This document presents a new measurement of inclusive b semileptonic branching fractions [special characters omitted] and [special characters omitted]. The [special characters omitted] and [special characters omitted] are separated by a means that uses correlation between the final state lepton charge and that of its parent b quark as a constraint. Monte Carlo counts of electrons and muons are calibrated to the data using a newly developed technique based on pairs of mutually independent tests for each particle hypothesis separately. The data sample consists of about 550,000 hadronic Z decays collected at the SLD between 1993 and 1998. Upon analysis of electron and muon counts in 61602 hadronic event hemispheres tagged as containing either a b or a b¯, we report [special characters omitted][special characters omitted]

The method of modal field theory is a new development in the field of nonperturbative quantum field theory. This approach reduces a quantum field theory to a finite-dimensional quantum mechanical system by expanding field configurations in terms of free-wave modes. In this dissertation we apply this method to three-dimensional &phis;4 theory using two kinds of modal field approaches: a spherical partial wave expansion and a periodic-box mode expansion. The resulting modal-field quantum-mechanical systems are analyzed with the use of the diffusion Monte Carlo method and by calculating the spectrum and eigenstates of the Hamiltonian directly. In the latter approach we employ the recently introduced quasi-sparse eigenvector method which is designed to diagonalize infinite-dimensional yet very sparse matrices. We study the phase structure of three-dimensional &phis;4 theory, computing the critical coupling and the critical exponents ν and β. We also investigate the spectrum of low-lying energy eigenstates and find evidence of a nonperturbative state in the broken-symmetry phase of the theory.

We report the observation of charm final states produced in the single diffractive dissociative reactions (1) pp → pX(D*+ → (D 0 → K−π+)π +) and (2) pp → pX( D*− → (D¯ 0 → K+π−)π −). These results are based on the over 5 billion event data sample acquired by Fermilab experiment E690 during the fixed target run of 1991. In this run, an 800 GeV/c incident proton beam was used with a liquid hydrogen target. We measure cross sections of [0.209 ± 0.050[special characters omitted](syst)] μb and [0.196 ± 0.043[special characters omitted](syst)] μb for reactions (1) and (2), respectively. These results are compared with model predictions and results from other experiments. Our results are significantly lower than predictions based on the diffractive model of Ingelman and Schlein using a flat or a hard pomeron structure function.

We studied [special characters omitted] theory and the string sector of compact QED 3 using nonperturbative methods. The phase structure of two dimensional [special characters omitted] theory was studied using Modal Field methods. The critical coupling strength and the critical exponent β were determined for various values of the momentum cutoff and box sizes. The asymptotic value of the critical coupling was found to be 2.5 ± 0.2. The low energy spectrum of the string sector of compact QED3 on the lattice was studied using Diagonalization/Monte Carlo techniques for various lattice sizes. The lattice potential and the string tension for the axial and the diagonal strings were also studied.

Close studies of the solitonic solutions of D = 11 [special characters omitted] = 1 supergravity theory provide a deeper understanding of the elusive M-theory and constitute steps towards its final formulation. In this work, we propose the use of calibration techniques to find localized intersecting brane solutions of the theory. We test this hypothesis by considering Kähler and special Lagrangian calibrations. We also discuss the interpretation of some of these results as branes wrapped or reduced over supersymmetric cycles of Calabi-Yau manifolds and we find the corresponding solutions in D = 5 [special characters omitted] = 2 supergravity.

Flavor-changing neutral current transitions are forbidden at tree level in the Standard Model and can only occur via higher order diagrams. Since the amplitudes for such loops are dominated by the heaviest known particles, and non-SM effects are expected to contribute at the same order as the SM, such processes are an ideal place to look for new physics. We present a measurement of the inclusive branching fraction for the flavor-changing neutral current process B → Xsℓ+ℓ− with a sample of 81.9 fb−1, collected with the BABAR detector at the Stanford Linear Accelerator Center. The final state is reconstructed from e+e − or μ+μ− pairs and a hadronic system consisting of one K± or K s and up to two pions, with at most one π0 . We observe a signal of 40 ± 10(stat) ± 2(syst) events and extract a branching fraction [special characters omitted] (B → Xsℓ +ℓ−) = (5.6 ± 1.5(stat) ± 0.6(exp. syst) ± 1.1(model syst)) × 10−6 for mll > 0.2 GeV.

The time dependence of Bd - Bd mixing has been measured in b b events containing one or more kaons at the SLD experiment at the Stanford Linear Accelerator Center. A simultaneous measurement of the “right sign production fraction” of kaons from B d decays has also been made. The initial state B hadron flavor was determined using the large forward-backward asymetry provided by the polarized electron beam of the SLC in combination with a jet charge technique and information from the opposite hemisphere. From a sample of 400,000 Z0 events collected by the SLD experiment at SLC from 1996 to 1998, the kaon right sign production fraction has been measured to be 0.797 ± 0.022 and the mass difference between the two Bd eigenstates has been measured to be Δ md = 0.503 ± 0.028 ± 0.020 ps−1 .

The unveiling of neutrino oscillation from observing the change in solar neutrino flux triggered physicists’ interest in studying the nature of the neutrino mass. The prevailing theory of explaining the tiny neutrino mass is called the “see-saw” mechanism, which postulates that the neutrino flavor eigenstate is the mixing between mass eigenstate of active neutrinos of a small mass and (left-) right-handed “sterile” (anti-)neutrinos of a large mass. The sterile neutrino is believed to be a new physics beyond the Standard Model, which can explain many other outstanding physical problems, like warm dark matter, asymmetry of baryon, etc. The HUNTER (Heavy Unseen Neutrinos from the Total Energy-momentum Reconstruction) experiment is a collaboration for searching for keV-mass range sterile neutrinos, and brings together an interdisciplinary team of researchers from Temple University, UCLA, Princeton University and the University of Hustonto develop an apparatus capable of searching for sterile neutrinos with high precision. In the HUNTER proposal, the radiation source generating neutrinos will be a cloud of atoms laser cooled and suspended by laser beams, the decay products except neutrinos will be detected by corresponding detectors, and their initial vector momenta will be reconstructed from the data recorded by the corresponding detectors. The missing mass in the decay, taken away by the neutrino, can then be evaluated from the energy and momentum conservation. The radiation sources of electron-capture decay are preferred for laboratory neutrino experiments because of the absence of energetic electrons in the decay products. 131-Cs is chosen by HUNTER to study the sterile neutrino mass and the mixing between sterile neutrinos and active neutrinos because of its short lifetime, simply decay products, and its alkali element spectral structure which enhances laser cooling and trapping. The Phase 1 HUNTER experiment targeting sterile neutrinos in the range 20-300 keV/c^2 requires the design of spectrometers with momentum resolution of a part in a thousand or better. To detect a 131-Xe ion, a spectrometer consisting of numbers of annular electrodes has been designed. The potentials of the electrodes of the ion spectrometer were carefully optimized to form an electrostatic lens, with time focusing and spatial focusing to achieve a high momentum resolution for ions despite the extended source presented by the magneto-optical trap. The optimization algorithm presented in this dissertation achieves a momentum precision of ∼0.12% (∼0.03%) for the high acceptance (high resolution) tune. An electron spectrometer was designed without “double focusing” for detecting the electrons produced in 131 Cs decays. The electron trajectories are guided by a uniform electric and magnetic field. An octagonal shaped, magnetic shield was designed to diminish the influence of external magnetic fields on the electron trajectories. The achieved electron momentum resolution is ∼0.1 keV including extended source effects, sufficient for the desired missing mass resolution. Other issues like the systematic errors of the ion spectrometer and the eddy current induced in the electrodes by periodically switching on/off the anti-Helmholtz coils of the magneto-optical trap were studied. The deformation of the spectrometer under its gravity was simulated using Autodesk Inventor. / Physics

We set a preliminary 95% C.L. exclusion on the oscillation frequency of [special characters omitted] mixing using a sample of 400,000 hadronic Z 0 decays collected by the SLD experiment at the SLC during the 1996–98 run. In this analysis, [special characters omitted] mesons are partially reconstructed by combining a fully reconstructed Ds with other [special characters omitted] decay products. The Ds decays are reconstructed via the &phis;π and K*K channels. The b-hadron flavor at production is determined by exploiting the large forward-backward asymmetry of polarized Z0 → bb¯ decays as well as information from the hemisphere opposite to the reconstructed B decay. The flavor of the [special characters omitted] at the decay vertex is determined by the charge of the D s. A total of 361 candidates passed the final event selection cuts. This analysis excludes the following values of the [special characters omitted] mixing oscillation frequency: Δms < 1.4 psec−1 and 2.5 < Δms < 5.3 psec−1 at the 95% confidence level.

Fueled by a recent conjecture of D. Bessis that non-Hermitian, [special characters omitted] symmetric Hamiltonians have positive and real energies, the study of such theories has recently received much attention. Most of the work has been done in the context of quantum mechanics. Several techniques have been used up to date, including numerical and variational approaches. Field theoretic techniques have also been used, but always applied to one dimensional theories. This class of quantum field theories is isomorphic to quantum mechanics. In this dissertation we present the first study of a non-Hermitian, [special characters omitted] symmetric quantum field theory. We apply the methods of Modal Field Theory and Quasy-sparse Eigenvector Diagonalization to the study of a scalar quantum field theory with a cubic interaction and an imaginary coupling constant. The spectrum is examined and found to be real and positive. The vacuum expectation value of the field is imaginary and shows a peak in the nonperturbative regime. The physical mass is found to increase monotonically with the coupling strength.