Updated directions of IceCube HESE events with the latest ice model using DirectFit

TL;DR

This paper applies the latest ice modeling improvements to reconstruct IceCube HESE events using DirectFit, resulting in more accurate event descriptions and updated source search results, enhancing the understanding of astrophysical neutrinos.

Contribution

It introduces an exact application of the latest ice model in event reconstruction, improving accuracy and updating previous analyses of IceCube HESE data.

Findings

Enhanced directional reconstruction of neutrino events.

More precise event parameter estimations.

Updated astrophysical neutrino source constraints.

Abstract

The initial evidence of astrophysical neutrinos by the IceCube Neutrino Observatory stemmed from the high-energy starting events (HESE) sample: a selection of the highest-energy neutrino interactions that occurred within the detector fiducial volume. Each event was reconstructed based on our best knowledge of the ice at the time, with the latest results published in a description of the sample using 7.5 years of data. Since then, several major improvements in ice modeling have occurred using in-situ calibration data. These include a microscopic description of ice anisotropy arising from ice crystal birefringence and a more complete mapping of the ice layer undulations across the detector. The improvements feed into more accurate descriptions of individual events, and can especially affect the directional reconstruction of particle showers. Here, we apply the latest ice model in an exact manner to reconstruct IceCube's high-energy events using DirectFit. This reconstruction samples posterior distributions across parameters of interest by performing full event resimulation and photon propagation at each step. We obtain improved per-event descriptions, as well as updates on previously published source searches using the aggregated sample.