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Home  ⪧  Research  ⪧  Astroparticle Physics  ⪧  DarkSide

DarkSide

The scientific goal of the DarkSide-20k experiment at the Gran Sasso INFN Laboratory is to discover dark matter by observing the signals generated by its scattering from nuclei in a detector where there is essentially no background from any other known physics source, building on the successful experience with a previous experiment, DS-50. Any event becomes a potential dark matter discovery.

Liquid argon is the material chosen as the target for the dark matter because of several attractive features. Liquid argon emits a burst of light (S1) whenever an interaction deposits energy in it, and ionization electrons produced in an interaction can be drifted many meters under the influence of a moderate electric field. The intensity of the S1 light signal is proportional to the energy deposited in the interaction and, specific to argon, the pulse shape of the light produced can be used to distinguish between an interaction with the electrons in the argon atom – a typical background - or an interaction with an argon nucleus – a candidate signal. The electron mobility can be exploited by applying an electric field throughout the argon to drift ionization electrons into the gas region above the liquid where they can generate a second light signal by electroluminescence (S2). The time delay between the prompt signal (S1) and the delayed signal (S2) depends on the depth of the interaction in the liquid, and the pattern of light from the S2 signal yields the transverse position of the electrons emerging from the liquid, thereby identifying the 3D position of the interaction. This capability allows events from surface backgrounds and multiple neutron scatters to be identified and rejected.

Natural argon found in the earth atmosphere itself suffers from the fact that it is intrinsically radioactive at a rate of 1Bq/kg (1 count per second for every kg of liquid argon), and the exploitation of the above features is only possible because of the discovery made with DS-50 of low radioactivity argon in underground CO2 wells with an activity 1400 times lower than atmospheric originally used in DS-50.

The detector consists of two elements – an inner dual-phase time projection chamber 
LAr TPC containing about 50 t of low radioactivity argon, the dark matter 'target', and 
a surrounding Veto detector to identify 
and remove the background induced by natural residual radioactivity of the detector materials all immersed in a large membrane cryostat containing 700 t of liquid natural argon bath used to shield the detector from external radiation. The octagonal LAr TPC will have a height of 350 cm and will be instrumented with a new kind of photosensor, arrays of SiPMs, arranged in assemblies called photodetector modules (PDMs). Each PDM has an area of 25 cm² with the LAr TPC containing 8280 PDMs covering a total area of 21 m². SiPMs promise a higher effective quantum efficiency, higher reliability at LAr temperature, and a much higher radiopurity than PMTs. All of these properties are crucial for DarkSide-20k since the the pulse shape discrimination capability depends critically on the light yield, while the large radioactivity budget of PMTs would be a limiting factor for neutron and gamma-induced backgrounds.

Unlike in DS-50, where a full digitization and recording of the waveform of each PMT could be achieved, a custom scheme for the sampling of the two-orders-of-magnitude higher channel count of the DarkSide-20k SiPM PDMs is being developed. The DAQ is designed to perform online digital pulse processing to identify the tiny signal generated by just a single photon hitting the photo-sensors and performing online event reconstruction also using machine learning technique for optimal performance.

The Rome DarkSide group is mainly focused on the design and construction of the big membrane cryostat, on the DAQ system and related software reconstruction and in the precision low energy calibration of LAr response.

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Websites:

• DarkSide International

Thesis Opportunities:

• Title: Development of the trigger and data acquisition systems of Darkside-20 experiment, implementing advanced digital signal processing for the 1 Ton prototype at CERN
  Description: The student will join the team constructing and running at CERN the series of prototypes of increasing size up to the ton-scale detector that will fully validate the Darkside-20k concept, in particular developing the trigger and DAQ systems requiring sophisticated digital signal processing for optimal reconstruction of the tiny scintillation and ionization signals in the Dark Matter energy range. Application of online machine learning algorithms is possible.
  Contact persons: Andrea Messina and Marco Rescigno.
• Title: Low-energy nuclear recoil calibration in a Liquid Argon dual phase TPC using neutron beams, and optimization of the Darkside detector for the low-mass dark matter in the mass range 1-10 GeV
  Description: Design and hands-on setup of the ReD experimental setup using neutron beams from radioactive sources and low-energy ion beams from the TANDEM accelerator of Laboratori Nazionali del Sud in Catania (LNS). Participation to the data analysis and to the measurement campaigns at LNS and elsewhere using a small liquid argon TPC and neutron detectors, aimed at increasing precision in the low energy nuclear recoil calibration that will further improve the current best limit for dark matter in the 1-10 GeV mass range.
  Contact person: Marco Rescigno.
• Title: Reconstruction of scintillation and ionization signals with the 1 Ton prototype of Darkside-20k, and characterisation of the performance of a Liquid Argon TPC with novel SiPM photosensors
  Description: The student will join the team constructing and running at CERN the series of prototypes of increasing size up to the ton-scale detector that will fully validate the Darkside-20k concept, participating to the design and implementation of the algorithms for the online and offline reconstruction of the scintillation and ionization signals. New machine learning algorithms for the spatial reconstruction and the nuclear/electron recoil discrimination will be developed and compared to the standard ones.
  Contact person: Valerio Ippolito.

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Local Coordinator

Sandro De Cecco

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