Development of a Cryogenic Anti-Coincidence System Based on Scintillating Crystals Read Out with Kinetic Inductance Detectors for BULLKID-DM

Abstract

The BULLKID-DM experiment has been proposed to search for WIMP-like dark matter particles with a mass of 1 GeV or lower and with a WIMP-nucleon interaction cross section down to $10^{-43}$ cm$^2$. To achieve this goal, the experiment utilizes a detector consisting of a stack of 16 silicon wafers instrumented with phonon-mediated superconducting Kinetic Inductance Detectors (KIDs), to be operated at the underground facility of the Laboratori Nazionali del Gran Sasso (LNGS), Italy. To reduce the residual background arising from $γ$-rays, neutrons, and muons, a cryogenic active anti-coincidence system (veto) operating at mK temperature, surrounding the main detector, is under development. The veto detector consists of segmented scintillating crystals read out by phonon-mediated KID light detectors. Current status and future developments of the veto system are presented. In particular, we focus on cryogenic tests of both bismuth germanate (BGO) and gadolinium aluminum gallium garnet (GAGG) crystals, which had been previously chosen as veto candidate crystals according to our preliminary studies on the dependence of their optical properties (i.e. light yield and scintillation decay time) on temperature. We finally present the operation and preliminary tests of a two-module veto prototype with multiplexed readout.