A Search for new physics in photon-lepton events in proton-antiproton collisions at {radical} s = 1.8 TeV (open access)

A Search for new physics in photon-lepton events in proton-antiproton collisions at {radical} s = 1.8 TeV

We present the results of a search in p{bar p} collisions at {radical}s = 1.8 TeV for anomalous production of events containing a photon with large transverse energy and a lepton (e or {mu}) with large transverse energy, using 86 pb{sup -1} of data collected at the Collider Detector at Fermilab during the 1994-95 collider run at the Fermilab Tevatron. The presence of large missing transverse energy (E{sub T}), additional photons, or additional leptons in these events is also analyzed. The results are consistent with standard model expectations, with the possible exception of photon-lepton events with large E{sub T}, for which the probability of a statistical fluctuation of the standard model expectation up to and above the observed level is 0.7%.
Date: April 30, 2001
Creator: Berryhill, J. W.
System: The UNT Digital Library
Top quark pair production in proton anti-proton collisions (open access)

Top quark pair production in proton anti-proton collisions

This thesis presents a measurement of the t{bar t} cross section in the all-jets channel, measured in p{bar p} collisions at a center of mass energy of 1.96 TeV, using data collected with the D0 detector. The dataset used for this analysis has an integrated luminosity equivalent to L = 162.5 {+-} 10.6 pb{sup -1}. A t{bar t} cross section measurement is a test of the Standard Model predictions for heavy quark production, and the first step towards measurements of the mass and other properties of the top quark. The presented measurement of the cross section for the process p{bar p} {yields} t{bar t} uses the decay channel where both top quarks decay to quarks. The top quark first decays to a b quark and a W boson, and then, for this particular channel, the W boson decays hadronically. Hence, events with six energetic quarks are expected, which ideally leads to events with six jets. These so called all-jets events have a significantly larger branching fraction than other t{bar t} decay channels. The large branching fraction in the all-jets channel means that a significant sample of t{bar t} candidates can be extracted, which can subsequently be used for studies of …
Date: April 1, 2005
Creator: Blekman, Freya & /NIKHEF, Amsterdam
System: The UNT Digital Library
Search for electroweak top quark production in the electron + jets channel in the D0 experiment at the Tevatron (open access)

Search for electroweak top quark production in the electron + jets channel in the D0 experiment at the Tevatron

None
Date: April 1, 2005
Creator: Busato, Emmanuel
System: The UNT Digital Library
Implementation of an interactive matching scheme for the Kapchinskij-Vladimirskij equations in the WARP code (open access)

Implementation of an interactive matching scheme for the Kapchinskij-Vladimirskij equations in the WARP code

The WARP code is a robust electrostatic particle-in-cell simulation package used to model charged particle beams with strong space-charge forces. A fundamental operation associated with seeding detailed simulations of a beam transport channel is to generate initial conditions where the beam distribution is matched to the structure of a periodic focusing lattice. This is done by solving for periodic, matched solutions to a coupled set of ODEs called the Kapchinskij-Vladimirskij (KV) envelope equations, which describe the evolution of low-order beam moments subject to applied lattice focusing, space-charge defocusing, and thermal defocusing forces. Recently, an iterative numerical method was developed (Lund, Chilton, and Lee, Efficient computation of matched solutions to the KV envelope equations for periodic focusing lattices, Physical Review Special Topics-Accelerators and Beams 9, 064201 2006) to generate matching conditions in a highly flexible, convergent, and fail-safe manner. This method is extended and implemented in the WARP code as a Python package to vastly ease the setup of detailed simulations. In particular, the Python package accommodates any linear applied lattice focusing functions without skew coupling, and a more general set of beam parameter specifications than its predecessor. Lattice strength iteration tools were added to facilitate the implementation of problems with …
Date: April 15, 2008
Creator: Chilton, Sven H.
System: The UNT Digital Library
Toward Femtosecond X-ray Spectroscopy at the Advanced Light Source (open access)

Toward Femtosecond X-ray Spectroscopy at the Advanced Light Source

The realization of tunable, ultrashort pulse x-ray sources promises to open new venues of science and to shed new light on long-standing problems in condensed matter physics and chemistry. Fundamentally new information can now be accessed. Used in a pump-probe spectroscopy, ultrashort x-ray pulses provide a means to monitor atomic rearrangement and changes in electronic structure in condensed-matter and chemical systems on the physically-limiting time-scales of atomic motion. This opens the way for the study of fast structural dynamics and the role they play in phase transitions, chemical reactions and the emergence of exotic properties in materials with strongly interacting degrees of freedom. The ultrashort pulse x-ray source developed at the Advanced Light Source at the Lawrence Berkeley Laboratory is based on electron slicing in storage rings, and generates {approx}100 femtosecond pulses of synchrotron radiation spanning wavelengths from the far-infrared to the hard x-ray region of the electromagnetic spectrum. The tunability of the source allows for the adaptation of a broad range of static x-ray spectroscopies to useful pump-probe measurements. Initial experiments are attempted on transition metal complexes that exhibit relatively large structural changes upon photo-excitation and which have excited-state evolution determined by strongly interacting structural, electronic and magnetic degrees …
Date: April 16, 2004
Creator: Chong, Henry Herng Wei
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
Exposure-Relevant Ozone Chemistry in Occupied Spaces (open access)

Exposure-Relevant Ozone Chemistry in Occupied Spaces

Ozone, an ambient pollutant, is transformed into other airborne pollutants in the indoor environment. In this dissertation, the type and amount of byproducts that result from ozone reactions with common indoor surfaces, surface residues, and vapors were determined, pollutant concentrations were related to occupant exposure, and frameworks were developed to predict byproduct concentrations under various indoor conditions. In Chapter 2, an analysis is presented of secondary organic aerosol formation from the reaction of ozone with gas-phase, terpene-containing consumer products in small chamber experiments under conditions relevant for residential and commercial buildings. The full particle size distribution was continuously monitored, and ultrafine and fine particle concentrations were in the range of 10 to>300 mu g m-3. Particle nucleation and growth dynamics were characterized.Chapter 3 presents an investigation of ozone reactions with aircraft cabin surfaces including carpet, seat fabric, plastics, and laundered and worn clothing fabric. Small chamber experiments were used to determine ozone deposition velocities, ozone reaction probabilities, byproduct emission rates, and byproduct yields for each surface category. The most commonly detected byproducts included C1?C10 saturated aldehydes and skin oil oxidation products. For all materials, emission rates were higher with ozone than without. Experimental results were used to predict byproduct exposure …
Date: April 1, 2009
Creator: Coleman, Beverly Kaye
System: The UNT Digital Library
WW production cross section measurement and limits on anomalous trilinear gauge couplings at sqrt(s) = 1.96-TeV (open access)

WW production cross section measurement and limits on anomalous trilinear gauge couplings at sqrt(s) = 1.96-TeV

The cross section for WW production is measured and limits on anomalous WW{gamma} and WWZ trilinear gauge couplings are set using WW {yields} ee/e{mu}/{mu}{mu} events collected by the Run II D0 detector at the Fermilab Tevatron Collider corresponding to 1 fb{sup -1} of integrated luminosity at {radical}s = 1.96 TeV. Across the three final states, 108 candidate events are observed with 40.8 {+-} 3.8 total background expected, consistent with {sigma}(p{bar p} {yields} WW) = 11.6 {+-} 1.8(stat) {+-} 0.7(syst) {+-} 0.7(lumi) pb. Using a set of SU(2){sub L} {direct_product} U(1){sub Y} conserving constraints, the one-dimensional 95% C.L. limits on trilinear gauge couplings are -0.63 < {Delta}{kappa}{sub {gamma}} < 0.99, -0.15 < {lambda}{sub {gamma}} < 0.19, and -0.14 < {Delta}g{sub 1}{sup Z} < 0.34.
Date: April 1, 2008
Creator: Cooke, Michael P. & U., /Rice
System: The UNT Digital Library
Baryon stopping and hadronic spectra in Pb-Pb collisions at 158 GeV/nucleon (open access)

Baryon stopping and hadronic spectra in Pb-Pb collisions at 158 GeV/nucleon

Baryon stopping and particle production in Pb+Pb collisions at 158 GeV/nucleon are studied as a function of the collision centrality using new proton, antiproton, charged kaon and charged pion production data measured with the NA49 experiment at the CERN Super Proton Synchrotron (SPS). Stopping, which is measured by the shift in rapidity of net protons or baryons from the initial beam rapidity, increases in more central collisions. This is expected from a geometrical picture of the collisions. The stopping data are quantitatively compared to models incorporating various mechanisms for stopping. In general, microscopic transport calculations which incorporate current theoretical models of baryon stopping or use phenomenological extrapolations from simpler systems overestimate the dependence of stopping on centrality. Approximately, the yield of produced pions scales with the number of nucleons participating in the collision. A small increase in yield beyond this scaling, accompanied by a small suppression in the yield of the fastest pions, reflects the variation in stopping with centrality. Consistent with the observations from central collisions of light and heavy nuclei at the SPS, the transverse momentum distributions of all particles are observed to become harder with increasing centrality. This effect is most pronounced for the heaviest particles. This …
Date: April 12, 2000
Creator: Cooper, Glenn E.
System: The UNT Digital Library
Search for the neutral MSSM Higgs bosons in the ditau decay channels at CDF Run II (open access)

Search for the neutral MSSM Higgs bosons in the ditau decay channels at CDF Run II

This thesis presents the results on a search for the neutral MSSM Higgs bosons decaying to tau pairs, with least one of these taus decays leptonically. The search was performed with a sample of 1.8 fb{sup -1} of proton-antiproton collisions at {radical}s = 1.96 TeV provided by the Tevatron and collected by CDF Run II. No significant excess over the Standard Model prediction was found and a 95% confidence level exclusion limit have been set on the cross section times branching ratio as a function of the Higgs boson mass. This limit has been translated into the MSSM Higgs sector parameter plane, tan{beta} vs. M{sub A}, for the four different benchmark scenarios.
Date: April 1, 2008
Creator: Cuenca Almenar, Cristobal & /Valencia U., IFIC
System: The UNT Digital Library
GAiN: Distributed Array Computation with Python (open access)

GAiN: Distributed Array Computation with Python

Scientific computing makes use of very large, multidimensional numerical arrays - typically, gigabytes to terabytes in size - much larger than can fit on even the largest single compute node. Such arrays must be distributed across a "cluster" of nodes. Global Arrays is a cluster-based software system from Battelle Pacific Northwest National Laboratory that enables an efficient, portable, and parallel shared-memory programming interface to manipulate these arrays. Written in and for the C and FORTRAN programming languages, it takes advantage of high-performance cluster interconnections to allow any node in the cluster to access data on any other node very rapidly. The "numpy" module is the de facto standard for numerical calculation in the Python programming language, a language whose use is growing rapidly in the scientific and engineering communities. numpy provides a powerful N-dimensional array class as well as other scientific computing capabilities. However, like the majority of the core Python modules, numpy is inherently serial. Our system, GAiN (Global Arrays in NumPy), is a parallel extension to Python that accesses Global Arrays through numpy. This allows parallel processing and/or larger problem sizes to be harnessed almost transparently within new or existing numpy programs.
Date: April 24, 2009
Creator: Daily, Jeffrey A.
System: The UNT Digital Library
Spin distribution in preequilibrium reactions for 48Ti + n. (open access)

Spin distribution in preequilibrium reactions for 48Ti + n.

Cross section measurements were made of prompt {gamma}-ray production as a function of incident neutron energy on a {sup 48}Ti sample. Partial {gamma}-ray cross sections for transitions in {sup 45-48}Ti, {sup 44-48}Sc, and {sup 42-45}Ca have been determined. Energetic neutrons were delivered by the Los Alamos National Laboratory spallation neutron source located at the LANSCE/WNR facility. The prompt-reaction {gamma} rays were detected with the large-scale Compton-suppressed germanium array for neutron induced excitations (GEANIE). Neutron energies were determined by the time-of-flight technique. The {gamma}-ray excitation functions were converted to partial {gamma}-ray cross sections taking into account the dead-time correction, target thickness, detector efficiency and neutron flux (monitored with an in-line fission chamber). The data are presented for neutron energies E{sub n} between 1 to 200 MeV. These results are compared with model calculations which include compound nuclear and pre-equilibrium emission. The model calculations are performed using the STAPRE reaction code for E{sub n} up to 20 MeV and the GNASH reaction code for E{sub n} up to 120 MeV. Using the GNASH reaction code the effect of the spin distribution in preequilibrium reactions has been investigated. The preequilibrium reaction spin distribution was calculated using the quantum mechanical theory of Feshbach, Kerman, …
Date: April 6, 2005
Creator: Dashdorj, D
System: The UNT Digital Library
Gas Transport and Control in Thick-Liquid Inertial Fusion PowerPlants (open access)

Gas Transport and Control in Thick-Liquid Inertial Fusion PowerPlants

None
Date: April 12, 2006
Creator: Debonnel, Christophe Sylvain
System: The UNT Digital Library
Measurement of the inclusive isolated prompt photon production cross section at the Tevatron using the CDF detector (open access)

Measurement of the inclusive isolated prompt photon production cross section at the Tevatron using the CDF detector

In this thesis we present the measurement of the inclusive isolated prompt photon cross section with a total integrated luminosity of 2.5 fb{sup -1} of data collected with the CDF Run II detector at the Fermilab Tevatron Collider. The prompt photon cross section is a classic measurement to test perturbative QCD (pQCD) with potential to provide information on the parton distribution function (PDF), and sensitive to the presence of new physics at large photon transverse momentum. Prompt photons also constitute an irreducible background for important searches such as H {yields} {gamma}{gamma}, or SUSY and extra-dimensions with energetic photons in the final state. The Tevatron at Fermilab (Batavia, U.S.A.) is currently the hadron collider that operates at the highest energies in the world. It collides protons and antiprotons with a center-of-mass energy of 1.96 TeV. The CDF and the D0 experiments are located in two of its four interaction regions. In Run I at the Tevatron, the direct photon production cross section was measured by both CDF and DO, and first results in Run II have been presented by the DO Collaboration based on 380 pb{sup -1}. Both Run I and Run II results show agreement with the theoretical predictions except …
Date: April 1, 2009
Creator: Deluca Silberberg, Carolina
System: The UNT Digital Library
Cross section measurements for quasi-elastic neutrino-nucleus scattering with the MINOS near detector (open access)

Cross section measurements for quasi-elastic neutrino-nucleus scattering with the MINOS near detector

The Main Injector Neutrino Oscillation Search (MINOS) is a long baseline neutrino oscillation experiment based at the Fermi National Accelerator Laboratory (FNAL) in Chicago, Illinois. MINOS measures neutrino interactions in two large iron-scintillator tracking/sampling calorimeters; the Near Detector on-site at FNAL and the Far Detector located in the Soudan mine in northern Minnesota. The Near Detector has recorded a large number of neutrino interactions and this high statistics dataset can be used to make precision measurements of neutrino interaction cross sections. The cross section for charged-current quasi-elastic scattering has been measured by a number of previous experiments and these measurements disagree by up to 30%. A method to select a quasi-elastic enriched sample of neutrino interactions in the MINOS Near Detector is presented and a procedure to fit the kinematic distributions of this sample and extract the quasi-elastic cross section is introduced. The accuracy and robustness of the fitting procedure is studied using mock data and finally results from fits to the MINOS Near Detector data are presented.
Date: April 1, 2008
Creator: Dorman, Mark Edward & London, /University Coll.
System: The UNT Digital Library
Measurement of cross-section (p anti-p --> Z0) x BF (Z0 --> tau anti-tau) at s**(1/2) = 1.96-TeV using the D0 detector at the Tevatron (open access)

Measurement of cross-section (p anti-p --> Z0) x BF (Z0 --> tau anti-tau) at s**(1/2) = 1.96-TeV using the D0 detector at the Tevatron

In this thesis the first measurement of {sigma}(p{bar p}) {yields} Z{sup 0} {yields} {tau}{bar {tau}} with the D0 detector at the Tevatron is presented. The tau pair candidates are recorded by the D0 detector using p{bar p} interactions at a center-of-mass energy of 1.96 TeV. Events in which one tau decays into a muon and the other tau final state is hadronic with one charged particle are selected for this analysis. The selection criteria for the hadronic tau decay are based on the tau final state, hence for two channels of one-prong taus: single charged pion ({tau}{sub {pi}}) and rho decays ({tau}{sub {rho}}). The selection is based on simple cuts on a number of discriminating variables and the cut values have been optimized for the best cross section measurement. Of hadronic tau candidates that have been reconstructed as {tau}{sub {pi}} candidates, 0.801 {+-} 0.017 {+-} 0.066 pass the selection cut; in the case of {tau}{sub {rho}} taus, the selection efficiency is 0.676 {+-} 0.009 {+-} 0.009. Of all QCD jets that are reconstructed as hadronic tau candidates, 0.0093 {+-} 0.0002 pass the {tau}{sub {pi}} selection cuts and 0.0122 {+-} 0.0002 the {tau}{sub {rho}} cuts. The cross section has been measured …
Date: April 1, 2004
Creator: Duensing, Silke & U., /Nijmegen
System: The UNT Digital Library
Measurements of the Differential Cross Sections for the Inclusive Production of a Photon and Heavy Flavor Jet (open access)

Measurements of the Differential Cross Sections for the Inclusive Production of a Photon and Heavy Flavor Jet

This thesis presents the first measurement of the differential production cross section of a heavy flavor (bottom or charm) jet and direct photon at the Fermilab Tevatron. These measurements were performed using data recorded with the D0 detector from proton-antiproton collisions at a center of mass energy of {radical}s = 1.96 TeV. These results probe a kinematic range for the photon transverse momentum of 30 < p{sub T}{sup {gamma}} < 150 GeV and rapidity of |y{sup {gamma}}| < 1.0 and for jet transverse momentum p{sub T}{sup jet} > 15 GeV and rapidity of |y{sup jet}| < 0.8. These results are compared to next-to-leading-order theoretical calculations.
Date: April 1, 2009
Creator: Duggan, Daniel
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
The inclusive jet cross-section in proton anti-proton collisions at s**(1/2) = 1.96-TeV using the MidPoint jet algorithm (open access)

The inclusive jet cross-section in proton anti-proton collisions at s**(1/2) = 1.96-TeV using the MidPoint jet algorithm

The following work presents a preliminary measurement of the inclusive jet cross section for jet transverse momenta from 61 to 620 GeV in the rapidity range 0.1 < |Y| < 0.7. The result is based on 218 pb{sup -1} of data collected by the CDF detector at the Fermi National Accelerator Lab. The data are consistent with NLO pQCD predictions based on the CTEQ6.1 parton distribution functions.
Date: April 1, 2005
Creator: Flanagan, Gene U.
System: The UNT Digital Library
A Study of B→c$\bar{c}$γK in the BaBar Experiment (open access)

A Study of B→c$\bar{c}$γK in the BaBar Experiment

The BABAR Collaboration is a high energy physics experiment located at the Stanford Linear Accelerator Center. The primary goal of the experiment is to study charge and parity violation in the B-meson sector, however the copious production of B mesons decaying to other final states allows for a wide-ranging physics program. In particular, one can access the charmonium system via colour-suppressed b → c decays of the type B → c$\bar{c}$K. This thesis presents a study of B →c$\bar{c}$γK decays where c$\bar{c}$ includes J/Ψ and Ψ(2S), and K includes K<sup>±</sup>, K<sub>S</sub><sup>0</sup> and K*(892). The particular emphasis is on a search for the radiative decays X(3872) → J/Ψγ and X(3872) → Ψ(2S)γ. The X(3872) state is a recently-discovered resonance of undetermined quark composition, speculatively a conventional charmonium state or exotic four-quark di-meson molecule. This research is also sensitive to the well-known radiative charmonium decays B → χ<sub>c1,2</sub>K, which are used as verification for the analysis technique. This dissertation sets the best B → χ<sub>c1</sub>K branching fraction measurements to date, and sees the first evidence for factorization-suppressed B<sup>0</sup> → χ<sub>c2</sub>}K*<sup>0</sup> decay at a level of 3.6σ. It also provides evidence for X(3872) → J/Ψγ and X(3872) → Ψ(2S)γ with 3.6σ and 3.3σ …
Date: April 1, 2009
Creator: Fulsom, Brian Gregory
System: The UNT Digital Library
Evidence for electroweak top quark production in proton-antiproton collisions at s**(1/2) = 1.96 TeV (open access)

Evidence for electroweak top quark production in proton-antiproton collisions at s**(1/2) = 1.96 TeV

We present the first evidence for electroweak single top quark production using nearly 1 fb{sup -1} of Tevatron Run II data at {radical}s = 1.96 TeV. We select single-top-like data events in the lepton+jets decay channel and separate them from backgrounds using the matrix element analysis method. This technique uses leading order matrix elements to compute an event probability for both signal and background hypotheses. Using the expected signal acceptance, background, and observed data we measure the single top quark cross section: {sigma}(p{bar p} {yields} tb + tqb + X) = 4.6{sub -1.5}{sup +}1.8 pb. The probability for the background to have fluctuated up to give at least the cross section measured in this analysis is 0.21%, which corresponds to a Gaussian equivalent significance of 2.9{sigma}.
Date: April 1, 2007
Creator: Gadfort, Thomas & /Washington U., Seattle
System: The UNT Digital Library
Heterotic orbifolds (open access)

Heterotic orbifolds

A review of orbifold geometry is given, followed by a review of the construction of four-dimensional heterotic string models by compactification on a six-dimensional Z{sub 3} orbifold. Particular attention is given to the details of the transition from a classical theory to a first-quantized theory. Subsequently, a discussion is given of the systematic enumeration of all standard-like three generation models subject to certain limiting conditions. it is found that the complete set is described by 192 models, with only five possibilities for the hidden sector gauge group. It is argued that only four of the hidden sector gauge groups are viable for dynamical supersymmetry breaking, leaving only 175 promising models in the class. General features of the spectra of matter states in all 175 models are discussed. Twenty patterns of representations are found to occur. Accommodation of the Minimal Supersymmetric Standard Model (MSSM) spectrum is addressed. States beyond those contains in the MSSM and nonstandard hypercharge normalization are shown to be generic, though some models do allow for the usual hypercharge normalization found in SU(5) embeddings of the Standard Model gauge group. Only one of the twenty patterns of representations, comprising seven of the 175 models, is found to be …
Date: April 1, 2002
Creator: Giedt, Joel
System: The UNT Digital Library
Behavior of the Diamond Difference and Low-Order Nodal Numerical Transport Methods in the Thick Diffusion Limit for Slab Geometry (open access)

Behavior of the Diamond Difference and Low-Order Nodal Numerical Transport Methods in the Thick Diffusion Limit for Slab Geometry

The objective of this work is to investigate the thick diffusion limit of various spatial discretizations of the one-dimensional, steady-state, monoenergetic, discrete ordinates neutron transport equation. This work specifically addresses the two lowest order nodal methods, AHOT-N0 and AHOT-N1, as well as reconsiders the asymptotic limit of the Diamond Difference method. The asymptotic analyses of the AHOT-N0 and AHOT-N1 nodal methods show that AHOT-N0 does not possess the thick diffusion limit for cell edge or cell average fluxes except under very limiting conditions, which is to be expected considering the AHOT-N0 method limits to the Step method in the thick diffusion limit. The AHOT-N1 method, which uses a linear in-cell representation of the flux, was shown to possess the thick diffusion limit for both cell average and cell edge fluxes. The thick diffusion limit of the DD method, including the boundary conditions, was derived entirely in terms of cell average scalar fluxes. It was shown that, for vacuum boundaries, only when {sigma}{sub t}, h, and Q are constant and {sigma}{sub a} = 0 is the asymptotic limit of the DD method close to the finite-differenced diffusion equation in the system interior, and that the boundary conditions between the systems will …
Date: April 17, 2007
Creator: Gill, D. F.
System: The UNT Digital Library
A Measurement of the Helicity of W Bosons Produced in Top-Quark Decays (open access)

A Measurement of the Helicity of W Bosons Produced in Top-Quark Decays

We have measured the fraction of longitudinally polarized W bosons produced top-quark decays. The result of the analysis in single-lepton t{bar t} events is fully consistent with the Standard Model expectation. The 2{sigma} discrepancy in the dilepton analysis is suggestive of new phenomena. However, given the significance of the discrepancy, any claim of new physics based on this analysis is highly speculative. It is worth noting that another analysis of the kinematic properties of these data finds a similar discrepancy [63]. It will be interesting to see if this discrepancy persists as more data are collected during run II of the Tevatron. In order to make a stronger statement about the nature of the tWb coupling with this method, larger statistics are required. However alternative methods, particularly the matrix-element method developed at D0 [36, 35], should be especially powerful, even with limited statistics.
Date: April 1, 2005
Creator: Goldschmidt, Nathan Joel
System: The UNT Digital Library