Speaker
Description
BULLKID-DM is an experiment searching for hypothetical WIMP-like particles with mass around 1 GeV/c$^2$ or below and nucleon cross-section below $10^{-41}$ cm$^2$.
The BULLKID experimental setup consists of a stack of 5.5 mm-thick of highly segmented monolithic silicon wafers, enclosed in copper frames. What makes BULLKID different from others solid-state detectors is the reduction of unnecessary holding material and the creation of a fully active volume that allows to achieve superior background rejection via fiducialization techniques. The aim of this detector is also to mitigate the Low Energy Excess, which is currently the background limiting the physics reach of other low energy experiments. For this reason, each wafer is carved into dice of 5 × 5 × 4.5 mm$^3$ and , leaving a 0.5 mm common disk. Each die is instrumented with a Kinetic Inductance Detector, a superconducting LC-resonator acting as a phonon detector. The common disk allows to avoid extra material to hold the dice. The current design relies on 3-inch silicon wafers containing 60 dice instrumented with aluminum KIDs. The current energy threshold is set to 160 eV. A first demonstrator, consisting of a stack of three wafers surrounded by a mild lead shield, has been instrumented in the Laboratory of Cryogenic Detectors at Sapienza University, and it has been successfully calibrated. The commissioning of the full-shielded demonstrator is foreseen in the next months at the Sapienza facilility and in the brand-new cryoplatform at Laboratori Nazionali del Gran Sasso (LNGS), where a reduction of both cosmic muons, by the Gran Sasso rock overburden, and ambient radiation is expected.
The second-phase of BULLKID-DM, is the deployment of the full-scale experimental setup at LNGS. The complete detector consists of approximately 2500 silicon dice, for a total active mass of $\approx$ 800 g, distributed between sixteen 100-mm diameter wafers. Deploying a kg-scale cryogenic calorimeter array with O(200~eV) energy threshold is the main challenge of BULLKID-DM and paves the way to a new era of high exposure measurements in rare event searches. Furthermore, some R\&D activities are also ongoing and include the characterization of germanium-based BULLKID detectors, which show a higher cross-sections for CE$\nu$NS interactions, the design and instrumentation of the 100-mm wafers and instrumentation of KIDs with dedicated phonon collecting structures which increase the responsivity of the sensors.