Grant: Subatomic Physics Envelope - Project

Normal matter only accounts for about 5% of the universe - the composition of the rest of the dark matter and dark energy in the universe remains a profound mystery. Identifying the dark matter, by constructing very sensitive detectors to search for rare interactions of dark matter particles with normal matter, is a top international scientific priority, with Canada playing a key role in these efforts. As part of the Global Argon Dark Matter Collaboration, a group of over 400 scientists from 100 institutions in 14 countries, we are mounting a phased approach to dark matter experiments using liquid argon; crucial components of the program are data collection and analysis with DEAP-3600 at SNOLAB (using 3300 kg of argon), construction of the DarkSide-20k detector (using 100 tonnes of argon) at LNGS, expected to start operating in 2026, R&D towards improving background control needed for current and next-generation experiments and the development of digital photodetectors. We anticipate increasing dark matter sensitivity with argon by a factor of 30 with DarkSide-20k, enabling an ultimate further factor of 10 with ARGO. This project will produce internationally-competitive research and contribute to the training of a highly-skilled workforce. We were awarded CFI funding in 2017 and 2020, for the development of a noble liquid detector R&D facility, toward the Canadian contributions to DarkSide-20k, and also for upgrading the DEAP-3600 experiment, and have submitted a third proposal to CFI in 2022 for additional support of DarkSide-20k and development of the argon program. Canada has primary responsibility for construction of the DarkSide-20k inner time-projection-chamber vessel and its low-background surface coatings, for the digitizing electronics and data acquisition DAQ system, and for shipping, storage and purity monitoring of underground argon. Upgrades to DEAP-3600, funded by CFI, include a novel wavelength-shifter coating developed for background suppression of surface alpha decays and updates to the liquid argon cooling and circulation in order to mitigate alpha backgrounds from particulates suspended in the liquid argon. With these upgrades, currently being installed, we expect to extend our understanding of background modelling in argon, and to demonstrate sensitivity to dark matter interactions at the full sensitivity of the detector, and with essentially no background events in the region of interest. Control of backgrounds to this level will be the best achieved to date, and inform the future phases of the dark matter program. Developments for ARGO include the conceptual design of the experiment in order to define the radioactivity control that will be required, determining the detailed physics sensitivity and the continued development of novel digital photodetectors. These developments will also inform DarkSide-20k.