Production, Characterization, and Acceleration of Optical Microbunches (open access)

Production, Characterization, and Acceleration of Optical Microbunches

Optical microbunches with a spacing of 800 nm have been produced for laser acceleration research. The microbunches are produced using a inverse Free-Electron-Laser (IFEL) followed by a dispersive chicane. The microbunched electron beam is characterized by coherent optical transition radiation (COTR) with good agreement to the analytic theory for bunch formation. In a second experiment the bunches are accelerated in a second stage to achieve for the first time direct net acceleration of electrons traveling in a vacuum with visible light. This dissertation presents the theory of microbunch formation and characterization of the microbunches. It also presents the design of the experimental hardware from magnetostatic and particle tracking simulations, to fabrication and measurement of the undulator and chicane magnets. Finally, the dissertation discusses three experiments aimed at demonstrating the IFEL interaction, microbunch production, and the net acceleration of the microbunched beam. At the close of the dissertation, a separate but related research effort on the tight focusing of electrons for coupling into optical scale, Photonic Bandgap, structures is presented. This includes the design and fabrication of a strong focusing permanent magnet quadrupole triplet and an outline of an initial experiment using the triplet to observe wakefields generated by an electron …
Date: June 20, 2008
Creator: Sears, Christopher M.S. & /SLAC, /Stanford U.
System: The UNT Digital Library
A study of muon neutrino disappearance with the MINOS detectors and the NuMI neutrino beam (open access)

A study of muon neutrino disappearance with the MINOS detectors and the NuMI neutrino beam

This thesis presents the results of an analysis of {nu}{sub {mu}} disappearance with the MINOS experiment, which studies the neutrino beam produced by the NuMI facility at Fermi National Accelerator Laboratory. The rates and energy spectra of charged current {nu}{sub {mu}} interactions are measured in two similar detectors, located at distances of 1 km and 735 km along the NuMI beamline. The Near Detector provides accurate measurements of the initial beam composition and energy, while the Far Detector is sensitive to the effects of neutrino oscillations. The analysis uses data collected between May 2005 and March 2007, corresponding to an exposure of 2.5 x 10{sup 20} protons on target. As part of the analysis, sophisticated software was developed to identify muon tracks in the detectors and to reconstruct muon kinematics. Events with reconstructed tracks were then analyzed using a multivariate technique to efficiently isolate a pure sample of charged current {nu}{sub {mu}} events. An extrapolation method was also developed, which produces accurate predictions of the Far Detector neutrino energy spectrum, based on data collected at the Near Detector. Finally, several techniques to improve the sensitivity of an oscillation measurement were implemented, and a full study of the systematic uncertainties was …
Date: June 1, 2008
Creator: Marshall, John Stuart & U., /Cambridge
System: The UNT Digital Library
Search for new physics coupling to the z boson (open access)

Search for new physics coupling to the z boson

We present the results of two searches for new particles that couple Z bosons in p{bar p} collisions at {radical}s = 1.96 TeV using the Collider Detector at Fermilab (CDF). In the first, we search for a long-lived parent of the Z boson using a data sample with a luminosity of 163 pb{sup -1}. Finding no significant excess above background, we set a limit on a fourth generation model as a function of mass and lifetime. In the second, we search for a particle that decays to a Z boson in conjunction with jets using a data sample with a luminosity of 1.06 fb{sup -1}. Finding no significant excess above background, we set a limit on a fourth generation model as a function of mass.
Date: June 1, 2007
Creator: Scott, Adam Liddle
System: The UNT Digital Library
Measurement of the Hadronic Mass Spectrum in B to Xulnu Decaysand Determination of the b-Quark Mass at the BaBar Experiment (open access)

Measurement of the Hadronic Mass Spectrum in B to Xulnu Decaysand Determination of the b-Quark Mass at the BaBar Experiment

I present preliminary results of the measurement of the hadronic mass spectrum and its first three spectral moments in inclusive charmless semileptonic B-meson decays. The truncated hadronic mass moments are used for the first determination of the b-quark mass and the nonperturbative parameters {mu}{sub {pi}}{sup 2} and {rho}{sub D}{sup 3} in this B-meson decay channel. The study is based on 383 x 10{sup 6} B{bar B} decays collected with the BABAR experiment at the PEP-II e{sup +}e{sup -} storage rings, located at the Stanford Linear Accelerator Center. The first, second central, and third central hadronic mass moment with a cut on the hadronic mass m{sub X}{sup 2} < 6.4GeV{sup 2} and the lepton momentum p* > 1 GeV are measured to be: M{sub 1} = (1.96 {+-} 0.34{sub stat} {+-} 0.53{sub syst}) GeV{sup 2}; U{sub 2} = (1.92 {+-} 0.59{sub stat} {+-} 0.87{sub syst}) GeV{sup 4}; and U{sub 3} = (1.79 {+-} 0.62{sub stat} {+-} 0.78{sub syst}) GeV{sup 6}; with correlation coefficients {rho}{sub 12} = 0.99, {rho}{sub 23} = 0.94, and {rho}{sub 13} = 0.88, respectively. Using Heavy Quark Effective Theory-based predictions in the kinetic scheme we extract: m{sub b} = (4.60 {+-} 0.13{sub stat} {+-} 0.19{sub syst} {+-} 0.10{sub …
Date: June 26, 2008
Creator: Tackmann, Kerstin & /UC, Berkeley /SLAC
System: The UNT Digital Library
Study of B_s Mixing at the D-Zero Detector at Fermilab Using the Semi-leptonic Decay B_s -> D_s mu nu X (open access)

Study of B_s Mixing at the D-Zero Detector at Fermilab Using the Semi-leptonic Decay B_s -> D_s mu nu X

B{sub s}{sup 0} mixing studies provide a precision test of Charge-Parity violation in the Standard Model. A measurement of {Delta}m{sub s} constrains elements of the CKM quark rotation matrix [1], providing a probe of Standard Model Charge-Parity violation. This thesis describes a study of B{sub s}{sup 0} mixing in the semileptonic decay B{sub s}{sup 0} {yields} D{sub s}{sup -} {mu}{sup +}{nu}X, where D{sub s}{sup -} {yields} {phi}{pi}{sup -}, using data collected at the D-Zero detector at Fermi National Accelerator in Batavia, Illinois. Approximately 2.8 fb{sup -1} of data collected between April 2002 and August 2007 was used, covering the entirety of the Tevatron's RunIIa (April 2002 to March 2006) and part of RunIIb (March 2006-August 2007). Taggers using both opposite-side and same-side information were used to obtain the flavor information of the B{sub s}{sup 0} meson at production. The charge of the muon in the decay B{sub s}{sup 0} {yields} D{sub s}{sup -}{mu}{sup +}{nu}X was used to determine the flavor of the B{sub s}{sup 0} at decay. The B{sub d}{sup 0} mixing frequency, {Delta}m{sub d}, was measured to verify the analysis procedure. A log-likelihood calculation was performed, and a measurement of {Delta}m{sub s} was obtained. The final result was {Delta}m{sub …
Date: June 1, 2008
Creator: Anzelc, Meghan
System: The UNT Digital Library
A Study of The Standard Model Higgs, WW and ZZ Production in Dilepton Plus Missing Transverse Energy Final State at CDF Run II (open access)

A Study of The Standard Model Higgs, WW and ZZ Production in Dilepton Plus Missing Transverse Energy Final State at CDF Run II

We report on a search for Standard Model (SM) production of Higgs to WW* in the two charged lepton (e, {mu}) and two neutrino final state in p{bar p} collisions at a center of mass energy {radical}s = 1.96 TeV. The data were collected with the CDF II detector at the Fermilab Tevatron and correspond to an integrated luminosity of 1.9fb{sup -1}. The Matrix Element method is developed to calculate the event probability and to construct a likelihood ratio discriminator. There are 522 candidates observed with an expectation of 513 {+-} 41 background events and 7.8 {+-} 0.6 signal events for Higgs mass 160GeV/c{sup 2} at next-to-next-to-leading logarithmic level calculation. The observed 95% C.L. upper limit is 0.8 pb which is 2.0 times the SM prediction while the median expected limit is 3.1{sub -0.9}{sup +1.3} with systematics included. Results for 9 other Higgs mass hypotheses ranging from 110GeV/c{sup 2} to 200GeV/c{sup 2} are also presented. The same dilepton plus large transverse energy imbalance (E{sub T}) final state is used in the SM ZZ production search and the WW production study. The observed significance of ZZ {yields} ll{nu}{nu} channel is 1.2{sigma}. It adds extra significance to the ZZ {yields} 4l channel …
Date: June 1, 2008
Creator: Hsu, Shih-Chieh & /UC, San Diego
System: The UNT Digital Library
Study of the heavy flavour fractions in z+jets events from proton-antiproton collisions at energy = 1.96 TeV with the CDF II detector at the Tevatron collider (open access)

Study of the heavy flavour fractions in z+jets events from proton-antiproton collisions at energy = 1.96 TeV with the CDF II detector at the Tevatron collider

The Standard Model of field and particles is the theory that provides the best description of the known phenomenology of the particle physics up to now. Data collected in the last years, mainly by the experiments at the big particle accelerators (SPS, LEP, TEVATRON, HERA, SLAC), allowed to test the agreement between measurements and theoretical calculations with a precision of 10{sup -3} {divided_by} 10{sup -4}. The Standard Model is a Quantum Field Theory based on the gauge symmetry group SU(3){sub C} x SU(2){sub L} x U(1){sub Y} , with spontaneous symmetry breaking. This gauge group includes the color symmetry group of the strong interaction, SU(3){sub C}, and the symmetry group of the electroweak interactions, SU(2){sub L} x U(1){sub Y}. The formulation of the Standard Model as a gauge theory guarantees its renormalizability, but forbids explicit mass terms for fermions and gauge bosons. The masses of the particles are generated in a gauge-invariant way by the Higgs Mechanism via a spontaneous breaking of the electroweak symmetry. This mechanism also implies the presence of a massive scalar particle in the mass spectrum of the theory, the Higgs boson. This particle is the only one, among the basic elements for the minimal formulation …
Date: June 1, 2008
Creator: Mastrandrea, Paolo & U., /Siena
System: The UNT Digital Library
First Measurement of sigma(gg -> ttbar)/sigma(ppbar -> ttbar) (open access)

First Measurement of sigma(gg -> ttbar)/sigma(ppbar -> ttbar)

The work presented here is the first measurement of the fraction of top quark pair production through gluon-gluon fusion. We use an integrated luminosity of 0.96 {+-} 0.06 fb{sup -1} of p{bar p} collisions at {radical}s of 1.96 TeV collected by the CDF II detector. We select t{bar t} candidates by identifying a high-p{sub T} lepton candidate, a large missing E{sub T} as evidence for a neutrino candidate and at least four high E{sub T} jets, one of which has to be identified as originating from a b quark. The challenge is to discriminate between the two production processes with the identical final state, gg {yields} t{bar t} and q{bar q} {yields} t{bar t}. We take advantage of the fact that compared to a quark, a gluon is more likely to radiate a low momentum gluon and therefore, one expects a larger number of charged particles with low p{sub T} in a process involving more gluons. Given the large uncertainties associated with the modeling of the low p{sub T} charged particle multiplicity, a data-driven technique was employed. Using calibration data samples, we show there exists a clear correlation between the observed average number of low p{sub T} charged particles and …
Date: June 1, 2008
Creator: Pashapour Alamdari, Shabnaz & U., /Toronto
System: The UNT Digital Library
A measurement of the top pair production cross-section in the dilepton channel using lepton plus track selection (open access)

A measurement of the top pair production cross-section in the dilepton channel using lepton plus track selection

Using 1.1 fb{sup -1} of data collected by the Collider Detector at Fermilab (CDF) from Run II of the Fermilab Tevatron, they measure the t{bar t} production cross section in events with two leptons, significant missing transverse energy, and {ge} 2 jets. As the Run II dataset grows, more stringent tests of Standard Model predictions for the top quark sector are becoming possible. The dilepton channel, where both top quarks decay t {yields} Wb {yields} {ell}{nu}b, is of particular interest due to its high purity even in the absence of a b jet 'tagging' requirement. Use of an isolated track as the second lepton significant increases the dilepton acceptance, at the price of some increase in background, particular from W + jets events where one of the jets is identified as a lepton. With the amount of data available, it has been possible to improve the estimate of the contribution from that background, reflected in a reduced systematic uncertainty. Assuming a branching ratio of BR(W {yields} {ell}{nu}) = 10.8% and a top mass of m{sub t} = 175 GeV/c{sup 2}, the measured cross-section is {sigma}(p{bar p} {yields} t{bar t}) = 8.3 {+-} 1.3(stat.) {+-} 0.7(syst.) {+-} 0.5(lumi.) pb. The result …
Date: June 1, 2007
Creator: Mills, Corrinne Elaine
System: The UNT Digital Library
Low Temperature Constrained Sintering of Cerium Gadolinium OxideFilms for Solid Oxide Fuel Cell Applications (open access)

Low Temperature Constrained Sintering of Cerium Gadolinium OxideFilms for Solid Oxide Fuel Cell Applications

Cerium gadolinium oxide (CGO) has been identified as an acceptable solid oxide fuel cell (SOFC) electrolyte at temperatures (500-700 C) where cheap, rigid, stainless steel interconnect substrates can be used. Unfortunately, both the high sintering temperature of pure CGO, >1200 C, and the fact that constraint during sintering often results in cracked, low density ceramic films, have complicated development of metal supported CGO SOFCs. The aim of this work was to find new sintering aids for Ce{sub 0.9}Gd{sub 0.1}O{sub 1.95}, and to evaluate whether they could be used to produce dense, constrained Ce{sub 0.9}Gd{sub 0.1}O{sub 1.95} films at temperatures below 1000 C. To find the optimal sintering aid, Ce{sub 0.9}Gd{sub 0.1}O{sub 1.95} was doped with a variety of elements, of which lithium was found to be the most effective. Dilatometric studies indicated that by doping CGO with 3mol% lithium nitrate, it was possible to sinter pellets to a relative density of 98.5% at 800 C--a full one hundred degrees below the previous low temperature sintering record for CGO. Further, it was also found that a sintering aid's effectiveness could be explained in terms of its size, charge and high temperature mobility. A closer examination of lithium doped Ce0.9Gd0.1O1.95 indicated that …
Date: June 30, 2007
Creator: Nicholas, Jason.D.
System: The UNT Digital Library
Search for Doubly-charged Higgs Boson Production in the Decay H++ H-- ---> mu+ mu+ mu- mu- with 1.1 fb**(-1) at D0 Detector (open access)

Search for Doubly-charged Higgs Boson Production in the Decay H++ H-- ---> mu+ mu+ mu- mu- with 1.1 fb**(-1) at D0 Detector

This work presents a search for the pair production of doubly-charged Higgs bosons in the process p{bar p} {yields} H{sup ++}H{sup --} {yields} {mu}{sup +}{mu}{sup +}{mu}{sup -}{mu}{sup -} using the data corresponding to an integrated luminosity of about 1.1 fb{sup -1}. This is the complete dataset of RunIIa taken from April 19, 2002 to February 22, 2006 by the D0 experiment at the Fermilab Tevatron Collider. In the absence of significant excess above standard model background, 95% confidence level mass limits of M(H{sub L}{sup {+-}{+-}}) > 150 GeV and M(H{sub R}{sup {+-}{+-}}) > 126.5 GeV are set for left-handed and right-handed doubly-charged Higgs bosons respectively assuming a 100% branching ratio into muons.
Date: June 1, 2007
Creator: Kim, Tae Jeong & U., /Korea
System: The UNT Digital Library
M dwarfs in the Local Milky Way: The Field Low-Mass Stellar Luminosity and Mass Functions (open access)

M dwarfs in the Local Milky Way: The Field Low-Mass Stellar Luminosity and Mass Functions

Modern sky surveys, such as the Sloan Digital Sky Survey (SDSS) and the Two-Micron All Sky Survey, have revolutionized how Astronomy is done. With millions of photometric and spectroscopic observations, global observational properties can be studied with unprecedented statistical significance. Low-mass stars dominate the local Milky Way, with tens of millions observed by SDSS within a few kpc. Thus, they make ideal tracers of the Galactic potential, and the thin and thick disks. In this thesis dissertation, I present my efforts to characterize the local low-mass stellar population, using a collection of observations from the Sloan Digital Sky Survey (SDSS). First, low-mass stellar template spectra were constructed from the co-addition of thousands of SDSS spectroscopic observations. These template spectra were used to quantify the observable changes introduced by chromospheric activity and metallicity. Furthermore, the average ugriz colors were measured as a function of spectral type. Next, the local kinematic structure of the Milky Way was quantified, using a special set of SDSS spectroscopic observations. Combining proper motions and radial velocities (measured using the spectral templates), along with distances, the full UVW space motions of over 7000 low-mass stars along one line of sight were computed. These stars were also separated …
Date: June 1, 2006
Creator: Bochanski, John J., Jr. & /Washington U., Seattle, Astron. Dept.
System: The UNT Digital Library
The Study of WGamma production at D0: Anomalous Coupling Limits and the Radiation Amplitude Zero (open access)

The Study of WGamma production at D0: Anomalous Coupling Limits and the Radiation Amplitude Zero

W{gamma} production is analyzed in the electron and muon decay channels with approximately 1 fb{sup -1} of data from p{bar p} collisions that were produced at a center-of-mass energy of {radical}s = 1.96 TeV and that were collected by the D0 detector at the Fermilab Tevatron collider. The inclusive p{bar p} {yields} {ell}{nu}{gamma} cross section is measured in both channels and is found to be consistent with the Standard Model expectation of 2.08 {+-} 0.05{sub PDF} pb for events with a photon E{sub T} > 11 GeV, {Delta}R{sub {ell}{sub {gamma}}} > 0.7, and {ell}{nu}{gamma} transverse mass greater than 90 GeV . The observed cross section is measured to be 2.05 {+-} 0.18{sub stat} {+-} 0.10{sub sys} {+-} 0.13{sub lumi} pb and a.72 {+-} 0.19{sub stat} {+-} 0.15{sub sys} {+-} 0.10{sub lumi} pb for the electron and muon channels respectively. The photon E{sub T} spectrum is examined for indications of anomalous WW{gamma} couplings. No evidence is found, and the following one-dimensional limits are set at a 95% confidence level: -0.18 < {lambda} < 0.18 and 0.16 < {kappa} < 1.84. The observed charge-signed photon-lepton rapidity difference is consistent with the Standard Model prediction and is indicative of the theoretically expected radiation …
Date: June 1, 2007
Creator: Pawloski, Gregory J. & U., /Rice
System: The UNT Digital Library
Measurement of the W Boson Mass with the D0 Run II Detector using the Electron P(T) Spectrum (open access)

Measurement of the W Boson Mass with the D0 Run II Detector using the Electron P(T) Spectrum

This thesis is a description of the measurement of the W boson mass using the D0 Run II detector with 770 pb{sup -1} of p{bar p} collision data. These collisions were produced by the Tevatron at {radical}s = 1.96 TeV between 2002 and 2006. We use a sample of W {yields} e{nu} and Z {yields} ee decays to determine the W boson mass with the transverse momentum distribution of the electron and the transverse mass distribution of the boson. We measure M{sub W} = XXXXX {+-} 37 (stat.) {+-} 26 (sys. theo.) {+-} 51 (sys. exp.) MeV = XXXXX {+-} 68 MeV with the transverse momentum distribution of the electron and M{sub W} = XXXXX {+-} 28 (stat.) {+-} 17 (sys. theo.) {+-} 51 (sys. exp.) MeV = XXXXX {+-} 61 MeV with the transverse mass distribution.
Date: June 1, 2008
Creator: Andeen, Timothy R., Jr.
System: The UNT Digital Library
Studies in High Current Density Ion Sources for Heavy Ion FusionApplications (open access)

Studies in High Current Density Ion Sources for Heavy Ion FusionApplications

This dissertation develops diverse research on small (diameter {approx} few mm), high current density (J {approx} several tens of mA/cm{sup 2}) heavy ion sources. The research has been developed in the context of a programmatic interest within the Heavy Ion Fusion (HIF) Program to explore alternative architectures in the beam injection systems that use the merging of small, bright beams. An ion gun was designed and built for these experiments. Results of average current density yield (<J>) at different operating conditions are presented for K{sup +} and Cs{sup +} contact ionization sources and potassium aluminum silicate sources. Maximum <J> values for a K{sup +} beam of {approx}90 mA/cm{sup 2} were observed in 2.3 {micro}s pulses. Measurements of beam intensity profiles and emittances are included. Measurements of neutral particle desorption are presented at different operating conditions which lead to a better understanding of the underlying atomic diffusion processes that determine the lifetime of the emitter. Estimates of diffusion times consistent with measurements are presented, as well as estimates of maximum repetition rates achievable. Diverse studies performed on the composition and preparation of alkali aluminosilicate ion sources are also presented. In addition, this work includes preliminary work carried out exploring the viability …
Date: June 1, 2002
Creator: Chacon-Golcher, E.
System: The UNT Digital Library
MRI of Heterogeneous Hydrogenation Reactions Using Parahydrogen Polarization (open access)

MRI of Heterogeneous Hydrogenation Reactions Using Parahydrogen Polarization

The power of magnetic resonance imaging (MRI) is its ability to image the internal structure of optically opaque samples and provide detailed maps of a variety of important parameters, such as density, diffusion, velocity and temperature. However, one of the fundamental limitations of this technique is its inherent low sensitivity. For example, the low signal to noise ratio (SNR) is particularly problematic for imaging gases in porous materials due to the low density of the gas and the large volume occluded by the porous material. This is unfortunate, as many industrially relevant chemical reactions take place at gas-surface interfaces in porous media, such as packed catalyst beds. Because of this severe SNR problem, many techniques have been developed to directly increase the signal strength. These techniques work by manipulating the nuclear spin populations to produce polarized} (i.e., non-equilibrium) states with resulting signal strengths that are orders of magnitude larger than those available at thermal equilibrium. This dissertation is concerned with an extension of a polarization technique based on the properties of parahydrogen. Specifically, I report on the novel use of heterogeneous catalysis to produce parahydrogen induced polarization and applications of this new technique to gas phase MRI and the characterization …
Date: June 25, 2008
Creator: Burt, Scott R & Burt, Scott R.
System: The UNT Digital Library
Microfabrication of an Implantable silicone Microelectrode array for an epiretinal prosthesis (open access)

Microfabrication of an Implantable silicone Microelectrode array for an epiretinal prosthesis

Millions of people suffering from diseases such as retinitis pigmentosa and macular degeneration are legally blind due to the loss of photoreceptor function. Fortunately a large percentage of the neural cells connected to the photoreceptors remain viable, and electrical stimulation of these cells has been shown to result in visual perception. These findings have generated worldwide efforts to develop a retinal prosthesis device, with the hope of restoring vision. Advances in microfabrication, integrated circuits, and wireless technologies provide the means to reach this challenging goal. This dissertation describes the development of innovative silicone-based microfabrication techniques for producing an implantable microelectrode array. The microelectrode array is a component of an epiretinal prosthesis being developed by a multi-laboratory consortium. This array will serve as the interface between an electronic imaging system and the human eye, directly stimulating retinal neurons via thin film conducting traces. Because the array is intended as a long-term implant, vital biological and physical design requirements must be met. A retinal implant poses difficult engineering challenges due to the size of the intraocular cavity and the delicate retina. Not only does it have to be biocompatible in terms of cytotoxicity and degradation, but it also has to be structurally …
Date: June 10, 2003
Creator: Maghribi, M
System: The UNT Digital Library
IMPROVING THE PHYSICS IMPACT OF NEXT-GENERATION 76GE NEUTRINOLESS DOUBLE-BETA DECAY EXPERIMENTS (open access)

IMPROVING THE PHYSICS IMPACT OF NEXT-GENERATION 76GE NEUTRINOLESS DOUBLE-BETA DECAY EXPERIMENTS

Summary and Conclusions - It was shown that segmentation and pulse-shape discrimination can improve the discovery sensitivity of a next-gen 0vBB-decay experiment by 90%. - However, when practical aspects are considered (such as instrumenting each segment with front-end electronics), the discovery sensitivity is decreased by 19%. - This has extremely important consequences to proposed next-gen experiments since the two active collaborations have strongly advocated the use of segmented detectors for all or part of the experiment. - New germanium detector technology, currently under development, has demonstrated excellent multi-site background rejection capabilities without the complexity of segmentation or complicated PSD algorithms. - The physically-segmented p-type germanium detector technology has proven to be a useful and practical tool in modern nuclear physics. The PSEG technology deserves further development as it has the potential for use in a variety of applications.
Date: June 2009
Creator: Hossbach, Todd W.
System: The UNT Digital Library
Microphysical Properties of Single and Mixed-Phase Arctic Clouds Derived from AERI Observations (open access)

Microphysical Properties of Single and Mixed-Phase Arctic Clouds Derived from AERI Observations

A novel new approach to retrieve cloud microphysical properties from mixed-phase clouds is presented. This algorithm retrieves cloud optical depth, ice fraction, and the effective size of the water and ice particles from ground-based, high-resolution infrared radiance observations. The theoretical basis is that the absorption coefficient of ice is stronger than that of liquid water from 10-13 mm, whereas liquid water is more absorbing than ice from 16-25 um. However, due to strong absorption in the rotational water vapor absorption band, the 16-25 um spectral region becomes opaque for significant water vapor burdens (i.e., for precipitable water vapor amounts over approximately 1 cm). The Arctic is characterized by its dry and cold atmosphere, as well as a preponderance of mixed-phase clouds, and thus this approach is applicable to Arctic clouds. Since this approach uses infrared observations, cloud properties are retrieved at night and during the long polar wintertime period. The analysis of the cloud properties retrieved during a 7 month period during the Surface Heat Budget of the Arctic (SHEBA) experiment demonstrates many interesting features. These results show a dependence of the optical depth on cloud phase, differences in the mode radius of the water droplets in liquid-only and mid-phase …
Date: June 1, 2003
Creator: Turner, David D.
System: The UNT Digital Library
Search for Resonances in the Photoproduction of Proton-Antiproton Pairs (open access)

Search for Resonances in the Photoproduction of Proton-Antiproton Pairs

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

Study of B-Meson Decays to Final States with a Single Charm Baryon

A study of B-meson decays to final states with a single charm baryon is presented based on data recorded by the BABAR detector at the Stanford Linear Accelerator Center. Although the B meson is the lightest bottom-flavored meson, it is heavy enough to decay to a baryon made of three quarks and an antibaryon made of three antiquarks. By studying the baryonic weak decays of the B meson, we can investigate baryon production mechanisms in heavy meson decays. In particular, we measure the rates of the decays B{sup -} {yields} {Lambda}{sub c}{sup +}{bar p}{pi}{sup -} and {bar B}{sup 0} {yields} {Lambda}{sub c}{sup +}{bar p}. Comparing these rates, we confirm an observed trend in baryonic B decays that the decay with the lower energy release, B{sup -} {yields} {Lambda}{sub c}{sup +}{bar p}{pi}{sup -}, is favored over {bar B}{sup 0} {yields} {Lambda}{sub c}{sup +}{bar p}. The dynamics of the baryon-antibaryon ({Lambda}{sub c}{sup +}{bar p}) system in the three-body decay also provide insight into baryon-antibaryon production mechanisms. The B{sup -} {yields} {Lambda}{sub c}{sup +}{bar p}{pi}{sup -} system is a laboratory for searches for excited {Sigma}{sub c} baryon states; we observe the resonant decays B{sup -} {yields} {Sigma}{sub c}(2455){sup 0}{bar p} and B{sup -} …
Date: June 2, 2009
Creator: Majewski, Stephanie A.
System: The UNT Digital Library
Search for the Standard Model Higgs boson in the missing energy topology with D0 (open access)

Search for the Standard Model Higgs boson in the missing energy topology with D0

A search for the Standard Model Higgs boson in the missing energy and acoplanar b-jet topology is reported, using an integrated luminosity of 0.93 fb{sup -1} recorded by the D0 detector at the Fermilab Tevatron p{bar p} Collider. The analysis includes signal contributions from p{bar p} {yields} ZH {yields} {nu}{bar {nu}}b{bar b}, as well as from WH production in which the charged lepton from the W boson decay is undetected. Neural networks are used to separate signal from background. In the absence of a signal, limits are set on {sigma}(p{bar p} {yields} VH) x B(H {yields} b{bar b}) at the 95% C.L. of 2.6-2.3 pb, for Higgs boson masses in the range 105-135 GeV, where V = W, Z. The corresponding expected limits range from 2.8 to 2.0 pb. Potential improvements to the analysis with an extended dataset totalling 4 fb{sup -1} are also discussed. Essential maintenance related to the increased luminosity and RunIIb upgrade was carried out on the impact parameter (IP) based b-tagging trigger tool and the effect of the changes on the b-tagger's performance was investigated.
Date: June 1, 2009
Creator: Christoudias, Theodoros
System: The UNT Digital Library
A Limit on the Branching Ratio of the Flavor-Changing Top Quark Decay t-->Zc (open access)

A Limit on the Branching Ratio of the Flavor-Changing Top Quark Decay t-->Zc

We have used the Collider Detector at Fermilab (CDF-II) to set upper limits on the branching ratio of the flavor-changing neutral-current (FCNC) top quark decay t {yields} Zc using a technique employing ratios of W and Z production, measured in 1.52 fb{sup -1} of p{bar p} data. The analysis uses a comparison of two decay chains, p{bar p} {yields} t{bar t} {yields} WbWb {yields} {ell}{nu}bjjb and p{bar p} {yields} t{bar t} ZcWb {yields} {ell}{sup +}{ell}{sup -} cjjb, to cancel systematic uncertainties in acceptance, efficiency, and luminosity. We validate the MC modeling of acceptance and efficiency for lepton identification over the multi-year dataset also using a ratio of W and Z production, in this case the observed ratio of inclusive production of W to Z-bosons, a technique that will be essential for precision comparisons with the standard model at the LHC. We introduce several methods of determining backgrounds to the W and Z samples. To improve the discrimination against SM backgrounds to top quark decays, we calculate the top mass for each event with two leptons and four jets assuming it is a t{bar t} event with one of the top quarks decaying to Zc. The upper limit on the Br(t …
Date: June 1, 2009
Creator: Paramonov, Alexander Andreevich
System: The UNT Digital Library
Measurement of the electroweak top quark production cross section and the CKM matrix element Vtb with the D0 experiment (open access)

Measurement of the electroweak top quark production cross section and the CKM matrix element Vtb with the D0 experiment

At particle accelerators the Standard Model has been tested and will be tested further to a great precision. The data analyzed in this thesis have been collected at the world's highest energetic-collider, the Tevatron, located at the Fermi National Accelerator Laboratory (FNAL) in the vicinity of Chicago, IL, USA. There, protons and antiprotons are collided at a center-of-mass energy of {radical}s = 1.96 TeV. The discovery of the top quark was one of the remarkable results not only for the CDF and D0 experiments at the Tevatron collider, but also for the Standard Model, which had predicted the existence of the top quark because of symmetry arguments long before already. Still, the Tevatron is the only facility able to produce top quarks. The predominant production mechanism of top quarks is the production of a top-antitop quark pair via the strong force. However, the Standard Model also allows the production of single top quarks via the electroweak interaction. This process features the unique opportunity to measure the |V{sub tb}| matrix element of the Cabbibo-Kobayashi-Maskawa (CKM) matrix directly, without assuming unitarity of the matrix or assuming that the number of quark generations is three. Hence, the measurement of the cross section of …
Date: June 1, 2009
Creator: Kirsch, Matthias
System: The UNT Digital Library