Browsing by Subject "Dark matter"

Now showing 1 - 6 of 6
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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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    Beyond the Standard Model applications of holography
    (2020-07) Buyukdag, Yusuf
    In this thesis, we explore beyond the Standard Model of particle physics by taking advantage of the holography approach. First of all, we consider a supersymmetric model that uses partial compositeness to explain the fermion mass hierarchy and predict the sfermion mass spectrum. Linear mixing between elementary superfields and supersymmetric operators with large anomalous dimensions is responsible for simultaneously generating the fermion and sfermion mass hierarchies. After supersymmetry is broken by the strong dynamics, partial compositeness causes the first- and second-generation sfermions to be split from the much lighter gauginos and third-generation sfermions. The sfermion mass scale is constrained by the observed 125 GeV Higgs boson, leading to stop masses and gauginos around 10--100 TeV and the first two generation sfermion masses around 100--1000 TeV. This gives rise to a splitlike supersymmetric model that explains the fermion mass hierarchy while simultaneously predicting an inverted sfermion mass spectrum consistent with the Large Hadron Collider and flavor constraints. The lightest supersymmetric particle is a gravitino in the keV to TeV range, which can play the role of dark matter. This brings us to the second topic that we consider, a novel realization of the Dynamical Dark Matter (DDM) framework in which the ensemble of particles collectively constitute dark matter and they are the composite states of a strongly-coupled conformal field theory. Cosmological abundances for these states are then generated through mixing with an additional, elementary state. As a result, the physical fields of the DDM dark sector at low energies are partially composite. We calculate the masses, lifetimes, and abundances of these states --- along with the effective equation of state of the entire ensemble. Our results suggest the existence of a potentially rich cosmology associated with partially composite DDM.
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    Characterizing the multicomponent density structure of galaxies
    (2012-12) Dhar, Barun Kumar
    Abridged) Quantifying the 3D spatial structure of galaxies forms a key element in furthering our understanding of the formation and evolution of galaxies and consequently the universe. What we observe, however, is a 2D projection (on the plane of the sky) of the intensity of light of galaxies. Inferring the intrinsic 3D distribution is critical for the understanding of galaxies, but technically difficult. Despite 80 years of research, we still do not have a consensus on a model that can describe the 2D projected light of galaxies over their entire spatial extent.In the first part of this work, I summarize existing models and then show how one can efficiently model the high resolution light profiles of galaxies to quantify both the 2D and the 3D distributions and also infer the existence of multiple components in a galaxy. Using data of 23 galaxies from the Virgo Cluster, I present models of their light profiles with mean residuals of ~ 3% (that is consistent with measurement errors) over a radial range spanning an order of up to 10^5 -- an unprecedented accuracy over such large spatial extent. Consequences of such models are discussed, especially an evidence for an universality in the functional form that describes both the baryonic and dark matter distributions. In the second part of this work, I demonstrate a novel way of obtaining projections of intrinsic quantities when the standard method does not yield analytical solutions, i.e. a procedure to perform otherwise difficult analytical integrations.
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    Development of CDMS-II surface event rejection techniques and their extensions to lower energy thresholds
    (2014-12) Hofer, Thomas James
    The CDMS-II phase of the Cryogenic Dark Matter Search, a dark matter direct-detection experiment, was operated at the Soudan Underground Laboratory from 2003 to 2008. The full payload consisted of 30 ZIP detectors, totaling approximately 1.1 kg of Si and 4.8 kg of Ge, operated at temperatures of 50 mK. The ZIP detectors read out both ionization and phonon pulses from scatters within the crystals; channel segmentation and analysis of pulse timing parameters allowed effective fiducialization of the crystal volumes and background rejection sufficient to set world-leading limits at the times of their publications. A full re-analysis of the CDMS-II data was motivated by an improvement in the event reconstruction algorithms which improved the resolution of ionization energy and timing information. The Ge data were re-analyzed using three distinct background-rejection techniques; the Si data from runs 125 - 128 were analyzed for the first time using the most successful of the techniques from the Ge re-analysis. The results of these analyses prompted a novel "mid-threshold" analysis, wherein energy thresholds were lowered but background rejection using phonon timing information was still maintained. This technique proved to have significant discrimination power, maintaining adequate signal acceptance and minimizing background leakage. The primary background for CDMS-II analyses comes from surface events, whose poor ionization collection make them difficult to distinguish from true nuclear recoil events. The novel detector technology of SuperCDMS, the successor to CDMS-II, uses interleaved electrodes to achieve full ionization collection for events occurring at the top and bottom detector surfaces. This, along with dual-sided ionization and phonon instrumentation, allows for excellent fiducialization and relegates the surface-event rejection techniques of CDMS-II to a secondary level of background discrimination. Current and future SuperCDMS results hold great promise for mid- to low-mass WIMP-search results.
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    Measurement of nuclear recoils in the CDMS II Dark Matter Search
    (2014-12) Fallows, Scott Mathew
    The Cryogenic Dark Matter Search (CDMS) experiment is designed to directly detect elastic scatters of weakly-interacting massive dark matter particles (WIMPs), on target nuclei in semiconductor crystals composed of Si and Ge. These scatters would occur very rarely, in an overwhelming background composed primarily of electron recoils from photons and electrons, as well as a smaller but non-negligible background of WIMP-like nuclear recoils from neutrons. The CDMS~II generation of detectors simultaneously measure ionization and athermal phonon signals from each scatter, allowing discrimination against virtually all electron recoils in the detector bulk. Pulse-shape timing analysis allows discrimination against nearly all remaining electron recoils taking place near detector surfaces. Along with carefully limited neutron backgrounds, this experimental program allowed for ``background-free'' operation of CDMS~II at Soudan, with less than one background event expected in each WIMP-search analysis. As a result, exclusionary upper-limits on WIMP-nucleon interaction cross section were placed over a wide range of candidate WIMP masses, ruling out large new regions of parameter space.These results, like any others, are subject to a variety of systematic effects that may alter their final interpretations. A primary focus of this dissertation will be difficulties in precisely calibrating the energy scale for nuclear recoil events like those from WIMPs.Nuclear recoils have suppressed ionization signals relative to electron recoils of the same recoil energy, so the response of the detectors is calibrated differently for each recoil type. The overall normalization and linearity of the energy scale for electron recoils in CDMS~II detectors is clearly established by peaks of known gamma energy in the ionization spectrum of calibration data from a $^{133}$Ba source. This electron-equivalent (keV$_mathrm{ee}$) energy scale enables calibration of the total phonon signal (keV$_mathrm{t}$) by enforcing unity yield for electron recoils, in aggregate. Subtracting an event's Luke phonon contribution from its calibrated total phonon energy (keV$_mathrm{t}$), as measured by the ionization signal, results in a valid measure of the true recoil energy (keV$_mathrm{r}$) for both electron and nuclear recoils.I discuss systematic uncertainties affecting the reconstruction of this recoil energy, the primary analysis variable, and use several methods to constrain their magnitude. I present the resulting adjusted WIMP limits and discuss their impact in the context of current and projected constraints on the parameter space for WIMP interactions.
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    Model-free analysis of quadruply imaged gravitationally lensed systems.
    (2015-04) Woldesenbet, Addishiwot
    Gravitational lensing has proven to be a very valuable tool as a probe to better understand our universe. Parametric modeling of one multiple image gravitational lens system at a time is a common practice in the field of lensing. Instead of individual lens modeling, an alternative approach is to use symmetries in different spaces to make conclusions about families of lenses. The latter method is the focus of this thesis. Three types of lenses are defined based on whether they do or do not obey two-fold and double mirror symmetries. The analysis concentrates on quadruply imaged systems, or quads, and uses only the relative polar angles of quads around the center of the lens. The analysis is statistical in nature, and model-free because its conclusions relate to whole classes of models, instead of specific models. The work done here is twofold. Firstly, exploratory analysis is done to check for possible existence of degeneracies. Type I lenses which obey both symmetries mentioned above are found to form a nearly invariant surface in the 3D space of relative image angles. In the same space, lenses that break the double mirror symmetry, grouped as Type II, form two distinct surfaces. In addition, degeneracy in this class of lenses is discovered. A preliminary study of the last group of lenses, Type III, that break both symmetries, is done. Secondly, quad distributions in the 3D space from each of the three families were compared to observed galaxy-lens quads. Three quarters of observed quads were inconsistent with the distribution of quads of Type I lenses. Type II lenses reproduce most individual lens systems but fail to reproduce the population properties of observed quads. Preliminary exploration of Type III lenses shows a very promising agreement with observations. Examples of Type IIIs are lenses with substructure (with clump masses larger than those responsible for flux ratio anomalies in quads), and lenses with luminous or dark nearby perturber galaxies, or line of sight structures.