Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 69-02, Section: B, page: 1071. Adviser: Kevin Pitts. Includes bibliographical references (leaves 142-145) Available on microfilm from Pro Quest Information and Learning.

<p> In this work, we consider two different models of dark matter and set limits on results of experiments. One is a dynamic dark matter scenario where we put limits on parameters observable by experiments DAMA and XMASS through nuclear recoil of detector atoms (direct detection). The second is a case of dark matter annihilation into positrons and electrons and the signal this would produce on measured values of positron flux and ratio of electron to positron (indirect detection). The values of these quantities as measured by FERMI and PAMELA experiments are observed and an explanation using a dark matter annihilation is presented vs astrophysical sources of particles. </p><p> We explore a dynamic dark matter scenario with an ensemble of dark matter particles that starts at <i>m</i>₀ and spans a comb of particles separated by <i>j</i>^&delta;&Delta;<i> m</i>. We verify the model by using &Delta;<i>m</i> = &infin; and comparing the predictions to a non dynamic model for the same mass <i> m</i>0. We then observe the wider set of possibilities available with the dynamic dark matter model compared with the single mass case vis a vis constraints set by <i>NaI</i> and <i>Xe</i> detectors published by the DAMA and XMASS collaborations and check for validity of model against these measurements. </p><p> The Fermi experiment has measured the cosmic ray electron+positron spectrum and positron fraction [&fcy;e+/(&fcy;e⁺+e^&minus;)], and PAMELA has measured the positron fraction with better precision. While the majority of cosmic ray electrons and positrons are of astrophysical origin, there may also be a contribution from dark matter annihilation in the galactic halo. The upcoming results of the AMS experiment will show measurements of these quantities with far greater precision. One dark matter annihilation scenario is where two dark matter particles annihilate directly to e⁺ and e^&minus; final states. In this article, we calculate the signature &ldquo;bumps&rdquo; in these measurements assuming a given density profile (NFW profile). If the dark matter annihilates to electrons and positrons with a cross section <i>&sigma;v</i> &sim; 10^&minus;26 cm³/s or greater, this feature may be discernible by AMS. However, we demonstrate that such a prominent spectral feature is already ruled out by the relative smoothness of the positron + electron cosmic ray spectrum as measured by Fermi. Hence we conclude that such a feature is undetectable unless the mass is less than &sim;40 GeV.</p><p>

<p> The high-energy universe is known to be violent. Ultra High Energy Cosmic Rays (UHECRs) have been observed with kinetic energies exceeding 10²⁰ eV. Their origin, despite decades of observations, remains elusive. A unique probe of the sources and production mechanisms of these high energy cosmic rays can be neutrinos, since they are inevitably produced when high-energy protons interact. The IceCube Neutrino Observatory, located at the geographical South Pole in Antarctica, continuously monitors a total volume of 1 km³ of clear Antarctic ice for neutrino interactions. For this purpose, a total of 5160 optical sensors (photomultiplier tubes) have been melted deep into the glacier at depths between 1450m and 2450m. In 2013 IceCube reported one of its biggest discoveries, the observation of highly energetic neutrinos that are consistent with a possible extra-galactic origin. </p><p> In this dissertation we use IceCube data (recorded from 2012 to 2015) to study the spectral properties of this astrophysical neutrino flux with focus on electron and tau neutrino flavors. We developed a new neutrino identification and muon background rejection method using state-of-the-art machine-learning techniques, more specifically multi-class gradient boosted decision trees. In addition to enlarging the number of detected neutrino events (>10x increase over previous works), we lowered the energy threshold to below 1 TeV and thereby greatly improved upon the control and treatment of systematic uncertainties. The sample contains ~400 astrophysical electron and tau neutrinos, which increases the significance of the original discovery to beyond 8 standard deviations. We find the astrophysical neutrino flux to be well described by a single power-law consistent with expectations from Fermi-type acceleration of high-energy particles at astrophysical sources and obtain leading constraints on its properties. We further studied the possibility of additional spectral complexity, which significantly increases measurement uncertainties. No evidence for such scenarios was found. Finally we searched for a contribution from atmospheric neutrinos related to heavy meson (charm) decay in Earth's atmosphere and derive a flux upper limit of 4.8 times the benchmark pQCD flux prediction at 90% confidence level, dominated by systematic uncertainties, especially related to photon transport in the glacial ice.</p><p>

We have begun development of a tool for investigating the bound state dynamics of single electron systems in intense fields. This was done by implementing the method of uniform complex scaling in a 1D test system in two different ways and have shown that the use of the "c-norm" in non-Hermitian quantum mechanics can fail for time dependent simulations. We have developed the method of complex backscaling which transforms the wavefunction from the complex scaled space back into real space and have shown that it is more robust than the "c-norm" and predicts the correct ionization when compared to simulations done in real space. We have also begun using the complex scaling method in a 2D NZ model but it seems that the nature of the potential requires a more difficult type of scaling which causes problems within the calculations.

<p> In this work, a novel method for charging solid state Marx generators is described for the first time. We first review the utility of modulators for powering high power microwave devices. The principal of operation of the Marx generator is then described starting with the classic topology and leading to solid state topologies. The concept of a generalized Marx generator is introduced and several methods of charging are discussed. A resonant cascaded transformers topology emerges from this discussion. Resonant modes are discussed and the topology is refined to take advantage of the pi/2 mode leading to the circuit that is the focus of this work. We begin our analysis of this circuit by considering the corresponding infinite biperiodic system and derive the characteristic dispersion relation. Motivation for closing the stopband is discussed and benefits of the pi/2 mode are noted. We proceed next to derive the matrix equation for the corresponding lossless system of coupled oscillators. To test and verify the analytic work, a five cell benchtop prototype of the charging system is built and its resonant modes are determined empirically. Capacitors in odd numbered resonators are each connected to the input of a voltage doubler circuit and high voltage dc is generated. A MOSFET is added to the output of each doubler circuit and pulsed output is demonstrated. A SPICE simulation of the physical circuit is created. The mode frequencies from the simulation are in good agreement with those measured and calculated. A practical high-power design is considered for the E2V/Teledyne MG7095 magnetron and simulated in SPICE.</p><p>

<p> Searches for violations of discrete symmetries can be sensitive probes of physics beyond the Standard Model. Many models, such as supersymmetric theories, introduce new particles at higher masses that include new <i> CP</i>-violating phases which are thought to be of order unity. Such phases could generate measurable permanant electric dipole moments (EDMs) of particles. The ACME collaboration has measured the electron's EDM to be consistent with zero with an order of magnitude improvement in precision compared to the previous best precision (J. Baron et al., ACME collaboration, <i> Science</i> <b>343</b> (2014), 269-272) with a spin precession measurement performed in the <i>H</i> state of a beam of thorium monoxide (ThO). This limit constrains time-reversal violating physics for particles with masses well into the TeV scale. In this thesis I discuss the details of this measurement with an emphasis on the data analysis, search for systematic errors, and systematic error models that contributed to this result. I also discuss implemented and planned upgrades to the experimental apparatus intended to both improve the statistical sensitivity and reduce its susceptibility to systematic errors. At this time, the upgraded apparatus has been demonstrated to have a statistical sensitivity to the electron EDM that is more than a factor of 10x more precise than our previous measurement. </p><p>

This dissertation presents two searches for the Standard Model Higgs boson produced in association with a vector boson and decaying via $H\to b\bar{b}$. Specifically, the processes are: \llbb\ alone, and again in combination with the \vvbb\ and \lvbb\ processes. The dataset used for the analysis consists of 4.7 fb$^{-1}$ at $\sqrt{s} = $7~TeV and 20.3 fb$^{-1}$at $\sqrt{s} = $8~TeV from LHC collisions. The search was optimized without bias to a particular mass of the Standard Model Higgs boson. Background processes contributing to the total number of observed events are estimated using a combination of Monte Carlo simluation and data-driven techniques. Utilizing a maximum-likelihood analysis, an observed upper limit on the cross section at the 95\% confidence interval for the \llbb\ channel is set at 2.76 times the Standard Model cross section with an expected limit of 2.54, and the observed upper limit for the combined search is 2.3 times the Standard Model cross section, with an expected limit of 1.01. Furthermore, compatibility with the Standard Model expectation is evaluated through the parameter $\mu$ = $\frac{\sigma_{observed}}{\sigma_{Standard Model}}$ and found to be $0.17\pm1.4$ for the \llbb\ analysis, and $1.09\pm0.61$ for the combined analysis, both consistent with the Standard Model expectation of 1.

We state and prove to all orders in perturbation theory a factorization theorem in Quantum Chromodynamics that concisely describes the separation of the physics associated with jet formation from that associated with the hard-scattering in high-energy particle collisions. We show how the factorization theorem, which provides an equality between amplitudes in gauge theories, can be readily applied to precision calculations of cross-sections. In the resulting factorized cross sections, the components relevant to jet production are universal and perturbatively calculable. Their renormalization group evolution can be used to sum large logarithms of scale ratios to all orders in perturbation theory, thus enabling quantitive predictions in the regime of disparate scales relevant to many important collider-physics observables. As an application, we calculate the observable 2-subjettiness at next-to-next-to-next-to-leading-logarithmic order for the decay of boosted heavy color-singlet particles such as Electroweak bosons. Our calculation is the first analytic calculation of a jet substructure observable. / Physics

The ATLAS detector at the Large Hadron Collider is a discovery machine that is able to probe into the multi-TeV scale and search for physics beyond the Standard Model. This thesis presents a search for chargino and neutralino production in final states with one lepton, two b-jets, and missing transverse momentum, consistent with R-parity conserving supersymmetric scenarios. The analysis is based on 20.3 fb^-1 of sqrt(s) = 8 TeV proton-proton collision data recorded with the ATLAS detector. Observations are found to be consistent with the Standard Model expectations and 95% confidence level limits are obtained in the context of both simplified supersymmetric models and phenomenological Minimal Supersymmetric Standard Models. / Physics

I give a high level overview of the state of particle physics in the introduction, accessible without any background in the field. I discuss improvements of theoretical and statistical methods used for collider physics. These include telescoping jets, a statistical method which was claimed to allow jet searches to increase their sensitivity by considering several interpretations of each event. We find that indeed multiple interpretations extend the power of searches, for both simple counting experiments and powerful multivariate fitting experiments, at least for h->bb at the LHC. Then I propose a method for automation of background calculations using SCET by appropriating the technology of Monte Carlo generators such as MadGraph. In the third chapter I change gears and discuss the future of the universe. It has long been known that our pocket of the standard model is unstable; there is a lower-energy configuration in a remote part of the configuration space, to which our universe will, eventually, decay. While the timescales involved are on the order of 10^400 years (depending on how exactly one counts) and thus of no immediate worry, I discuss the shortcomings of the standard methods and propose a more physically motivated derivation for the decay rate. I then make various observations about the structure of decays in quantum field theory. / Physics