A combined maximum-likelihood analysis of the high-energy astrophysical neutrino flux measured with IceCube

Authors
Aartsen, M.G.; Abraham, K.; Ackermann, M.; Adams, J.; Aguilar, J. A.; Golup, Geraldina Tamara; Wallraff, M.; Wandkowsky, N.; Weaver, Ch.; Wendt, C.; Westerhoff, S.; Whelan, B. J.; Whitehorn, N.; Wichary, C.; Wiebe, K.; Wiebusch, C.H.; Wille, L.; Williams, D.R.; Wissing, H.; Wolf, M.; Wood, T.R.; Woschnagg, K.; Xu, D.L.; Xu, X.W.; Xu, Y.; Yanez, J.P.; Yodh, G.; Yoshida, S.; Zarzhitsky, P.; Zoll, M.; The IceCube Collaboration
Publication Year
2015
Language
English
Format
article
Status
Published version
Description
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, νμ-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})\times {10}^{-18}\;{\mathrm{GeV}}^{-1}\;{{\rm{s}}}^{-1}\;{\mathrm{sr}}^{-1}\;{\mathrm{cm}}^{-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 νe 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%).
Fil: Aartsen, M.G.. University of Adelaide; Australia
Fil: Abraham, K.. Technische Universitat Munchen; Alemania
Fil: Ackermann, M.. Deutsches Elektronen Synchrotron; Alemania
Fil: Adams, J.. University Of Canterbury; Nueva Zelanda
Fil: Aguilar, J. A.. Université Libre de Bruxelles; Bélgica
Fil: Golup, Geraldina Tamara. Comisión Nacional de Energía Atómica. Gerencia del Area de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina
Fil: Wallraff, M.. Rwth Aachen University; Alemania
Fil: Wandkowsky, N.. University of Wisconsin; Estados Unidos
Fil: Weaver, Ch.. University of Wisconsin; Estados Unidos
Fil: Wendt, C.. University of Wisconsin; Estados Unidos
Fil: Westerhoff, S.. University of Wisconsin; Estados Unidos
Fil: Whelan, B. J.. University of Adelaide; Australia
Fil: Whitehorn, N.. University of Wisconsin; Estados Unidos
Fil: Wichary, C.. Rwth Aachen University; Alemania
Fil: Wiebe, K.. Johannes Gutenberg Universitat Mainz; Alemania
Fil: Wiebusch, C.H.. Rwth Aachen University; Alemania
Fil: Wille, L.. University of Wisconsin; Estados Unidos
Fil: Williams, D.R.. University of Alabama at Birmingahm; Estados Unidos
Fil: Wissing, H.. University of Maryland; Estados Unidos
Fil: Wolf, M.. Stockholms Universitet; Suecia
Fil: Wood, T.R.. Universidad de Ginebra; Suiza
Fil: Woschnagg, K.. University of California; Estados Unidos
Fil: Xu, D.L.. University of Alabama at Birmingahm; Estados Unidos
Fil: Xu, X.W.. Chiba University; Japón
Fil: Xu, Y.. Stony Brook University; Estados Unidos
Fil: Yanez, J.P.. Deutsches Elektronen Synchrotron; Alemania
Fil: Yodh, G.. South Dakota School of Mines and Technology; Estados Unidos
Fil: Yoshida, S.. Chiba University; Japón
Fil: Zarzhitsky, P.. University of Alabama at Birmingahm; Estados Unidos
Fil: Zoll, M.. Stockholms Universitet; Suecia
Fil: The IceCube Collaboration. No especifica;
Subject
Neutrinos
Astroparticle Physics
Methods: Data Analysis
Astronomía
Ciencias Físicas
CIENCIAS NATURALES Y EXACTAS
Access level
Open access
License
https://creativecommons.org/licenses/by-nc-sa/2.5/ar/
Repository
CONICET Digital (CONICET)
Institution
Consejo Nacional de Investigaciones Científicas y Técnicas
OAI Identifier
oai:ri.conicet.gov.ar:11336/62855