Improved measurements of the TeV-PeV extragalactic neutrino spectrum from joint analyses of IceCube tracks and cascades

TL;DR

This paper presents joint analyses of over 10 years of IceCube data revealing a broken power-law spectrum of astrophysical neutrinos, including the highest energy neutrino observed, with significant implications for their production mechanisms.

Contribution

It introduces two new analyses that strongly favor a broken power-law spectrum over a single power-law, providing refined spectral constraints and robust validation.

Findings

Rejects single power-law spectrum with >4σ significance

Detects highest energy neutrino at 11.4 PeV

Provides insights into neutrino production processes

Abstract

The IceCube South Pole Neutrino Observatory has discovered the presence of a diffuse astrophysical neutrino flux at energies of TeV and beyond using neutrino induced muon tracks and cascade events from neutrino interactions. We present two analyses sensitive to neutrino events in the energy range \SI{1}{TeV} to \SI{10}{PeV}, using more than 10 years of IceCube data. Both analyses consistently reject a neutrino spectrum following a single power-law with significance $>4\,\sigma$ in favor of a broken power law. We describe the methods implemented in the two analyses, the spectral constraints obtained, and the validation of the robustness of the results. Additionally, we report the detection of a muon neutrino in the MESE sample with an energy of $11.4^{+2.46}_{-2.53} $\,\si{PeV}, the highest energy neutrino observed by IceCube to date. The results presented here show insights into the spectral shape of astrophysical neutrinos, which has important implications for inferring their production processes in a multi-messenger picture.