First direct search for Dark Matter with multi-tons argon detector – FIDAR

The existence of dark matter, supported by a variety of astrophysical measurements, is one of the main puzzles in fundamental physics. As of today, one of the most favored candidates as a dark matter particle is a weakly interacting massive particle (WIMP) in the mass range above 1 GeV and below 10 TeV. Noble liquids are ideal target material and dual-phase noble liquid time projection chambers (TPC) are the present leading technology for WIMP search. DarkSide-20k, the next generation of liquid argon TPC, will be the largest ever built for dark matter searches with a target of 50 tons of purified liquid argon and 200000 silicon photo-multipliers (SiPMs). The use of these two assets will allow to fully profit from the liquid argon scintillation pulse shape discrimination between WIMP and electron/photon signals. As proven by the first-generation experiments, this discrimination is so strong that it enables to remove completely this type of background. Together with the very efficient muon and neutron veto detectors surrounding the TPC, DarkSide-20k intends to perform an instrumental background-free search for high mass WIMP (< 0.1 event for 200 ton.year excluding neutrino interactions). For that, DarkSide-20k is gathering all successful developments carried out for ten years with first-generation (smaller) liquid argon TPCs. The fundamental concepts of the experiment are already well established and the two main challenges come from the scaling of the technologies to higher dimensions and the use of SiPMs instead of the standard photo-multipliers used in previous liquid argon experiments. DarkSide-20k construction has begun at Gran Sasso National Laboratory at the end of 2022 and DarkSide-20k plans to start taking data in 2027. The goal of the FIDAR project is to perform a background-free high mass WIMP search with the first month of DarkSide-20k data to probe for WIMPs below the sensitivity of existing liquid argon detectors. Of course, the ability to suppress the background in such a large TPC depends strongly on event reconstruction, i.e. the optimal exploitation of the SiPM potential as well as the usage of modern machine learning techniques for event reconstruction, as proposed in this project. In turn, both event reconstruction and data analysis rely on the detector calibration. In DarkSide-20k, APC is in charge of the offline (simulation and data reconstruction) and CPPM is responsible for building a guide pipe calibration system to circulate radioactive sources around the TPC. The FIDAR project aims at strengthening further the existing APC-CPPM collaboration, already well established in 2020-22 on the DarkSide-50 (first generation liquid argon TPC) data analysis leading to the world best limits for low mass WIMP. To reach this goal, we plan to install and exploit the DarkSide-20k calibration system to validate the event reconstruction, measure the background and signal energy scales, and be ready to analyze first data with an analysis framework tested on realistic simulations. Funding the FIDAR project will enable to reinforce the French teams with two new students at the critical time of DarkSide-20k installation and data taking.