Detector Development and Test Facility Commissioning for SuperCDMS
Dark Matter , CDMS
SuperCDMS, the next stage of the Cryogenic Dark Matter Search (CDMS), uses cylindrical germa- nium crystals as particle detectors to measure phonon and ionization signals resulting from particle interactions. The aim of CDMS is to identify and measure interactions from dark matter particles (WIMPs). Phonons produced during a particle interaction are absorbed by sensors on the detector surface and are measured through the change in the sensors' temperature dependent resistance. Electrodes on the detector surface create an electric eld causing charges released during an inter- action to drift through the detector and produce an ionization signal. Surface events, which are interactions that occur within a few m from the electrodes, cause a reduced ionization signal due to di usion of some of the initially hot charge carriers into the electrode. Because the ability of CDMS to discriminate between a WIMP interaction and background radiation is based on the ratio of phonon to ionization energies, surface events cause a signal similar to a WIMP interaction and are currently the largest source of background. A detector test facility at Queen's University has been commissioned to characterize detectors and test new detector technology. Multiple detectors have been characterized and many tungsten samples have been measured. Two sets of experiments were performed to test new detector designs. To possibly reduce surface events, an insulating layer was deposited on a germanium detector be- neath the electrode to prevent back di usion of charge into the electrode. To possibly simplify the phonon sensor production process, di erent cryogenic glues were used to attach silicon wafers with a tungsten lm to the crystal surface and phonon propagation through these glues was measured. The most e ective cryogenic glue for coupling tungsten samples to CDMS detectors was found to be Araldite epoxy. Both experiments were successful at measuring interactions. Energy calibrations were performed on both charge and phonon sensors. Further research is required to determine the success of reducing surface events with an insulating layer.