Energy Loss Due to Defect Formation from $^{206}$Pb Recoils in SuperCDMS Germanium Detectors

TL;DR

This study measures the energy loss from defect formation caused by lead recoils in germanium detectors at cryogenic temperatures, providing key data for improving dark matter search sensitivity.

Contribution

It presents the first experimental determination of the average displacement threshold energy in germanium, crucial for dark matter detection analysis.

Findings

Energy loss due to defect formation is approximately 6% at 103 keV.

First experimental value for germanium displacement threshold energy: ~19.7 eV.

Implications for future germanium-based dark matter experiments.

Abstract

The Super Cryogenic Dark Matter Search experiment (SuperCDMS) at the Soudan Underground Laboratory studied energy loss associated with Frenkel defect formation in germanium crystals at mK temperatures using in situ $^{210}$Pb sources. We examine the spectrum of $^{206}$Pb nuclear recoils near its expected 103 keV endpoint energy and determine an energy loss of $\left(6.08\pm0.18\right)$ %, which we attribute to defect formation. From this result and using TRIM simulations, we extract the first experimentally determined average displacement threshold energy of $\left(19.7^{+0.6}_{-0.5}\right)$ eV for germanium. This has implications for the analysis thresholds of future germanium-based dark matter searches.