Performance of a Kinetic Inductance Phonon-Mediated Detector at the NEXUS Cryogenic Facility

TL;DR

This study evaluates a prototype kinetic inductance phonon-mediated detector for dark matter searches, demonstrating improved energy resolution but limited phonon collection efficiency, with insights into device performance and noise characteristics.

Contribution

The paper presents the first characterization of a KIPM detector at Fermilab, showing enhanced baseline resolution and modeling of pulse shape and noise to inform future detector improvements.

Findings

Baseline energy resolution of 2.1 eV, twice the state-of-the-art.

Energy deposition resolution limited to 318 eV due to phonon collection efficiency.

Quasiparticle lifetime and noise spectra analyzed to understand sensor performance.

Abstract

Microcalorimeters that leverage microwave kinetic inductance detectors to read out phonon signals in the particle-absorbing target, referred to as kinetic inductance phonon-mediated (KIPM) detectors, offer an attractive detector architecture to probe dark matter (DM) down to the fermionic thermal relic mass limit. A prototype KIPM detector featuring a single aluminum resonator patterned onto a 1-gram silicon substrate was operated in the NEXUS low-background facility at Fermilab for characterization and evaluation of this detector architecture's efficacy for a dark matter search. An energy calibration was performed by exposing the bare substrate to a pulsed source of 470 nm photons, resulting in a baseline resolution on the energy absorbed by the phonon sensor of $2.1\pm0.2$ eV, a factor of two better than the current state-of-the-art, enabled by millisecond-scale quasiparticle lifetimes. However, due to the sub-percent phonon collection efficiency, the resolution on energy deposited in the substrate is limited to $\sigma_E=318 \pm 28$ eV. We further model the signal pulse shape as a function of device temperature to extract quasiparticle lifetimes, as well as the observed noise spectra, both of which impact the baseline resolution of the sensor.