Production and characterization of veto Photon-Detection Units for the DarkSide-20k experiment

Abstract The DarkSide-20k (DS-20k) experiment, currently under construction at the Gran Sasso National Laboratory (LNGS), represents a significant advancement in the field of direct Dark Matter (DM) detection. Utilizing a dual-phase Liquid Argon Time Projection Chamber (LArTPC) DS-20k is designed to extend the sensitivity limits in the search for Weakly Interacting Massive Particles (WIMPs), a leading DM candidate. A crucial component of the experiment is the active veto system, which acts as a shield against external and instrumental background sources, minimizing background and enhancing accuracy of DM detection. The system features innovative near-UV cryogenic Silicon PhotoMultipliers (SiPMs) for light readout. Universities and research institutes in the UK and Poland are responsible for producing and testing the veto Photon-Detection Units (vPDUs) that will be fitted on the Inner and Outer Veto. This paper presents the status of the production and characterization of the vPDUs, along with the quality assurance and quality control (QA/QC) procedures implemented to ensure the reliability and efficiency of the photon-detection systems.