The ASTAROTH project

The most discussed topic in direct searches for dark matter is arguably the verification of the DAMA claim. In fact, the observed annual modulation of the signal rate in an array of NaI(Tl) detectors can be interpreted as the awaited signature of dark matter interactions. Several experimental groups are currently engaged in the attempt to verify such a game-changing claim with the same target material. However, all present-day designs are based on a light readout via Photomultiplier Tubes, whose high noise makes it challenging to achieve a low background in the 1–6 keV energy region of the signal. Even harder would be to break below 1 keV energy threshold, where a large fraction of the signal potentially awaits to be uncovered. ASTAROTH is an R&D project to overcome these limitations by using Silicon Photomultiplier (SiPM) matrices to collect scintillation light from NaI(Tl). The all-active design based on cubic crystals is operating in the 87–150 K temperature range where SiPM noise can be even 100× lower than that of PMTs. The cryostat was developed following an innovative design and is based on a copper chamber immersed in a liquid-argon bath that can be instrumented as a veto detector. We have characterized separately the crystal and the SiPM response at low temperature, and we have proceeded to the first operation of a NaI(Tl) crystal read by SiPMs in cryogeny.