The spectrum and flavor composition of the astrophysical neutrinos in IceCube

TL;DR

This paper analyzes IceCube astrophysical neutrino data, fitting energy spectra with models that include flavor composition and spectral index, finding a best-fit spectral index around 2.7-2.8, and concluding the standard flavor ratio is consistent with observations.

Contribution

It introduces a detailed spectral and flavor composition model for IceCube neutrino data, comparing different normalization schemes and spectral indices.

Findings

Best-fit spectral index is approximately 2.7-2.8.

Standard 1:1:1 flavor ratio is consistent with data.

Flavor and normalization models show similar fit quality.

Abstract

We fit the energy distribution of the IceCube starting events by a model which involves four parameters in the neutrino spectrum, namely three normalizations $n_e,n_\mu,n_\tau$ and a common power-law index $\gamma$, with a fixed background simulated by IceCube. It is found that the best fit index is $\gamma = 2.7$ with $\chi^2_{\rm min} = 32.3/24\,{\rm dof}$. As for the two parameter model involving a democratic normalization and an index, the best fit is at $\gamma = 2.8$ with $\chi^2_{\rm min} = 33.9/26\,{\rm dof}$. The flavored model and the democratic model do not have much difference in the quality of the (energy-spectrum) fit. The standard $1:1:1$ composition is not disfavored by the current data.