Speaker
Description
Kinetic inductance phonon-mediated (KIPM) detectors are superconducting microcalorimeters that show promise in applications toward low-threshold rare-event searches. Despite an excellent sensor energy resolution, the overall energy resolution of KIPM detectors is limited by an observed single-percent phonon collection efficiency. Monte Carlo simulations of charge and phonon processes using the Geant4 Condensed Matter Physics (G4CMP) package provide a microphysical picture of KIPM detectors that is not directly accessible through experimental measurements. By comparing these simulations to position-dependent pulsed LED measurements of a KIPM detector, we illustrate the mechanisms of phonon loss that underpin our low phonon collection efficiency. In this talk, we will present simulation results of position-dependent phonon energy collection as well as phonon lifetimes. We will then compare these results to pulsed LED measurements, which were enabled by use of a micro-electro-mechanical system to steer the optical beam over the full footprint of the 2.2 cm $\times$ 2.2 cm silicon chip. We will also illustrate new developments in the G4CMP software package for state-of-the-art modeling of phonon-quasiparticle processes in superconducting thin films.
