Advances in IceCube ice modelling and what to expect from the Upgrade

TL;DR

This paper discusses recent advances in modelling the optical properties of ice in the IceCube Neutrino Observatory, focusing on birefringence effects and the expected improvements from the upcoming IceCube Upgrade.

Contribution

It introduces a new parametrization of birefringence effects in ice and discusses how calibration tools in the IceCube Upgrade can enhance ice modelling accuracy.

Findings

Birefringence causes anisotropic light attenuation aligned with ice flow.

Photon trajectories are curved due to asymmetric light diffusion in birefringent ice.

Calibration instrumentation can significantly improve ice optical property models.

Abstract

The IceCube Neutrino Observatory instruments about 1 km$^3$ of deep, glacial ice at the geographic South Pole using 5160 photomultipliers to detect Cherenkov light from relativistic, charged particles. Most IceCube science goals rely on precise understanding and modelling of the optical properties of the instrumented ice. A peculiar light propagation effect observed by IceCube is an anisotropic attenuation, which is aligned with the local flow of the ice. Recent efforts have shown this effect is most likely due to curved photon trajectories resulting from the asymmetric light diffusion in the birefringent polycrystalline microstructure of the ice. This new model can be optimized by adjusting the average orientation, size and shape of the ice crystals. We present the parametrization of the birefringence effect in our photon propagation simulation, the fitting procedures and results. The anticipated potential of calibration instrumentation in the upcoming IceCube Upgrade to improve on known shortcomings of the current ice modelling is also discussed.