Search for Extremely High Energy Neutrinos with IceCube

Abstract

Extremely high energy (EHE) neutrinos (with energies above $10^7$ GeV) are produced in interactions of the highest energy cosmic rays. A primary contribution to the EHE neutrino flux is expected from so-called cosmogenic neutrinos produced when ultra high energy cosmic rays interact with ambient photon backgrounds. Observations of these EHE neutrinos with IceCube can probe the nature of cosmic rays beyond the energies for resonant photo-pion production (GZK cutoff). We present a new event selection of extremely high energy neutrinos by more effectively identifying and rejecting high multiplicity muon bundles with respect to previous analyses. Furthermore, we show the expected improvements of the quasi-differential upper limits on the EHE neutrino flux using 12 years of IceCube data.