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Quantum electrodynamics with the spear magnetic detector

Description: One makes a study of quantum electrodynamic processes which are present at the SPEAR colliding beam magnetic detector. We begin by describing the experiment performed by the SLAC-LBL collaboration and the results concerning the strong interaction. Then the interactions e$sup +$e$sup -$ $Yields$ e$sup +$e$sup -$ and e$sup +$e$sup -$ $Yields$ $mu$$sup +$$mu$$sup -$ are considered along with their third-order radiative corrections. These events, previously used to determine new limits for cutoff parameters in QED breakdown models, are further studied to show that the full distribution in coplanarity angle fits the theoretical prediction well. The major focus is on the fourth order two-photon process, e$sup +$e$sup -$ $Yields$ e$sup +$e$sup -$A$sup +$A$sup -$, which only recently has been realized to be significant in such experiments. Cross sections are derived and calculated exactly for this process and the results compared to a Weizacker-Williams equivalent photon calculation. The two-photon data are then isolated and fit to the calculation. A special experiment was done where the small-angle scattered electron or positron is ''tagged'' along with particles in the main detector. Cross sections and coplanarity distributions are measured and compared to calculation. Through these studies, one feels confident that one understand the nature of the two-photon process in the detector. One further explores the hadronic physics of the two-photon process, e$sup +$e$sup -$ $Yields$ e$sup +$e$sup -$ hadrons, measuring pion cross sections, searching for resonances, and discussing future experiments. (auth)
Date: September 1, 1975
Creator: Zipse, J.E.
Partner: UNT Libraries Government Documents Department

Multipole Analysis of Circular Cylindircal Magnetic Systems

Description: This thesis deals with an alternate method for computing the external magnetic field from a circular cylindrical magnetic source. The primary objective is to characterize the magnetic source in terms of its equivalent multipole distribution. This multipole distribution must be valid at points close to the cylindrical source and a spherical multipole expansion is ill-equipped to handle this problem; therefore a new method must be introduced. This method, based upon the free-space Green's function in cylindrical coordinates, is developed as an alternative to the more familiar spherical harmonic expansion. A family of special functions, called the toroidal functions or Q-functions, are found to exhibit the necessary properties for analyzing circular cylindrical geometries. In particular, the toroidal function of zeroth order, which comes from the integral formulation of the free-space Green's function in cylindrical coordinates, is employed to handle magnetic sources which exhibit circular cylindrical symmetry. The toroidal functions, also called Q-functions, are the weighting coefficients in a ''Fourier series-like'' expansion which represents the free-space Green's function. It is also called a toroidal expansion. This expansion can be directly employed in electrostatic, magnetostatic, and electrodynamic problems which exhibit cylindrical symmetry. Also, it is shown that they can be used as an alternative to the Elliptic integral formulation. In fact, anywhere that an Elliptic integral appears, one can replace it with its corresponding Q-function representation. A number of problems, using the toroidal expansion formulation, are analyzed and compared to existing known methods in order to validate the results. Also, the equivalent multipole distribution is found for most of the solved problems along with its corresponding physical interpretation. The main application is to characterize the external magnetic field due to a six-pole permanent magnet motor in terms of its equivalent multipole distribution.
Date: January 9, 2006
Creator: Selvaggi, J
Partner: UNT Libraries Government Documents Department

Observation of the doubly strange b-Baryon Omega(b)-

Description: This thesis reports the first experimental evidence of the doubly strange b-baryon {Omega}{sub b}{sup -} (ssb) following the decay channel {Omega}{sub b}{sup -} {yields} J/{psi}(1S) {mu}{sup +}{mu}{sup -} {Omega}{sup -} {Lambda} K{sup -} p {pi}{sup -} in p{bar p} collisions at {radical}s = 1.96 Tev. Using approximately 1.3 fb{sup -1} of data collected with the D0 detector at the Fermilab Tevatron Collider, they observe 17.8 {+-} 4.9(stat) {+-} 0.8(syst) {Omega}{sub b}{sup -} signal events at 6.165 {+-} 0.010(stat) {+-} 0.013(syst) GeV/c{sup 2} with a corresponding significance of 5.4 {sigma}, meaning that the probability of the signal coming from a fluctuation in the background is 6.7 x 10{sup -8}. The theoretical model we have to describe what we believe are the building blocks of nature and the interactions between them, is known as Standard Model. The Standard Model is the combination of Electroweak Theory and Quantum Chromodynamics into a single core in the attempt to include all interactions of subatomic particles except those due to gravity in a simple framework. This model has proved highly accurate in predicting certain interactions, but it does not explain all aspects of subatomic particles. For example, it cannot say how many particles there should be or what their masses are. The search goes on for a more complete theory, and in particular an unified field theory describing the strong, weak, and electromagnetic forces. Twelve elementary particles are known in the Standard Model: the Fermions. They have spin -1/2 and obey the Pauli Exclusion Principle. Fermions are divided into six Quarks: up u, down d, charm c, strange s, top t and, bottom b; and six Leptons: electron e, muon {mu}, tau {tau}, electron neutrino {nu}{sub e}, muon neutrino {nu}{sub {mu}} and, tau neutrino {nu}{sub {tau}}. Quarks interact via the strong force because they carry color ...
Date: February 1, 2011
Creator: Hernandez Orduna, de Jesus, Jose
Partner: UNT Libraries Government Documents Department

Forward-Backward Asymmetry at High Mass in $t\bar{t}$ Production in $p\bar{p}$ Collisions at $\sqrt{s} = 1.96$ TeV

Description: Current understanding of particle physics postulates that there are 17 fundamental particles that interact via four fundamental forces - gravity, the strong force, the weak force, and the electromagnetic force. These fundamental particles can be classified by their spins into bosons, which are the force-carrying particles with integer spins, and fermions, which have half-integer spins. Fermions can be further divided into quarks and leptons. The particles and three of the four forces - all but gravity - are described by the Standard Model, a local SU(3) x SU(2) x U(1) gauge theory. Electromagnetic and weak interactions as described by Electroweak Theory or Quantum Electrodynamics, SU(2) x U(1). Strong interactions are described by Quantum Chromodynamics or QCD, SU(3). Fermions are grouped into three generations as shown in Table 1.1. Each generation consists of a leptonic doublet containing a charged and a neutral lepton and a weak isospin doublet containing two quarks. The first generation, containing the electron, the electron neutrino, the up quark, and the down quark, is the lightest generation and is thus the most frequently found in nature. The second generation contains the muon, the muon neutrino, the strange quark, and the charm quark. The third generation contains the tau, the tau neutrino, the bottom quark, and the top quark.
Date: April 1, 2011
Creator: Eppig, Andrew
Partner: UNT Libraries Government Documents Department

High-Throughput Analysis With 96-Capillary Array Electrophoresis and Integrated Sample Preparation for DNA Sequencing Based on Laser Induced Fluorescence Detection

Description: The purpose of this research was to improve the fluorescence detection for the multiplexed capillary array electrophoresis, extend its use beyond the genomic analysis, and to develop an integrated micro-sample preparation system for high-throughput DNA sequencing. The authors first demonstrated multiplexed capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC) separations in a 96-capillary array system with laser-induced fluorescence detection. Migration times of four kinds of fluoresceins and six polyaromatic hydrocarbons (PAHs) are normalized to one of the capillaries using two internal standards. The relative standard deviations (RSD) after normalization are 0.6-1.4% for the fluoresceins and 0.1-1.5% for the PAHs. Quantitative calibration of the separations based on peak areas is also performed, again with substantial improvement over the raw data. This opens up the possibility of performing massively parallel separations for high-throughput chemical analysis for process monitoring, combinatorial synthesis, and clinical diagnosis. The authors further improved the fluorescence detection by step laser scanning. A computer-controlled galvanometer scanner is adapted for scanning a focused laser beam across a 96-capillary array for laser-induced fluorescence detection. The signal at a single photomultiplier tube is temporally sorted to distinguish among the capillaries. The limit of detection for fluorescein is 3 x 10{sup -11} M (S/N = 3) for 5-mW of total laser power scanned at 4 Hz. The observed cross-talk among capillaries is 0.2%. Advantages include the efficient utilization of light due to the high duty-cycle of step scan, good detection performance due to the reduction of stray light, ruggedness due to the small mass of the galvanometer mirror, low cost due to the simplicity of components, and flexibility due to the independent paths for excitation and emission.
Date: December 31, 2001
Creator: Xue, Gang
Partner: UNT Libraries Government Documents Department

Study of Conductance Quantization by Cross-Wire Junction

Description: The thesis studied quantized conductance in nanocontacts formed between two thin gold wires with one of the wires coated by alkainthiol self assembly monolayers (SAM), by using the cross-wire junction. Using the Lorenz force as the driving force, we can bring the two wires in contact in a controlled manner. We observed conductance with steps of 2e2 / h. The conductance plateaus last several seconds. The stability of the junction is attributed to the fact that the coating of SAM improves the stability and capability of the formed contact.
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Date: May 2004
Creator: Zheng, Tao
Partner: UNT Libraries