Measuring the Astrophysical $\bar{\nu}:\nu$ Ratio with IceCube

Abstract

Recent measurements of astrophysical neutrinos have expanded our understanding of their nature and origin. However, very little is still known about the astrophysical $\bar{\nu}:\nu$ ratio. The only prior measurement is the recent, single Glashow event seen by IceCube. Understanding the astrophysical $\bar{\nu}:\nu$ ratio has a bearing on multiple questions, including the astrophysical spectral shape and neutrino production mechanisms. This analysis uses a new approach to measuring the astrophysical muon $\bar{\nu}:\nu$ ratio at various energies. It uses inelasticity, the fraction of the initial neutrino energy carried away by the hadronic shower. Inelasticity probes the $\bar{\nu}:\nu$ ratio due to the fact that at energies below roughly 100 TeV, valence quarks dominate in deep inelastic scattering interactions, leading to different neutrino and antineutrino inelasticities and cross-sections. We use 10.3 years of IceCube data consisting of starting tracks at energies between 1 TeV and 1 PeV with a self-veto selection that enhances astrophysical event purity in the down-going direction. Based on this sample and analysis method, we present the first measurement of the astrophysical $\bar{\nu}:\nu$ ratio at sub-PeV energies.