The existence of gravitational effects which do not arise from normal matter is well established; their source is a deep mystery. One possibility motivated by considerations in elementary particle physics is that this “dark matter” consists of undiscovered elementary particles; Weakly Interacting Massive Particles (WIMPs) are one possibility. Evidence for such WIMPs may come from experiments at the Large Hadron Collider at CERN or from sensitive astronomical instruments detecting radiation produced by WIMP-WIMP annihilations in galaxy halos. The orbital motion of the WIMPs in the dark matter halo pervading the galaxy should also result in WIMP-nucleus collisions of sufficient energy to be detected directly by sensitive laboratory apparatus.
The proposed thesis is focused on direct search for WIMPs with the DarkSide experiment, based on the double-phase Liquid Argon time projection chamber (TPC) technique. The DarkSide program combines novel technologies capable of providing a strong suppression of all possible sources of background, able of mimicking the signal expected from a WIMP while retaining a high sensitivity to dark matter interactions.
The DarkSide-50 detector, with a fiducial mass of 50 kg, has been taking data at the Gran Sasso National Laboratories since 2015 and has already achieved the best results with this technique. With three years of data, it will achieve a sensitivity comparable to that of other experiments.
The DarkSide programme envisages a future phase with a detector of 20 ton fiducial mass, named DarkSide-20k, which would achieve the ultimate sensitivity to WIMPs and would have unprecedented potential for solar neutrinos
The thesis project is articulated along three main axes:
1) final analysis of the DarkSide-50 data, including study of the backgrounds and their rejection through detailed Monte-Carlo simulation;
2) simulation studies in view of the DarkSide-20k detector, to evaluate its performance and sensitivity;
3) realization and data analysis of the ARIS test setup for precision measurements of Liquid Argon response, in particular to evaluate the sensitivity of the technique to directional information.