- Open Access
Ultrahigh-Energy Event KM3-230213A within the Global Neutrino Landscape
Phys. Rev. X 15, 031016 – Published 15 July, 2025
DOI: https://doi.org/10.1103/yypk-zmb8
Abstract
On February 13th, 2023, the KM3NeT/ARCA telescope detected a neutrino candidate with an estimated energy in the hundreds of PeV. In this article, the observation of this ultrahigh-energy neutrino is discussed in light of null observations above tens of PeV from the IceCube and Pierre Auger observatories. Performing a joint fit of all experiments under the assumption of an isotropic flux, the best-fit single-flavor flux normalization is in the 90% energy range of the KM3NeT event. Furthermore, the ultrahigh-energy data are then fit together with the IceCube measurements at lower energies, either with a single power law or with a broken power law, allowing for the presence of a new component in the spectrum. A slight preference for a break in the PeV regime is found for one of the three investigated IceCube samples and no such preference for the other two. In all cases, the observed tension between KM3NeT and other datasets is mild to moderate (), and increased statistics are required to resolve this apparent tension and better characterize the neutrino landscape at ultrahigh energies.
Physics Subject Headings (PhySH)
Popular Summary
The KM3NeT telescope recently detected an ultrahigh-energy neutrino with an energy 20–30 times higher than any previously seen. This surprising result has sparked interest because similar events have not been reported by the IceCube or Pierre Auger observatories, despite their longer operation and larger detectors. Our study aims to assess whether this inconsistency could signal something new in the neutrino energy spectrum or if it is simply a statistical fluctuation. We find that while the tension between the datasets is moderate, it is statistically consistent with chance. Current data are not enough to draw firm conclusions on whether the observation hints at a new ultrahigh-energy component in the spectrum.
To carry out this analysis, we use published data from IceCube and Pierre Auger for neutrinos with energies above 10 PeV. We apply two statistical methods to estimate the tension of the KM3NeT result with the lack of similar events from the other observatories. We also test whether a two-component model (rather than a single power law) better explains the energy distribution of all available data, including lower-energy measurements from IceCube.
If confirmed, the presence of a new component in the neutrino spectrum would be a breakthrough. It could mean we are seeing cosmogenic neutrinos for the first time, produced when cosmic rays interacted with the cosmic microwave background, or it could point to a new kind of astrophysical source. Future observations will be key to clarifying the nature of this high-energy event and what it tells us about the Universe.
Article Text
References (47)
- S. Aiello et al. (KM3NeT Collaboration), Observation of an ultra-high-energy cosmic neutrino with KM3NeT, Nature (London) 638, 376 (2025).
- S. Adrian-Martinez et al. (KM3NeT Collaboration), Letter of intent for KM3NeT 2.0, J. Phys. G 43, 084001 (2016).
- S. Aiello et al. (KM3NeT Collaboration), The KM3NeT multi-PMT optical module, J. Instrum. 17, P07038 (2022).
- M. Meier (IceCube Collaboration), Recent cosmogenic neutrino search results with IceCube and prospects with IceCube-Gen2, in Proceedings of the 58th Rencontres de Moriond on Very High Energy Phenomena in the Universe (2024), arXiv:2409.01740.
- J. I. Illana, P. Lipari, M. Masip, and D. Meloni, Atmospheric lepton fluxes at very high energy, Astropart. Phys. 34, 663 (2011).
- S. Ostapchenko, M. V. Garzelli, and G. Sigl, On the prompt contribution to the atmospheric neutrino flux, Phys. Rev. D 107, 023014 (2023).
- J. Babson et al. (DUMAND Collaboration), Cosmic ray muons in the deep ocean, Phys. Rev. D 42, 3613 (1990).
- I. A. Belolaptikov et al. (Baikal Collaboration), The Baikal underwater neutrino telescope: Design, performance and first results, Astropart. Phys. 7, 263 (1997).
- A. Silvestri (AMANDA Collaboration), The AMANDA neutrino telescope, Int. J. Mod. Phys. A 20, 3096 (2005).
- P. A. Rapidis (NESTOR Collaboration), The NESTOR underwater neutrino telescope project, Nucl. Instrum. Methods Phys. Res., Sect. A 602, 54 (2009).
- P. Piattelli (NEMO Collaboration), The Neutrino Mediterranean Observatory project, Nucl. Phys. B, Proc. Suppl. 143, 359 (2005).
- M. Ageron et al. (ANTARES Collaboration), ANTARES: The first undersea neutrino telescope, Nucl. Instrum. Methods Phys. Res., Sect. A 656, 11 (2011).
- A. Albert et al. (ANTARES Collaboration), The ANTARES detector: Two decades of neutrino searches in the Mediterranean Sea, Phys. Rep. 1121–1124, 1 (2025).
- C. Spiering, Towards high-energy neutrino astronomy. A historical review, Eur. Phys. J. H 37, 515 (2012).
- R. Abbasi et al. (IceCube Collaboration), Observation of high-energy neutrinos from the Galactic plane, Science 380, adc9818 (2023).
- R. Abbasi et al. (IceCube Collaboration), Evidence for neutrino emission from the nearby active galaxy NGC 1068, Science 378, 538 (2022).
- C. A. Argüelles, F. Halzen, and N. Kurahashi, From the dawn of neutrino astronomy to a new view of the extreme universe, arXiv:2405.17623.
- K. Kotera and A. V. Olinto, The astrophysics of ultrahigh energy cosmic rays, Annu. Rev. Astron. Astrophys. 49, 119 (2011).
- O. Adriani et al. (KM3NeT Collaboration), On the potential galactic origin of the ultra-high-energy event KM3-230213A, arXiv:2502.08387.
- O. Adriani et al. (KM3NeT, MessMapp Group, Fermi-LAT, Owens Valley Radio Observatory 40-m Telescope Group, SVOM Collaborations), Characterising candidate blazar counterparts of the ultra-high-energy event KM3-230213A, arXiv:2502.08484.
- O. Adriani et al. (KM3NeT Collaboration), On the potential cosmogenic origin of the ultra-high-energy event KM3-230213A, arXiv:2502.08508.
- A. Abdul Halim et al. (Pierre Auger Collaboration), Latest results from the searches for ultra-high-energy photons and neutrinos at the Pierre Auger Observatory, Proc. Sci., ICRC2023 (2023) 1488.
- S. Aiello et al. (KM3NeT Collaboration), Astronomy potential of KM3NeT/ARCA, Eur. Phys. J. C 84, 885 (2024).
- S. Aiello et al. (KM3NeT Collaboration), Data for the KM3-202313A high energy event observation (2025), 10.5281/zenodo.13366058.
- A. Anker et al., A search for cosmogenic neutrinos with the ARIANNA test bed using 4.5 years of data, J. Cosmol. Astropart. Phys. 03 (2020) 053.
- P. W. Gorham et al. (ANITA Collaboration), Constraints on the ultrahigh-energy cosmic neutrino flux from the fourth flight of ANITA, Phys. Rev. D 99, 122001 (2019).
- A. Connolly et al. (ARA Collaboration), Recent results from The Askaryan Radio Array, Proc. Sci., ICRC2019 (2021) 858.
- A. Avrorin et al., The gigaton volume detector in Lake Baikal, Nucl. Instrum. Methods Phys. Res., Sect. A 639, 30 (2011).
- M. Agostini et al. (P-ONE Collaboration), The Pacific Ocean Neutrino Experiment, Nat. Astron. 4, 913 (2020).
- Z. P. Ye et al. (TRIDENT Collaboration), A multi-cubic-kilometre neutrino telescope in the western Pacific Ocean, Nat. Astron. 7, 1497 (2023).
- M. G. Aartsen et al. (IceCube-Gen2 Collaboration), IceCube-Gen2: The window to the extreme Universe, J. Phys. G 48, 060501 (2021).
- R. Abbasi et al. (IceCube Collaboration), The IceCube high-energy starting event sample: Description and flux characterization with 7.5 years of data, Phys. Rev. D 104, 022002 (2021).
- R. Abbasi et al. (IceCube Collaboration), Characterization of the astrophysical diffuse neutrino flux using starting track events in IceCube, Phys. Rev. D 110, 022001 (2024).
- R. Abbasi et al. (IceCube Collaboration), Improved characterization of the astrophysical muon–neutrino flux with 9.5 years of IceCube data, Astrophys. J. 928, 50 (2022).
- M. G. Aartsen et al. (IceCube Collaboration), Differential limit on the extremely-high-energy cosmic neutrino flux in the presence of astrophysical background from nine years of IceCube data, Phys. Rev. D 98, 062003 (2018).
- M. G. Aartsen et al. (IceCube Collaboration), Detection of a particle shower at the Glashow resonance with IceCube, Nature (London) 591, 220 (2021); 592, E11 (2021).
- A. Albert et al. (ANTARES Collaboration), Constraints on the energy spectrum of the diffuse cosmic neutrino flux from the ANTARES neutrino telescope, J. Cosmol. Astropart. Phys. 08 (2024) 038.
- S. S. Wilks, The large-sample distribution of the likelihood ratio for testing composite hypotheses, Ann. Math. Stat. 9, 60 (1938).
- M. Maltoni and T. Schwetz, Testing the statistical compatibility of independent data sets, Phys. Rev. D 68, 033020 (2003).
- A. Gelman, X.-L. Meng, and H. Stern, Posterior predictive assessment of model fitness via realized discrepancies, Statistica Sinica 6, 733 (1996), https://www.jstor.org/stable/24306036.
- R. Naab, E. Ganster, and Z. Zhang (IceCube Collaboration), Measurement of the astrophysical diffuse neutrino flux in a combined fit of IceCube’s high energy neutrino data, in Proceedings of the 38th International Cosmic Ray Conference (2023), arXiv:2308.00191.
- M. A. Acero et al. (NOvA Collaboration), Monte Carlo method for constructing confidence intervals with unconstrained and constrained nuisance parameters in the NOvA experiment, J. Instrum. 20, T02001 (2022).
- H. Jeffreys, The Theory of Probability, Oxford Classic Texts in the Physical Sciences (OUP, Oxford, 1998).
- J. Buchner, UltraNest—a robust, general purpose Bayesian inference engine, J. Open Source Software 6, 3001 (2021).
- J. A. Aguilar et al. (RNO-G Collaboration), Design and sensitivity of the Radio Neutrino Observatory in Greenland (RNO-G)., J. Instrum. 16, P03025 (2021); 18, E03001 (2023).
- J. Álvarez-Muñiz et al. (GRAND Collaboration), The giant radio array for neutrino detection (GRAND): Science and design, Sci. China Phys. Mech. Astron. 63, 219501 (2020).
- A. Aab et al. (Pierre Auger Collaboration), Limits on point-like sources of ultra-high-energy neutrinos with the Pierre Auger Observatory, J. Cosmol. Astropart. Phys. 11 (2019) 004.
