The detection of a dark matter (DM) particle would deeply contribute to the understanding of the Universe and would shine light on new Physics. The WIMP is an extensively studied DM candidate that would induce nuclear recoils inside a detector. The largest direct projects searching for WIMPs will soon reach the “neutrino floor”, a boundary beyond which a WIMP signal cannot be distinguished from the irreducible background due to neutrinos. The only known principle to overpass this background is to measure the direction of the induced recoils and to correlate it with the expected incoming direction of the WIMPs. This is the principle of directional detection.
In this talk we will introduce MIMAC, a directional detector that measures simultaneously the energy of a particle and reconstructs its track in 3D in an adaptable energy range [150 eV , 30 MeV]. MIMAC is a gaseous µ-TPC in which one can adapt the experimental conditions (target mass, spin, pressure, etc.) to particular DM candidates phenomenology.
We will focus on the study of directionality in the keV-range for which there is a lack of experimental data. In this low energy region, the lengths of the WIMP-induced nuclear recoils lie in the sub-millimeter range. We will show that the diffusion of the primary electrons, usually considered as a limiting phenomenon, improve our directional performances for sub-millimeter tracks! Measuring low-energy recoils implies to operate at high-gain, for which many ions are produced in the avalanche process. We have developed SimuMimac, a simulation tool that investigates the influence of the ions on the signal formation and the 3D reconstruction. SimuMimac agrees with the measurements and shines light on possible deconvolutions of the signal induced by the ions.
Low-energy electrons are of interest to understand the background but also, for instance, to search for Axion-Like Particles. In this talk we will present 3D tracks of electrons down to 150eV. At these energies, only a few primary electrons are generated by the ionization process. We will show that MIMAC is sensitive to the fluctuation of the number of primary electrons and that we can use this phenomenon to determine the gain per primary electrons.