JE2: Direct Dark Matter Search

> Read the articles connected to the project.


  • darkside

    In the last two decades, cosmological data from observations of the cosmic microwave background fluctuations, large-scale galaxy surveys, studies of large scale structure formation and of the dynamics of galaxy clusters, have all provided a wide range of astronomical evidences of the existence of gravitational effects, not arising from normal matter. The source of this deep mystery is a non-ordinary matter, called “dark” because it is invisible. Understanding the “dark matter”, which constitutes about 1/4 of our Universe, is one of the most important challenges in modern cosmology.


    One possibility, motivated by considerations in elementary particle physics, is that dark matter consists of undiscovered elementary particles. A leading candidate explanation is that Dark Matter is composed of Weakly Interacting Massive Particle (WIMP) formed in the early universe and gravitationally clustered together with the standard baryonic matter.


    Several terrestrial experiments are searching for WIMP collisions with ordinary nuclei, whose recoils could in principle be observed at low energies (< 100 keV). The very low interaction rates expected in this kind of research push the experiments to explore new avenues to increase the sensitivity to the WIMPs trough their scattering with target nuclei.


    Liquid argon based detectors offers at the same time the advantage of a target scalable to multi-ton masses, and the unique add-on key feature of the excellent pulse shape discrimination power to disentangle WIMP signal from electron-like background.


    Figure 1 Two-phase Argon TPC scheme (left) and design of the DarkSide-50 liquid argon TPC

    Figure 1 Two-phase Argon TPC scheme (left) and design of the DarkSide-50 liquid argon TPC (right)


    In particular, two-phase liquid argon time projection chambers (LAr TPCs), which detect scintillation light and ionization generated by recoiling nuclei, are particularly promising since they guarantee a high accuracy for determining 3-D event positions.


    The DarkSide Program


    DarkSide is a multi-staged program for developing two-phase LAr TPCs using several innovative techniques to positively identify Dark Matter signals and to understand and suppress background. DarkSide-50 has already demonstrated the exceptional LAr discrimination power (>107) for rejecting electron-like background, the low 39Ar contamination in LAr extracted from deep underground, and the high efficiency of an active neutron veto to strongly suppress neutron background. The DarkSide program is intended to progress to multi-ton detectors with high sensitivity for WIMP detection.


    The LabEx UnivEarthS JE2 team works on the data analysis of DarkSide-50, leading all the simulation activities.


    Figure 2 Scheme of the three DarkSide detectors

    Figure 2 Scheme of the three DarkSide detectors


    The DarkSide-20k Technological Challenge


    The next DarkSide phase will use 20-ton fiducial mass liquid argon as target for searching for WIMP interactions. To improve the sensitivity and reduce the background, the detector will be equipped with a new class of photo-sensors, the Silicon Pohotomultiplier (SiPMs) arrays, replacing the standard Photomultiplier Tubes (PMTs).


    The SiPMs are arrays of Silicon based avalanche photodiodes (APD). The dimension of each single APD can vary from 20 to 100 μm, and their density can be up to 1000 mm-2. The capability of SiPM to clearly identify single photoelectrons allows studying in great detail the scintillation of liquid argon at low energies, a key element for the correct interpretation of data from the DarkSide detector.


    SiPMs provide also direct advantages when compared to the standard PMTs. The dark noise, in fact, strongly suppressed for the SiPMs at the liquid argon temperature, can be lower than for the standard PMTs. Further, the amount of material used for the SiPM, considerably lower than for standard PMTs, and the radio-purity of the SiPM materials, allow to reduce the neutron contamination from (alpha,n) reactions, the most dangerous background in DarkSide. The limited sizes of the SiPMs allow, also, to increase the liquid argon active mass in the TPC, enhancing the sensitivity to the direct dark matter detection.


    The LabEx UnivEarthS JE2 team will characterize the behavior of SiPMs (and of their associated electronics) in a liquid argon environment.

    WP leader Davide Franco APC CR1/ CNRS
    WP member Alessandra Tonazzo APC Professor, Université Paris-Diderot
    WP member Quentin Riffard APC Post-doc, Université Paris-Diderot
    WP member Paolo Agnes Houston U. Post-doc, associated at APC




    To go further, you can visit these pages :

    Official DarkSide webpage:

    Aris Project webpage :



    The LabEx JE2 program was developed to characterize liquid argon (LAr) response to electron and nuclear recoils, in the energy range of interest for the direct dark matter search. LAr scintillation, ionization, and ion-electron recombination effects are, in fact, poorly modeled and represent the main sources of systematics in dark matter experiments. LAr scintillation yield depends on a double mechanism: the direct excitation of argon molecules, and the recombination between electrons and ions, after the ionization of argon. Both the processes lead to an excited state of the argon molecule. The interacting particle recoil energy is then estimated by counting, with photomultiplier tubes, the overall emitted photons, following the argon de–excitation. The WIMP signal is expected at very low energies, a few tenth of keV, in a region where the models are unable to predict the scintillation response, and where calibrations with radioactive sources are extremely challenging.

    The most accredited scintillation models are the Thomas–Imel and the Doke’s modified Birks’ law. Both of them are based on the same ion-electron recombination physics, albeit with different descriptions governed by short– or long–track limits.
    Unfortunately, none of them, alone, is able to predict the primary scintillation efficiency at low energies in LAr. A model able to accurately describe scintillation, ionization, and recombination effects in LAr, in presence of electric fields, is of great impact of the dark matter search, by boosting the sensitivity and improving future detector designs.

    The LabEx JE2 program was developed on two main branches:

    1. construction of a LAr response model based on the DarkSide-50 data;
    2. measurement of LAr properties with a small-scale TPC exposed to neutron/gamma beams.


    Both the primary objectives of the JE2 program have been successfully achieved, with a great impact on the dark matter search field. In addition, the JE2 team has exploited G4DS/PARIS to demonstrate the exceptional power of a very large double-phase LAr TPC in the solar neutrino sector (D. Franco et al., JCAP 1608 (2016) 8, 017) and is currently working on evaluating the sensitivity to supernova neutrinos.

    As additional goal, the LabEx JE2 organized and partially funded the first “Dark Matter Day in France”, held at APC, which was the first initiative to federate the dark matter search community in France. The meeting was a success in terms of number of participants and discussions, and it has been decided to repeat it on a yearly basis. This year it will be held at LPNHE.


  • Official DarkSide webpage:


    DarkSide Collaboration,
    Low-mass Dark Matter Search with the DarkSide-50 Experiment
    Phys. Rev. Lett. 121 (2018) 081307

    DarkSide Collaboration,
    Constraints on Sub-GeV Dark Matter-Electron Scattering from the DarkSide-50 Experiment
    arXiv:1802.06998 (2018) (accepted by PRL)

    DarkSide Collaboration,
    DarkSide-50 532-day Dark Matter Search with Low-Radioactivity Argon
    arXiv:1802.07198 (2018)

    DarkSide Collaboration,
    Electroluminescence pulse shape and electron diffusion in liquid argon measured in a dual-phase TPC
    arXiv:1802.01427 (2018)

    P. Agnes et al. (ARIS Collaboration)
    Measurement of the liquid argon energy response to nuclear and electronic recoils
    Phys. Rev. D97 (2018) 11 112005


    DarkSide Collaboration
    The Electronics, Trigger and Data Acquisition System for the Liquid Argon Time Projection Chamber of the DarkSide-50 Search for Dark Matter
    Journal of Instrumentation Dec. 2017, vol.12, no.12, P12011 (23 pp.). DOI: 10.1088/1748-0221/12/12/P12011

    DarkSide Collaboration,
    DarkSide-20k: A 20 Tonne Two-Phase LAr TPC for Direct Dark Matter Detection at LNGS
    2017, arXiv:1707.08145, submitted to Physics Letters B

    DarkSide Collaboration
    Simulation of argon response and light detection in the DarkSide-50 dual phase TPC,
    october 2017, JINST, arXiv:1707.05630

    D. Franco and N. Saviano,
    Particle Physics in the Cosmos
    Proceeding of Science NOW2016 (2017) 095

    DarkSide Collaboration,
    CALIS – a CALibration Insertion System for the DarkSide-50 dark matter search experiment
    Journal of Instrumentation Dec. 2017, vol.12, no.12, T12004 (19 pp.). ISSN: 1748-0221 (print), Publisher: IOP Publishing Country of Publication: UK DOI: 10.1088/1748-0221/12/12/T12004

    DarkSide Collaboration,
    Effect of Low Electric Fields on Alpha Scintillation Light Yield in Liquid Argon
    2017 JINST 12 P01021 DOI: 10.1088/1748-0221/12/01/P01021

    DarkSide Collaboration,
    DarkSide-20k: A 20 Tonne Two-Phase LAr TPC for Direct Dark Matter Detection at LNGS

    arXiv:1707.08145 (2017)