<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>

<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>

<p> An interpretation of CMS searches for evidence of supersymmetry in the context of the minimal supersymmetric Standard Model (MSSM) is given. It is found that supersymmetric particles with color charge are excluded in the mass range below about 400 GeV, but neutral and weakly-charged sparticles remain non-excluded in all mass ranges. Discussion of the non-excluded regions of the model parameter space is given, including details on the strengths and weaknesses of existing searches, and recommendations for future analysis strategies. Advancements in the modeling of events arising from quantum chromodynamics and electroweak boson production, which are major backgrounds in searches for new physics at the LHC, are also presented. These methods have been implemented as components of CMS searches for supersymmetry in proton-proton collisions resulting in purely hadronic events (i.e., events with no identified leptons) at a center of momentum energy of 13 TeV. These searches, interpreted in the context of simplified models, exclude supersymmetric gluons (gluinos) up to masses of 1400 to 1600 GeV, depending on the model considered, and exclude scalar top quarks with masses up to about 800 GeV, assuming a massless lightest supersymmetric particle. A search for non-excluded supersymmetry models is also presented, which uses multivariate discriminants to isolate potential signal candidate events. The search achieves sensitivity to new physics models in background-dominated kinematic regions not typically considered by analyses, and rules out supersymmetry models that survived 7 and 8 TeV searches performed by CMS.</p>

The main objective of this thesis is to study and investigate the production of massive vector bosons (W+ and W−). This a priori mentioned production is not sensitive to hot nuclear matter effects because of the weak coupling nature of these vector bosons. Thus, in heavy ion collisions they provide a good reference for the medium-induced effects on other probes. The production mechanism of these vector bosons is highly isospin dependent and thus they are affected by the initial state effects. Initial state effects include isospin, Fermi motion, EMC effect, shadowing and nuclear absorption. Hence their production in lead-lead (Pb-Pb) and proton-lead (p-Pb) collisions can be used to test some of these initial state effects. In this thesis only two of these initial state effects will be considered namely, isospin and shadowing (referring to shadowing and anti-shadowing). Eke, these vector bosons can be used to provide a non-arbitrary reference to the probes affected by the medium. Traditionally, in heavy ion collisions, hard processes are expected to scale with the number of binary collision thus a precise study of these vector bosons can be used to test the factorisation assumed in models used to determine centrality. This unique property of electroweak (W) bosons makes them essential probes to study the possible inherent bias in centrality determination. In proton-proton (pp) collisions, their production can be used to obtain information on quark parton distribution functions (PDF). The data used in the analysis was collected by A Large Ion Collider Experiment (ALICE) at the Large Hadron Collider (LHC). The ALICE detector is designed to study ultrarelativistic heavy-ion collisions, in which a hot and dense, strongly-interacting medium is created. The production of W bosons is studied in p-Pb, p-p and Pb-Pb collisions at 5.023, 8 and 5.023 TeV centre-of-mass energies, respectively. The forward muon spectrometer with the pseudorapidity acceptance −4.0 < ŋ < −2.5 is used. W bosons are studied via the inclusive single muon differential pT spectrum.

No description available.

Emission computed tomography involves external measurements of gamma photons emitted from within the object under investigation in order to map the radioactive distribution into a two-dimensional array within a slice of interest. Both positron emission tomography (PET) and single photon emission computed tomography (SPECT) constitute the two types of emission computed tomography. PET and SPECT differ radically in almost every aspect of system design; radionuc1ide employed, radiation detectors and arrangement, collimation (electronic, mechanical), processing electronics as well as data acquisition, handling and correction. A prototype scanning-rig incorporating two collimated BOO scintillation detectors has been used to carry out PET experiments utilising 6SOe line sources (positron-emitter) and a perspex phantom of 50-mm in diameter to simulate a small animal i.e. a rat's head. Modifications for the experimental scanning-rig allowed the collection of the singles events in the PET studies in such a way that they could be reconstructed to provide SPECT images for the radioactive distribution under investigation. This property allowed a simultaneous collection of PET and SPECT data for the same object under exactly the same conditions. Two data sets are generated from each tomographic experiment; one is for PET and the other is for SPECT. Each data set is corrected separately for the required corrections i.e. scattering and attenuation before reconstruction, and then two images are produced for each study. The outcome from this work is the comparison between the two images of PET and positron SPECT obtained. The line spread function curves taken for various depths and the image profiles for studies in air and perspex show that PET provides better spatial resolution than positron SPECT. This property of PET is further confirmed by the MTF curves and the fidelity test. Using a collimation aperture of 3- mm wide, the spatial resolution values in air were found to be 3.2 +/- 0.45 mm and 7.4 +/- 0.45 mm FWHM for PET and SPECT respectively. The images of the two line sources with a 10-mm centre-to-centre separation are partially resolved in the SPECT images whereas a sufficient separation between the two sources is achieved in PET. Image combination has been applied in order to obtain a hybrid image which contains the advantages from both PET and SPECT. A straightforward averaging and multiplication of the two images of PET and SPECT were found useful to provide images with enhanced quality. The multiplication process provided images with significantly improved quality for the PE T images. When evaluating the image quality of the line source in air, the fidelity test values are 0.71 and -1.11 for PET and SPECT respectively. The image combination resulted in an image with fidelity values of 0.92 when the two images are multiplied and 0.12 when their averaging was obtained.

A non-covariant but approximately relativistic two-body wave equation describing the quantum mechanics of two fermions interacting with one another through a potential containing scalar, pseudoscalar and vector parts is presented. It is based on a generalisation of the equation introduced by Breit in 1929. After expressing the sixteen component twobody wavefunction in terms of a radial and an angular function by means of the multi pole expansion, the initial equation can be reduced into a set of sixteen radial equations which, in turn, can be classified in accordance to the parity and the state of the wavefunctions involved. The adequacy of the reduced equations in describing real problems is discussed, first, by applying the theory to a QED problem, the calculation of the lowest bound states, 1So and 351, of positronium to order 0'4. Second, the knowledge of the bottomium and charrnoniurn spectra serves as a laboratory to test both the efficiency of the potential which is supposed to represent the interaction between two quarks leading to the formation of mesons, and the reliability of the Breit equation. The final results are presented in such a form as to allow a direct comparison with both experimental data and existing theories. Results are, also, obtained for a stronger Coulomb-like vector potential as well as for a scalar square well potential. The former case is applied to a bound state of a monopoleantimonopole system.

No description available.

No description available.