Deep-underground dark matter search with a COSINUS detector prototype

TL;DR

This paper reports the first underground measurement of a NaI cryogenic calorimeter with a novel readout scheme, demonstrating improved particle discrimination and setting competitive limits on dark matter interactions with a small exposure.

Contribution

It introduces the first underground operation of a NaI cryogenic detector using the remoTES readout, enhancing discrimination and sensitivity in dark matter searches.

Findings

Significant improvement in e-/γ to nuclear recoil discrimination.

Five-fold enhancement in nuclear recoil baseline resolution.

Set a limit on dark matter nucleon cross-section with small exposure.

Abstract

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 $e^-$/$\gamma$-events to nuclear recoils was observed with a five-fold improvement in the nuclear recoil baseline resolution, achieving $\sigma$ = 441 eV. Furthermore, we present a limit on the spin-independent dark-matter nucleon elastic scattering cross-section achieving a sensitivity of $\mathcal{O}$(pb) with an exposure of only 11.6 g d.