The Dark Matter problem

A variety of astrophysical and cosmological observations indicate that 83% of the matter in the Universe is non-baryonic and non-luminous, and its nature is one of the fundamental puzzles in physics today. An attractive solution for the so-called Dark Matter (DM) problem can be given by the particle physics in the form of a massive (~100 GeV) weakly-interacting neutral particle (WIMP) predicted in the super-symmetric extension of the Standard Model. If such particle exists, it could have been produced shortly after the Big Bang and, if sufficiently stable, eventually formed a relic gas in the present universe. The most promising way to detect WIMP interactions with matter is via their rare elastic scattering with atomic nuclei through:

χ+(A,Z)at rest → χ+(A,Z)recoil

DM direct search requires the capability of measuring recoil energies in the region of a few tens of keV with negligible backgrounds. From the experimental point of view those constraints call for massive (~ton scale) detectors with an excellent rejection power of the natural sources of radiation. For example, assuming a “canonical” WIMP halo model of 100 GeV mass, a WIMP-proton cross-section of 10-44 cm2 (10-8 pb) would yield about 1 recoil event per day per ton above 30 keVr for an argon detector.

Dual-phase argon (Ar) time projection chambers (TPC) offer the best prospect to detect dark matter signals. The elastic scattering of WIMPs from argon nuclei is measurable by observing free electrons from ionization and photons from scintillation, which are produced by the recoiling Ar nucleus interacting with neighbouring atoms. The kinetic energy of these recoils is in the range of 1-100 keV. The advantage of having a dual-phase (gas-liquid) detection technique lies in the fact that both scintillation light and ionization charge can be measured at the same time, providing a powerful discrimination method between nuclear recoils and electron recoils produced by background events. The ionization and scintillation signals are measured by two arrays of light sensors (like Silicon Photomultipliers) placed on the top and bottom parts of the active region.

The CIEMAT dark matter group is currently involved in the analysis of the dark matter data of the DEAP-3600 experiment at SNOLAB in Canada and is carrying out a major R&D program in particle detectors based on noble gases, investigating frontiers aspects of this technology. At the same time, our group has a primary role in the design and construction of the DarkSide-20k detector at LNGS laboratory in Italy. This experiment will be the most sensitive for direct detection of dark matter in operation during the next decade. We are playing leading roles in several software and hardware activities like the Monte Carlo simulation, the background calculation and the detector construction. Find more information selecting them in the PROJECTS and RESEARCH OUTPUT menu bars.