On the flavor composition of the high-energy neutrino events in IceCube

Abstract

The IceCube experiment has recently reported the observation of 28 high-energy (> 30 TeV) neutrino events, separated into 21 showers and 7 muon tracks, consistent with an extraterrestrial origin. In this letter we compute the compatibility of such an observation with possible combinations of neutrino flavors with relative proportion (alpha_e:alpha_mu:alpha_tau). Although the 7:21 track-to-shower ratio is naively favored for the canonical (1:1:1) at Earth, this is not true once the atmospheric muon and neutrino backgrounds are properly accounted for. We find that, for an astrophysical neutrino E^(-2) energy spectrum, (1:1:1) at Earth is disfavored at 81% C.L. If this proportion does not change, 6 more years of data would be needed to exclude (1:1:1) at Earth at 3 sigma C.L. Indeed, with the recently-released 3-year data, that flavor composition is excluded at 92% C.L. The best-fit is obtained for (1:0:0) at Earth, which cannot be achieved from any flavor ratio at sources with averaged oscillations during propagation. If confirmed, this result would suggest either a misunderstanding of the expected background events, or a misidentification of tracks as showers, or even more compellingly, some exotic physics which deviates from the standard scenario.

5 pages, 2 figures. Minor corrections to match the published version in PRL

References in corpus (13)

• Global status of neutrino oscillation parameters after Neutrino-2012
• Global fit to three neutrino mixing: critical look at present precision
• Prompt neutrino fluxes from atmospheric charm
• Flavor Composition and Energy Spectrum of Astrophysical Neutrinos
• Neutrinos from WIMP Annihilations Obtained Using a Full Three-Flavor Monte Carlo Approach
• Neutrino Decays over Cosmological Distances and the Implications for Neutrino Telescopes
• Flavor Ratios of Astrophysical Neutrinos: Implications for Precision Measurements
• Energy dependent neutrino flavor ratios from cosmic accelerators on the Hillas plot
• An Analysis of Cosmic Neutrinos: Flavor Composition at Source and Neutrino Mixing Parameters
• High energy neutrino yields from astrophysical sources I: Weakly magnetized sources
• Oscillation effects on high-energy neutrino fluxes from astrophysical hidden sources
• Cosmic Neutrino Flavor Ratios with Broken ${\nu }_{\mu }-{\nu }_{\tau }$ Symmetry
• On the transport equations of cosmic neutrinos passing through Earth and secondary nu_mu fluxes

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