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Magnetic nanoparticles for applications in oscillating magnetic field

Description: Enzymatic and thermochemical catalysis are both important industrial processes. However, the thermal requirements for each process often render them mutually exclusive: thermochemical catalysis requires high temperature that denatures enzymes. One of the long-term goals of this project is to design a thermocatalytic system that could be used with enzymatic systems in situ to catalyze reaction sequences in one pot; this system would be useful for numerous applications e.g. conversion of biomass to biofuel and other commodity products. The desired thermocatalytic system would need to supply enough thermal energy to catalyze thermochemical reactions, while keeping the enzymes from high temperature denaturation. Magnetic nanoparticles are known to generate heat in an oscillating magnetic field through mechanisms including hysteresis and relaxational losses. We envisioned using these magnetic nanoparticles as the local heat source embedded in sub-micron size mesoporous support to spatially separate the particles from the enzymes. In this study, we set out to find the magnetic materials and instrumental conditions that are sufficient for this purpose. Magnetite was chosen as the first model magnetic material in this study because of its high magnetization values, synthetic control over particle size, shape, functionalization and proven biocompatibility. Our experimental designs were guided by a series of theoretical calculations, which provided clues to the effects of particle size, size distribution, magnetic field, frequency and reaction medium. Materials of theoretically optimal size were synthesized, functionalized, and their effects in the oscillating magnetic field were subsequently investigated. Under our conditions, the materials that clustered e.g. silica-coated and PNIPAM-coated iron oxides exhibited the highest heat generation, while iron oxides embedded in MSNs and mesoporous iron oxides exhibited the least bulk heating. It is worth noting that the specific loss power of PNIPAM-coated Fe{sub 3}O{sub 4} was peculiarly high, and the heat loss mechanism of this material remains to be ...
Date: December 15, 2010
Creator: Peeraphatdit, Chorthip
Partner: UNT Libraries Government Documents Department

Measurement of Single Spin Asymmetries in Semi-Inclusive Deep Inelastic Scattering Reaction n↑ ( e,e' pi{sup +}) X at Jefferson Lab

Description: What constitutes the spin of the nucleon? The answer to this question is still not completely understood. Although we know the longitudinal quark spin content very well, the data on the transverse quark spin content of the nucleon is still very sparse. Semi-inclusive Deep Inelastic Scattering (SIDIS) using transversely polarized targets provide crucial information on this aspect. The data that is currently available was taken with proton and deuteron targets. The E06-010 experiment was performed at Jefferson Lab in Hall-A to measure the single spin asymmetries in the SIDIS reaction n↑(e, e′π{sup ±}/K{sup ±})X using transversely polarized {sup 3}He target. The experiment used the continuous electron beam provided by the CEBAF accelerator with a beam energy of 5.9 GeV. Hadrons were detected in a high-resolution spectrometer in coincidence with the scattered electrons detected by the BigBite spectrometer. The kinematic coverage focuses on the valence quark region, x = 0.19 to 0.34, at Q{sup 2} = 1.77 to 2.73 (GeV/c){sup 2}. This is the first measurement on a neutron target. The data from this experiment, when combined with the world data on the proton and the deuteron, will provide constraints on the transversity and Sivers distribution functions on both the u and d-quarks in the valence region. In this work we report on the single spin asymmetries in the SIDIS n↑(e, e′π{sup +})X reaction.
Date: June 1, 2010
Creator: Allada, Kalyan
Partner: UNT Libraries Government Documents Department

Measurement of single-target spin asymmetries in the electroproduction of negative pions in the semi-inclusive deep inelastic reaction n{up_arrow}(e,e'{pi}{sup -})X on a transversely polarized {sup 3}He target

Description: The experiment E06010 measured the target single spin asymmetry (SSA) in the semiinclusive deep inelastic (SIDIS) n{up_arrow}(e, e'{pi}{sup -})X reaction with a transversely polarized {sup 3}He target as an e#11;ective neutron target. This is the very #12;rst independent measurement of the neutron SSA, following the measurements at HERMES and COMPASS on the proton and the deuteron. The experiment acquired data in Hall A at Je#11;erson Laboratory with a continuous electron beam of energy 5.9 GeV, probing the valence quark region, with x = 0.13 {rt_arrow} 0.41, at Q{sup 2} = 1.31 {rt_arrow} 3.1 GeV{sup 2}. The two contributing mechanisms to the measured asymmetry, viz, the Collins effect and the Sivers effect can be realized through the variation of the asymmetry as a function of the Collins and Sivers angles. The neutron Collins and Sivers moments, associated with the azimuthal angular modulations, are extracted from the measured asymmetry for the very #12;first time and are presented in this thesis. The kinematics of this experiment is comparable to the HERMES proton measurement. However, the COMPASS measurements on deuteron and proton are in the low-x region. The results of this experiment are crucial as the first step toward the extraction of quark transversity and Sivers distribution functions in SIDIS. With the existing results on proton and deuteron, these new results on neutron will provide powerful constraints on the transversity and Sivers distributions of both the u and d-quarks in the valence region.
Date: June 1, 2010
Creator: Dutta, Chiranjib
Partner: UNT Libraries Government Documents Department

Input/Output of ab-initio nuclear structure calculations for improved performance and portability

Description: Many modern scientific applications rely on highly computation intensive calculations. However, most applications do not concentrate as much on the role that input/output operations can play for improved performance and portability. Parallelizing input/output operations of large files can significantly improve the performance of parallel applications where sequential I/O is a bottleneck. A proper choice of I/O library also offers a scope for making input/output operations portable across different architectures. Thus, use of parallel I/O libraries for organizing I/O of large data files offers great scope in improving performance and portability of applications. In particular, sequential I/O has been identified as a bottleneck for the highly scalable MFDn (Many Fermion Dynamics for nuclear structure) code performing ab-initio nuclear structure calculations. We develop interfaces and parallel I/O procedures to use a well-known parallel I/O library in MFDn. As a result, we gain efficient I/O of large datasets along with their portability and ease of use in the down-stream processing. Even situations where the amount of data to be written is not huge, proper use of input/output operations can boost the performance of scientific applications. Application checkpointing offers enormous performance improvement and flexibility by doing a negligible amount of I/O to disk. Checkpointing saves and resumes application state in such a manner that in most cases the application is unaware that there has been an interruption to its execution. This helps in saving large amount of work that has been previously done and continue application execution. This small amount of I/O provides substantial time saving by offering restart/resume capability to applications. The need for checkpointing in optimization code NEWUOA has been identified and checkpoint/restart capability has been implemented in NEWUOA by using simple file I/O.
Date: December 15, 2010
Creator: Laghave, Nikhil
Partner: UNT Libraries Government Documents Department

A Measurement of the neutron electric form factor at very large momentum transfer using polaried electrions scattering from a polarized helium-3 target

Description: Knowledge of the electric and magnetic elastic form factors of the nucleon is essential for an understanding of nucleon structure. Of the form factors, the electric form factor of the neutron has been measured over the smallest range in Q{sup 2} and with the lowest precision. Jefferson Lab experiment 02-013 used a novel new polarized {sup 3}He target to nearly double the range of momentum transfer in which the neutron form factor has been studied and to measure it with much higher precision. Polarized electrons were scattered off this target, and both the scattered electron and neutron were detected. G{sup n}{sub E} was measured to be 0.0242 ± 0.0020(stat) ± 0.0061(sys) and 0.0247 ± 0.0029(stat) ± 0.0031(sys) at Q{sup 2} = 1.7 and 2.5 GeV{sup 2}, respectively.
Date: October 1, 2010
Creator: Kelleher, Aidan
Partner: UNT Libraries Government Documents Department

Developing new optical imaging techniques for single particle and molecule tracking in live cells

Description: Differential interference contrast (DIC) microscopy is a far-field as well as wide-field optical imaging technique. Since it is non-invasive and requires no sample staining, DIC microscopy is suitable for tracking the motion of target molecules in live cells without interfering their functions. In addition, high numerical aperture objectives and condensers can be used in DIC microscopy. The depth of focus of DIC is shallow, which gives DIC much better optical sectioning ability than those of phase contrast and dark field microscopies. In this work, DIC was utilized to study dynamic biological processes including endocytosis and intracellular transport in live cells. The suitability of DIC microscopy for single particle tracking in live cells was first demonstrated by using DIC to monitor the entire endocytosis process of one mesoporous silica nanoparticle (MSN) into a live mammalian cell. By taking advantage of the optical sectioning ability of DIC, we recorded the depth profile of the MSN during the endocytosis process. The shape change around the nanoparticle due to the formation of a vesicle was also captured. DIC microscopy was further modified that the sample can be illuminated and imaged at two wavelengths simultaneously. By using the new technique, noble metal nanoparticles with different shapes and sizes were selectively imaged. Among all the examined metal nanoparticles, gold nanoparticles in rod shapes were found to be especially useful. Due to their anisotropic optical properties, gold nanorods showed as diffraction-limited spots with disproportionate bright and dark parts that are strongly dependent on their orientation in the 3D space. Gold nanorods were developed as orientation nanoprobes and were successfully used to report the self-rotation of gliding microtubules on kinesin coated substrates. Gold nanorods were further used to study the rotational motions of cargoes during the endocytosis and intracellular transport processes in live mammalian cells. New rotational information ...
Date: December 15, 2010
Creator: Sun, Wei
Partner: UNT Libraries Government Documents Department

Electroproduction de pions neutres dans le Hall A au Jefferson Laboratory

Description: The past decade has seen a strong evolution of the study of the hadron structure through exclusive processes, allowing to access to a more complete description of this structure. Exclusive processes include DVCS (Deeply Virtual Compton Scattering) as well as hard exclusive meson production. This document is particularly focussed on the latter, and more particularly on exclusive neutral pion production. In this thesis is described the analysis of triple coincidence events H(e, e'{gamma}{gamma})X, which were a consequent by-product of the DVCS experiment which occured during Fall 2004 at Jefferson Lab Hall A, to extract the ep {yields} ep{pi}{sup 0} cross section. This cross section has been measured at two values of four-momentum transfer Q{sup 2} = 1.9 GeV{sup 2} and Q{sup 2} = 2.3 GeV{sup 2}. The statistical precision for these measurements is achieved at better than 5 %. The kinematic range allows to study the evolution of the extracted cross section as a function of Q{sup 2} and W. Results are be confronted with Regge inspired calculations and Generalized (GPD) predictions. An intepretation of our data within the framework of semi-inclusive deep inelastic scattering is also discussed.
Date: June 1, 2010
Creator: Fuchey, Eric
Partner: UNT Libraries Government Documents Department

Metal thin film growth on multimetallic surfaces: From quaternary metallic glass to binary crystal

Description: The work presented in this thesis mainly focuses on the nucleation and growth of metal thin films on multimetallic surfaces. First, we have investigated the Ag film growth on a bulk metallic glass surface. Next, we have examined the coarsening and decay of bilayer Ag islands on NiAl(110) surface. Third, we have investigated the Ag film growth on NiAl(110) surface using low-energy electron diffraction (LEED). At last, we have reported our investigation on the epitaxial growth of Ni on NiAl(110) surface. Some general conclusions can be drawn as follows. First, Ag, a bulk-crystalline material, initially forms a disordered wetting layer up to 4-5 monolayers on Zr-Ni-Cu-Al metallic glass. Above this coverage, crystalline 3D clusters grow, in parallel with the flatter regions. The cluster density increases with decreasing temperature, indicating that the conditions of island nucleation are far-from-equilibrium. Within a simple model where clusters nucleate whenever two mobile Ag adatoms meet, the temperature-dependence of cluster density yields a (reasonable) upper limit for the value of the Ag diffusion barrier on top of the Ag wetting layer of 0.32 eV. Overall, this prototypical study suggests that it is possible to grow films of a bulk-crystalline metal that adopt the amorphous character of a glassy metal substrate, if film thickness is sufficiently low. Next, the first study of coarsening and decay of bilayer islands has been presented. The system was Ag on NiAl(110) in the temperature range from 185 K to 250 K. The coarsening behavior, has some similarities to that seen in the Ag(110) homoepitaxial system studied by Morgenstern and co-workers. At 185 K and 205 K, coarsening of Ag islands follows a Smoluchowski ripening pathway. At 205 K and 250 K, the terrace diffusion limited Ostwald ripening dominants. The experimental observed temperature for the transition from SR to OR is 205 ...
Date: December 15, 2010
Creator: Jing, Dapeng
Partner: UNT Libraries Government Documents Department

Extending the frontiers of mass spectrometric instrumentation and methods

Description: The focus of this dissertation is two-fold: developing novel analysis methods using mass spectrometry and the implementation and characterization of a novel ion mobility mass spectrometry instrumentation. The novel mass spectrometry combines ion trap for ion/ion reactions coupled to an ion mobility cell. The long term goal of this instrumentation is to use ion/ion reactions to probe the structure of gas phase biomolecule ions. The three ion source - ion trap - ion mobility - qTOF mass spectrometer (IT - IM - TOF MS) instrument is described. The analysis of the degradation products in coal (Chapter 2) and the imaging plant metabolites (Appendix III) fall under the methods development category. These projects use existing commercial instrumentation (JEOL AccuTOF MS and Thermo Finnigan LCQ IT, respectively) for the mass analysis of the degraded coal products and the plant metabolites, respectively. The coal degradation paper discusses the use of the DART ion source for fast and easy sample analysis. The sample preparation consisted of a simple 50 fold dilution of the soluble coal products in water and placing the liquid in front of the heated gas stream. This is the first time the DART ion source has been used for analysis of coal. Steven Raders under the guidance of John Verkade came up with the coal degradation projects. Raders performed the coal degradation reactions, worked up the products, and sent them to me. Gregg Schieffer developed the method and wrote the paper demonstrating the use of the DART ion source for the fast and easy sample analysis. The plant metabolite imaging project extends the use of colloidal graphite as a sample coating for atmospheric pressure LDI. DC Perdian and I closely worked together to make this project work. Perdian focused on building the LDI setup whereas Schieffer focused on the MSn analysis ...
Date: December 15, 2010
Creator: Schieffer, Gregg
Partner: UNT Libraries Government Documents Department

Microstructures and oxidation behavior of some Molybdenum based alloys

Description: The advent of Ni based superalloys revolutionized the high temperature alloy industry. These materials are capable of operating in extremely harsh environments, comprising of temperatures around 1050 C, under oxidative conditions. Demands for increased fuel efficiency, however, has highlighted the need for materials that can be used under oxidative conditions at temperatures in excess of 1200 C. The Ni based superalloys are restricted to lower temperatures due to the presence of a number of low melting phases that melt in the 1250 - 1450 C, resulting in softening of the alloys above 1000 C. Therefore, recent research directions have been skewed towards exploring and developing newer alloy systems. This thesis comprises a part of such an effort. Techniques for rapid thermodynamic assessments were developed and applied to two different systems - Mo-Si alloys with transition metal substitutions (and this forms the first part of the thesis) and Ni-Al alloys with added components for providing high temperature strength and ductility. A hierarchical approach towards alloy design indicated the Mo-Ni-Al system as a prospective candidate for high temperature applications. Investigations on microstructures and oxidation behavior, under both isothermal and cyclic conditions, of these alloys constitute the second part of this thesis. It was seen that refractory metal systems show a marked microstructure dependence of oxidation.
Date: December 15, 2010
Creator: Ray, Pratik Kumar
Partner: UNT Libraries Government Documents Department

Devitrification kinetics and phase selection mechanisms in Cu-Zr metallic glasses

Description: Metallic glasses have been a promising class of materials since their discovery in the 1960s. Indeed, remarkable chemical, mechanical and physical properties have attracted considerable attention, and several excellent reviews are available. Moreover, the special group of glass forming alloys known as the bulk metallic glasses (BMG) become amorphous solids even at relatively low cooling rates, allowing them to be cast in large cross sections, opening the scope of potential applications to include bulk forms and net shape structural applications. Recent studies have been reported for new bulk metallic glasses produced with lower cooling rates, from 0.1 to several hundred K/s. Some of the application products of BMGs include sporting goods, high performance springs and medical devices. Several rapid solidification techniques, including melt-spinning, atomization and surface melting have been developed to produce amorphous alloys. The aim of all these methods is to solidify the liquid phase rapidly enough to suppress the nucleation and growth of crystalline phases. Furthermore, the production of amorphous/crystalline composite (ACC) materials by partial crystallization of amorphous precursor has recently given rise to materials that provide better mechanical and magnetic properties than the monolithic amorphous or crystalline alloys. In addition, these advances illustrate the broad untapped potential of using the glassy state as an intermediate stage in the processing of new materials and nanostructures. These advances underlie the necessity of investigations on prediction and control of phase stability and microstructural dynamics during both solidification and devitrification processes. This research presented in this dissertation is mainly focused on Cu-Zr and Cu-Zr-Al alloy systems. The Cu-Zr binary system has high glass forming ability in a wide compositional range (35-70 at.% Cu). Thereby, Cu-Zr based alloys have attracted much attention according to fundamental research on the behaviors of glass forming alloys. Further motivation arising from the application of this system ...
Date: December 15, 2010
Creator: Kalay, Ilkay
Partner: UNT Libraries Government Documents Department

Dislocation dynamics simulations of plasticity at small scales

Description: As metallic structures and devices are being created on a dimension comparable to the length scales of the underlying dislocation microstructures, the mechanical properties of them change drastically. Since such small structures are increasingly common in modern technologies, there is an emergent need to understand the critical roles of elasticity, plasticity, and fracture in small structures. Dislocation dynamics (DD) simulations, in which the dislocations are the simulated entities, offer a way to extend length scales beyond those of atomistic simulations and the results from DD simulations can be directly compared with the micromechanical tests. The primary objective of this research is to use 3-D DD simulations to study the plastic deformation of nano- and micro-scale materials and understand the correlation between dislocation motion, interactions and the mechanical response. Specifically, to identify what critical events (i.e., dislocation multiplication, cross-slip, storage, nucleation, junction and dipole formation, pinning etc.) determine the deformation response and how these change from bulk behavior as the system decreases in size and correlate and improve our current knowledge of bulk plasticity with the knowledge gained from the direct observations of small-scale plasticity. Our simulation results on single crystal micropillars and polycrystalline thin films can march the experiment results well and capture the essential features in small-scale plasticity. Furthermore, several simple and accurate models have been developed following our simulation results and can reasonably predict the plastic behavior of small scale materials.
Date: December 15, 2010
Creator: Zhou, Caizhi
Partner: UNT Libraries Government Documents Department

Study of the (e,e'p) quasi-elastic reaction in complex nuclei: theory and experiment

Description: Experimental coincidence cross section and transverse-longitudinal asymmetry A{sub TL} have been obtained for the quasielastic (e,e'p) reaction in {sup 16}O, {sup 12}C, and {sup 208}Pb in constant q-ω kinematics in the missing momentum range -350 < p{sub miss} < 350 MeV/c. In these experiments, performed in experimental Hall A of the Thomas Jefferson National Accelerator Facility (JLAB), the beam energy and the momentum and angle of the scattered electrons were kept fixed, while the angle between the proton momentum and the momentum transfer q was varied in order to map out the missing momentum distribution. The experimental cross section and A{sub TL} asymmetry have been compared with Monte Carlo simulations based on Distorted Wave Impulse Approximation (DWIA) calculations with both relativistic and non-relativistic spinor structure. The spectroscopic factors obtained for both models are in agreement with previous experimental values, while A{sub TL} measurements favor the relativistic DWIA calculation. This thesis describes the details of the experimental setup, the calibration of the spectrometers, the techniques used in the data analysis to derive the final cross sections and the A{sub TL}, the ingredients of the theoretical calculations employed and the comparison of the results with the simulations based on these theoretical models.
Date: March 1, 2010
Creator: Herraiz, Joaquin Lopez
Partner: UNT Libraries Government Documents Department

Angle-resolved photoemission spectroscopy (ARPES) studies of cuprate superconductors

Description: This dissertation is comprised of three different angle-resolved photoemission spectroscopy (ARPES) studies on cuprate superconductors. The first study compares the band structure from two different single layer cuprates Tl{sub 2}Ba{sub 2}CuO{sub 6+{delta}} (Tl2201) T{sub c,max} {approx} 95 K and (Bi{sub 1.35}Pb{sub 0.85})(Sr{sub 1.47}La{sub 0.38})CuO{sub 6+{delta}} (Bi2201) T{sub c,max} {approx} 35 K. The aim of the study was to provide some insight into the reasons why single layer cuprate's maximum transition temperatures are so different. The study found two major differences in the band structure. First, the Fermi surface segments close to ({pi},0) are more parallel in Tl2201 than in Bi2201. Second, the shadow band usually related to crystal structure is only present in Bi2201, but absent in higher T{sub c} Tl2201. The second study looks at the different ways of doping Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} (Bi2212) in-situ by only changing the post bake-out vacuum conditions and temperature. The aim of the study is to systematically look into the generally overlooked experimental conditions that change the doping of a cleaved sample in ultra high vacuum (UHV) experiments. The study found two major experimental facts. First, in inadequate UHV conditions the carrier concentration of Bi2212 increases with time, due to the absorption of oxygen from CO{sub 2}/CO molecules, prime contaminants present in UHV systems. Second, in a very clean UHV system at elevated temperatures (above about 200 K), the carrier concentration decreases due to the loss of oxygen atoms from the Bi-O layer. The final study probed the particle-hole symmetry of the pseudogap phase in high temperature superconducting cuprates by looking at the thermally excited bands above the Fermi level. The data showed a particle-hole symmetric pseudogap which symmetrically closes away from the nested FS before the node. The data is consistent with a charge density wave (CDW) origin of the ...
Date: December 15, 2010
Creator: Palczewski, Ari Deibert
Partner: UNT Libraries Government Documents Department

Reducing the losses of optical metamaterials

Description: The field of metamaterials is driven by fascinating and far-reaching theoretical visions, such as perfect lenses, invisibility cloaking, and enhanced optical nonlinearities. However, losses have become the major obstacle towards real world applications in the optical regime. Reducing the losses of optical metamaterials becomes necessary and extremely important. In this thesis, two approaches are taken to reduce the losses. One is to construct an indefinite medium. Indefinite media are materials where not all the principal components of the permittivity and permeability tensors have the same sign. They do not need the resonances to achieve negative permittivity, {var_epsilon}. So, the losses can be comparatively small. To obtain indefinite media, three-dimensional (3D) optical metallic nanowire media with different structures are designed. They are numerically demonstrated that they are homogeneous effective indefinite anisotropic media by showing that their dispersion relations are hyperbolic. Negative group refraction and pseudo focusing are observed. Another approach is to incorporate gain into metamaterial nanostructures. The nonlinearity of gain is included by a generic four-level atomic model. A computational scheme is presented, which allows for a self-consistent treatment of a dispersive metallic photonic metamaterial coupled to a gain material incorporated into the nanostructure using the finite-difference time-domain (FDTD) method. The loss compensations with gain are done for various structures, from 2D simplified models to 3D realistic structures. Results show the losses of optical metamaterials can be effectively compensated by gain. The effective gain coefficient of the combined system can be much larger than the bulk gain counterpart, due to the strong local-field enhancement.
Date: December 15, 2010
Creator: Fang, Anan
Partner: UNT Libraries Government Documents Department

Dark matter limits froma 15 kg windowless bubble chamber

Description: The COUPP collaboration has successfully used bubble chambers, a technology previously applied only to high-energy physics experiments, as direct dark matter detectors. It has produced the world's most stringent spin-dependent WIMP limits, and increasingly competitive spin-independent limits. These limits were achieved by capitalizing on an intrinsic rejection of the gamma background that all other direct detection experiments must address through high-density shielding and empirically-determined data cuts. The history of COUPP, including its earliest prototypes and latest results, is briefly discussed in this thesis. The feasibility of a new, windowless bubble chamber concept simpler and more inexpensive in design is discussed here as well. The dark matter limits achieved with a 15 kg windowless chamber, larger than any previous COUPP chamber (2 kg, 4 kg), are presented. Evidence of the greater radiopurity of synthetic quartz compared to natural is presented using the data from this 15 kg device, the first chamber to be made from synthetic quartz. The effective reconstruction of the three-dimensional positions of bubbles in a highly distorted optical field, with ninety-degree bottom lighting similar to cloud chamber lighting, is demonstrated. Another innovation described in this thesis is the use of the sound produced by bubbles recorded by an array of piezoelectric sensors as the primary means of bubble detection. In other COUPP chambers, cameras have been used as the primary trigger. Previous work on bubble acoustic signature differentiation using piezos is built upon in order to further demonstrate the ability to discriminate between alpha- and neutron-induced events.
Date: December 1, 2010
Creator: Szydagis, Matthew Mark & U., /Chicago
Partner: UNT Libraries Government Documents Department

Measurement of the t tbar cross section at the Run II Tevatron using Support Vector Machines

Description: This dissertation measures the t{bar t} production cross section at the Run II CDF detector using data from early 2001 through March 2007. The Tevatron at Fermilab is a p{bar p} collider with center of mass energy {radical}s = 1.96 TeV. This data composes a sample with a time-integrated luminosity measured at 2.2 {+-} 0.1 fb{sup -1}. A system of learning machines is developed to recognize t{bar t} events in the 'lepton plus jets' decay channel. Support Vector Machines are described, and their ability to cope with a multi-class discrimination problem is provided. The t{bar t} production cross section is then measured in this framework, and found to be {sigma}{sub t{bar t}} = 7.14 {+-} 0.25 (stat){sub -0.86}{sup +0.61}(sys) pb.
Date: August 1, 2010
Creator: Whitehouse, Benjamin Eric & U., /Tufts
Partner: UNT Libraries Government Documents Department

Measurement of the \textit{CP} Violating Phase $\boldsymbol{\sin(2\beta_{s})}$ using $\boldsymbol{B^{0}_{s}\rightarrow J/\psi\phi}$ Decays at CDF

Description: A B{sub s}{sup 0} meson can oscillate into its anti-particle, the {bar B}{sub s}{sup 0} meson, before decaying. CP violation in this system is made possible by the presence of amplitudes from both mixed and unmixed B{sub s}{sup 0} meson decays. The CP violating phase {beta}s appears in the interference between the decay amplitudes. The quantity sin(2{beta}s) is expected to be small in the standard model. Thus, measuring a large value for sin(2{beta}s) would be an unequivocal sign of new physics participation in the B{sub s}{sup 0} mixing loop diagram. In this thesis, we present a latest measurement of sin(2{beta}s), using 5.2 fb{sup -1} of data collected at CDF from p{bar p} collisions at a center of mass energy of {radical}s = 1.96 TeV. A time-dependent angular analysis, with the production flavor of the B{sub s}{sup 0} meson identified with flavor tagging methods, is used to extract sin(2{beta}s) from {approx}6500 B{sub s}{sup 0} {yields} J/{psi}{phi} decays. Other parameters of interest, such as the B{sub s}{sup 0} lifetime and the decay width difference {Delta}{Lambda} between the heavy and light B{sub s}{sup 0} mass eigenstates are determined to high precision. Also, the effect of potential contributions to the final state from B{sub s}{sup 0} {yields} J/{psi}f{sub 0} and B{sub s}{sup 0} {yields} J/{psi}K{sup +}K{sup -} decays is considered for the first time. We present 68% and 95% confidence regions in the {beta}s - {Delta}{Lambda} plane. The probability that the observed central value is a fluctuation of the data from the standard model expected value of {beta}s is calculated to be 44%. The observed confidence region shows better agreement with the standard model prediction than previous measurements.
Date: May 1, 2010
Creator: Pueschel, Elisa & U., /Carnegie Mellon
Partner: UNT Libraries Government Documents Department

Measurement of the Top Quark Mass in the Di-lepton Channel using the Dalitz-Goldstein Method

Description: This dissertation describes a measurement of the mass of the top quark using a method developed by G. Goldstein and R.H. Dalitz. It is based on 2.0 fb{sup -1} of data collected by the Collider Detector Facility at Fermi National Accelerator Laboratories. Di-lepton events were observed from colliding protons with anti-protons with {radical}s = 1.96 TeV in the Tevatron Collider. A total of 145 candidate events were observed with 49 expected to be from background. These events include two neutrinos which elude detection. The method begins by assuming an initial top quark mass and solves for the neutrino momenta using a geometrical construction. The method samples over a range of likely top quark masses choosing the most consistent mass via a likelihood function. An important distinguishing feature of this method from others is its lack of dependence on the missing transverse energy, a quantity that is poorly measured by the experiment. This analysis determines the top quark mass to be M{sub top} = 172.3 {+-} 3.4(stat.) {+-} 2.0(syst.) GeV/c{sup 2} (M{sub top} = 170.5 {+-} 3.7(stat.) {+-} 1.8(syst.) GeV/c{sup 2} with b-tagging).
Date: October 1, 2010
Creator: Hare, Matthew Frederick & U., /Tufts
Partner: UNT Libraries Government Documents Department

Measurement of ww + wz production cross section and study of the dijet mass spectrum in the lnu + jets final state at CDF

Description: We present the measurement of the WW and WZ production cross section in p{bar p} collisions at {radical}s = 1.96 TeV, in a final state consisting of an electron or muon, neutrino and jets. The data analyzed were collected by the CDF II detector at the Tevatron collider and correspond to 4.3 fb{sup -1} of integrated luminosity. The analysis uses a fit to the dijet mass distribution to extract the diboson contribution. We observe 1582 {+-} 275(stat.) {+-} 107(syst.) diboson candidate events and measure a cross section of {sigma}{sub WW/WZ} = 18.1 {+-} 3.3(stat.) {+-} 2.5(syst.) pb, consistent with the Standard Model prediction of 15.9 {+-} 0.9 pb. The best fit to the dijet mass of the known components shows a good agreement with the data except for the [120, 160] GeV/c{sup 2} mass range, where an excess is observed. We perform detailed checks of our background model and study the significance of the excess, assuming an additional gaussian component with a width compatible with the expected dijet mass resolution. A standard {Delta}{sub {chi}}{sup 2} test of the presence of the additional component, returns a p-value of 4.2 x 10{sup -4} when standard sources of systematics are considered, corresponding to a significance of 3.3{sigma}.
Date: December 1, 2010
Creator: Cavaliere, Viviana & U., /Siena
Partner: UNT Libraries Government Documents Department

Measurement of the Ratio of Inclusive Cross Sections !(p-p!Z+b-jet) !(p-p!Z+jet) in the Dilepton Final States

Description: The inclusive production of b-jets with a Z boson is an important background to searches for the Higgs boson in associated ZH {yields} llb{bar b} production at the Fermilab Tevatron collider. This thesis describes the most precise measurement to date of the ratio of inclusive cross sections {sigma}(p{bar p} {yields} Z + b-jet)/{sigma}(p{bar p} {yields} Z + jet) when a Z boson decays into two electrons or muons. The measurement uses a data sample from p{bar p} collisions at the center of mass energy {radical}s = 1.96 TeV corresponding to an integrated luminosity of 4.2 fb{sup -1} collected by the D0 detector. The measured ratio {sigma}(Z + b-jet)/{sigma}(Z + jet) is 0.0187 {+-} 0.0021(stat) {+-} 0.0015(syst) for jets with transverse momentum p{sub T} > 20 GeV and pseudorapidity |{eta}| {le} 2.5. The measurement is compared with the next-to-leading order theoretical predictions from MCFM and is found to be consistent within uncertainties.
Date: October 1, 2010
Creator: Smith, Kenneth James
Partner: UNT Libraries Government Documents Department

Search for the Standard Model Higgs Boson in p anti-p Interactions with the Decay Mode H --> W+W- --> mu+nu mu-anti-nu at the D0 Experiment

Description: A search for the standard model Higgs boson in p{bar p} collisions resulting in two muons and large missing transverse energy is presented. The analysis uses 4.2 fb{sup -1} of integrated luminosity at a center-of-mass energy of {radical}s = 1.96 TeV collected between April 2002 and December 2008 with the D0 detector at the Fermilab Tevatron collider. No significant excess above the background estimation is observed and limits are derived on Higgs boson production.
Date: April 1, 2010
Creator: Johnston, Dale Morgan & U., /Nebraska
Partner: UNT Libraries Government Documents Department

Search for V H and Technicolor Producion in the qqbb Final State Using the RunII D0 Detector

Description: A search for dijet resonance production in a four-jet all-hadronic final state from the D0 detector at Fermilab's Tevatron is presented. The data set, acquired at a p{bar p} center-of-mass energy of {radical}s = 1.96 TeV, contains primarily multijet events and represents approximately 1 fb{sup -1} of data. The cross section limits for associated Higgs production and Technicolor processes are determined through a background subtraction method using data to estimate the background. This four-jet channel is potentially very powerful, but is extremely challenging due to the large multijet background from QCD processes. Background rejection is performed by utilizing b-tagging, pre-selection cuts, a multi-variate boosted decision tree discriminant, and the correlated information contained in the M(bb) and M(jj) dijet invariant masses. The search for V H (WH+ZH) processes yields a 95% confidence level observed upper limit of 20.4 pb on the VH cross section for a Higgs mass of 115 GeV/c{sup 2}. Additionally, a 95% confidence level observed upper limit of 16.7 pb was set for a Higgs boson mass of 125 GeV/c{sup 2} and 24.6 pb was set for a Higgs boson mass of 135 GeV/c{sup 2}. The same data set was used to place limits on the Technicolor process {rho}{sub TC} {yields} W{pi}{sub TC} where the technirho mass was fixed to 240 GeV/c{sup 2}. For a technipion mass of 115 GeV/c{sup 2} we find a 95% confidence level observed upper limit on the cross section of 49 pb. The technipion masses of 125 GeV/c{sup 2} and 140 GeV/c{sup 2}, the 95% confidence level observed upper limits are 57 pb and 71 pb, respectively.
Date: April 1, 2010
Creator: Clutter, Justace R. & U., /Kansas
Partner: UNT Libraries Government Documents Department