From photoelectrons to bytes: development and integration of photosensors and data acquisition for the DarkSide-20k experiment

The search for Dark Matter (DM) remains one of the most compelling challenges in contemporary physics. The DarkSide-20k experiment, a dual-phase liquid argon Time Projection Chamber (TPC) under construction at the Laboratori Nazionali del Gran Sasso (LNGS), aims to directly detect Weakly Interacting Massive Particles (WIMPs) with unprecedented sensitivity. This thesis presents the development, integration, and characterisation of the photodetector and the data acquisition system that form the backbone of DarkSide-20k. The first part of the work focuses on the design, production, and characterisation of cryogenic Silicon Photo-Multipliers (SiPMs), integrated into objects called \textit{Tiles}. A large-scale quality assurance and control program was established to certify thousands of photodetector Tiles, ensuring uniform performance in terms of optical properties and noise characteristics. The implementation of automated testing procedures, a centralised production database, and real-time monitoring tools enabled consistent tracking and validation across multiple assembly sites. The second part of the thesis describes the architecture and implementation of the DarkSide-20k Data Acquisition (DAQ) system. A triggerless acquisition, segmented into fixed-length time slices, is envisaged to manage the high data throughput of the detector, combining waveform digitisation, real-time data processing, and online data reduction. Extensive simulation studies and prototype validation through the \textit{Quadrant} DAQ prototype were conducted to assess system performance, understand busy logic, and ensure scalability to the full detector. The final part of the thesis presents results from \textsc{Proto-0}, the first operational prototype of the DarkSide-20k TPC. The prototype provided a crucial testbed for the DarkSide-20k photosensors and DAQ system, enabling a thorough detector characterisation, studies of scintillation (S1) and electroluminescence (S2) signals, and validation of the triggerless data acquisition system envisaged for DarkSide-20k. A dedicated reconstruction framework was developed for \textsc{Proto-0}, providing a valuable platform for testing and benchmarking event reconstruction algorithms. Together, these developments demonstrate the readiness of the DarkSide-20k technologies and methodologies, marking essential milestones toward the next generation of liquid argon Dark Matter detectors. The results reported herein contribute directly to the realisation of a multi-ton experiment capable of probing WIMP-nucleon cross sections below $10^{-48}\,\mathrm{cm^2}$, advancing the frontier of direct Dark Matter searches.