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 8–115Â 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 .