Speaker
Description
DarkSide-20k, the next-generation dual-phase liquid argon TPC under construction at LNGS, aims to significantly advance the search for WIMP dark matter. A key requirement for reaching its sensitivity goals is the use of underground argon, strongly depleted in cosmogenic $^{39}$Ar with respect to atmospheric argon, whose natural activity would otherwise represent a major background at the multi-tonne scale.
The underground argon procurement chain includes extraction at the Urania plant in the USA and cryogenic purification at the Aria facility in Italy. Within this framework, DArT-in-ArDM represents a fundamental step, providing a direct and ultra-sensitive measurement of the residual $^{39}$Ar activity in argon samples and validating their radiopurity throughout production, purification, handling, and delivery to DarkSide-20k.
DArT is a small single-phase liquid argon detector operated inside the refurbished ArDM detector at the Canfranc Underground Laboratory, LSC, Spain. ArDM provides both the cryogenic environment for stable long-term operation and an active veto against external backgrounds, enabling $^{39}$Ar measurements in underground argon with target sensitivities at the sub-mBq/kg level.
In this talk, we present the final DArT-in-ArDM detector configuration and its performance during several months of stable operation with underground argon samples. These results build on the commissioning campaign performed with the dedicated DArT test setup, which included measurements with atmospheric and underground argon and enabled a precision measurement of the $^{39}$Ar activity in atmospheric argon.
A full simulation framework based on G4DS has been developed to model the detector response and the relevant signal and background contributions. The comparison between data and Monte Carlo, together with a dedicated sensitivity study, constrains the dominant backgrounds, assesses the ArDM veto performance, and demonstrates the capability of DArT-in-ArDM to resolve the low residual $^{39}$Ar activities expected in underground argon.
These results demonstrate the readiness of DArT-in-ArDM for the underground argon assay campaign and establish its role in the DarkSide-20k quality-control strategy, from argon procurement to final detector filling.