The Flavour Composition of the High-Energy IceCube Neutrinos

TL;DR

This paper analyzes high-energy neutrino data from IceCube, revealing potential deviations from expected flavor ratios and discussing implications for astrophysical sources and neutrino physics.

Contribution

It provides a detailed flavor and spectral analysis of IceCube neutrinos, highlighting deviations from the expected 1:1:1 flavor ratio and exploring possible explanations.

Findings

Deficit of muon neutrinos (tracks) observed.

Absence of high-energy electron antineutrinos near Glashow resonance.

Energy-dependent analysis impacts flavor ratio conclusions.

Abstract

We present an in-depth analysis of the flavour and spectral composition of the 36 high-energy neutrino events observed after three years of observation by the IceCube neutrino telescope. While known astrophysical sources of HE neutrinos are expected to produce a nearly $(1:1:1)$ flavour ratio (electron : muon : tau) of neutrinos at earth, we show that the best fits based on the events detected above $E_\nu \ge 28$ TeV do not necessarily support this hypothesis. Crucially, the energy range that is considered when analysing the HE neutrino data can have a profound impact on the conclusions. We highlight two intriguing puzzles: an apparent deficit of muon neutrinos, seen via a deficit of track-like events; and an absence of $\bar \nu_e$'s at high energy, seen as an absence of events near the Glashow resonance. We discuss possible explanations, including the misidentification of tracks as showers, and a broken power law, in analogy to the observed HE cosmic ray spectrum.