A combined maximum-likelihood analysis of the high-energy astrophysical neutrino flux measured with IceCube
- Department of Physics, University of Adelaide, Adelaide, 5005 (Australia)
- Technische Universität München, D-85748 Garching (Germany)
- DESY, D-15735 Zeuthen (Germany)
- Dept. of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch (New Zealand)
- Université Libre de Bruxelles, Science Faculty CP230, B-1050 Brussels (Belgium)
- Dept. of Physics and Wisconsin IceCube Particle Astrophysics Center, University of Wisconsin, Madison, WI 53706 (United States)
- Oskar Klein Centre and Dept. of Physics, Stockholm University, SE-10691 Stockholm (Sweden)
- Erlangen Centre for Astroparticle Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg, D-91058 Erlangen (Germany)
- Dept. of Physics, Pennsylvania State University, University Park, PA 16802 (United States)
- Institute of Physics, University of Mainz, Staudinger Weg 7, D-55099 Mainz (Germany)
- III. Physikalisches Institut, RWTH Aachen University, D-52056 Aachen (Germany)
- Physics Department, South Dakota School of Mines and Technology, Rapid City, SD 57701 (United States)
- Dept. of Physics and Astronomy, University of California, Irvine, CA 92697 (United States)
- Dept. of Physics, University of California, Berkeley, CA 94720 (United States)
- Dept. of Physics and Center for Cosmology and Astro-Particle Physics, Ohio State University, Columbus, OH 43210 (United States)
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 ≳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, ν{sub μ}-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{sub −1.2}{sup +1.1})×10{sup −18} GeV{sup −1} s{sup −1} sr{sup −1} cm{sup −2}. Under the same assumptions, an unbroken power law with index −2 is disfavored with a significance of 3.8σ (p = 0.0066%) with respect to the best fit. This significance is reduced to 2.1σ (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 ν{sub 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 3.6σ (p = 0.014%).
- OSTI ID:
- 22882774
- Journal Information:
- Astrophysical Journal, Vol. 809, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Since 2009, the country of publication for this journal is the UK.; ISSN 0004-637X
- Country of Publication:
- United Kingdom
- Language:
- English
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