Impact of the position effects in the energy calibration of the BULLKID detector

Abstract

BULLKID is a cryogenic solid-state detector based on an array of silicon dice equipped with Kinetic Inductance Detectors (KIDs) for low-mass dark matter searches and coherent elastic neutrino-nucleus scattering. Energy calibration can be performed using optical LED photon bursts, which are absorbed within the first few hundred nanometers of the substrate. An energy calibration using a $^{241}$Am gamma-ray source revealed a $<10\%$ discrepancy with the LED calibration. A recent study by Matava and Williams suggested that phonon statistics and phonon collection varying with the interaction position could explain such a discrepancy. This work evaluates the impact of these effects on the calibration of the BULLKID detector, demonstrating they both have a negligible effect. We clarify the results obtained during the $^{241}$Am calibration regarding the origin of the observed discrepancy.