SIMULTANEOUS MEASUREMENT OF PHONONS AND IONIZATION USING SICADS

Our group at Stanford has configured a double-sided Silicon Crystal Ac oustic Detector (SiCAD) for simultaneous measurement of both phonons a nd ionization. This detector operates at approximately 370mK and consi sts of Ti Transition Edge Sensors (TES), having microsecond resolution times, patterned on both sides of a 300 mum thick Si wafer. Distingui shing an electron-recoil event from a nuclear-recoil event is possible due to the different partitioning of energy into phonons vs. ionizati on for the two types of event. This is a powerful background rejection technique for neutrino physics experiments and dark matter searches w here the events of interest are nuclear-recoils. In addition, the phon on sensor is position sensitive. In particular, it determines the dept h of an event and can be used to reject events occurring near the surf ace. This detector also allows us to refine our recent measurement of the fraction of phonon energy propagating ballistically from nuclear-r ecoil events1.