Simulating the Phonon Collection Efficiency in Kinetic Inductance Phonon-Mediated Detectors

Kinetic inductance phonon-mediated (KIPM) detectors are microcalorimeters that leverage microwave kinetic inductance detectors (MKIDs) to sense phonon signals. KIPM detectors are a promising technology for detecting sub-GeV particle dark matter (DM) because of their potential eV-scale sensitivity. To improve the design of these detectors, we use G4CMP simulations to study the effects of detector geometry on measurable physical parameters including the phonon collection efficiency (η_ph), the efficiency with which energy deposited in the substrate is absorbed by the sensor. Increasing η_ph by optimizing detector design enables detection of rare events such as DM by maximizing signal. In this presentation, I will discuss simulating η_ph for a KIPM detector tested at the Northwestern EXperimental Underground Site to study phonon absorption at substrate-sensor interfaces and phonon loss to insensitive detector elements. As outcomes of this presented work, we compare simulated η_ph to experimentally measured values and demonstrate a KIPM detector simulation chain from energy deposition in the substrate to realistic readout signals.