Speaker
Description
We present the first measurements of the COSINUS silicon light detector instrumented with a transition edge sensor (TES) in the new underground setup at LNGS. The detector is operated as a cryogenic light detector for a NaI target crystal, where the measurement of scintillation light in coincidence with the phonon signal enables particle discrimination and thus allows COSINUS to test the DAMA/LIBRA claim with the same target material. While the detector has previously been studied extensively in the above-ground Munich setup, its operation at LNGS constitutes an important milestone in the commissioning of the experiment. Despite its comparatively large mass and geometrically complex design, the detector demonstrates strong performance in its first measurement in the new setup. In this contribution, we focus on the initial detector characterization and on the observed low-energy excess (LEE). We discuss first commissioning results, the detector response in the low-energy region, and the implications of these observations for the understanding of the LEE.