Probing the PeV region in the astrophysical neutrino spectrum using <math display="inline"><msub><mi>ν</mi><mi>μ</mi></msub></math> from the Southern sky

de Wasseige, Gwenhaël;Genton, Eliot;Kruiswijk, Karlijn;Lamoureux, Mathieu;IceCube;et.al.
(2025) Physical review D — Vol. 112 (2025)

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Abstract
IceCube has observed a diffuse astrophysical neutrino flux over the energy region from a few TeV to a few PeV. At PeV energies, the spectral shape is not yet well measured due to the low statistics of the data. This analysis probes the gap between 1 and 10 PeV by using high-energy downgoing muon neutrinos. To reject the large atmospheric muon background, two complementary techniques are combined. The first technique selects events with high stochasticity to reject atmospheric muon bundles whose stochastic energy losses are smoothed due to high muon multiplicity. The second technique vetoes atmospheric muons with the IceTop surface array. Using 9 yrs of data, we found two neutrino candidate events in the signal region, consistent with expectation from background, each with relatively high signal probabilities. A joint maximum likelihood estimation is performed using this sample and an independent 9.5-yr sample of tracks to measure the neutrino spectrum. A likelihood ratio test is done to compare the single power-law (SPL) vs <math display="inline"><mrow><mi>SPL</mi><mo>+</mo><mi>cutoff</mi></mrow></math> hypothesis; the <math display="inline"><mrow><mi>SPL</mi><mo>+</mo><mi>cutoff</mi></mrow></math> model is not significantly better than the SPL. High-energy astrophysical objects from four source catalogs are also checked around the direction of the two events. No significant coincidence was found.
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de Wasseige, G., Genton, E., Kruiswijk, K., Lamoureux, M., Lazar, J., Raab, C., Myhr, P., Vereecken, M., IceCube, & et al. (2025). Probing the PeV region in the astrophysical neutrino spectrum using <math display=“inline”><msub><mi>ν</mi><mi>μ</mi></msub></math> from the Southern sky. Physical review D, 112. https://doi.org/10.1103/2hnq-1fsx (Original work published 2025)