Analysis of the 4-year IceCube high-energy starting events

TL;DR

This paper analyzes four years of IceCube high-energy neutrino data, constraining the astrophysical neutrino flux's spectrum, flavor composition, and isotropy, and exploring potential asymmetries between hemispheres.

Contribution

It provides updated constraints on the neutrino flux spectrum, flavor composition, and isotropy using a larger dataset and compares single versus two-component flux models.

Findings

Results are consistent with previous IceCube findings but suggest a slightly softer spectrum.

Current data do not detect neutrino-antineutrino asymmetry.

No conclusive evidence for North-South asymmetry from HESE data alone.

Abstract

After four years of data taking, the IceCube neutrino telescope has detected 54 high-energy starting events (HESE, or contained-vertex events) with deposited energies above 20TeV. They represent the first ever detection of high-energy extraterrestrial neutrinos and therefore, the first step in neutrino astronomy. In order to study the energy, flavor and isotropy of the astrophysical neutrino flux arriving at Earth, we perform different analyses of two different deposited energy intervals, [10 TeV $-$ 10 PeV] and [60 TeV $-$ 10 PeV]. We first consider an isotropic unbroken power-law spectrum and constrain its shape, normalization and flavor composition. Our results are in agreement with the preliminary IceCube results, although we obtain a slightly softer spectrum. We also find that current data are not sensitive to a possible neutrino-antineutrino asymmetry in the astrophysical flux. Then, we show that although a two-component power-law model leads to a slightly better fit, it does not represent a significant improvement with respect to a single power-law flux. Finally, we analyze the possible existence of a North-South asymmetry, hinted at by the combination of the HESE sample with the through-going muon data. If only using HESE data, the scarce statistics from the northern hemisphere does not allow us to reach any conclusive answer, which indicates that the HESE sample alone is not driving the potential North-South asymmetry.