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Browsing by Subject "CDMS"

Now showing 1 - 5 of 5
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    Advanced analysis and background techniques for the cryogenic dark matter search.
    (2010-01) Qiu, Xinjie
    The Cryogenic Dark Matter Search (CDMS) used Ge and Si detectors, operated at 50mK, to look for Weakly Interacting Massive Particles (WIMPs) which may make up most of the dark matter in our universe. This dissertation describes the simulation, analysis, and results of the first WIMP-search data runs of the CDMS experiment between October 2006 and July 2007 with its 5 Towers of detectors at the Soudan Underground Laboratory. A blind analysis, incorporating improved techniques for event reconstruction and data quality monitoring, resulted in zero observed events. The results of this work place the most stringent limits yet set upon the WIMP-nucleon spin-independent cross section for WIMP masses above 44 GeV/c2, as well as setting competitive limits on spin-dependent WIMP-nucleon interactions.
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    A Computational Evaluation Of Neutron Capture Efficiency In Plastic Scintillators
    (2016-10-05) Schmitz, Ryan; Poehlmann, David-Michael; Rogers, Hannah; Barker, D'Ann; Cushman, Priscilla
    A Monte Carlo study using GEANT4 was performed on the neutron capture efficiency rates achieved by Gd-loaded plastic scintillators. A "deposition efficiency" parameter was defined as the percentage of incident neutrons which were captured in the Gd-loaded scintillator, and whose emitted gammas deposited energy above a certain threshold in a larger layer of plastic scintillator. Deposition efficiency curves were collected for varying thresholds and Gd concentrations, and the results are discussed here.
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    A dark matter search using the final CDMS-II data and 100 mm SuperCDMS germanium detector ionization test
    (2014-07) Zhang, Jianjie
    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 4.4×10-44cm2 for a WIMP mass of 70 GeV, which is a factor of 1.6 improvement compared to the original c58 classic timing analysis.
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    Metal-Doped Plastic Scintillator for Neutron Detection
    (2018) Poehlmann, David-Michael T
    The Super Cryogenic Dark Matter Search (SuperCDMS) is an experiment that looks for dark matter, specifically weakly-interacting massive particles (WIMPs) via nuclear recoils with germanium and silicon atoms. Currently, the SuperCDMS SNOLAB dark matter detector, the successor to SuperCDMS Soudan, is being developed for placement at the SNOLAB research facility in Canada. As the sensitivity of this detector is increased, the suppression of neutron backgrounds through the traditional methods of using highly radiopure materials and passive shielding becomes much more difficult. Single-scatter neutron events can produce nuclear recoils that are indistinguishable from WIMP interactions. These events can be detected by replacing some of the passive neutron shielding with an active neutron veto composed of a metal-loaded plastic scintillator.