Improved Modeling of Detector Response Effects in Phonon-Based Crystal Detectors Used for Dark Matter Searches

Various dark matter search experiments employ phonon-based crystal detectorsoperated at cryogenic temperatures. Some of these detectors, including certainsilicon detectors used by the SuperCDMS collaboration, are able to achievesingle-charge sensitivity when a voltage bias is applied across the detector.The total amount of phonon energy measured by such a detector is proportionalto the number of electron-hole pairs created by the interaction. However,crystal impurities and surface effects can cause propagating charges to eitherbecome trapped inside the crystal or create additional unpaired charges,producing non-quantized measured energy as a result. A new analytical model fordescribing these detector response effects in phonon-based crystal detectors ispresented. This model improves upon previous versions by demonstrating how thedetector response, and thus the measured energy spectrum, is expected to differdepending on the source of events. We use this model to extract detectorresponse parameters for SuperCDMS HVeV detectors, and illustrate how thisrobust modelling can help statistically discriminate between sources of eventsin order to improve the sensitivity of dark matter search experiments.