Sodium iodide (NaI) based cryogenic scintillating calorimeters using quantum sensors for signal read out have shown promising first results towards a model-independent test of the annually modulating signal detected by the DAMA/LIBRA dark matter experiment. The COSINUS collaboration has previously reported on the first above-ground measurements using a dual channel readout of phonons and light based on transition edge sensors (TESs) that allows for particle discrimination on an event-by-event basis. In this letter, we outline the first underground measurement of a NaI cryogenic calorimeter read out via the novel remoTES scheme. A 3.67 g NaI absorber with an improved silicon light detector design was operated at the Laboratori Nazionali del Gran Sasso, Italy. A significant improvement in the discrimination power of e−/γ-events to nuclear recoils was observed with a five-fold improvement in the nuclear recoil baseline resolution, achieving σ = 441 eV. Furthermore, we present a limit on the spin-independent dark-matter nucleon elastic scattering cross-section achieving a sensitivity of O(pb) with an exposure of only 11.6 g d.
@article{arxiv.2307.11139,
title = {Deep-underground dark matter search with a COSINUS detector prototype},
author = {The COSINUS Collaboration and G. Angloher and M. R. Bharadwaj and I. Dafinei and N. Di Marco and L. Einfalt and F. Ferroni and S. Fichtinger and A. Filipponi and T. Frank and M. Friedl and A. Fuss and Z. Ge and M. Heikinheimo and M. N. Hughes and K. Huitu and M. Kellermann and R. Maji and M. Mancuso and L. Pagnanini and F. Petricca and S. Pirro and F. Proebst and G. Profeta and A. Puiu and F. Reindl and K. Schaeffner and J. Schieck and D. Schmiedmayer and C. Schwertner and K. Shera and M. Stahlberg and A. Stendahl and M. Stukel and C. Tresca and F. Wagner and S. Yue and V. Zema and Y. Zhu},
journal= {arXiv preprint arXiv:2307.11139},
year = {2025}
}