Calibration of Infrared Photons in Cryogenic Germanium Detectors

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Ghaith, Muad
Dark Matter , Cryogenic Detectors , SuperCDMS , WIMP
A significant evidence from galaxies and astrophysical observations, suggests that ~ 85% of the matter in our Universe is invisible matter. The observations of the so-called “dark matter” suggest that it consists of non-relativistic, non-baryonic particles, which seldom interact with baryonic matter, or with each other. Many experiments are searching for dark matter, each of which is based on a particular dark matter candidate. Weakly Interacting Massive Particles (WIMPs) are one of the well-motivated candidates for dark matter. So far, no answers were provided by the Standard Model of particle physics to the dark matter puzzle. The Super Cryogenic Dark Matter Search experiment (SuperCDMS) is considered one of the pioneer experiments in the direct search for WIMPs. It is based primarily on deploying germanium and silicon detectors at cryogenic temperatures to search for direct WIMP-nucleus elastic scattering interaction through which lattice vibrations are generated and sensed in one of the coldest detectors ever built. The new phase of SuperCDMS experiment at SNOLAB is aiming to be sensitive to the lower WIMP mass scale. Therefore, a lower background and detector threshold energy is a necessity, and the detectors need to be calibrated and tested for the new proposed sensitivity. The tests include high bias voltages, which are required to increase the gain in signal-to-noise ratio and to allow for the detection of low energy events using the phonon signal. However, the upper limit and polarity for the bias voltage need further studies in order to understand the variation of the detector’s response to high voltage. Therefore, we performed the breakdown measurement (chapter 4) at Queen’s Test Facility. Moreover, detectors have to be calibrated before being utilized in measuring low energy interactions, and that is what lead to the use of infrared photons. Once we can calibrate and understand the behavior of infrared photons in germanium detectors, they can be utilized in calibrating germanium detectors at the lower energy scale. Therefore, we performed the infrared calibration measurement which represents the bulk of the work in my thesis.
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