KM3NeT - Research

Blog for highlights during day-to-day KM3NeT research activities such as pitches for new papers, talks and posters during international conferences and (internal) workshops, comments on events in astroparticle physics and particle physics etc.

A set of dedicated studies on KM3-230213A

20 February 2025 – Recently the KM3NeT Collaboration has published evidence for the cosmic neutrino with the highest energy ever detected (the article on Nature can be accessed from here). This event is identified as KM3-230213A.

In a set of dedicated studies, the Collaboration has investigated the possible sources of the event and the implications that may be derived from it.

These studies are included in a set of articles which have recently been released:

The ultra-high-energy event KM3-230213A within the global neutrino landscape

The compatibility of the occurrence of KM3-230213A with the constraints placed by other experiments is explored.

Read the full article here: https://arxiv.org/abs/2502.08173

 

On the Potential Galactic Origin of the Ultra-High-Energy Event KM3-230213A 

The possibility that KM3-230213A may have originated in our Galaxy is discussed. The study did not allow to identify plausible mechanisms and sources which could sustain such hypothesis, leading to the conclusion that the neutrino is most likely of extra-Galactic origin.

Read the full article here: https://arxiv.org/abs/2502.08387

Characterising Candidate Blazar Counterparts of the Ultra-High-Energy Event KM3-230213A

In this paper the possibility is explored that KM3-230213A may have originated in a distant blazar. The study concerned a set of 17 blazars, which were identified as plausible sources of high-energy neutrinos due to their multiwavelength properties, highlighting in particular three of them. This work involved plenty of facilities: KM3NeT, VLA, VLBA, RATAN-600, OVRO, Swift, Fermi, SRG/eROSITA, Gaia, CRTS, ATLAS, ZTF, WISE/NEOWISE, Chandra and ROSAT!

Read the full article here: https://arxiv.org/abs/2502.08484

On the potential cosmogenic origin of the ultra-high-energy event KM3-230213A

The intriguing possibility that KM3-230213A may be of cosmogenic origin, i.e. it was originated from the interaction of ultra-high-energy cosmic rays with ambient photon and matter fields, is discussed in this paper, leading to hypotheses for reconciling the occurrence of this event with the latest measurements of cosmic rays of extreme energy.

Read the full article here: https://arxiv.org/abs/2502.08508

KM3NeT Constraint on Lorentz-Violating Superluminal Neutrino Velocity

The Lorentz symmetry, the fundamental principle which states that nothing can go faster than the speed of light in vacuum, is tested in this study. By looking at the energy of KM3-230213A and the distance travelled, the difference between neutrino and light speed was constrained to less than 1 part in 1000 billion billion, which represents the most stringent limit ever set using this method of analyzing high-energy neutrinos.

Read the full article here: https://arxiv.org/abs/2502.08508

Limits on the violation of the Lorentz principle (see the article for full details)

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.

Neutrino 2024 Poster Winner: Isabel Goos

03 July 2024 – In June, KM3NeT scientist participated to the XXXI International Conference on Neutrino Physics and Astrophysics (Neutrino 2024), held in Milan, Italy, and organized by the University of Milano – Bicocca, the University of Milan and the Istituto Nazionale di Fisica Nucleare (INFN).

As one of the largest conferences in astroparticle physics, neutrino physics and cosmology, it was the occasion to share latest findings, innovative concepts and future outlooks among experts of the field.

Isabel Goos at Neutrino 2024 (credits Neutrino2024)

During the conference, Isabel Goos, KM3NeT’s researcher at the University of Paris Cité, was awarded one of the four prizes for the best-poster award. In her poster, titled “KM3NeT’s sensitivity to the next core-collapse supernova”, she discusses how individual multi-PMT optical modules of KM3NeT can be used as standalone detectors for the detection of low-energy neutrinos from Core Collapsed Super Novae. It has been selected among 460 accepted posters, of which 319 eligible for this acknowledgement.

KM3NeT joins in congratulating Isabel on her great achievement!

In total, KM3NeT presented 17 posters, covering topics including neutrino astronomy, neutrino oscillations, dark matter & exotics, cosmic-ray studies and technologies for neutrino physics.

KM3NeT at Neutrino2024.

 

 

 

 

 

In addition, four members of the KM3NeT Collaboration had a plenary talk: João Coelho, who discussed the latests results from KM3NeT; Maurizio Spurio, debating open problems in neutrino astrophysics;  Naoko Kurahashi Neilson, contributing on the present and future of high-energy neutrino astronomy, and Jürgen Brunner presenting future detectors for atmospheric neutrinos.

Neutrino 2026 will be held at the University of California – Irvine. Looking forward to sharing our advancements also on that occasion!

Three new KM3NeT papers

Recently, three KM3NeT papers were accepted by peer-reviewed scientific journals and came on line.

Note, that KM3NeT has an open science policy which means that all papers can be read open access, i.e. without a paywall.

 

1. Following up gravitational wave events – a scientific paper. In the paper ‘Searches for neutrino counterparts of gravitational wavesfrom the LIGO/Virgo third observing run with KM3NeT‘ we report the results of a neutrino follow-up study of gravitational wave sources detected by the LIGO-Virgo interferometers in 2019–2020.

The search focuses both on MeV neutrinos and high-energy neutrinos. No significant excess was observed for any of the sources. Upper limits on the neutrino emission from individual sources and the typical emission from binary black hole mergers were computed and compared with the constraints from other neutrino telescopes.

JCAP04(2024)026, DOI: 10.1088/1475-7516/2024/04/026

In the picture upper limits on the total neutrino fluence for both analyses in comparison with the results of other observatories.

 

2. Differential Sensitivity of ARCA – a scientific paper. In the paper titled ‘Differential Sensitivity of the KM3NeT/ARCA Detector to a Diffuse Neutrino Flux and to Point-like Source Emission: Exploring the Case of Starburst Galaxies‘, for the first time, KM3NeT presents the expected differential sensitivity of the full ARCA detector for both diffuse and point-like neutrino fluxes.

In particular, this study is applied to Starburst Galaxies, demonstrating that the ARCA detector, when completed, can trace TeV neutrinos from these sources. For instance, with ARCA it will be possible to discriminate between different astrophysical components in NGC 1068 after 3 years of data taking, strengthening the observations of the IceCube Neutrino Observatory.

In the pictures: (left) the sensitivities of the ARCA detector after 10 years of operation as a function of neutrino energy, compared to measurements of the IceCube neutrino observatory; (right) the discovery neutrino flux as a function of operation time.

Astroparticle Physics, Volume 162, DOI: 10.1016/j.astropartphys.2024.102990

 

3. Powering optical modules – a technical paper. The optical modules in the KM3NeT neutrino telescope in the deep Mediterranean Sea receive electrical power from the control station on the shore. An electronics board – dubbed the Power Board – in each optical module is described in the paper ‘The Power Board of the KM3NeT Digital Optical Module: design, upgrade, and production’. The board arranges powering individual components in the module at different voltage levels. The Power Board has been subjected to rigorous test to ensure reliable operation in the deep sea for more than a decade.

In the picture a photo of the Power Board with the various DC/DC converters generating the voltages needed.

Electronics 2024,13(11), 2044, DOI: 10.3390/electronics13112044

 

In addition, three new pre-prints were stored on the arXiv and submitted to the relevant scientific journals for peer-review:

  • Astronomy potential of KM3NeT/ARCA, arXiv:2402.08363, submitted to EPJ-C

  • Atmospheric muons measured with the KM3NeT detectors in comparison with updated numeric predictions, arXiv: 2403.11946, submitted to EPJ-C

  • Search for Neutrino Emission from GRB 221009A using the KM3NeT ARCA and ORCA detectors, arXiv: 2404.05354, submitted to JCAP

We will report on these once they are accepted for print by the journals.

Paper alert

20 November 2023 – Recently, KM3NeT published on the arXiv pre-prints of two new papers:

1 – Embedded software of the KM3NeT Central Logic Board

This KM3NeT technical paper describes the embedded software running in the data acquisition of the telescope. Located in the deep Mediterranean Sea, the hardware of the telescope is not directly accessible. The implemented software facilitates remote management of the deployed hardware and safe reconfiguration of firmware. It runs on the central electronics board of each optical module of the KM3NeT detectors. The central logic board coordinates the readout of all equipment inside the module and manages the communication and data transmission over optical fibers connecting the module to the control station on shore.

Read the details at arXiv.2308.01032

(Accepted for publication in Computer Physics Communications)

 

2 – KM3NeT neutrino follow-up of gravitational wave sources

In this paper the KM3NeT Collaboration reports the results of a neutrino follow-up study made with ORCA data of gravitational wave sources detected by LIGO–Virgo in 2019-2020. The search focuses both on MeV neutrinos and high-energy neutrinos. No significant excess was observed for any of the sources.

Upper limits on the neutrino emission from individual sources and the typical emission from binary black hole mergers are computed and compared with the constraints from other neutrino telescopes.

Since May 2023, the Collaboration is performing real-time follow-ups of the GW triggers detected by LIGO-Virgo-KAGRA in their fourth observing run, with both ORCA and ARCA detectors with much larger instrumented volumes than in the previous searches.

In the figure the comparison of 90% upper limits on the neutrino fluence from gravitational wave sources for ANTARES, IceCube, Super-Kamiokande and KM3NeT.

 

Read the details at arXiv.2311.03804

The paper has been submitted for publication after peer-review.

 

KM3NeT in the ICRC2023 proceedings

The ICRC is the International Cosmic Ray Conference. It is one of the major conferences in astroparticle physics and covers many subfields. In 2023, the 38th International Cosmic Ray Conference (ICRC) took place in Nagoya, Japan.

KM3NeT researchers actively participated to present the work of the Collaboration and many contributions to the proceedings of the conference were published. The full proceedings of ICRC2023 can be found at here. Below you find the individual KM3NeT contributions, categorised in the various scientific and technological fields.

Neutrino astronomy using the KM3NeT/ARCA detector

Solar and heliospheric physics

Multi-messenger and gravitational waves

Neutrino oscillation physics using the KM3NeT/ORCA detector

Charged cosmic ray physics

Dark matter and exotics

Calibration

Data acquisition

Reconstruction and analysis tools

Outreach

 

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.

 

Neutrino emission from our Galaxy! New observations by the IceCube Collaboration

29 June 2023 – The KM3NeT Collaboration congratulates the IceCube Collaboration after today’s announcement of an evidence in IceCube of high-energy neutrinos originating from our own Galaxy.

“Congratulations to the IceCube Collaboration for this great result. For the KM3NeT Collaboration it is a very important observation” says Paschal Coyle, the KM3NeT Spokesperson.

While IceCube has previously reported evidence for several sources of extragalactic neutrinos, the detection of neutrinos from the Milky Way has proved difficult,  due to the IceCube’s location at the South Pole, where a signal from within our Galaxy is observed as downgoing events and is therefore subject to a large background of atmospheric muons. Furthermore, as the signal was observed in the cascade channel, which has a limited angular resolution, it was not possible to determine if the signal is due to a diffuse source or a collection of unresolved point sources.

A telescope located in the Northern hemisphere, such as KM3NeT, observes our Galaxy using upgoing events, which have significantly less background than downgoing events and are therefore easier to detect. This in fact allowed ANTARES to report the first hint of a neutrino emission from the Galaxy (see the news item on the ANTARES web-site).

Moreover, the KM3NeT telescope will be able to observe the signal in the muon neutrino channel in addition to the electron neutrino channel and both with a much better angular resolution than IceCube.

“IceCube has confirmed our Galaxy is a guaranteed source of high-energy neutrinos. KM3NeT looks forward to unravelling the origins of this Galactic signal with unprecedented precision” concludes Paschal Coyle.

New publication: The KM3NeT broadcast optical system

1 February 2023 – Via a long-distance electro-optical network the more than 6000 optical modules of KM3NeT in the deep sea are provided with a point-to-point connection to the control station on shore. The optical layer is presented in full details:

S. Aiello et al. 2023 JINST 18 T02001 DOI 10.1088/1748-0221/18/02/T02001

Abstract:

The optical data transport system of the KM3NeT neutrino telescope at the bottom of the Mediterranean Sea will provide more than 6000 optical modules in the detector arrays with a point-to-point optical connection to the control stations onshore. The ARCA and ORCA detectors of KM3NeT are being installed at a depth of about 3500 m and 2500 m, respectively and their distance to the control stations is about 100 kilometers and 40 kilometers. In particular, the two detectors are optimised for the detection of cosmic neutrinos with energies above about 1 TeV (ARCA) and for the detection of atmospheric neutrinos with energies in the range 1 GeV–1 TeV (ORCA). The expected maximum data rate is 200 Mbps per optical module. The implemented optical data transport system matches the layouts of the networks of electro-optical cables and junction boxes in the deep sea. For efficient use of the fibres in the system the technology of Dense Wavelength Division Multiplexing is applied. The performance of the optical system in terms of measured bit error rates, optical budget are presented. The next steps in the implementation of the system are also discussed.

The architecture of the KM3NeT broadcast optical system
The architecture of the optical layer connecting the ARCA detector of KM3NeT in the deep sea with the control station on shore.

New publication: The KM3NeT multi-PMT optical module

27 July 2022 – Long-term operation in the deep sea puts challenging requirements on detectors. A review of the design and construction of the KM3NeT optical module has been published:

S. Aiello et al. 2022 JINST 17 P07038 DOI 10.1088/1748-0221/17/07/P07038

Abstract:

The optical module of the KM3NeT neutrino telescope is an innovative multi-faceted large area photodetection module. It contains 31 three-inch photomultiplier tubes in a single 0.44 m diameter pressure-resistant glass sphere. The module is a sensory device also comprising calibration instruments and electronics for power, readout and data acquisition. It is capped with a breakout-box with electronics for connection to an electro-optical cable for power and long-distance communication to the onshore control station. The design of the module was qualified for the first time in the deep sea in 2013. Since then, the technology has been further improved to meet requirements of scalability, cost-effectiveness and high reliability. The module features a sub-nanosecond timing accuracy and a dynamic range allowing the measurement of a single photon up to a cascade of thousands of photons, suited for the measurement of the Cherenkov radiation induced in water by secondary particles from interactions of neutrinos with energies in the range of GeV to PeV. A distributed production model has been implemented for the delivery of more than 6000 modules in the coming few years with an average production rate of more than 100 modules per month. In this paper a review is presented of the design of the multi-PMT KM3NeT optical module with a proven effective background suppression and signal recognition and sensitivity to the incoming direction of photons.

Rendering of a KM3NeT DOM
Rendering of a KM3NeT optical module with bollards attached to mechanically supporting cables in the deep-sea. In the cut out, the interior of the module with photomultipliers and electronics is visible. The black break-out box connects to the electro-optical network for electrical power and long-distance data communication toward the control station on shore.