A Search for the Production of Technicolor Particles at the D-Zero Detector (open access)

A Search for the Production of Technicolor Particles at the D-Zero Detector

A search for the Technicolor processes p{bar p} {yields} {rho}{sub T}{sup {+-}} {yields} W{sup {+-}}{pi}{sub T}{sup 0} {yields} {mu}{nu}b{bar b} and p{bar p} {yields} {rho}{sub T}{sup 0} {yields} W{sup {+-}}{pi}{sub T}{sup {+-}} {yields} {mu}{nu}b{bar c} is conducted at the D0 detector. Selection requirements are individually optimized for each of twenty mass hypotheses by means of a random grid search. No excess is seen in a 291 pb{sup -1} data set and 95% confidence level upper limits are set on the Technicolor production cross section. The mass combinations M{sub {rho}} = 195 GeV/c{sup 2}, M{sub {pi}} = 100 GeV/c{sup 2} and M{sub {rho}} = 200 GeV/c{sup 2}, M{sub {pi}} = 105 GeV/c{sup 2} are excluded for the choice of the Technicolor scale parameter M{sub V} = 500 GeV.
Date: July 1, 2006
Creator: Desai, Satish Vijay
System: The UNT Digital Library
Design of a boron neutron capture enhanced fast neutron therapy assembly (open access)

Design of a boron neutron capture enhanced fast neutron therapy assembly

The use of boron neutron capture to boost tumor dose in fast neutron therapy has been investigated at several fast neutron therapy centers worldwide. This treatment is termed boron neutron capture enhanced fast neutron therapy (BNCEFNT). It is a combination of boron neutron capture therapy (BNCT) and fast neutron therapy (FNT). It is believed that BNCEFNT may be useful in the treatment of some radioresistant brain tumors, such as glioblastoma multiform (GBM). A boron neutron capture enhanced fast neutron therapy assembly has been designed for the Fermilab Neutron Therapy Facility (NTF). This assembly uses a tungsten filter and collimator near the patient's head, with a graphite reflector surrounding the head to significantly increase the dose due to boron neutron capture reactions. The assembly was designed using Monte Carlo radiation transport code MCNP version 5 for a standard 20x20 cm{sup 2} treatment beam. The calculated boron dose enhancement at 5.7-cm depth in a water-filled head phantom in the assembly with a 5x5 cm{sup 2} collimation was 21.9% per 100-ppm {sup 10}B for a 5.0-cm tungsten filter and 29.8% for a 8.5-cm tungsten filter. The corresponding dose rate for the 5.0-cm and 8.5-cm thick filters were 0.221 and 0.127 Gy/min, respectively; about …
Date: August 1, 2006
Creator: Wang, Zhonglu & Tech, /Georgia
System: The UNT Digital Library
A Measurement of the Top Quark Mass in the Dilepton Decay Channel at CDF II (open access)

A Measurement of the Top Quark Mass in the Dilepton Decay Channel at CDF II

The top quark, the most recently discovered quark, is the most massive known fundamental fermion. Precision measurements of its mass, a free parameter in the Standard Model of particle physics, can be used to constrain the mass of the Higgs Boson. In addition, deviations in the mass as measured in different channels can provide possible evidence for new physics. We describe a measurement of the top quark mass in the decay channel with two charged leptons, known as the dilepton channel, using data collected by the CDF II detector from p{bar p} collisions with {radical}s = 1.96 TeV at the Fermilab Tevatron. The likelihood in top mass is calculated for each event by convolving the leading order matrix element describing q{bar q} {yields} t{bar t} {yields} b{ell}{nu}{sub {ell}}{bar b}{ell}'{nu}{sub {ell}'} with detector resolution functions. The presence of background events in the data sample is modeled using similar calculations involving the matrix elements for major background processes. In a data sample with integrated luminosity of 1.0 fb{sup -1}, we observe 78 candidate events and measure M{sub t} = 164.5 {+-} 3.9(stat.) {+-} 3.9(syst.) GeV/c{sup 2}, the most precise measurement of the top quark mass in this channel to date.
Date: August 1, 2006
Creator: Jayatilaka, Bodhitha A.
System: The UNT Digital Library
Search for MSSM Higgs decaying to tau pairs in ppbar collision at s**(1/2) = 1.96 TeV at CDF (open access)

Search for MSSM Higgs decaying to tau pairs in ppbar collision at s**(1/2) = 1.96 TeV at CDF

This thesis presents the search for neutral Minimal Supersymmetric extension of Standard Model (MSSM) Higgs bosons decaying to tau pairs where one of the taus decays leptonically, and the other one hadronically. CDF Run II data with L{sub int} = 310 pb{sup -1} are used. There is no evidence of MSSM Higgs existence, which results in the upper limits on {sigma}(p{bar p} {yields} {phi}) x BR({phi} {yields} {tau}{tau}) in m{sub A} range between 115 and 250 GeV. These limits exclude some area in tan {beta} vs m{sub A} parameter space.
Date: May 1, 2006
Creator: Jang, Dongwook
System: The UNT Digital Library
The Nature of the Distinctive Microscopic Features in R5(SixGe1-x)4 Magnetic Refrigeration Materials (open access)

The Nature of the Distinctive Microscopic Features in R5(SixGe1-x)4 Magnetic Refrigeration Materials

Magnetic refrigeration is a promising technology that offers a potential for high energy efficiency. The giant magnetocaloric effect of the R{sub 5}(Si{sub x}, Ge{sub 1-x}){sub 4} alloys (where R=rare-earth and O {le} x {le} 1), which was discovered in 1997, make them perfect candidates for magnetic refrigeration applications. In this study the microstructures of Gd{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} alloys have been characterized using electron microscopy techniques, with the focus being on distinctive linear features first examined in 1999. These linear features have been observed in R{sub 5}(Si{sub x}, Ge{sub 1-x}){sub 4} alloys prepared from different rare-earths (Gd, Tb, Dy and Er) with different crystal structures (Gd{sub 5}Si{sub 4}-type orthorhombic, monoclinic and Gd{sub 5}Ge{sub 4}-type orthorhombic). Systematic scanning electron microscope studies revealed that these linear features are actually thin-plates, which grow along specific directions in the matrix material. The crystal structure of the thin-plates has been determined as hexagonal with lattice parameters a=b=8.53 {angstrom} and c=6.40 {angstrom} using selected area diffraction (SAD). Energy dispersive spectroscopy analysis, carried out in both scanning and transmission electron microscopes, showed that the features have a composition approximating to R{sub 5}(Si{sub x},Ge{sub 1-x}){sub 3}.phase. Orientation relationship between the matrix and the thin-plates has been calculated …
Date: May 1, 2006
Creator: Ugurlu, Ozan
System: The UNT Digital Library
Measurement of J/psi meson and b-hadron production cross section at sqrt(s) = 1.96 TeV (open access)

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

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 …
Date: March 1, 2006
Creator: Yamashita, Tomohiro & U., /Okayama
System: The UNT Digital Library
Analysis of Bs flavor oscillations at CDF (open access)

Analysis of Bs flavor oscillations at CDF

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 …
Date: September 1, 2006
Creator: Leonardo, Nuno T.
System: The UNT Digital Library
Measuring the branching ratio of the rare decay pi0 --> e+ e- (open access)

Measuring the branching ratio of the rare decay pi0 --> e+ e-

A precise branching ratio measurement of the rare decay {pi}{sup 0} {yields} e{sup +}e{sup -} has been made. The measurement was made with the rare kaon decay experiment KTeV at Fermilab where the source of {pi}{sup 0}s was K{sub L} {yields} {pi}{sup 0}{pi}{sup 0}{pi}{sup 0} decaying in flight. A total of 794 fully reconstructed K{sub L} {yields} 3{pi}{sup 0} events consistent with two of the intermediate {pi}{sup 0}s decaying into {gamma}{gamma} and one into e{sup +}e{sup -} were collected. An estimated 53.2 {+-} 11.0 of these events were expected to be background. Normalizing to the {pi}{sup 0} Dalitz decay they found Br({pi}{sup 0} {yields} e{sup +}e{sup -}, (m{sub e{sup +}e{sup -}}/m{sub {pi}{sup 0}}){sup 2} > 0.95) = (6.44 {+-} 0.25(stat) {+-} 0.22(syst)) x 10{sup -8} where internal radiation, {pi}{sup 0} {yields} e{sup +}e{sup -}({gamma}), was limited by the requirement (m{sub e{sup +}e{sup -}}/m{sub {pi}{sup 0}}){sup 2} > 0.95 which separated it from the tree level Dalitz decay, {pi}{sup 0} {yields} e{sup +}e{sup -}P{gamma}.
Date: February 1, 2006
Creator: Niclasen, Rune
System: The UNT Digital Library
Efficient Execution of Electronic Structure Calculations on SMP Clusters (open access)

Efficient Execution of Electronic Structure Calculations on SMP Clusters

Applications augmented with adaptive capabilities are becoming common in parallel computing environments. For large-scale scientific applications, dynamic adjustments to a computationally-intensive part may lead to a large pay-off in facilitating efficient execution of the entire application while aiming at avoiding resource contention. Application-specific knowledge, often best revealed during the run-time, is required to initiate and time these adjustments. In particular, General Atomic and Molecular Electronic Structure System (GAMESS) is a program for ab initio quantum chemistry that places significant demands on the high-performance computing platforms. Certain electronic structure calculations are characterized by high consumption of a particular resource, such as CPU, main memory, or disk I/O. This may lead to resource contention among concurrent GAMESS jobs and other programs in the dynamically changing environment. Thus, it is desirable to improve GAMESS calculations by means of dynamic adaptations. In this thesis, we show how an application- or algorithm-specific knowledge may play a significant role in achieving this goal. The choice of implementation is facilitated by a module-driven middleware easily integrated with GAMESS that assesses resource consumption and invokes GAMESS adaptations to the system environment. We show that the throughput of GAMESS jobs may be improved greatly as a result of such …
Date: May 1, 2006
Creator: Ustemirov, Nurzhan
System: The UNT Digital Library
Rare-Earth Transition-Metal Intermetallics: Structure-bonding-Property Relationships (open access)

Rare-Earth Transition-Metal Intermetallics: Structure-bonding-Property Relationships

Our explorations of rare-earth, transition metal intermetallics have resulted in the synthesis and characterization, and electronic structure investigation, as well as understanding the structure-bonding-property relationships. Our work has presented the following results: (1) Understanding the relationship between compositions and properties in LaFe{sub 13-x}Si{sub x} system: A detailed structural and theoretical investigation provided the understanding of the role of a third element on stabilizing the structure and controlling the transformation of cubic NaZn{sub 13}-type structures to the tetragonal derivative, as well as the relationship between the structures and properties. (2) Synthesis of new ternary rare-earth iron silicides RE{sub 2-x}Fe{sub 4}Si{sub 14-y} and proposed superstructure: This compound offers complex structural challenges such as fractional occupancies and their ordering in superstructure. (3) Electronic structure calculation of FeSi{sub 2}: This shows that the metal-semiconductor phase transition depends on the structure. The mechanism of band gap opening is described in terms of bonding and structural distortion. This result shows that the electronic structure calculations are an essential tool for understanding the relationship between structure and chemical bonding in these compounds. (4) Synthesis of new ternary rare-earth Zinc aluminides Tb{sub 3}Zn{sub 3.6}Al{sub 7.4}: Partially ordered structure of Tb{sub 3}Zn{sub 3.6}Al{sub 7.4} compound provides new insights into …
Date: May 1, 2006
Creator: Han, Mi-Kyung
System: The UNT Digital Library
Electron Transfer Reactivity Patterns at Chemically Modified Electrodes: Fundamentals and Application to the Optimization of Redox Recycling Amplification Systems (open access)

Electron Transfer Reactivity Patterns at Chemically Modified Electrodes: Fundamentals and Application to the Optimization of Redox Recycling Amplification Systems

Electroanalytical chemistry is often utilized in chemical analysis and Fundamental studies. Important advances have been made in these areas since the advent of chemically modified electrodes: the coating of an electrode with a chemical film in order to impart desirable, and ideally, predictable properties. These procedures enable the exploitation of unique reactivity patterns. This dissertation presents studies that investigate novel reaction mechanisms at self-assembled monolayers on gold. In particular, a unique electrochemical current amplification scheme is detailed that relies on a selective electrode to enable a reactivity pattern that results in regeneration of the analyte (redox recycling). This regenerating reaction can occur up to 250 times for each analyte molecule, leading to a notable enhancement in the observed current. The requirements of electrode selectivity and the resulting amplification and detection limit improvements are described with respect to the heterogeneous and homogeneous electron transfer rates that characterize the system. These studies revealed that the heterogeneous electrolysis of the analyte should ideally be electrochemically reversible, while that for the regenerating agent should be held to a low level. Moreover, the homogeneous reaction that recycles the analyte should occur at a rapid rate. The physical selectivity mechanism is also detailed with respect to …
Date: May 1, 2006
Creator: Bergren, Adam Johan
System: The UNT Digital Library
CPT conservation and atmospheric neutrinos in the MINOS far detector (open access)

CPT conservation and atmospheric neutrinos in the MINOS far detector

The MINOS Far Detector is a 5400 ton iron calorimeter located at the Soudan state park in Soudan Minnesota. The MINOS far detector can observe atmospheric neutrinos and separate charge current {nu}{sub {mu}} and {bar {nu}}{sub {mu}} interactions by using a 1.4 T magnetic field to identify the charge of the produced muon. The CPT theorem requires that neutrinos and anti-neutrinos oscillate in the same way. In a fiducial exposure of 5.0 kilo-ton years a total of 41 candidate neutrino events are observed with an expectation of 53.1 {+-} 7.6(system.) {+-} 7.2(stat.) unoscillated events or 31.6 {+-} 4.7(system.) {+-} 5.6(stat.) events with {Delta}m{sup 2} = 2.4 x 10{sup -3} eV{sup 2}, sin{sup 2}(2{theta}) = 1.0 as oscillation parameters. These include 28 events which can have there charge identified with high confidence. These 28 events consist of 18 events consistent with being produced by {nu}{sub {mu}} and 10 events being consistent with being produced by {bar {nu}}{sub {mu}}. No evidence of CPT violation is observed.
Date: February 1, 2006
Creator: Becker, Bernard Raymond
System: The UNT Digital Library
Improvement of Photon Buildup Factors for Radiological Assessment (open access)

Improvement of Photon Buildup Factors for Radiological Assessment

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.
System: The UNT Digital Library
Search for t-Channel Single Top Quark Production in p anti-p Collisions at 1.96 TeV (open access)

Search for t-Channel Single Top Quark Production in p anti-p Collisions at 1.96 TeV

I have performed a search for t-channel single top quark production in p{bar p} collisions at 1.96 TeV on a 366 pb{sup -1} dataset collected with the D0 detector from 2002-2005. The analysis is restricted to the leptonic decay of the W boson from the top quark to an electron or muon, tq{bar b} {yields} lv{sub l}b q{bar b} (l = e,{mu}). A powerful b-quark tagging algorithm derived from neural networks is used to identify b jets and significantly reduce background. I further use neural networks to discriminate signal from background, and apply a binned likelihood calculation to the neural network output distributions to derive the final limits. No direct observation of single top quark production has been made, and I report expected/measured 95% confidence level limits of 3.5/8.0 pb.
Date: June 1, 2006
Creator: Perea, Philip Michael & /UC, Riverside
System: The UNT Digital Library
SEARCH FOR HIGH-MASS RESONANCES DECAYING TO e-mu IN ppbar COLLISIONS AT s**(1/2) = 1.96 TeV (open access)

SEARCH FOR HIGH-MASS RESONANCES DECAYING TO e-mu IN ppbar COLLISIONS AT s**(1/2) = 1.96 TeV

We describe a general search for resonances decaying to a neutral e{mu} final state in p{bar p} collisions at a center-of-mass energy of 1.96 TeV. Using a data sample representing 344 pb{sup -1} of integrated luminosity recorded by the CDF II experiment, we compare Standard Model predictions with the number of observed events for invariant masses between 50 and 800 GeV/c{sup 2}. Finding no significant excess (5 events observed vs. 7.7 {+-} 0.8 expected for M{sub e{mu}} > 100 GeV/c{sup 2}), we set limits on sneutrino and Z' masses as functions of lepton family number violating couplings.
Date: August 1, 2006
Creator: Hahn, Kristian Allan
System: The UNT Digital Library
Exclusive interactions in p anti-p collisions at s**(1/2) = 1.96 TeV (open access)

Exclusive interactions in p anti-p collisions at s**(1/2) = 1.96 TeV

This thesis presents two exclusive production processes in p{bar p} collisions at {radical}s = 1.96 TeV, using the Collider Detector Facility at Fermi National Accelerator Laboratory. An observation of exclusive e{sup +}e{sup -} production through {gamma}{gamma} {yields} e{sup +}e{sup -} is presented, as well as evidence for exclusive production of {gamma}{gamma} through gg {yields} {gamma}{gamma} (via a quark loop). The exclusive e{sup +}e{sup -} production observation is based on 16 candidate events, with a background estimate of 2.1{sub -0.3}{sup +0.7}. Each event has an e{sup +}e{sup -} pair (E{sub T} (e) > 5 GeV, |{eta}(e)| < 2) and nothing else observable in the CDF detector. The measured cross section is 1.6{sub -0.3}{sup +0.5}(stat) {+-} 0.3(sys) pb, while the predicted cross section is 1.711 {+-} 0.008 pb. The kinematic properties of the events are consistent with the predictions of the LPAIR Monte Carlo. The evidence for exclusive {gamma}{gamma} production consists of 3 candidate events, with a background estimate of 0.0{sub -0.0}{sup +0.2} events. Each event has two photons (E{sub T}{gamma}) > 5 GeV, |{eta}({gamma})| < 1 and nothing else observable in the CDF detector. The measured cross section for these events is 0.14{sub -0.04}{sup +0.14}(stat) {+-} (sys) pb. It agrees with …
Date: May 1, 2006
Creator: Hamilton, Andrew & U., /Alberta
System: The UNT Digital Library
Electroweak Production of the Top Quark in the Run II of the D0 Experiment (open access)

Electroweak Production of the Top Quark in the Run II of the D0 Experiment

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 …
Date: April 1, 2006
Creator: Clement, Benoit & /Strasbourg, IReS
System: The UNT Digital Library
Study of the decay K(L) -> pi+- e-+ nu e+ e- to probe the semileptonic K-pi structure (open access)

Study of the decay K(L) -> pi+- e-+ nu e+ e- to probe the semileptonic K-pi structure

The authors observed a new neutral kaon decay mode, K{sub L} {yields} {pi}{sup {+-}}e{sup {-+}}{bar {nu}}e{sup +}e{sup -} for the first time. Based on the 20225 events including 1018 {+-} 25 background events, they determined the branching ratio, B(K{sub L} {yields} {pi}{sup {+-}}e{sup {-+}}{bar {nu}}e{sup +}e{sup -}; M{sub e{sup +}e{sup -}} > 5 MeV/c{sup 2}, E*{sub e{sup +}e{sup -}} > 30 MeV) = (1.281 {+-} 0.041) x 10{sup -5}. This branching ratio agrees with a theoretical prediction based on the chiral perturbation theory ({chi}PT) calculation at {Omicron}(p{sup 4}). Most of the kinematical distributions agree with the {chi}PT {Omicron}(p{sup 4}) calculation. They also measured one of the low energy coupling constants for the {chi}PT {Omicron}(p{sup 4}), L{sub 9}{sup r} = (8.0 {+-} 1.6) x 10{sup -3}. The M{sub e{sup +}e{sup -}} distribution below 100 MeV showed a 3 {sigma} deviation from the {chi}PT {Omicron}(p{sup 4}) calculation. This requires further studies in theory and experiments.
Date: September 1, 2006
Creator: Kotera, Katsushige & U., /Osaka
System: The UNT Digital Library
Structure and Function Evolution of Thiolate Monolayers on Gold (open access)

Structure and Function Evolution of Thiolate Monolayers on Gold

The use of n-alkanethiolate self-assembled monolayers on gold has blossomed in the past few years. These systems have functioned as models for common interfaces. Thiolate monolayers are ideal because they are easily modified before or after deposition. The works contained within this dissertation include interfacial characterization (inbred reflection absorption spectroscopy, ellipsometry, contact angle, scanning probe microscopy, and heterogeneous electron-transfer kinetics) and various modeling scenarios. The results of these characterizations present ground-breaking insights into the structure, function, and reproducible preparation of these monolayers. Surprisingly, three interfacial properties (electron-transfer, contact angle, and ellipsometry) were discovered to depend directly on the odd-even character of the monolayer components. Molecular modeling was utilized to investigate adlayer orientation, and suggests that these effects are adlayer structure specific. Finally, the electric force microscopy and theoretical modeling investigations of monolayer samples are presented, which show that the film dielectric constant, thickness, and dipole moment directly affect image contrast. In addition, the prospects for utilization of this emerging technique are outlined.
Date: May 1, 2006
Creator: Edwards, Grant Alvin
System: The UNT Digital Library
Diffractively produced Z bosons in the muon decay channel in p-pbar collisions at s**(1/2) = 1.96 TeV, and the measurement of the efficiency of the D0 Run II luminosity monitor (open access)

Diffractively produced Z bosons in the muon decay channel in p-pbar collisions at s**(1/2) = 1.96 TeV, and the measurement of the efficiency of the D0 Run II luminosity monitor

The first analysis of diffractively produced Z bosons in the muon decay channel is presented, using data taken by the D0 detector at the Tevatron at {radical}s = 1.96 TeV. The data sample corresponds to an integrated luminosity of 109 pb{sup -1}. The diffractive sample is defined using the fractional momentum loss {zeta} of the intact proton or antiproton measured using the calorimeter and muon detector systems. In a sample of 10791 (Z/{gamma})* {yields} {mu}{sup +}{mu}{sup -} events, 24 diffractive candidate events are found with {zeta} < 0.02. The first work towards measuring the cross section times branching ratio for diffractive production of (Z/{gamma})* {yields} {mu}{sup +}{mu}{sup -} is presented for the kinematic region {zeta} < 0.02. The first work towards measuring the cross section times branching ratio for diffractive production of (Z/{gamma})* {yields} {mu}{sup +}{mu}{sup -} is presented for the kinematic region {zeta} < 0.02. The systematic uncertainties are not yet sufficiently understood to present the cross section result. In addition, the first measurement of the efficiency of the Run II D0 Luminosity Monitor is presented, which is used in all cross section measurements. The efficiency is: {var_epsilon}{sub LM} = (90.9 {+-} 1.8)%.
Date: April 1, 2006
Creator: Edwards, Tamsin L.
System: The UNT Digital Library
Exploration of R2XM2 (R=Sc, Y, Ti, Zr, Hf, rare earth; X=main group element; M=transition metal, Si, Ge): Structural Motifs, the novel Compound Gd2AlGe2 and Analysis of the U3Si2 and Zr3Al2 Structure Types (open access)

Exploration of R2XM2 (R=Sc, Y, Ti, Zr, Hf, rare earth; X=main group element; M=transition metal, Si, Ge): Structural Motifs, the novel Compound Gd2AlGe2 and Analysis of the U3Si2 and Zr3Al2 Structure Types

In the process of exploring and understanding the influence of crystal structure on the system of compounds with the composition Gd{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} several new compounds were synthesized with different crystal structures, but similar structural features. In Gd{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4}, the main feature of interest is the magnetocaloric effect (MCE), which allows the material to be useful in magnetic refrigeration applications. The MCE is based on the magnetic interactions of the Gd atoms in the crystal structure, which varies with x (the amount of Si in the compound). The crystal structure of Gd{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} can be thought of as being formed from two 3{sup 2}434 nets of Gd atoms, with additional Gd atoms in the cubic voids and Si/Ge atoms in the trigonal prismatic voids. Attempts were made to substitute nonmagnetic atoms for magnetic Gd using In, Mg and Al. Gd{sub 2}MgGe{sub 2} and Gd{sub 2}InGe{sub 2} both possess the same 3{sup 2}434 nets of Gd atoms as Gd{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4}, but these nets are connected differently, forming the Mo{sub 2}FeB{sub 2} crystal structure. A search of the literature revealed that compounds with the composition R{sub 2}XM{sub 2} (R=Sc, Y, Ti, …
Date: May 1, 2006
Creator: McWhorter, Sean William
System: The UNT Digital Library
First Principles Calculations for X-ray Resonant Spectra and Elastic Properties (open access)

First Principles Calculations for X-ray Resonant Spectra and Elastic Properties

In this thesis, we discuss applications of first principles methods to x-ray resonant spectra and elastic properties calculation. We start with brief reviews about theoretical background of first principles methods, such as density functional theory, local density approximation (LDA), LDA+U, and the linear augmented plane wave (LAPW) method to solve Kohn-Sham equations. After that we discuss x-ray resonant scattering (XRMS), x-ray magnetic circular dichroism (XMCD) and the branching problem in the heavy rare earths Ledges. In the last chapter we discuss the elastic properties of the second hardest material AlMgB{sub 14}.
Date: May 1, 2006
Creator: Lee, Yongbin
System: The UNT Digital Library
Measurement of the strange - antistrange asymmetry at NLO in QCD from NuTeV dimuon data (open access)

Measurement of the strange - antistrange asymmetry at NLO in QCD from NuTeV dimuon data

A measurement of the asymmetry between the strange and antistrange quark distributions, from a next to leading order QCD analysis of dimuon events measured by the NuTeV experiment at Fermilab is presented. Neutrino charged current events with two muons in the final state provide a direct means for studying charm production and measuring the strange sea. NuTeV's sign selected beam allows independent measurement of the strange and antistrange seas. An improved measurement of the neutrino and antineutrino forward dimuon cross section tables, using the complete charged current event sample for normalization is performed. These tables are then analyzed at NLO to measure the strange and antistrange seas. Detector acceptance is modeled using an NLO charm cross section differential in all variables required. The strange quark distribution is found to have an integrated momentum weighted asymmetry of +0.00196 {+-} 0.00046(stat) {+-} 0.00045(syst) {+-} 0.00182(external). The charm mass is found to be 1.41 {+-} 0.10(stat) {+-} 0.08(syst) {+-} 0.12(external) GeV.
Date: March 1, 2006
Creator: Mason, David Alexander & U., /Oregon
System: The UNT Digital Library
Measurement of b-quark Jet Shapes at CDF (open access)

Measurement of b-quark Jet Shapes at CDF

The main topic of this thesis is the measurement of b-quark jet shapes at CDF. CDF is an experiment located at Fermilab, in the United States, which studies proton-antiproton collisions at a center of mass energy of 1.96TeV. To reach this energy, the particles are accelerated using the Tevatron accelerator which is currently the highest energy collider in operation. The data used for this analysis were taken between February 2002 and September 2004 and represent an integrated luminosity of about 300 pb{sup -1}. This is the first time that b-quark jet shapes have been measured at hadron colliders. The basis of this measurement lies in the possibility of enhancing the b-quark jet content of jet samples by requiring the jets to be identified as having a displaced vertex inside the jet cone. Such jets are called tagged. This enhances the b-quark jet fraction from about 5% before tagging to 20-40% after tagging, depending on the transverse momentum of the jets. I verified that it is possible to apply this secondary vertex tagging algorithm to different cone jet algorithms (MidPoint and JetClu) and different cone sizes (0.4 and 0.7). I found that the performance of the algorithm does not change significantly, …
Date: March 1, 2006
Creator: Lister, Alison
System: The UNT Digital Library