The SuperCDMS Experiment
The next generation of the CDMS Experiment is SuperCDMS, which aims to increase the limits on WIMP detection by two orders of magnitude. SCDMS is currently underway at the Soudan mine laboratory but will soon move to a deeper facility atSNOLAB located in the Vale Inco Mine in Sudbury Canada. The SNOLAB facility, as it is deeper underground, will provide better shielding from cosmological radiation. This will allow for increased limits which will increase the probability of correctly identifying a dark matter particle.
The SuperCDMS detectors are based off of the CDMS II detectors. The following discussion highlights the difference between the two models. Before reading below, make sure to learn about the CDMS II detectors here. Both versions use a combination of phonon and charge detection in germanium and silicon crystals.
The most significant difference between CDMS II and SuperCDMS is the change from ZIP to iZIP (Inter-digitized Z-sensitive Ionization and Phonon) detectors. The largest source of noise in the ZIP detectors occurred from surface events which contaminate the results, as surface events are most likely not WIMPS but instead a different form of radiation. In the ZIP detectors the electrons and holes (caused by a collision by a particle with the crystal's nucleus) drift to opposite sides. Remember that the one side of the detectors is under positive voltage and the other has a negative voltage so that electrons and holes drift to opposite sides. After a surface event on one side, the large distance to the opposite side that the electrons or holes have to travel made it difficult to understand exactly where the collision was occurring. To solve this issue, the iZIP was designed to cause electrons and holes to drift to opposite sides as before; however, for surface events both electrons and the holes drift to the same side. This was done by having ground voltages dispersed on each side. For example, on the positive side of the detector, small neutral areas would draw any holes created near the surface, but holes more toward the center would drift toward the side with a negative voltage. The iZip effectively eliminates the problem of the ZIP detectors, since surface events would only be detected on one side and are thus easily eliminated.
Other more minor changes from ZIP to iZip detectors are an new design for the TES to optimize size and efficiency of energy detection by changing the shape of the TES and reducing the size of the aluminum fins.
Information adapted from the collaboration website at cdms.berkeley.edu