The Proof-of-Principle of the SABRE experiment for the search of galactic dark matter through annual modulation

The SABRE experiment aims to detect the annual modulation of the dark matter interaction rate by means of ultra-high purity NaI(Tl) crystals immersed in a liquid scintillator (LS) active veto. Located at the Laboratori Nazionali del Gran Sasso, in Italy, it is currently in a Proof-of-Principle phase to assess the radiopurity of the crystals as well as the efficiency of the LS veto. The results on the radiopurity of a 3.4 kg NaI(Tl) crystal grown within the SABRE Collaboration will be presented and discussed. The crystal has an unprecedented low potassium content, which has been determined with direct counting to be lower than 4.7 ppb at 90% C.L.. The average background rate in the [1-6] keV energy region of interest is (1.20 ± 0.05) counts/day/kg/keV, which represents an important breakthrough after DAMA/LIBRA. Moreover, further developments based on data from zone refining purification tests are discussed, and a projected background rate for future SABRE detectors lower than 0.2 counts/day/kg/keV in [1-6] keV is determined. Assuming this value as the average background level in the region of interest, after 3 years of data taking with a total mass of 50 kg, the SABRE experiment is expected to be sensitive to spin-independent WIMP-nucleon scattering cross sections down to 1.3×10−42 cm2 for a WIMP mass of 30–40 GeV. With the predicted background level, based on data reported in this thesis, the SABRE experiment will definitely probe the DAMA/LIBRA finding with high statistical significance in a few years.