The energy resolution and the energy deposition processes in disordered targets for rare-event searches

Abstract

Underground rare-event search is a substantial branch in particle physics, in which particle dark matter (DM) direct detection and neutrinoless double β decay (0νββ) are two major topics. The elusive nature of the signals puts stringent requirements on the detector contamination level. Some particular interactions also require specific materials to build the detectors. Many of them are disordered materials, for example, noble liquids and amorphous selenium (aSe). This work attempts to understand the energy response of ionizing particles in disordered materials. The scope is limited to ionization and scintillation detectors, precisely the dual-phase noble liquid time projection chambers (TPC) and the aSe ionization detectors. Part of the energy deposited by the incident particle loses to heat through nuclear and electronic quenching; then charge recombination takes place. Models describing the signal yield and fluctuations are built and tested with measurements. On the frontier of DM direct detection, the models are applied to the low-mass DM search in the DarkSide-50 experiment with ionization-only signals. A reanalysis of the same data set is carried out to search for sub-GeV DM with the Migdal effect. The direction dependency in charge recombination is measured to be negligible in nuclear recoils from DM candidates. On the frontier of 0νββ search, this work introduces two conceptual designs of detectors with sensitivities beyond the currently proposed next-generation detectors. The first design is a 82Se enriched aSe-complementary metal-oxide-semiconductor hybrid imaging detector with high spatial resolution. The second design is a 136Xe enriched liquid argon xenon mixture dual-phase TPC.