Optical imaging in dual-phase xenon time projection chambers for neutrinoless double beta decay searches

Dual-phase xenon time projection chambers (TPCs) are the leading technology for WIMP dark matter searches and have also demonstrated competitive sensitivities to neutrinoless double beta decays (0$\nu \beta \beta$) of \ce{^{136}Xe}. However, the large energy disparity between these two signals requires different detector optimizations. In particular, 0$\nu \beta \beta$\ searches in liquid xenon desire efficient rejection of closely located multiscatters of background gamma rays near the 0$\nu \beta \beta$\ energy, a capability achieved only in the vertical dimension in existing dual-phase xenon TPCs. We propose a highly customized, wide-angle optical system that can be conveniently integrated into large xenon TPCs and provide mm-scale transverse position resolution for MeV signals by imaging gas electroluminescence light. This approach preserves a TPC’s low-energy sensitivity and optimizes a single experiment for both dark matter and 0$\nu \beta \beta$\ searches. This paper discusses the design, simulated performance, and implications of the imaging system for future liquid xenon-based 0$\nu \beta \beta$\ searches.