Observation of an ultra-high-energy cosmic neutrino with KM3NeT The KM3NeT Collaboration Aiello, S. Díaz García, Antonio Francisco Gutiérrez González, Miguel Navas Concha, Sergio The KM3NeT Collaboration acknowledges the generous hospitality and support of the Laboratori Nazionali del Sud, Italy. We acknowledge the financial support of: KM3NeT-INFRADEV2 project, financed by the European Union Horizon Europe Research and Innovation Programme under grant agreement no. 101079679; Funds for Scientific Research (FRS-FNRS); Francqui Foundation; Belgian American Educational Foundation; Czech Science Foundation (GAČR 24-12702S); Agence Nationale de la Recherche (contract ANR-15-CE31-0020); Centre National de la Recherche Scientifique (CNRS); Commission Européenne (FEDER fund and Marie Curie Program); LabEx UnivEarthS (ANR-10-LABX-0023 and ANR-18-IDEX-0001), Paris Île-de-France Region, Normandy Region (Alpha, Blue-waves and Neptune), France; the Provence-Alpes-Côte d’Azur Delegation for Research and Innovation (DRARI), the Provence-Alpes-Côte d’Azur region, the Bouches-du-Rhône Departmental Council, the Metropolis of Aix-Marseille Provence and the City of Marseille through the CPER 2021-2027 NEUMED project; the CNRS Institut National de Physique Nucléaire et de Physique des Particules (IN2P3); Shota Rustaveli National Science Foundation of Georgia (SRNSFG, FR-22-13708), Georgia. This work is part of the MuSES project, which has received financing from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 101142396). This work was supported by the European Research Council, ERC Starting grant MessMapp, under contract no. 949555; the General Secretariat of Research and Innovation (GSRI), Greece; Istituto Nazionale di Fisica Nucleare (INFN) and Ministero dell’Università e della Ricerca (MUR), through PRIN 2022 programme (grant PANTHEON 2022E2J4RK, Next Generation EU) and PON R&I programme (Avviso n. 424 del 28 febbraio 2018, Progetto PACK-PIR01 00021), Italy; IDMAR project Po-Fesr Sicilian Region az. 1.5.1. A.D.B., W.I.I., M.B., A.N., G.P., I.C.R. and A.Sim. have been supported by the Italian Ministero dell’Università e della Ricerca (MUR), Progetto CIR01 00021 (Avviso n. 2595 del 24 dicembre 2019); KM3NeT4RR MUR Project National Recovery and Resilience Plan (NRRP), Mission 4 Component 2 Investment 3.1, financed by the European Union - NextGenerationEU, CUP I57G21000040001, Concession Decree MUR no. n. Prot. 123 del 21/06/2022; Ministry of Higher Education, Scientific Research and Innovation, Morocco, and the Arab Fund for Economic and Social Development, Kuwait; Nederlandse organisatie voor Wetenschappelijk Onderzoek (NWO), the Netherlands; the grant ‘AstroCeNT: Particle Astrophysics Science and Technology Centre’, carried out within the International Research Agendas programme of the Foundation for Polish Science financed by the European Union under the European Regional Development Fund; the programme ‘Excellence initiative-research university’ for the AGH University in Krakow; the ARTIQ project: UMO-2021/01/2/ST6/00004 and ARTIQ/0004/2021; Ministry of Research, Innovation and Digitalisation, Romania; Slovak Research and Development Agency under contract no. APVV-22-0413; Ministry of Education, Research, Development and Youth of the Slovak Republic; MCIN for PID2021-124591NB-C41, -C42, -C43 and PDC2023-145913-I00 financed by MCIN/AEI/10.13039/501100011033 and by ‘ERDF A way of making Europe’, for ASFAE/2022/014 and ASFAE/2022 /023 with funding from the EU NextGenerationEU (PRTR-C17.I01) and Generalitat Valenciana, for grant AST22_6.2 with funding from Consejería de Universidad, Investigación e Innovación and Gobierno de España and European Union - NextGenerationEU, for CSIC-INFRA23013 and for CNS2023-144099, Generalitat Valenciana for CIDEGENT/2018/034, /2019/043, /2020/049, /2021/23, for CIDEIG/2023/20, for CIPROM/2023/51 and for GRISOLIAP/2021/192 and EU for MSC/101025085, Spain; Khalifa University internal grants (ESIG-2023-008 and RIG-2023-070), United Arab Emirates; the European Union’s Horizon 2020 research and innovation programme (ChETEC-INFRA - project no. 101008324). The detection of cosmic neutrinos with energies above a teraelectronvolt (TeV) offers a unique exploration into astrophysical phenomena. Electrically neutral and interacting only by means of the weak interaction, neutrinos are not deflected by magnetic fields and are rarely absorbed by interstellar matter: their direction indicates that their cosmic origin might be from the farthest reaches of the Universe. High-energy neutrinos can be produced when ultra-relativistic cosmic-ray protons or nuclei interact with other matter or photons, and their observation could be a signature of these processes. Here we report an exceptionally high-energy event observed by KM3NeT, the deep-sea neutrino telescope in the Mediterranean Sea, which we associate with a cosmic neutrino detection. We detect a muon with an estimated energy of120+110−60 petaelectronvolts (PeV). In light of its enormous energy and near-horizontal direction, the muon most probably originated from the interaction of a neutrino of even higher energy in the vicinity of the detector. The cosmic neutrino energy spectrum measured up to now falls steeply with energy. However, the energy of this event is much larger than that of any neutrino detected so far. This suggests that the neutrino may have originated in a different cosmic accelerator than the lower-energy neutrinos, or this may be the first detection of a cosmogenic neutrino, resulting from the interactions of ultra-high-energy cosmic rays with background photons in the Universe. 2025-02-17T07:46:38Z 2025-02-17T07:46:38Z 2025-02-12 journal article The KM3NeT Collaboration. Observation of an ultra-high-energy cosmic neutrino with KM3NeT. Nature 638, 376–382 (2025). [https://doi.org/10.1038/s41586-024-08543-1] https://hdl.handle.net/10481/102374 10.1038/s41586-024-08543-1 eng http://creativecommons.org/licenses/by-nc-nd/4.0/ open access Attribution-NonCommercial-NoDerivatives 4.0 Internacional Springer Nature