Journal
ASTROPHYSICAL JOURNAL
Volume 809, Issue 1, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/809/1/98
Keywords
astroparticle physics; methods: data analysis; neutrinos
Categories
Funding
- U.S. National Science Foundation-Office of Polar Programs
- U.S. National Science Foundation-Physics Division
- University of Wisconsin Alumni Research Foundation
- Grid Laboratory Of Wisconsin (GLOW) at the University of Wisconsin-Madison
- Open Science Grid (OSG)
- U.S. Department of Energy
- National Energy Research Scientific Computing Center
- Louisiana Optical Network Initiative (LONI)
- Natural Sciences and Engineering Research Council of Canada
- WestGrid
- Compute/Calcul Canada
- Swedish Research Council, Sweden
- Swedish Polar Research Secretariat, Sweden
- Swedish National Infrastructure for Computing (SNIC), Sweden
- Knut and Alice Wallenberg Foundation, Sweden
- German Ministry for Education and Research (BMBF), Germany
- Deutsche Forschungsgemeinschaft (DFG), Germany
- Helmholtz Alliance for Astroparticle Physics (HAP), Germany
- Research Department of Plasmas with Complex Interactions (Bochum), Germany
- Fund for Scientific Research (FNRS-FWO)
- FWO Odysseus programme
- Flanders Institute to encourage scientific and technological research in industry (IWT)
- Belgian Federal Science Policy Office (Belspo)
- University of Oxford, United Kingdom
- Marsden Fund, New Zealand
- Australian Research Council
- Japan Society for Promotion of Science (JSPS)
- Swiss National Science Foundation (SNSF), Switzerland
- National Research Foundation of Korea (NRF)
- Danish National Research Foundation, Denmark (DNRF)
- Direct For Mathematical & Physical Scien [1307472] Funding Source: National Science Foundation
- Division Of Physics [1307472] Funding Source: National Science Foundation
- Division Of Physics
- Direct For Mathematical & Physical Scien [1403586] Funding Source: National Science Foundation
- Division Of Physics
- Direct For Mathematical & Physical Scien [1205796, 1205403, 1505296, 1505594] Funding Source: National Science Foundation
- STFC [ST/J000507/1, ST/L000474/1] Funding Source: UKRI
- Science and Technology Facilities Council [ST/J000507/1, ST/L000474/1] Funding Source: researchfish
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Evidence for an extraterrestrial flux of high-energy neutrinos has now been found in multiple searches with the IceCube detector. The first solid evidence was provided by a search for neutrino events with deposited energies greater than or similar to 30 TeV and interaction vertices inside the instrumented volume. Recent analyses suggest that the extraterrestrial flux extends to lower energies and is also visible with throughgoing, nu(mu)-induced tracks from the Northern Hemisphere. Here, we combine the results from six different IceCube searches for astrophysical neutrinos in a maximum-likelihood analysis. The combined event sample features high-statistics samples of shower-like and track-like events. The data are fit in up to three observables: energy, zenith angle, and event topology. Assuming the astrophysical neutrino flux to be isotropic and to consist of equal flavors at Earth, the all-flavor spectrum with neutrino energies between 25 TeV and 2.8 PeV is well described by an unbroken power law with best-fit spectral index -2.50 +/- 0.09 and a flux at 100 TeV of (6.7(-1.2)(+1.1)) x 10(-18) GeV-1 s(-1) sr(-1) cm(-2). Under the same assumptions, an unbroken power law with index -2 is disfavored with a significance of 3.8 sigma (p = 0.0066%) with respect to the best fit. This significance is reduced to 2.1 sigma (p = 1.7%) if instead we compare the best fit to a spectrum with index -2 that has an exponential cut-off at high energies. Allowing the electron-neutrino flux to deviate from the other two flavors, we find a nu(e) fraction of 0.18 +/- 0.11 at Earth. The sole production of electron neutrinos, which would be characteristic of neutron-decay-dominated sources, is rejected with a significance of 3.6 sigma ( p = 0.014%).
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