A dark matter search using the final CDMS-II data and 100 mm SuperCDMS germanium detector ionization test

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A dark matter search using the final CDMS-II data and 100 mm SuperCDMS germanium detector ionization test

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Astrophysical observations indicate that approximately 85% of the matter in the universe is nonluminous, nonbaryonic, and nonrelativistic (cold) dark matter. Weakly Interacting Massive Particles (WIMPs) are a particularly well motivated dark matter particle candidate. They would be thermally produced in the early universe and their relics account for the current dark matter abundance. WIMP candidate particles are naturally provided by extensions to the Standard Model of particle physics, such as supersymmetry. The Cryogenic Dark Matter Search (CDMS) experiment operates cryogenic germanium and silicon particle detectors in the low-background environment of the Soudan Underground Laboratory in northern Minnesota to search for WIMP-nucleus scatters while rejecting electron-recoil background. The detectors simultaneously measure the ionization and phonon energies of each scattering event. The difference in ionization yield (ratio of ionization energy to recoil energy) discriminates nuclear recoils from the electron-recoil background efficiently.More sensitive detectors are required to probe the WIMP parameter space with lower WIMP-nucleon scattering cross sections. To support the R&D effort especially the detector R&D and characterization of the SuperCDMS experiment, a new CDMS test facility has been developed on the University of Minnesota campus. This thesis documents the test facility and the work involved in its development. In the test facility, we performed the first ionization collection efficiency measurements of the ionization test devices. The test devices are fabricated with detector-grade germanium crystals that are 100 mm in diameter, which is the largest available, and 33 mm in thickness. The measured efficiencies are consistent with the earlier measurements conducted with smaller Ge crystals, demonstrating that these 100 mm crystals can be used for development of the next generation dark matter detectors.Improvements of data analysis methods can also potentially improve the sensitivity of an experiment. The data taken during the last four runs of CDMS II with total raw exposure 612 kg-day were reprocessed with improved ionization pulse reconstruction algorithm. We present the classic timing analysis with the reprocessed data in this thesis. For the four runs combined, this analysis resulted in a new WIMP-nucleon cross section 4.4×10<super>-44</super>cm<super>2</super> for a WIMP mass of 70 GeV, which is a factor of 1.6 improvement compared to the original c58 classic timing analysis.


University of Minnesota Ph.D. dissertation. July 2014. Major: Physics. Advisor: Vuk Mandic. 1 computer file (PDF); xvi, 315 pages, appendices A-C.

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Zhang, Jianjie. (2014). A dark matter search using the final CDMS-II data and 100 mm SuperCDMS germanium detector ionization test. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/165779.

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