Characteristics of Cherenkov Radiation in Naturally Occuring Ice

TL;DR

This paper revisits the theory of Cherenkov radiation in ice, analyzing how ice crystal anisotropy affects radiation yield and angle, with implications for neutrino detection experiments like IceCube.

Contribution

It provides a consistent, error-free theoretical framework for Cherenkov radiation in uniaxial crystals, specifically applied to ice in neutrino telescopes, and assesses the impact of crystal anisotropy.

Findings

Anisotropy causes at most about 1% variation in Cherenkov yield and angle.

The effect is negligible for current detectors but relevant for future high-precision instruments.

Proposes an experiment to test the formalism and discusses anisotropy effects in lead tungstate crystals.

Abstract

We revisit the theory of Cherenkov radiation in uniaxial crystals. Historically, a number of flawed attempts have been made at explaining this radiation phenomenon and a consistent error-free description is nowhere available. We apply our calculation to a large modern day telescope - IceCube. Being located at the Antarctica, this detector makes use of the naturally occuring ice as a medium to generate Cherenkov radiation. However, due to the high pressure at the depth of the detector site, large volumes of hexagonal ice crystals are formed. We calculate how this affects the Cherenkov radiation yield and angular dependence. We conclude that the effect is small, at most about a percent, and would only be relevant in future high precision instruments like e.g. Precision IceCube Next Generation Upgrade (PINGU). For radio-Cherenkov experiments which use the presence of a clear Cherenkov cone to determine the arrival direction, any variation in emission angle will directly and linearly translate into a change in apparent neutrino direction. In closing, we also describe a simple experiment to test this formalism, and calculate the impact of anisotropy on light-yields from lead tungstate crystals as used, for example, in the CMS calorimeter at the CERN LHC.