So far, the flavor composition of high-energy astrophysical neutrinos, i.e., the proportion of electron, muon, and tau neutrinos in their total diffuse flux, has been measured by IceCube only as averaged over the range of observed neutrino energies, between roughly 10 TeV and a few PeV. 

This is in spite of the flavor composition likely having a dependence on the neutrino energy, since different neutrino production mechanisms could become accessible at different energies. And, in addition, a myriad of proposed new-physics models could modify the flavor composition in an energy-dependent manner.

Yet, so far, the intrinsic challenge of measuring flavor, combined with the limited number of detected neutrinos, made it unfeasible to measure only the energy-averaged flavor composition, thus washing out our sensitivity to the above energy-dependent effects.

In a new paper led by postdocs Qinrui Liu and Damiano Fiorillo we measure for the first time the energy dependence of the flavor composition using present-day IceCube data—7.5 years of HESE events—and make projections for measurements that use the combined detection of HESE plus through-going muons by multiple planned neutrino telescopes: Baikal-GVD, IceCube-Gen2, KM3NeT, P-ONE, TAMBO, and TRIDENT.

We find no significant evidence for a transition in the flavor composition from low to high energies, but show that in the near future the combined capabilities of the above neutrino telescopes will likely make it possible to detect such a transition, especially if it occurs around 200 TeV. 

While the measurement will remain challenging, we expect ongoing and future improvements in event reconstruction and flavor identification to boost our projections beyond what we have shown.

Read more at:

Identifying Energy-Dependent Flavor Transitions in High-Energy Astrophysical Neutrino Measurements
Qinrui Liu, Damiano F. G. Fiorillo, Carlos A. Argüelles, Mauricio Bustamante, Ningqiang Song, Aaron C. Vincent
2312.07549 astro-ph