Monday November 11 14h00in Aula Dof the physics department.

Title: “The DarkSide-20k experiment for direct search of Dark Matter at LNGS, status and perspectives”

Speaker: Prof. Sandro De Cecco - Sapienza Università di Roma Physics Department & INFN Roma.

Abstract:

The nature of dark matter is still a central question in fundamental physics. The Weakly Interacting Massive Particles paradigm, fulfills the requirements to be a dark matter candidate as supported by both cosmology and particle physics. To date, the WIMPs are searched with a large variety of direction techniques and a large phase space region is already excluded but none of the current experiments reached the irreducible neutrino fog background due to coherent elastic scattering of solar and atmospheric neutrinos on detector targets. Dual-phase noble liquid Time Projection Chambers (TPCs) are the present leading technology in this field, main advantage is to provide simultaneous access to the scintillation (S1) and to ionization (S2) signals, allowing for the event topology reconstruction and for the discrimination between electron and WIMP-like (or nuclear) recoils. A number of TPC's, such as Xenon1T, PandaX, and LUX, successfully profit from liquid xenon target masses, which guarantee an excellent radio-purity and a high stopping power for penetrating radiation. Liquid argon (LAr) has similar properties but suffers of the intrinsic contamination of cosmogenic ³⁹Ar, a problem recently solved by the DarkSide collaboration with the use of depleted Argon from underground origin (UAr) through the URANIA plant and further purification based on cryogenic distillation with the ARIA project.

DarkSide is a multi-stage program, began in 2010 with the construction of DarkSide-10 (DS-10), a 10 kg liquid argon (LAr) prototype detector and later with DarkSide-50 (DS-50), with 50 kg target mass that was installed underground at LNGS inside an active neutron veto based on a boron-loaded organic scintillator,  in turn  inside a 1000 ton water Cherenkov muon veto.  The acquisition started in Nov 2013, with the detector filled with  argon extracted from atmosphere (AAr), naturally exposed to cosmic rays, and in 2025 with a depleted argon target on which the residual contamination was measured to be about a factor 1400 lower than in AAr. In addition, LAr is intrinsically characterized by a unique discrimination power (>10⁸) between nuclear and electron recoils, exploiting the scintillation pulse shape. DS-50 probed the potential of LAr TPCs, operating with UAr: the outcome of the dark matter search is a null result with a ~20 ton-days exposure with zero reducible background. The future generation of multi-ton liquid argon detectors was designed and approved to be able to perform  dark matter direct search completely free of backgrounds and in a real discovery mode.

Building on the successful experience of DS-50, the four world-leading argon dark matter projects (ArDM at LSC, DS-50 at LNGS, DEAP-3600 and MiniCLEAN at SNOLab) agreed on joining forces to carry out a unified program forming the Global Argon Dark Matter Collaboration (GADMC) for the next generation experiment the DarkSide-20k a dual-phase LAr TPC with a fiducial mass of 20 ton and with 50 tons of instrumented target mass of low radioactivity argon. DS-20k has a highly innovative design: the TPC will be immersed in a 600 ton liquid AAr bath within a membrane proto-DUNE like cryostat, a solution that allows to host the entire TPC in an ultra-pure acrylic vessel immersed in ~100 tons of low radioactivity UAr separated from the AAr bath by a radio pure SS vessel. The Inner detector will be equipped with ~15~m² of cryogenic silicon photomultipliers (SiPMs), characterized by higher radiopurity, very high photon detection efficiency (~40% photodetection efficiency), low noise (0.1-1 Hz/mm²), and high single electron resolution. The Inner detector will be surrounded by an active volume of UAr also instrumented with SiPMs that will act as an active neutron veto. Particular attention is given to the extreme radio purity of the detector materials. DarkSide-20k is expected to be free of any instrumental background for exposure of 200 tonne x year and it is expected to attain a WIMP-nucleon cross-section exclusion sensitivity of 7 x 10^-48 cm^2 for a WIMP mass of 1 TeV.

The Darkside-20k detector construction has now started and the its commissioning is foreseen in late 2026. The talk will describe the current status of Darkside-20k development and construction. The talk will also give an overview of the recently published results on dark matter limits by the predecessor experiment DarkSide-50, in particular on revised low-mass dark matter WIMPs search with the full dataset including the dark matter-nucleon interactions via Migdal effect, and on the recently published perspectives for DarkSide-20k in the light WIMP search that will allow to improve DS-50 limit by more than one order of magnitude in less than one year of operation of DarkSide-20k. Current results and future perspectives positions DarkSide-20k at the world lead in search sensitivity on a wide range of dark matter particles masses from the GeV to tens of TeV scale.