Darkside

One of the main hypotheses regarding the nature of Dark Matter (DM) is that it consists of Weakly Interactive Massive Particles (WIMPs) formed in the primordial universe. In principle, WIMPs could be detected in terrestrial experiments through their collisions with ordinary nuclei, resulting in low-energy nuclear recoils (<100 keV) that can be observed. However, the predicted probability of such collisions is extremely small, requiring detectors with large target masses (1–100 tons) located in deep underground sites to suppress the background from Standard Model particles.

Among the various detection technologies in use, one of the most promising involves the use of dual-phase Argon Liquid-Time Projection Chambers (LAr TPCs), which detect both scintillation light and charges produced by ionization following nuclear recoil. A detector based on these technologies, DarkSide-50 (DS-50, with an active mass of 50 kg of liquid argon), successfully completed its experimental campaign at the Gran Sasso National Laboratory (LNGS) of the National Institute for Nuclear Physics (INFN).

DarkSide-20k, currently under construction in Hall-C of LNGS, is the successor to DarkSide-50.

The inner detector is a LAr-TPC (Liquid Argon Time Projection Chamber) containing ultra-low radioactivity argon sourced from underground reserves (UAr, with an active volume of approximately 50 tons), read by SiPM-based (Silicon Photomultiplier) photodetectors. The TPC is surrounded by a PMMA (poly(methyl methacrylate)) shell loaded with gadolinium, which acts as a neutron moderator with a high capture probability, used to suppress events induced by neutron background.

The TPC is enclosed within two additional layers of atmospheric argon (AAr), which serve as veto detectors for cosmic muons and gamma rays produced in the PMMA due to neutron capture. DarkSide-20k is designed to operate in a "zero-background" condition, meaning that all sources of natural or instrument-induced radioactive backgrounds are reduced to less than 0.1 events for an exposure of 200 ton-years. All ionizing radiation backgrounds will be entirely removed using a combined approach of pulse shape discrimination (PSD) of the primary scintillation light and its comparison with the ionization component.

Thanks to its exceptional sensitivity, the DarkSide-20k experiment, expected to begin in 2027, is a strong candidate for the discovery of Dark Matter. Alternatively, it will be capable of excluding a significant portion of the parameter space.