Author: Michela Lai
After the success of the DarkSide-50 experiment, the natural first step for the Global Argon Dark Matter Collaboration—bringing together the joint efforts of DarkSide-50, miniCLEAN, ArDM and DEAP-3600—is to scale up from a 50 kg liquid argon target to a multi-tonne one, while maintaining an ultra-low background level from the radioactivity of detector materials.
DarkSide-20k (DS20k), currently under construction at the Laboratori Nazionali del Gran Sasso (LNGS), envisions a 50-tonne volume of ultra-pure underground argon, extracted from the URANIA plant, housed in a dual-phase Time Projection Chamber (TPC) similar to that of DarkSide-50. This TPC is submerged in a 32-tonne underground single-phase liquid argon chamber serving as the Inner Veto, which itself is enclosed within the Outer Veto—comprising 650 tonnes of atmospheric single-phase liquid argon.
The TPC is, of course, the very core of the experiment, where we aim to detect elusive WIMP dark matter candidates. The veto systems are designed to reject background events induced by standard particles, which produce scintillation light in at least one veto layer and the TPC—unlike the expected signal from WIMPs.
Specifically, the Outer Veto is designed to reject events caused by the small number of muons that penetrate into the underground lab. The Inner Veto, on the other hand, leverages the neutron-capturing power of hydrogen in the acrylic that separates the TPC vessel from the Inner Veto bath. When neutrons interact with the acrylic, they emit gamma rays that shine in both the TPC and the IV, producing a unique coincidence signal that helps distinguish neutrons from WIMPs.
Given that we expect only a few dozen WIMP-induced events per year in liquid argon (with the exact number depending on the WIMP mass and its likelihood to interact via elastic scattering), the full suppression and rejection of background events has driven every aspect of the experiment’s design—from material selection to the development of our Photodetection Units (PDUs), which populate all three nested chambers. This same principle continues to guide the detailed assembly of the detector.
Thanks to these efforts, over a planned 10-year data-taking period beginning in early 2028, the experiment will be capable of excluding—or potentially detecting for the first time—any WIMP candidate with a dark matter–nucleon cross-section as low as 5 × 10⁻⁴⁸ cm², for candidates as heavy as 1 TeV/c².
The next step will be ARGO, featuring a 400-tonne core detector—marking the final milestone needed to definitively confirm or exclude the detectability of these elusive particles in direct detection experiments.
In addition to the WIMP search, while construction progresses and PDUs are being characterized, we are also developing the analysis software and simulation tools—both for post-processing at CNAF and for real-time data acquisition. Alongside dedicated performance monitoring, we are expanding the physics case by asking: What are all the possible ways to exploit these 732 tonnes of argon?
From neutrino physics to light dark matter candidates, we’ve only just scratched the surface.
Stay tuned!
