Search for Extremely High Energy Neutrinos with IceCube

TL;DR

This paper presents a new method for detecting extremely high energy neutrinos with IceCube, improving event selection and setting more stringent upper limits on neutrino fluxes over 12 years.

Contribution

It introduces an enhanced event selection technique that better rejects muon bundles, leading to improved sensitivity in EHE neutrino searches.

Findings

New event selection reduces background from muon bundles.

12-year data analysis sets tighter upper limits on EHE neutrino flux.

Method enhances IceCube's capability to probe cosmic ray interactions.

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.