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Search for Resonances in the Photoproduction of Proton-Antiproton Pairs

Description: Results are reported on the reaction {gamma}p {yields} p{bar p}p with beam energy in the range 4.8-5.5 GeV. The data were collected at the Thomas Jefferson National Accelerator Facility in CLAS experiment E01-017(G6C). The focus of this study is an understanding of the mechanisms of photoproduction of proton-antiproton pairs, and to search for intermediate resonances, both narrow and broad, which decay to p{bar p}. The total measured cross section in the photon energy range 4.8-5.5 GeV is {sigma} = 33 {+-} 2 nb. Measurement of the cross section as a function of energy is provided. An upper limit on the production of a narrow resonance state previously observed with a mass of 2.02 GeV/c{sup 2} is placed at 0.35 nb. No intermediate resonance states were observed. Meson exchange production appears to dominate the production of the proton-antiproton pairs.
Date: June 30, 2006
Creator: Stokes, Burnham
Partner: UNT Libraries Government Documents Department

Structural Investigations of Surfaces and Orientation-SpecificPhenomena in Nanocrystals and Their Assemblies

Description: Studies of colloidal nanocrystals and their assemblies are presented. Two of these studies concern the atomic-level structural characterization of the surfaces, interfaces, and interiors present in II-VI semiconductor nanorods. The third study investigates the crystallographic arrangement of cobalt nanocrystals in self-assembled aggregates. Crystallographically-aligned assemblies of colloidal CdSe nanorods are examined with linearly-polarized Se-EXAFS spectroscopy, which probes bonding along different directions in the nanorod. This orientation-specific probe is used, because it is expected that the presence of specific surfaces in a nanorod might cause bond relaxations specific to different crystallographic directions. Se-Se distances are found to be contracted along the long axis of the nanorod, while Cd-Se distances display no angular dependence, which is different from the bulk. Ab-initio density functional theory calculations upon CdSe nanowires indicate that relaxations on the rod surfaces cause these changes. ZnS/CdS-CdSe core-shell nanorods are studied with Se, Zn, Cd, and S X-ray absorption spectroscopy (XAS). It is hypothesized that there are two major factors influencing the core and shell structures of the nanorods: the large surface area-to-volume ratio, and epitaxial strain. The presence of the surface may induce bond rearrangements or relaxations to minimize surface energy; epitaxial strain might cause the core and shell lattices to contract or expand to minimize strain energy. A marked contraction of Zn-S bonds is observed in the core-shell nanorods, indicating that surface relaxations may dominate the structure of the nanorod (strain might otherwise drive the Zn-S lattice to accommodate the larger CdS or CdSe lattices via bond expansion). EXAFS and X-ray diffraction (XRD) indicate that Cd-Se bond relaxations might be anisotropic, an expected phenomenon for a rod-shaped nanocrystal. Ordered self-assembled aggregates of cobalt nanocrystals are examined with transmission electron microscopy (TEM) and selected-area electron diffraction (SAED). SAED patterns from multilayered assemblies show that the nanocrystals have preferred crystallographic orientations. ...
Date: June 17, 2006
Creator: Aruguete, Deborah Michiko
Partner: UNT Libraries Government Documents Department

Mechanisms for fatigue and wear of polysilicon structural thinfilms

Description: Fatigue and wear in micron-scale polysilicon structural films can severely impact the reliability of microelectromechanical systems (MEMS). Despite studies on fatigue and wear behavior of these films, there is still an on-going debate regarding the precise physical mechanisms for these two important failure modes. Although macro-scale silicon does not fatigue, this phenomenon is observed in micron-scale silicon. It is shown that for polysilicon devices fabricated in the MUMPs foundry and SUMMiT process stress-lifetime data exhibits similar trends in ambient air, shorter lifetimes in higher relative humidity environments and no fatigue failure at all in high vacuum. Transmission electron microscopy of the surface oxides of the samples show an approximate four-fold thickening of the oxide at stress concentrations after fatigue failure, but no thickening after fracture in air or after fatigue cycling in vacuo. It is found that such oxide thickening and fatigue failure (in air) occurs in devices with initial oxide thicknesses of {approx}4-20 nm. Such results are interpreted and explained by a reaction layer fatigue mechanism; specifically, moisture-assisted subcritical cracking within a cyclic stress-assisted thickened oxide layer occurs until the crack reaches a critical size to cause catastrophic failure. Polysilicon specimens from the SUMMiT process are used to study wear mechanisms in micron-scale silicon in ambient air. Worn parts are examined by analytical scanning and transmission electron microscopy, while temperature changes are monitored using infrared microscopy. These results are compared with the development of values of static coefficients of friction (COF) with number of wear cycles. Observations show amorphous debris particles ({approx}50-100 nm) created by fracture through the silicon grains ({approx}500 nm), which subsequently oxidize, agglomerate into clusters and create plowing tracks. A nano-crystalline layer ({approx}20-200 nm) forms at worn regions. No dislocations or extreme temperature increases are found, ruling out plasticity and temperature-assisted mechanisms. The COF reaches a ...
Date: December 1, 2006
Creator: Alsem, Daniel Henricus
Partner: UNT Libraries Government Documents Department

On the Mechanical Properties and Microstructure of Nitinol forBiomedical Stent Applications

Description: This dissertation was motivated by the alarming number of biomedical device failures reported in the literature, coupled with the growing trend towards the use of Nitinol for endovascular stents. The research is aimed at addressing two of the primary failure modes in Nitinol endovascular stents: fatigue-crack growth and overload fracture. The small dimensions of stents, coupled with their complex geometries and variability among manufacturers, make it virtually impossible to determine generic material constants associated with specific devices. Instead, the research utilizes a hybrid of standard test techniques (fracture mechanics and x-ray micro-diffraction) and custom-designed testing apparatus for the determination of the fracture properties of specimens that are suitable representations of self-expanding Nitinol stents. Specifically, the role of texture (crystallographic alignment of atoms) and the austenite-to-martensite phase transformation on the propagation of cracks in Nitinol was evaluated under simulated body conditions and over a multitude of stresses and strains. The results determined through this research were then used to create conservative safe operating and inspection criteria to be used by the biomedical community for the determination of specific device vulnerability to failure by fracture and/or fatigue.
Date: December 15, 2006
Creator: Robertson, Scott W.
Partner: UNT Libraries Government Documents Department

Nanoscale chemical and mechanical characterization of thin films:sum frequency generation (SFG) vibrational spectroscopy at buriedinterfaces

Description: Sum frequency generation (SFG) surface vibrational spectroscopy was used to characterize interfaces pertinent to current surface engineering applications, such as thin film polymers and novel catalysts. An array of advanced surface science techniques like scanning probe microscopy (SPM), x-ray photoelectron spectroscopy (XPS), gas chromatography (GC) and electron microscopy were used to obtain experimental measurements complementary to SFG data elucidating polymer and catalyst surface composition, surface structure, and surface mechanical behavior. Experiments reported in this dissertation concentrate on three fundamental questions: (1) How does the interfacial molecular structure differ from that of the bulk in real world applications? (2) How do differences in chemical environment affect interface composition or conformation? (3) How do these changes correlate to properties such as mechanical or catalytic performance? The density, surface energy and bonding at a solid interface dramatically alter the polymer configuration, physics and mechanical properties such as surface glass transition, adhesion and hardness. The enhanced sensitivity of SFG at the buried interface is applied to three systems: a series of acrylates under compression, the compositions and segregation behavior of binary polymer polyolefin blends, and the changes in surface structure of a hydrogel as a function of hydration. In addition, a catalytically active thin film of polymer coated nanoparticles is investigated to evaluate the efficacy of SFG to provide in situ information for catalytic reactions involving small mass adsorption and/or product development. Through the use of SFG, in situ total internal reflection (TIR) was used to increase the sensitivity of SFG and provide the necessary specificity to investigate interfaces of thin polymer films and nanostructures previously considered unfeasible. The dynamic nature of thin film surfaces is examined and it is found that the non-equilibrium states contribute to practical applications of acrylates, blends and hydrogels. Lastly, nanoparticle surfaces and the catalytic activity and selectivity of ...
Date: May 19, 2006
Creator: Kweskin, S.J.
Partner: UNT Libraries Government Documents Department

Synthesis and Manipulation of Semiconductor Nanocrystals inMicrofluidic Reactors

Description: Microfluidic reactors are investigated as a mechanism tocontrol the growth of semiconductor nanocrystals and characterize thestructural evolution of colloidal quantum dots. Due to their shortdiffusion lengths, low thermal masses, and predictable fluid dynamics,microfluidic devices can be used to quickly and reproducibly alterreaction conditions such as concentration, temperature, and reactiontime, while allowing for rapid reagent mixing and productcharacterization. These features are particularly useful for colloidalnanocrystal reactions, which scale poorly and are difficult to controland characterize in bulk fluids. To demonstrate the capabilities ofnanoparticle microreactors, a size series of spherical CdSe nanocrystalswas synthesized at high temperature in a continuous-flow, microfabricatedglass reactor. Nanocrystal diameters are reproducibly controlled bysystematically altering reaction parameters such as the temperature,concentration, and reaction time. Microreactors with finer control overtemperature and reagent mixing were designed to synthesize nanoparticlesof different shapes, such as rods, tetrapods, and hollow shells. The twomajor challenges observed with continuous flow reactors are thedeposition of particles on channel walls and the broad distribution ofresidence times that result from laminar flow. To alleviate theseproblems, I designed and fabricated liquid-liquid segmented flowmicroreactors in which the reaction precursors are encapsulated inflowing droplets suspended in an immiscible carrier fluid. The synthesisof CdSe nanocrystals in such microreactors exhibited reduced depositionand residence time distributions while enabling the rapid screening aseries of samples isolated in nL droplets. Microfluidic reactors werealso designed to modify the composition of existing nanocrystals andcharacterize the kinetics of such reactions. The millisecond kinetics ofthe CdSe-to-Ag2Se nanocrystal cation exchange reaction are measured insitu with micro-X-ray Absorption Spectroscopy in silicon microreactorsspecifically designed for rapid mixing and time-resolved X-rayspectroscopy. These results demonstrate that microreactors are valuablefor controlling and characterizing a wide range of reactions in nLvolumes even when nanoscale particles, high temperatures, causticreagents, and rapid time scales are involved. These experiments providethe foundation for future microfluidic investigations into the mechanismsof nanocrystal growth, crystal ...
Date: December 19, 2006
Creator: Chan, Emory Ming-Yue
Partner: UNT Libraries Government Documents Department

Potential Applications of Microtesla Magnetic Resonance ImagingDetected Using a Superconducting Quantum Interference Device

Description: This dissertation describes magnetic resonance imaging (MRI) of protons performed in a precession field of 132 {micro}T. In order to increase the signal-to-noise ratio (SNR), a pulsed 40-300 mT magnetic field prepolarizes the sample spins and an untuned second-order superconducting gradiometer coupled to a low transition temperature superconducting quantum interference device (SQUID) detects the subsequent 5.6-kHz spin precession. Imaging sequences including multiple echoes and partial Fourier reconstruction are developed. Calculating the SNR of prepolarized SQUID-detected MRI shows that three-dimensional Fourier imaging yields higher SNR than slice-selection imaging. An experimentally demonstrated field-cycling pulse sequence and post-processing algorithm mitigate image artifacts caused by concomitant gradients in low-field MRI. The magnetic field noise of SQUID untuned detection is compared to the noise of SQUID tuned detection, conventional Faraday detection, and the Nyquist noise generated by conducting biological samples. A second-generation microtesla MRI system employing a low-noise SQUID is constructed to increase SNR. A 2.4-m cubic, eddy-current shield with 6-mm thick aluminum walls encloses the experiment to attenuate external noise. The measured noise is 0.75 fT Hz{sup -1/2} referred to the bottom gradiometer loop. Solenoids wound from 30-strand braided wire to decrease Nyquist noise and cooled by either liquid nitrogen or water polarize the spins. Copper wire coils wound on wooden supports produce the imaging magnetic fields and field gradients. Water phantom images with 0.8 x 0.8 x 10 mm{sup 3} resolution have a SNR of 6. Three-dimensional 1.6 x 1.9 x 14 mm{sup 3} images of bell peppers and 3 x 3 x 26 mm{sup 3} in vivo images of the human arm are presented. Since contrast based on the transverse spin relaxation rate (T{sub 1}) is enhanced at low magnetic fields, microtesla MRI could potentially be used for tumor imaging. The measured T{sub 1} of ex vivo normal and cancerous prostate tissue ...
Date: May 18, 2006
Creator: Myers, Whittier R.
Partner: UNT Libraries Government Documents Department

Improvement of Photon Buildup Factors for Radiological Assessment

Description: Slant-path buildup factors for photons between 1 keV and 10 MeV for nine radiation shielding materials (air, aluminum, concrete, iron, lead, leaded glass, polyethylene, stainless steel, and water) are calculated with the most recent cross-section data available using Monte Carlo and discrete ordinates methods. Discrete ordinates calculations use a 244-group energy structure that is based on previous research at Los Alamos National Laboratory (LANL), but extended with the results of this thesis, and its focused studies on low-energy photon transport and the effects of group widths in multigroup calculations. Buildup factor calculations in discrete ordinates benefit from coupled photon/electron cross sections to account for secondary photon effects. Also, ambient dose equivalent (herein referred to as dose) buildup factors were analyzed at lower energies where corresponding response functions do not exist in literature. The results of these studies are directly applicable to radiation safety at LANL, where the dose modeling tool Pandemonium is used to estimate worker dose in plutonium handling facilities. Buildup factors determined in this thesis will be used to enhance the code's modeling capabilities, but should be of interest to the radiation shielding community.
Date: July 1, 2006
Creator: Schirmers, F.G.
Partner: UNT Libraries Government Documents Department

Pipeline Structural Health Monitoring Using Macro-fiber Composite Active Sensors

Description: The United States economy is heavily dependent upon a vast network of pipeline systems to transport and distribute the nation's energy resources. As this network of pipelines continues to age, monitoring and maintaining its structural integrity remains essential to the nation's energy interests. Numerous pipeline accidents over the past several years have resulted in hundreds of fatalities and billions of dollars in property damages. These accidents show that the current monitoring methods are not sufficient and leave a considerable margin for improvement. To avoid such catastrophes, more thorough methods are needed. As a solution, the research of this thesis proposes a structural health monitoring (SHM) system for pipeline networks. By implementing a SHM system with pipelines, their structural integrity can be continuously monitored, reducing the overall risks and costs associated with current methods. The proposed SHM system relies upon the deployment of macro-fiber composite (MFC) patches for the sensor array. Because MFC patches are flexible and resilient, they can be permanently mounted to the curved surface of a pipeline's main body. From this location, the MFC patches are used to monitor the structural integrity of the entire pipeline. Two damage detection techniques, guided wave and impedance methods, were implemented as part of the proposed SHM system. However, both techniques utilize the same MFC patches. This dual use of the MFC patches enables the proposed SHM system to require only a single sensor array. The presented Lamb wave methods demonstrated the ability to correctly identify and locate the presence of damage in the main body of the pipeline system, including simulated cracks and actual corrosion damage. The presented impedance methods demonstrated the ability to correctly identify and locate the presence of damage in the flanged joints of the pipeline system, including the loosening of bolts on the flanges. In addition to ...
Date: March 1, 2006
Creator: Thien, A.B.
Partner: UNT Libraries Government Documents Department

The Sorption/Desorption Behavior of Uranium in Transport Studies Using Yucca Mountain Alluvium

Description: Yucca Mountain, Nevada is the proposed site of a geologic repository for the disposal of spent nuclear fuel and high-level radioactive waste in the United States. In the event repository engineered barriers fail, the saturated alluvium located south of Yucca Mountain is expected to serve as a natural barrier to the migration of radionuclides to the accessible environment. The purpose of this study is to improve the characterization of uranium retardation in the saturated zone at Yucca Mountain to support refinement of an assessment model. The distribution of uranium desorption rates from alluvium obtained from Nye County bore holes EWDP-19IM1, EWDP-10SA, EWDP-22SA were studied to address inconsistencies between results from batch sorption and column transport experiments. The alluvium and groundwater were characterized to better understand the underlying mechanisms of the observed behavior. Desorption rate constants were obtained using an activity based mass balance equation and column desorption experiments were analyzed using a mathematical model utilizing multiple sorption sites with different first-order forward and reverse reaction rates. The uranium desorption rate constants decreased over time, suggesting that the alluvium has multiple types of active sorption sites with different affinities for uranium. While a significant fraction of the initially sorbed uranium desorbed from the alluvium quite rapidly, a roughly equivalent amount remained sorbed after several months of testing. The information obtained through this research suggests that uranium may experience greater effective retardation in the alluvium than simple batch sorption experiments would suggest. Electron Probe Microanalysis shows that uranium is associated with both clay minerals and iron oxides after sorption to alluvial material. These results provide further evidence that the alluvium contains multiple sorption sites for uranium.
Date: February 15, 2006
Creator: Scism, C. D.
Partner: UNT Libraries Government Documents Department

Nanocrystal Solar Cells

Description: This dissertation presents the results of a research agenda aimed at improving integration and stability in nanocrystal-based solar cells through advances in active materials and device architectures. The introduction of 3-dimensional nanocrystals illustrates the potential for improving transport and percolation in hybrid solar cells and enables novel fabrication methods for optimizing integration in these systems. Fabricating cells by sequential deposition allows for solution-based assembly of hybrid composites with controlled and well-characterized dispersion and electrode contact. Hyperbranched nanocrystals emerge as a nearly ideal building block for hybrid cells, allowing the controlled morphologies targeted by templated approaches to be achieved in an easily fabricated solution-cast device. In addition to offering practical benefits to device processing, these approaches offer fundamental insight into the operation of hybrid solar cells, shedding light on key phenomena such as the roles of electrode-contact and percolation behavior in these cells. Finally, all-inorganic nanocrystal solar cells are presented as a wholly new cell concept, illustrating that donor-acceptor charge transfer and directed carrier diffusion can be utilized in a system with no organic components, and that nanocrystals may act as building blocks for efficient, stable, and low-cost thin-film solar cells.
Date: December 15, 2006
Creator: Gur, Ilan
Partner: UNT Libraries Government Documents Department

Ultrasonic Digital Communication System for a Steel Wall Multipath Channel: Methods and Results

Description: As of the development of this thesis, no commercially available products have been identified for the digital communication of instrumented data across a thick ({approx} 6 n.) steel wall using ultrasound. The specific goal of the current research is to investigate the application of methods for digital communication of instrumented data (i.e., temperature, voltage, etc.) across the wall of a steel pressure vessel. The acoustic transmission of data using ultrasonic transducers prevents the need to breach the wall of such a pressure vessel which could ultimately affect its safety or lifespan, or void the homogeneity of an experiment under test. Actual digital communication paradigms are introduced and implemented for the successful dissemination of data across such a wall utilizing solely an acoustic ultrasonic link. The first, dubbed the ''single-hop'' configuration, can communicate bursts of digital data one-way across the wall using the Differential Binary Phase-Shift Keying (DBPSK) modulation technique as fast as 500 bps. The second, dubbed the ''double-hop'' configuration, transmits a carrier into the vessel, modulates it, and retransmits it externally. Using a pulsed carrier with Pulse Amplitude Modulation (PAM), this technique can communicate digital data as fast as 500 bps. Using a CW carrier, Least Mean-Squared (LMS) adaptive interference suppression, and DBPSK, this method can communicate data as fast as 5 kbps. A third technique, dubbed the ''reflected-power'' configuration, communicates digital data by modulating a pulsed carrier by varying the acoustic impedance at the internal transducer-wall interface. The paradigms of the latter two configurations are believed to be unique. All modulation methods are based on the premise that the wall cannot be breached in any way and can therefore be viably implemented with power delivered wirelessly through the acoustic channel using ultrasound. Methods, results, and considerations for future research are discussed herein.
Date: February 16, 2006
Creator: Murphy, TL
Partner: UNT Libraries Government Documents Department

Heat Transfer Analysis and Assessment of Kinetics Systems for PBX 9501

Description: The study of thermal decomposition in high explosive (HE) charges has been an ongoing process since the early 1900s. This work is specifically directed towards the analysis of PBX 9501. In the early 1970s, Dwight Jaeger of Los Alamos National Laboratory (LANL) developed a single-step, two-species kinetics system that was used in the development of one of the first finite element codes for thermal analyses known as EXPLO. Jaeger's research focused on unconfined spherical samples of HE charges to determine if varied heating ramps would cause detonation or deflagration. Tarver and McGuire of Lawrence Livermore National Laboratory (LLNL) followed soon after with a three-step, four-species kinetics system that was developed for confined spheres under relatively fast heating conditions. Peter Dickson et al. of LANL then introduced a kinetics system with four steps and five species that included bimolecular products to capture the effects of the endothermic phase change that the HE undergoes. The results of four experiments are examined to study the effectiveness of these kinetics systems. The experiments are: (1) The LLNL scaled thermal explosion (STEX) experiments on confined cylindrical charges with long heating ramps in the range of 90 hours. (2) The LLNL one-dimensional time to explosion (ODTX) experiments on spherical charges that include confined, partially confined, and aged HE experiments. (3) The LANL unconfined one-dimensional experiments for small spheres. (4) The Naval Air Warfare Center Weapons Division at China Lake experiments on small confined cylinders. The three kinetics systems are applied to each of the four experiments with the use of the finite element analysis (FEA) heat conduction solver COYOTE. The numerical results using the kinetics systems are compared to each other and to the experimental data to determine which kinetics systems are best suited for analyzing conditions such as time to ignition, containment, heating time, and ...
Date: July 31, 2006
Creator: Jorenby, Jeffrey W.
Partner: UNT Libraries Government Documents Department


Description: Single Particle Aerosol Mass Spectrometry (SPAMS) was evaluated as a real-time detection technique for single particles of high explosives. Dual-polarity time-of-flight mass spectra were obtained for samples of 2,4,6-trinitrotoluene (TNT), 1,3,5-trinitro-1,3,5-triazinane (RDX), and pentaerythritol tetranitrate (PETN); peaks indicative of each compound were identified. Composite explosives, Comp B, Semtex 1A, and Semtex 1H were also analyzed, and peaks due to the explosive components of each sample were present in each spectrum. Mass spectral variability with laser fluence is discussed. The ability of the SPAMS system to identify explosive components in a single complex explosive particle ({approx}1 pg) without the need for consumables is demonstrated. SPAMS was also applied to the detection of Chemical Warfare Agent (CWA) simulants in the liquid and vapor phases. Liquid simulants for sarin, cyclosarin, tabun, and VX were analyzed; peaks indicative of each simulant were identified. Vapor phase CWA simulants were adsorbed onto alumina, silica, Zeolite, activated carbon, and metal powders which were directly analyzed using SPAMS. The use of metal powders as adsorbent materials was especially useful in the analysis of triethyl phosphate (TEP), a VX stimulant, which was undetectable using SPAMS in the liquid phase. The capability of SPAMS to detect high explosives and CWA simulants using one set of operational conditions is established.
Date: October 23, 2006
Creator: Martin, A
Partner: UNT Libraries Government Documents Department

An Analysis Framework Addressing the Scale and Legibility of Large Scientific Data Sets

Description: Much of the previous work in the large data visualization area has solely focused on handling the scale of the data. This task is clearly a great challenge and necessary, but it is not sufficient. Applying standard visualization techniques to large scale data sets often creates complicated pictures where meaningful trends are lost. A second challenge, then, is to also provide algorithms that simplify what an analyst must understand, using either visual or quantitative means. This challenge can be summarized as improving the legibility or reducing the complexity of massive data sets. Fully meeting both of these challenges is the work of many, many PhD dissertations. In this dissertation, we describe some new techniques to address both the scale and legibility challenges, in hope of contributing to the larger solution. In addition to our assumption of simultaneously addressing both scale and legibility, we add an additional requirement that the solutions considered fit well within an interoperable framework for diverse algorithms, because a large suite of algorithms is often necessary to fully understand complex data sets. For scale, we present a general architecture for handling large data, as well as details of a contract-based system for integrating advanced optimizations into a data flow network design. We also describe techniques for volume rendering and performing comparisons at the extreme scale. For legibility, we present several techniques. Most noteworthy are equivalence class functions, a technique to drive visualizations using statistical methods, and line-scan based techniques for characterizing shape.
Date: November 20, 2006
Creator: Childs, H R
Partner: UNT Libraries Government Documents Department

Analysis of Bs flavor oscillations at CDF

Description: The search for and study of flavor oscillations in the neutral B{sub s}B{sub s} meson system is an experimentally challenging task. It constitutes a flagship analysis of the Tevatron physics program. In this dissertation, they develop an analysis of the time-dependent B{sub s} flavor oscillations using data collected with the CDF detector. The data samples are formed of both fully and partially reconstructed B meson decays: B{sub s} {yields} D{sub s}{pi}({pi}{pi}) and B{sub s} {yields} D{sub s}lv. A likelihood fitting framework is implemented and appropriate models and techniques developed for describing the mass, proper decay time, and flavor tagging characteristics of the data samples. The analysis is extended to samples of B{sup +} and B{sup 0} mesons, which are further used for algorithm calibration and method validation. The B mesons lifetimes are extracted. The measurement of the B{sup 0} oscillation frequency yields {Delta}m{sub d} = 0.522 {+-} 0.017 ps{sup -1}. The search for B{sub s} oscillations is performed using an amplitude method based on a frequency scanning procedure. Applying a combination of lepton and jet charge flavor tagging algorithms, with a total tagging power {epsilon}'D{sup 2} of 1.6%, to a data sample of 355 pb{sup -1}, a sensitivity of 13.0 ps{sup -1} is achieved. They develop a preliminary same side kaon tagging algorithm, which is found to provide a superior tagging power of about 4.0% for the B{sub s} meson species. A study of the dilution systematic uncertainties is not reported. From its application as is to the B{sub s} samples the sensitivity is significantly increased to about 18 ps{sup -1} and a hint of a signal is seen at about 175. ps{sup -1}. They demonstrate that the extension of the analysis to the increasing data samples with the inclusion of the same side tagging algorithm is capable of providing ...
Date: September 1, 2006
Creator: Leonardo, Nuno T. & /MIT
Partner: UNT Libraries Government Documents Department

B-tagging and the search for neutral supersymmetric Higgs bosons at D0

Description: A search for neutral supersymmetric Higgs bosons and work relating to the improvement of the b-tagging and trigger capabilities at the D0 detector during Run II of the Fermilab Tevatron collider is presented. The search for evidence of the Higgs sector in the Standard Model (SM) and supersymmetric extensions of the SM are a high priority for the D0 collaboration, and b-tagging and good triggers are a vital component of these searches. The development and commissioning of the first triggers at D0 which use b-tagging is outlined, along with the development of a new secondary vertex b-tagging tool for use in the Level 3 trigger. Upgrades to the Level 3 trigger hit finding code, which have led to significant improvements in the quality and efficiency of the tracking code, and by extension the b-tagging tools, are also presented. An offline Neural Network (NN) b-tagging tool was developed, trained on Monte Carlo and extensively tested and measured on data. The new b-tagging tool significantly improves the b-tagging performance at D0, for a fixed fake rate relative improvements in signal efficiency range from {approx} 40% to {approx} 15%. Fake rates, for a fixed signal efficiency, are typically reduced to between a quarter and a third of their value. Finally, three versions of the search for neutral supersymmetric Higgs bosons are presented. The latest version of the analysis makes use of almost 1 fb{sup -1} of data, the new NN b-tagger and the new b-tagging triggers, and has set one of the world's best limits on the supersymmetric parameter tan{beta} in the mass range 90 to 150 GeV.
Date: October 1, 2006
Creator: Scanlon, Tim & /Imperial Coll., London
Partner: UNT Libraries Government Documents Department

An Experimental Investigation of the Structural Wave Scattering Due to Impedance Discontinuities on a Cylindrical Structure

Description: Experimental, numerical, and analytical work has shown that the response of a shell to a distributed force wave possesses unique characteristics which are dependent on the nature of structure attached to the shell. Specific characteristics which influence the response are the distribution of the discontinuities around the circumference (periodic/aperiodic), the impedance of the discontinuities relative to that of the shell, and the type of impedance (mass or stiffness). Traditional shell theory predicts low frequency, radial-dominated structural mode shapes of a shell with a sinusoidal distribution of displacement amplitudes. Due to the orthogonal nature of these mode shapes, the response of the structure to a traveling radial force wave with sinusoidal content at a given harmonic is due solely to the response of the mode shape with harmonic content of the same order. Introduction of impedance discontinuities to a shell yield complex mode shapes, which may be characterized by the summation of several harmonic components. These modes are no longer orthogonal in the presence of discontinuities, yielding harmonic content across various modal orders. As a result, a purely sinusoidal forcing function can excite several modes of the structure. Structural scattering as discussed in this paper refers to the phenomena in which a force wave at a given harmonic scatters into the response of modes with different harmonics. An experimental investigation into the harmonic scattering behavior of a shell due to mass discontinuities is presented in this paper. Knowledge of the key structural characteristics which influence scattering and their behavior will allow for a diagnostic tool when assessing the structural response of more complex cylindrical structures. Experimentally obtained data presented in this paper demonstrates some expected scattering characteristics of a cylindrical shell in the presence of periodically and aperiodically distributed masses. Some unique characteristics of the response of a shell in the ...
Date: February 15, 2006
Creator: Glotzbecker, RJ
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

Electroweak production of the top quark in the Run II of the D0 experiment

Description: The work exposed in this thesis deals with the search for electroweak production of top quark (single top) in proton-antiproton collisions at {radical}s = 1.96 TeV. This production mode has not been observed yet. Analyzed data have been collected during the Run II of the D0 experiment at the Fermilab Tevatron collider. These data correspond to an integrated luminosity of 370 pb{sup -1}. In the Standard Model, the decay of a top quark always produce a high momentum bottom quark. Therefore bottom quark jets identification plays a major role in this analysis. The large lifetime of b hadrons and the subsequent large impact parameters relative to the interaction vertex of charged particle tracks are used to tag bottom quark jets. Impact parameters of tracks attached to a jet are converted into the probability for the jet to originate from the primary vertex. This algorithm has a 45% tagging efficiency for a 0.5% mistag rate. Two processes (s and t channels) dominate single top production with slightly different final states. The searched signature consists in 2 to 4 jets with at least one bottom quark jet, one charged lepton (electron or muon) and missing energy accounting for a neutrino. This final state is background dominated and multivariate techniques are needed to separate the signal from the two main backgrounds: associated production of a W boson and jets and top quarks pair production. The achieved sensitivity is not enough to reach observation and we computed upper limits at the 95% confidence level at 5 pb (s-channel) and 4.3 pb (t-channel) on single top production cross-sections.
Date: April 1, 2006
Creator: Clement, Benoit & /Strasbourg, IReS
Partner: UNT Libraries Government Documents Department

First observation of the Bs->K+K- decay mode, and measurement of the B0 and Bs mesons decay-rates into two-body charmless final states at CDF

Description: The authors searched for decays of the type B{sub (s)}{sup 0} {yields} h{sup +}h{prime}{sup -} (where h, h{prime} = K or {pi}) in a sample corresponding to 180 pb{sup -1} of p{bar p} collisions at {radical}s = 1.96 TeV, collected by the upgraded Collider Detector at the Fermilab Tevatron. A total signal of approximately 900 events was reconstructed, and the relative branching fractions ({Beta}) of each decay mode were determined with a likelihood fit.
Date: November 1, 2006
Creator: Tonelli, Diego & /Pisa, Scuola Normale Superiore
Partner: UNT Libraries Government Documents Department

Measurement of J/psi meson and b-hadron production cross section at sqrt(s) = 1.96 TeV

Description: A new measurement of the inclusive and differential production cross sections of J/{psi} mesons and b-hadrons in proton-antiproton collisions at {radical}s = 1960 GeV is presented. The data correspond to an integrated luminosity of 39.7 pb{sup -1} collected by the CDF Run II detector. The integrated cross section for inclusive J/{psi} production for all transverse momenta from 0 to 20 GeV/c in the rapidity range |y| < 0.6 is found to be 4.08 {+-} 0.02(stat){sub -0.33}{sup +0.36}(syst) {mu}b. The fraction of J/{psi} events from the decay of the long-lived b-hadrons is separated by using the lifetime distribution in all events with p{sub T}(J/{psi}) > 1.25 GeV/c. The total cross section for b-hadrons, including both hadrons and anti-hadrons, decaying to J/{psi} with transverse momenta greater than 1.25 GeV/c in the rapidity range |y(J/{psi})| < 0.6, is found to be 0.330 {+-} 0.005(stat){sub -0.033}{sup +0.036}(syst) {mu}b. Using a Monte Carlo simulation of the decay kinematics of b-hadrons to all final states containing a J/{psi}, the first measurement of the total single b-hadron cross section down to zero transverse momentum is extracted at sqrts = 1960 GeV. The total single b-hadron cross section integrated over all transverse momenta for b-hadrons in the rapidity range |y| < 0.6 is found to be 17.6 {+-} 0.4(stat){sub -2.3}{sup +2.5}(syst) {mu}b.
Date: March 1, 2006
Creator: Yamashita, Tomohiro & U., /Okayama
Partner: UNT Libraries Government Documents Department