Demonstration of Surface Electron Rejection with Interleaved Germanium Detectors for Dark Matter Searches

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The SuperCDMS experiment in the Soudan Underground Laboratory searches for dark matter with a 9-kg array of cryogenic germanium detectors.

• Symmetric sensors on opposite sides measure both charge and phonons from each particle interaction, providing excellent discrimination between electron and nuclear recoils, and between surface and interior events.
• Surface event rejection capabilities were tested with two $^{210}$Pb sources producing $\sim$130 beta decays/hr.
• In $\sim$800 live hours, no events leaked into the 8--115 keV signal region, giving upper limit leakage fraction $1.7 \times 10^{-5}$ at 90% C.L., corresponding to $< 0.6$ surface event background in the future 200-kg SuperCDMS SNOLAB experiment.