Extending the reach of liquid argon time projection chambers to new fundamental physics

The goal of the Deep Underground Neutrino Experiment (DUNE) is to resolve open questions, such as the mass ordering and the Charge Parity (CP) violation in neutrino physics. The chosen technology for the measurement of the high energy beam neutrinos is based on large scale Liquid Argon Time Projection Chambers (LArTPCs). This thesis presents the development, construction, and quality assurance of the light readout system for the Full Scale Demonstrator (FSD), a demonstrator for the Liquid Argon Near Detector (ND-LAr) that is based on a novel, fully modular LArTPC concept. A detailed performance study at room temperature of the light collection detectors, the ArgonCube Light (ArCLight), based on a light trap concept, is provided. The current, fully cryogenically qualified design uses dichroic mirrors at the edges and achieves a performance improvement of 1.6±0.1 compared to an ArCLight without an edge mirror foil. Further performance improvements are observed for alternative mirror configurations. However, this mirror version is not validated for cryogenic operation. Novel wavelength-shifting materials are investigated for further development of the light trap concept. It is shown that some of these candidate materials demonstrate promising behaviour, although further development and understanding are required to reach the performance and stability demands of next generation detectors. The thesis further introduces SoLAr, a novel LArTPC concept, and reports the first experimental results of its prototypes. The novel concept simultaneously collects charge and light on a pixelated anode plane. The operation of floating Silicon Photomultipliers (SiPMs) was validated without any observable performance degradation. In the larger SoLAr prototype-v2, the reconstruction of extended tracks was demonstrated. A dedicated light calibration system for ND-LAr was developed as part of this work, enabling the characterisation of every SiPM in the FSD. The system design, implementation, and long term stability studies are presented. Stable operation of the Light Readout System (LRS) for the FSD is demonstrated. The thesis documents the construction of the FSD, the FSD light system, the light detector commissioning, and the measurement of the photon detection efficiency (PDE) across the assembled module. A PDE of 0.085 %±0.023 % for the ArCLights and 0.495 %±0.168 % for the Light Collection Modules (LCMs), fibre based light collection modules of the FSD, is evaluated. Finally, a double-pulse timing study performed on real data demonstrates a timing resolution better than 150 ns, confirming the capability of the system to support precision event reconstruction. Overall, this work delivers technological developments and demonstrator-scale validation studies that directly support the readiness of the ND-LAr detector and demonstrate possible pathways for future LArTPCs with enhanced sensitivity to low-energy interactions, extending the reach for new fundamental physics. Overall, this work delivers technological developments and demonstrator-scale validation studies that directly support the readiness of the ND-LAr detector and demonstrate possible pathways for future LArTPCs with enhanced sensitivity to low-energy interactions, extending the reach for new fundamental physics.