Characterization of the PeV astrophysical neutrino energy spectrum with IceCube using down-going tracks

TL;DR

This paper presents a new method for detecting PeV astrophysical neutrinos using down-going tracks in IceCube, filling the energy gap between 1 and 10 PeV, and aims to better characterize the neutrino spectrum.

Contribution

The study introduces a novel event selection technique combining stochasticity and surface veto to improve sensitivity to PeV neutrinos in IceCube data.

Findings

Enhanced detection of PeV neutrinos in the 1-10 PeV range.

Improved signal-to-background ratio through combined techniques.

Contribution to understanding the neutrino energy spectrum and potential spectral cut-offs.

Abstract

The IceCube Neutrino Observatory has observed a diffuse flux of astrophysical neutrinos with energies from TeV to a few PeV. Recent IceCube analyses have limited sensitivity to PeV neutrinos because upward-going neutrino fluxes are attenuated by the Earth while the Extremely High Energy (EHE) result targets cosmogenic neutrinos only above 10 PeV. In this work, we present a new event selection that fills the gap between 1 PeV and 10 PeV. This sample is obtained by selecting high-energy down-going through-going tracks from 8 years of data. To reduce the atmospheric muon backgrounds and achieve a high signal-to-background ratio, we combine two techniques. The first technique selects events with high stochasticity because single muons created by neutrinos lose energy more stochastically than atmospheric muon bundles whose energy losses are smoothened due to large muon multiplicities. The second technique uses the IceTop surface array as a veto of atmospheric background events. To characterize the astrophysical neutrino flux and test the existence of a cut-off in the neutrino energy spectrum at a few PeV, a global fit will be performed by combining this sample with results from the 7-year High Energy Starting Events (HESE) analysis.