mer, this exhibition is aimed at the general public as well as primary and secondary school students.

Posters, photos, miniatures, objects and mini-interviews about KM3NeT are displayed, showing the scientific and technological efforts done by the Collaboration since the beginnings of the experiment to the present day. The KM3NeT-INFRADEV2 project is also represented to highlight the Collaboration’s commitment towards the full implementation of a reliable and sustainable KM3NeT international Research Infrastructure. A section is also dedicated to women in science, presenting the involvement of women scientists, engineers and technicians in KM3NeT.

 

An exhibition that will take its visitors to a depth of more than 2400 metres and behind the scenes of international research!

 

Some of the objects presented at the exhibit (by Chiara Lastoria)

 

Some pictures of the exhibition opening, on the 14th of September (by Victoria Ciarlet)

 

More information on the exhibition: https://cppm.in2p3.fr/abysses-cosmos

KM3NeT presented at conferences worldwide

15 September 2023 – This summer, KM3NeT members participated in conferences all over the world to present the latest results and  developments of our Collaboration.

Besides TAUP in Vienna, EPS-HEP in Hamburg, and TeVPA in Naples, KM3NeT-ers have massively attended the 38th International Cosmic Ray Conference (ICRC), in Nagoya, Japan. Since the ICRC is among the largest conferences in the field of astroparticle physics, it was an ideal opportunity for reporting the progress of the collaboration in neutrino astronomy, neutrino physics, multi-messenger astronomy, cosmic rays, and dark matter searches.

In total, KM3NeT presented 10 talks and 28 posters at the ICRC, in addition to a plenary talk given by prof. Antoine Kouchner, the spokesperson of the ANTARES Collaboration, on catching neutrinos in the Mediterranean Sea.

Interested?

The full proceedings of ICRC2023 can be found here. For your convenience, the contributions of KM3NeT to the proceedings are available here and are also on arXiv: https://arxiv.org/abs/2309.05016.

KM3NeT members at the ICRC2023.
Antoine Kouchner, spokesperson of the ANTARES Collaboration, presenting at the ICRC2023 an overview of recent work achieved by ANTARES and KM3NeT.
Some of the talks given by KM3NeT members at the ICRC2023.
Some of the posters presented by KM3NeT members at the ICRC2023.

 

Three more detection units for KM3NeT/ORCA

1 May 2023 – During a two days sea operation, 27-28 April 2023, three detection units were successfully connected to the ORCA detector of KM3NeT in a record time of just over 24 hours. In addition, an acoustic beacon was recovered for battery replacement. The total number of deployed ORCA units is now 18, as visible in the sonar scan above.

As usual, the operation was performed with two ships: the Castor of Foselev, for deployment of the detection units, and the Janus II of SAAS (formerly Comex), equipped with a deep-sea remotely operated vehicle, for submarine operations.

Many thanks to the crews offshore as well as to the team who performed the functional tests of the new detection units from the shore station!