The ReD experiment in DarkSide's Program: nuclear recoils for Dark Matter studies

While there is strong astrophysical and cosmological evidence for dark matter (DM), its precise nature is one of the most significant open questions in modern physics. Weakly interacting massive particles (WIMPs) are a particularly compelling class of dark matter candidates with masses up to about 10 TeV and couplings to ordinary matter at the weak scale. Direct detection experiments are aiming to observe the low energy (<150 keV) scattering of dark matter off normal matter. No conclusive signals have been observed yet. The DarkSide Program aims at direct WIMP dark matter detection using dual-phase (liquid and vapor) Liquid Argon Time Projection Chambers (LAr TPCs). The program is staged with detectors of increasing mass and sensibility, installed at Laboratori Nazionali del Gran Sasso (LNGS) in Italy. Inside the DarkSide Program the DarkSide-50 experiment is currently operating with an active mass of about 50 kg of Underground Argon (UAr), which is greatly reduced in radioactive 39Ar. Next DarkSide Program step is then the DarkSide-20k experiment, with an fiducial mass of 20 t for a total exposure of 100 t yr to be accumulated in a run of 5 yr. With this exposure and beyond, at which the onset of neutino-induced nuclear recoils has to be considered, sensitivity to the direction of the nuclear recoils originating from WIMP scatter would be a very highly desirable capability for a direct dark matter detection experiment. Inside DarkSide Program the Recoil Directionality (ReD) experiment first aim to reveals directionality signature in energy nuclear recoils of the order of expected WIMP-Ar scattering recoils. Also a more systematic study on nuclear recoil is needed down to very low energy recoil ( O(1 keVNR)). In order to have directional experiment with controlled recoil energy, it is necessary the use of low energy and as mono-energetic as possible neutrons in a closed kinematics approach. To this end ReD in now installed (at the moment of writing even running) at Laboratori Nazionali del Sud (LNS) in Catania, Italy, where neutrons are produced via p(7Li; n)7Be reaction using their Tandem accelerator. Moreover in the ReD experiment are implemented more potential DarkSide-20k future solutions, so that ReD is also part of DarkSide-20k R&D specific program. In the first part of this work, after an introduction on the necessity to introduce the DM to explain some cosmological phenomenons that vice versa would remain without explanations, a description on LAr TPCs operating principle is delineate, as a brief description on the DarkSide Program. Particular attention is reserved on Argon physics in those parts that have impact on TPCs technology or potentially on ReD experiment results. ReD is an ongoing experiment, more in the commissioning phase that in the data taking phase. Or better, we can say on the transition phase between the two phases. Like in each small R&D activity, I have had the fortune to face almost every aspect of this research, from alternative configurations studies, to the hardware, going through on Monte Carlo simulations up to the data analysis. As it is not useful to report all these activities, I have decided to focus this work on the last configuration we choice (although something on alternative configurations and activities is also reported). Therefore in the second part of this work I describe the ReD experiment and its constituent systems in the LNS configuration, as also I report some preliminary results on data took during the first two technical beamtimes, on June and July, 2018. At the time of writing (September, 2018) a third data taking is ongoing at LNS.