The Experiments
The DarkSide experiments, located deep beneath Italy’s Gran Sasso mountain are a series of cutting-edge dark matter searches designed to detect one of the universe’s greatest mysteries. Beginning with DarkSide-10, followed by DarkSide-50, and now DarkSide-20k underpinned by DarkSide-Proto, each experiment has built upon the success of the last by developing increasingly sensitive liquid argon detector technology.
DarkSide-20k
Figure 1. Simplified schematic of the DarkSide-20k detector. The Inner Detector, consisting of the octagonal-shaped TPC (grey) with acrylic walls (green) and the Inner Veto (cyan), are enclosed in a steel vessel and surrounded by the Outer Veto, insulated from room temperature (yellow) within a membrane cryostat (red).
DarkSide-20k, currently under construction at the Laboratori Nazionali del Gran Sasso (LNGS), houses 50 tonnes of ultra-pure underground argon (UAr) in a dual-phase Time Projection Chamber (TPC). This TPC is surrounded by a 32 tonne single-phase UAr detector serving as the Inner Veto, which itself is enclosed within the Outer Veto—comprising 650 tonnes of single-phase atmospheric liquid argon. Interactions in the argon produce charge and scintillation light which are ultimately detected by planes of silicon photomultiplier (SiPM) array detectors. The TPC is designed to detect interactions of elusive 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 dark matter interactions.
DarkSide-50
Figure 2. Rendering of the DarkSide-50 Time Projection Chamber. Figure from Phys.Lett.B 743 (2015) 456-466
The DarkSide-50 (DS-50) detector featured a dual-phase Time Projection Chamber (TPC) which successfully operated underground at LNGS from 2013-19. The active UAr mass contained in the TPC was (46.4 ± 0.7) kg. Interactions in the TPC produce charge and scintillation light, ultimately detected with two planes of 3” photomultiplier tubes (PMTs). This structure, depicted in Fig.2, is surrounded by a 4 m diameter Liquid Scintillator Veto, containing an organic scintillating liquid loaded with boron that acts as a neutron veto, and a Water Cherenkov Veto to identify cosmic rays. DarkSide-50 set the most stringent bounds on the spin-independent dark matter-nucleon interaction cross section for dark matter particles with masses in the [1.2, 3.6] GeV/c2 range, as well as leading constraints on the parameter space of hidden sector dark matter-electron interactions, axion-like particles, and sterile neutrino dark matter candidates.
DarkSide Proto
Figure 3. The DarkSide Proto Time Projection Chamber
DarkSide-Proto (DS Proto) is a project born within DS-20k to investigate and optimize the production of the ionization signal (S2) in the dual-phase TPC and validate many of the novel technologies featured in DS-20k. DS Proto is equipped with a compact TPC instrumented with two of the 20×20 cm2 SiPM array photon detection units (PDUs) developed for DS-20k. The main feature of DS Proto is the flexible TPC design with independently moving components (during operation), which enables study of S2 formation versus geometrical factors as well as electrical properties. The results obtained by the scientific programme of DS Proto are used to fine-tune the design of DS-20k and, more broadly, will result in a better understanding for the engineering of future dual-phase experiments. DS Proto is located within the cryogenic laboratory of INFN Naples.
The DarkSide Collaboration aims to unveil the nature of dark matter through liquid argon detector technology and innovative underground experiments. It is located at the Laboratori Nazional del Gran Sasso in L’Aquila, Italy.