Characterization of the Three-Flavor Composition of Cosmic Neutrinos with IceCube

TL;DR

This study analyzes 11.4 years of IceCube data to measure the flavor composition of cosmic neutrinos across a broad energy range, confirming consistency with standard oscillation models and constraining source production mechanisms.

Contribution

First measurement of cosmic neutrino flavor composition at TeV energies using flavor-dependent event morphologies, providing new insights into neutrino oscillations and sources.

Findings

Best-fit flavor ratio is 0.30:0.37:0.33, consistent with standard oscillations.

All flavor fractions are >0 at 90% confidence, assuming a broken power law.

Neutron decay as a source is outside the 99% confidence interval.

Abstract

Neutrinos oscillate over cosmic distances. Using 11.4 years of IceCube data, the flavor composition of the all-sky neutrino flux from 5\,TeV--10\,PeV is studied. We report the first measurement down to the $\mathcal{O}$(TeV) scale using events classified into three flavor-dependent morphologies. The best fit flavor ratio is $f_e:f_{\mu}:f_{\tau}\,=\,0.30:0.37:0.33$, consistent with the standard three-flavor neutrino oscillation model. Each fraction is constrained to be $>0$ at $>$ 90\% confidence level, assuming a broken power law for cosmic neutrinos. We infer the flavor composition of cosmic neutrinos at their sources, and find production via neutron decay lies outside the 99\% confidence interval.