The IceCube high-energy starting event sample: Description and flux characterization with 7.5 years of data

TL;DR

This paper updates the analysis of IceCube's high-energy starting events with 7.5 years of data, providing refined flux measurements and source searches, confirming an astrophysical neutrino spectrum consistent with an unbroken power law.

Contribution

It presents a detailed description of the HESE sample, improved flux measurements, and a comprehensive source search using extended data and updated models.

Findings

Astrophysical neutrino flux is compatible with an unbroken power law.

Preferred spectral index is approximately 2.87.

Results are consistent with isotropic flux models.

Abstract

The IceCube Neutrino Observatory has established the existence of a high-energy all-sky neutrino flux of astrophysical origin. This discovery was made using events interacting within a fiducial region of the detector surrounded by an active veto and with reconstructed energy above 60 TeV, commonly known as the high-energy starting event sample, or HESE. We revisit the analysis of the HESE sample with an additional 4.5 years of data, newer glacial ice models, and improved systematics treatment. This paper describes the sample in detail, reports on the latest astrophysical neutrino flux measurements, and presents a source search for astrophysical neutrinos. We give the compatibility of these observations with specific isotropic flux models proposed in the literature as well as generic power-law-like scenarios. Assuming $\nu_e:\nu_\mu:\nu_\tau=1:1:1$, and an equal flux of neutrinos and antineutrinos, we find that the astrophysical neutrino spectrum is compatible with an unbroken power law, with a preferred spectral index of ${2.87}^{+0.20}_{-0.19}$ for the $68.3\%$ confidence interval.