First use of large area SiPM matrices coupled with NaI(Tl) scintillating crystal for low energy dark matter search

Abstract: The long-standing claim of dark matter detection by the DAMA experiment remains a crucial open question in astroparticle physics. A key step towards its independent verification is the development of NaI(Tl)-based detectors with improved sensitivity at low energies. The majority of NaI(Tl)-based experiments rely on conventional photomultiplier tubes (PMTs) as single photon detectors, which present technological limitations in terms of light collection, intrinsic radioactivity and a high noise contribution at keV energies. ASTAROTH is an R&D project developing a NaI(Tl)-based detector where the scintillation light is read out by silicon photomultipliers (SiPM) matrices. SiPMs exhibit high photon detection efficiency, negligible radioactivity, and, most importantly, a dark noise nearly two orders of magnitude lower than PMTs, when operated at cryogenic temperature. To this end, ASTAROTH features a custom-designed cryostat based on a bath of cryogenic fluid, able to safely operate the detector and the read-out electronics down to about 80K. We report the first experimental characterization of 360 g NaI(Tl) detector read out by a large area (5 cm x 5 cm) SiPM matrix. The photoelectron yield obtained with a preliminary configuration is 7.2 photoelectrons/keV, which is rather promising, also in light of several planned developments. The signal-to-noise ratio and the energy threshold attainable with SiPMs is expected to improve the sensitivity for dark matter searches beyond the reach of current-generation PMT-based detectors. This result is the first proof of the viability of this technology and sets a milestone toward the design of future large-scale experiments.