Measuring the Argon 39 depletion factor with DART

The DarkSide-20k (DS-20k) Dark Matter search experiment will operate with 23-ton radio-pure underground argon (UAr), extracted from the Urania plant in Cortez (USA) and purified in the Aria distillation plant (Sardinia, Italy). The 39Ar depletion factor in UAr with respect to atmospheric argon is expected to be around 1400. Assessing the purity of UAr in terms of 39Ar is key for the physics programme of DS-20k. DART is a small (∼1 L) chamber that will measure the depletion factor of 39Ar in UAr. The detector will be immersed in the LAr active volume of ArDM (LSC, Spain), which will act as a veto for gammas stemming from the detector materials and from the surrounding rock. DART will use the SiPMs constructed for DS-20k and the cryogenic and DAQ systems of ArDM. Data taking is planned for 2018. In this talk, I will review the status of the DART project, which comprises the chamber design and construction, as well as the background studies necessary to assess the expected performance of DART. This presentation was used for the Low-Radioactivity Underground Argon Workshop held at Pacific Northwest National Laboratory in Richland, Washington on March 19 - 20, 2018