Dual-phase noble liquid Time Projection Chambers (TPCs) are the present leading technology in the field of direct dark matter search. The ``dual phase'' technique has the main advantage to provide simultaneous access to the scintillation (S1) and to the 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.
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. In 2012 APC joined the DarkSide collaboration, one year before DarkSide-50 (DS-50), with 50 kg target mass, was operational. DS-50 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, which produce 39Ar by spallation on 40Ar The DarkSide collaboration solved the problem of such contamination by extracting underground argon (UAr) from a CO2 well, ~2 km deep, and thus shielded against cosmogenic 39Ar production. The residual contamination was measured by DS-50, with an analysis led by the APC team, to be about a factor 1400 lower than in AAr.
In addition, LAr is intrinsically characterized by an extraordinary discrimination power (>108) between nuclear and electron recoils, exploiting the scintillation pulse shape. DS-50 probed the potential of LAr, operating with UAr: the outcome of the dark matter search is a null result with a ~20 ton-days exposure. The discrimination between events induced by natural radioactivity and nuclear recoils - the potential candidate dark matter events - confirms once more that a future generation of multi-ton liquid argon detectors will also be able to operate completely free of background and in a real discovery mode.
In addition, the analysis of very-low energy events in DS-50, to which APC has strongly contributed, has led to the world-best limits for masses below 6 GeV/c2. The improvement with respect to competing experiments is of one order of magnitude, thus bringing DarkSide into the lead.
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 DarkSide phase, DarkSide-20k (DS-20k) a dual-phase LAr TPC with a fiducial mass of 20 ton. DS-20k has a highly innovative design: the TPC will be immersed in a 600 ton LAr bath, a solution that allows to host the entire TPC in an ultra-pure acrylic vessel, and it will be equipped with ~15~m2 of 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.
Within DS-20k, the APC team is in charge of coordinating simulations, data reconstruction development, and sensitivity studies for dark matter search and for neutrino physics too, like the evaluation of the DS-20k potential in solar and core-collapse supernova neutrino detection. In addition, the group conceived ARIS (Argon Response Ionization and Scintillation), a small scale dual-phase LAr TPC which was exposed to interaction of neutrons produced by the 7Li(p, 7Be)n reaction at the ALTO facility in Orsay. ARIS provided in 2018, among other results, the most accurate measurement of the nuclear recoil quenching factor in LAr.
The APC DarkSide Team
- FRANCO Davide (CNRS)
- TONAZZO Alessandra (Professor UPC)
- HESSEL Timothée (PhD)
- HUGUES Théo (PhD / Astrocent)
- RODE Julie (PHD)
- Official Darkside webpage: http://darkside.lngs.infn.it
- Darkside in France: https://darkside.in2p3.fr
- Calibration of the liquid argon ionization response to low energy electronic and nuclear recoils with DarkSide-50, DarkSide Collaboration, Phys.Rev.D 104 (2021) 8, 082005
- Performance of the ReD TPC, a novel double-phase LAr detector with Silicon Photomultiplier Readout, DarkSide Collaboration, Eur.Phys.J.C 81 (2021) 11, 1014
- Separating 39Ar from 40Ar by cryogenic distillation with Aria for dark matter searches, DarkSide Collaboration, Eur.Phys.J.C 81 (2021) 4
- Sensitivity of future liquid argon dark matter search experiments to core-collapse supernova neutrinos, DarkSide Collaboration, JCAP 03 (2021) 043
- SiPM-matrix readout of two-phase argon detectors using electroluminescence in the visible and near infrared range, DarkSide Collaboration, Eur.Phys.J.C 81 (2021) 2, 153
- Effective field theory interactions for liquid argon target in DarkSide-50 experiment, DarkSide Collaboration, Phys. Rev.D 101 (2020) 6, 062002
- Design and construction of a new detector to measure ultra-low radioactive-isotope contamination of argon, DarkSide Collaboration, JINST 15 (2020) 02 P02024
- Low-mass Dark Matter Search with the DarkSide-50 Experiment, DarkSide Collaboration, Phys. Rev. Lett. 121 (2018) 081307
- Constraints on Sub-GeV Dark Matter-Electron Scattering from the DarkSide-50 Experiment, DarkSide Collaboration, Phys. Rev. Lett. 121, 111303 (2018)
- DarkSide-50 532-day Dark Matter Search with Low-Radioactivity Argon , DarkSide Collaboration, Phys. Rev. D 98 (2018) 102006