Measurement of the Cosmic Neutrino Flux from the Southern Sky using 10 years of IceCube Starting Track Events

TL;DR

This paper reports the first measurement of the astrophysical diffuse neutrino flux from the southern sky using 10 years of IceCube starting track events, extending the energy reach to lower energies and analyzing potential galactic plane sources.

Contribution

It introduces a new analysis of starting track events in IceCube to measure the diffuse astrophysical neutrino flux, including the first southern sky measurement and galactic plane search.

Findings

Measured astrophysical flux: 1.68^{+0.19}_{-0.22} at 100 TeV

Spectral index: 2.58^{+0.10}_{-0.09}

No significant galactic plane neutrino emission detected

Abstract

The measurement of a diffuse astrophysical neutrino flux using starting track events marks the first time IceCube has observed and subsequently measured the astrophysical diffuse flux using a dataset composed primarily of starting track events. Starting tracks combine an excellent angular and energy resolution. This enables us to take advantage of the self-veto effect in the southern sky reducing the atmospheric neutrino rate allowing us to detect astrophysical neutrinos to energies well below 100 TeV. We measure the astrophysical flux as $\phi^{per-flavor}_{Astro}=1.68^{+0.19}_{-0.22}$(at 100 TeV) and $\gamma_{Astro} = 2.58^{+0.10}_{-0.09}$ assuming a single power law flux. The astrophysical flux 90% sensitive energy range is 3 TeV to 500 TeV, extending IceCube's reach to the low energy astrophysical flux by an order of magnitude. A brief summary of tests performed to search for neutrinos from the galactic plane using this dataset is also provided. With this sample, we did not find statistically significant evidence for emission from the galactic plane. We then tested the impact of these galactic plane neutrinos on the isotropic diffuse flux, with at most 10% effect on the overall normalization and negligible impact to the spectral index.