Search for weakly interacting massive particles with the Cryogenic Dark Matter Search experiment

Abstract

From individual galaxies, to clusters of galaxies, to in between the cushions of your sofa, Dark Matter appears to be pervasive on every scale. With increasing accuracy, recent astrophysical measurements, from a variety of experiments, are arriving at the following cosmological model : a flat cosmology (Ω k = 0) with matter and energy densities contributing roughly 1/3 and 2/3 (Ω m = 0.35, Ω Λ = 0.65). Of the matter contribution, it appears that only ∼ 10% (Ω b ∼ 0.04) is attributable to baryons. Astrophysical measurements constrain the remaining matter to be non-realtivistic, interacting primarily gravitationally. Various theoretical models for such Dark Matter exist. A leading candidate for the non-baryonic matter are Weakly Interacting Massive Particles (dubbed WIMPS). These particles, and their relic density may be naturally explained within the framework of Super-Symmetry theories. Super-Symmetry also offers predictions as to the scattering rates of WIMPs with baryonic matter allowing for the design and tailoring of experiments that search specifically for the WIMPs. The Cryogenic Dark Matter Search experiment is searching for evidence of WIMP interactions in crystals of Ge and Si. Using cryogenic detector technology to measure both the phonon and ionization response to a particle recoil the CDMS detectors are able to discriminate between electron and nuclear recoils, thus reducing the large rates of electron recoil backgrounds to levels with which a Dark Matter search is not only feasible, but far-reaching. This thesis will describe in some detail the physical principles behind the CDMS detector technology, highlighting the final step in the evolution of the detector design and characterization techniques. In iv addition, data from a 100 day long exposure of the current run at the Stanford Underground Facility will be presented, with focus given to detector performance as well as to the implications on allowable WIMP mass-cross-section parameter space. v It is almost impossible to express, within the scope of one or two pages, the immense debts of gratitude I owe to the numerous people who have, directly and indirectly, made this possible. By this I refer not just to the dissertation itself, but the entire Ph.D. process that began when I arrived at Stanford five years ago. Let me begin by thanking Marcia Keating, Dawn Hyde, and Kathleen Guan who were extremely patient and helpful whenever I ran into their offices with the latest emergency regarding the progress of my degree or status of my student visa or (most important of all) my paycheck. Along with the rest of the physics department administerial staff; Rosenna Yau, Cindy Mendel, and Jennifer Conan-Tice, they made it possible for me to concentrate on my work here at Stanford rather than the logistics of my student status. Of course, none of the research that I did would have been possible without the help and support of the Cabrera group. The groups administrative assistant, Linda Hubly, was instrumental in the acquisition of various experimental equipm...

The Cryogenic Dark Matter Search (CDMS II) Experiment - First Results from the Soudan Mine

“…7.2 that this limit is consistent with our expected sensitivity. [40], CDMS I -SUF (blue dashed) [41,43], CDMS II -SUF (blue solid) [42,37], ZEPLIN (magenta solid), CRESST (magenta dashed), and CDMS II -Soudan (black solid). The red region is the DAMA detection claim [39].…”

“…The top figure shows exclusion curves for five models considered by EROS [7] and the bottom figure shows exclusion curves for the eight models WIMP elastic scattering rate for Ge, Si, and Xe. Figure from [37]. .…”

“…Exclusion curves for EDELWEISS (black dashed) [40], CDMS I -SUF (blue dashed) [41,43], CDMS II -SUF (blue solid) [42,37], ZEPLIN (magenta solid), and CRESST (magenta dashed). Cyan region corresponds to allowed models from Fig.…”

“…Under optimal bias conditions, α is usually around 100. Details of ETF are discussed in detail elsewhere [53,54,55,37]. One particularly useful aspect of ETF is that it is a negative feedback process and therefore, stable.…”

Optimizing the design and analysis of cryogenic semiconductor dark matter detectors for maximum sensitivity

“…Before deriving the small signal dynamics and noise about the equilbrium point for the more complex system, let's discuss how the equilibrium itself varies with a change in the voltage biasing [54] and how one can measure R n and R p . Experimentally, the simplest method of doing this is simply to voltage bias with a slow triangle wave so that the voltage drop across L is negligible (Fig.…”