article · Physical Review X
In February 2023, the KM3NeT/ARCA telescope recorded an ultrahigh-energy neutrino candidate with an estimated energy in the hundreds of PeV. This detection presents an interesting context when compared to the absence of similar detections above tens of PeV by the IceCube and Pierre Auger observatories. A joint analysis across all three experimental setups, assuming an isotropic energy spectrum, establishes a best-fit single-flavour neutrino flux normalisation for the energy range of the observed event. Combining these ultrahigh-energy data with lower-energy IceCube observations indicates only a slight preference for an energy spectrum break in the PeV regime for one out of three data samples analysed, with no preference in the remaining two. Overall, the statistical tension between the KM3NeT candidate and the non-detections in other experiments remains mild to moderate, indicating that larger datasets will be essential to fully understand ultrahigh-energy cosmic neutrinos.
Neutrinos are fundamental particles that travel across the universe without being deflected, offering direct insights into extreme cosmic phenomena. Reconciling a rare, extremely high-energy detection with null results from other global observatories helps astrophysicists refine models of cosmic particle acceleration. Clarifying whether current theoretical frameworks hold or whether new physics must be introduced depends on resolving these subtle observational differences.
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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 <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:msup><a:mi>E</a:mi><a:mrow><a:mo>−</a:mo><a:mn>2</a:mn></a:mrow></a:msup></a:math> flux, the best-fit single-flavor flux normalization is <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mrow><c:msup><c:mrow><c:mi>E</c:mi></c:mrow><c:mrow><c:mn>2</c:mn></c:mrow></c:msup><c:msubsup><c:mrow><c:mi mathvariant="normal">Φ</c:mi></c:mrow><c:mrow><c:mi>ν</c:mi><c:mo>+</c:mo><c:mover accent="true"><c:mrow><c:mi>ν</c:mi></c:mrow><c:mrow><c:mo stretchy="false">¯</c:mo></c:mrow></c:mover></c:mrow><c:mrow><c:mn>1</c:mn><c:mi mathvariant="normal">f</c:mi></c:mrow></c:msubsup><c:mo>=</c:mo><c:mn>7.5</c:mn><c:mo>×</c:mo><c:msup><c:mrow><c:mn>10</c:mn></c:mrow><c:mrow><c:mo>−</c:mo><c:mn>10</c:mn></c:mrow></c:msup><c:mtext> </c:mtext><c:mtext> </c:mtext><c:mi>GeV</c:mi><c:mtext> </c:mtext><c:msup><c:mrow><c:mi>cm</c:mi></c:mrow><c:mrow><c:mo>−</c:mo><c:mn>2</c:mn></c:mrow></c:msup><c:mtext> </c:mtext><c:msup><c:mrow><c:mi mathvariant="normal">s</c:mi></c:mrow><c:mrow><c:mo>−</c:mo><c:mn>1</c:mn></c:mrow></c:msup><c:mtext> </c:mtext><c:msup><c:mrow><c:mi>sr</c:mi></c:mrow><c:mrow><c:mo>−</c:mo><c:mn>1</c:mn></c:mrow></c:msup></c:mrow></c:math> 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 (<j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline"><j:mrow><j:mn>1.6</j:mn><j:mi>σ</j:mi><j:mi>–</j:mi><j:mn>2.9</j:mn><j:mi>σ</j:mi></j:mrow></j:math>), and increased statistics are required to resolve this apparent tension and better characterize the neutrino landscape at ultrahigh energies.
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DOI: 10.1103/yypk-zmb8
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