Design of a Cosmic-Ray Muon-Tagged Water-Cherenkov Calibration Facility for IceCube Optical Modules

Abstract

The IceCube Neutrino Observatory detects astrophysical neutrinos with 5,160 optical modules frozen into South Pole ice. The recently deployed IceCube Upgrade and the planned IceCube-Gen2 extension introduce modules with richer angular acceptance and more complex timing response than the original Digital Optical Module (DOM), yet once frozen into a borehole, a module becomes permanently inaccessible. Thorough pre-deployment characterization is therefore essential. This thesis presents the design of a laboratory-scale calibration facility that uses naturally occurring cosmic-ray muons as a tagged Cherenkov source. An external three-layer scintillator telescope, composed of 3 x 3 arrays of 200 mm EJ-200 tiles with dual-ended silicon-photomultiplier (SiPM) readout, reconstructs the trajectory of each downgoing muon above a black-polypropylene water tank (approximately 2 m diameter, 0.9 m height) containing the module under test. A custom Geant4-based simulation framework, TankSim, incorporating the Cosmic-ray Shower Library (CRY) and ROOT-based analysis, guided the optimization through a 180-configuration parameter scan and high-statistics confirmation runs of 200,000 events. The key finding is that calibration accuracy is governed primarily by timing fidelity rather than by raw spatial granularity: a dedicated jitter sweep shows that reconstruction degrades rapidly above approximately 200 ps RMS of added electronics jitter, setting a concrete timing budget for the readout chain. The practical baseline achieves 145.5 mm bottom-of-tank position uncertainty (p68) and 4.56 degree angular resolution with 54 SiPM channels. A three-board readout architecture (SiPM carrier, tile controller with fast discriminators, and FPGA-based layer controller) was developed to preserve this timing information from scintillator to digital timestamp.