Development and performance evaluation of the wavelength-shifting optical module for the IceCube upgrade

Abstract

The IceCube Neutrino Observatory excels at detecting high-energy neutrinos via Cherenkov light in glacial ice. At lower energies, however, the high dark noise of the optical sensors dominates the signal, severely limiting sensitivity to astrophysical events such as supernovae. The Wavelength-shifting Optical Module (WOM) provides an elegant solution by improving detection efficiency and extending sensitivity into the ultraviolet (UV) range, which is largely inaccessible to standard IceCube optical modules. The WOM features a cylindrical wavelength-shifting tube that absorbs UV-photons and re-emits them at longer wavelengths, which are then guided via total internal reflection to photomultiplier tubes (PMTs) located at both ends. This design enhances UV sensitivity and reduces noise by decoupling the photosensitive area from the PMTs. These features are particularly beneficial for the upcoming IceCube Upgrade, the next development to IceCube, with a denser instrumentation optimized to lower the energy threshold of detected neutrinos.

This thesis presents the complete development cycle of the WOM, from simulation-based design and material selection to laboratory characterization and in-situ integration studies. A comprehensive performance evaluation is included, covering PMT quantum efficiency, time resolution, angular response, and effective area. In addition, an optimized production process and extensive optical and environmental testing demonstrate the WOM’s suitability for deployment in the IceCube Upgrade. While its performance varies across different Upgrade use cases, it shows strong potential for broader applications, particularly in low-background or UV-sensitive detection environments.