Too rare or not too rare Rare event searches in dual-phase xenon TPCs

This thesis explores the search for extremely rare physical processes using low-background dual-phase xenon time projection chambers (TPCs). One of these rare processes is neutrinoless double beta decay, a hypothetical double weak decay in which no neutrinos are emitted. Its observation would establish the Majorana nature of neutrinos and demonstrate lepton number violation. Lepton-number-violating processes may also be connected to the matter–antimatter asymmetry observed in the Universe today, addressing one of the most fundamental open questions in particle physics and cosmology. The first part of this thesis introduces the theoretical framework of double beta decay and reviews the current experimental landscape of 0𝜈ββ decay searches. Detecting rare processes requires detectors with exceptional sensitivity and background suppression, which can be achieved in dual-phase xenon TPCs. We discuss the working principle of this detector, with particular emphasis on the XENONnT experiment, the fourth generation of XENON detectors. The steady increase in size and the incorporation of advancing technologies of these different generations could not have been possible without the contributions from small scale research and development (R&D) setups. One of these setups is XAMS (Xenon Amsterdam), in which recently two novel type of light sensors have been installed and characterized, aimed at evaluating their applicability in future generation detectors. In the final chapter of this thesis the study of xenon activation processes in XENONnT is discussed. In particular, the production and decay of xenon-137 are investigated in the context of background modeling for the search for the 0𝜈ββ decay of xenon-136.