JE2: Direct Dark Matter Search
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.
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. In the current phase, the DarkSide-50 detector has 50 kg LAr fiducial mass and is running since November 2013. 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.
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.
POSITION NAME SURNAME LABORATORY NAME GRADE, EMPLOYER 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
- ARIS: dual phase liquid argon TPC commissioned at UCLA and exposed at the LICORNE neutron beam at IPNO for 14 days. Goals: measurement of the quenching effect of nuclear recoils, the recombination probability and of the singlet to triplet state ratio in presence of an electric field.
- DarkSide: improvements on the DarkSide sensitivity to the direct dark matter search thanks to ARIS result.
To go further, you can visit these pages :
Official DarkSide webpage: http://darkside.lngs.infn.it/
Aris Project webpage : http://aris.in2p3.fr/
Official DarkSide webpage: http://darkside.lngs.infn.it/
– The Electronics, Trigger and Data Acquisition System for the Liquid Argon Time Projection Chamber of the DarkSide-50 Search for Dark Matter, DarkSide Collaboration, arXiv:1707.09889
(submitted to JINST)
– DarkSide-20k: A 20 Tonne Two-Phase LAr TPC for Direct Dark Matter Detection at LNGS, DarkSide Collaboration, arXiv:1707.08145, submitted to PLB
– Simulation of argon response and light detection in the DarkSide-50 dual phase TPC, DarkSide Collaboration, arXiv:1707.05630, accepted by JINST
– Particle Physics in the Cosmos, D. Franco and N. Saviano, PoS NOW2016 (2017) 095
– CALIS – a CALibration Insertion System for the DarkSide-50 dark matter search experiment, DarkSide Collaboration, arXiv:1611.02750, accepted by NIM A
– Effect of Low Electric Fields on Alpha Scintillation Light Yield in Liquid Argon, DarkSide Collaboration, JINST 12 (2017) no.01, P01021