Final results of CALDER: kinetic inductance light detectors to search for rare events

The next generation of bolometric experiments searching for rave events, in particular for the neutrino-less double beta decay, needs fast, high-sensitivity and easy-to-scale cryogenic light detectors. The CALDER project (2014-2020) developed a new technology for light detection at cryogenic temperature. In this paper we describe the achievements and the final prototype of this project, consisting of a 5×5cm2, 650?m thick silicon substrate coupled to a single kinetic inductance detector made of a three-layer aluminum-titanium-aluminum. The baseline energy resolution is 34 ± 1 (stat)± 2 (syst) eV RMS and the response time is 120?s. These features, along with the natural multiplexing capability of kinetic inductance detectors, meet the requirements of future large-scale experiments.