Low-energy spectrum of the BULLKID detector array operated on surface

TL;DR

This paper reports on the first continuous surface operation of the BULLKID detector array, demonstrating its capability to detect low-energy events relevant for dark matter and neutrino research, with effective background rejection.

Contribution

It introduces the BULLKID detector array operated on the surface and showcases its performance in low-energy detection and background rejection without radiation shielding.

Findings

Flat energy spectrum down to 160 eV threshold

Effective background rejection from array segmentation

Successful operation in a surface environment

Abstract

We present the first continuous operation in a surface lab of BULLKID, a detector for searches of light Dark Matter and precision measurements of the coherent and elastic neutrino-nucleus scattering. The detector consists of an array of 60 cubic silicon particle absorbers of 0.34 g each, sensed by cryogenic kinetic inductance detectors. The data presented focusses on one of the central elements of the array and on its surrounding elements used as veto. The energy spectrum resulting from an exposure of 39 hours to ambient backgrounds, obtained without radiation shields, is flat at the level of $(2.0\pm0.1\,{\rm stat.}\pm0.2\,{\rm syst.})\times10^6$ counts / keV kg days down to the energy threshold of $160\pm13$ eV. The data analysis demonstrates the unique capability of rejecting backgrounds generated from interactions in other sites of the array, stemming from the segmented and monolithic structure of the detector.