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No description available.

This work presents a study of high-spin states in the nucleus ¹⁹⁶Tl via γ-spectroscopy. ¹⁹⁶Tl was produced via the ¹⁹⁷Au(⁴He,5n) ¹⁹⁶Tl reaction at a beam energy of 63 MeV. The γ-γ coincidence measurements were performed using the AFRODITE γ-spectrometer array at iThemba LABS. The previous level scheme of ¹⁹⁶Tl has been extended up to an excitation of 4071 keV including 24 new γ-ray transitions. The spin and parity assignment to levels was made from the directional correlation of oriented nuclei (DCO) and linear polarization anisotropy ratios. An analysis of the B(M1)/B(E2) ratios was found to be consistent with the configuration of πh₉/₂♁vi₁₃/₂ for the ground state band. Although no chiral band was found in ¹⁹⁶TI and ¹⁹⁸TI.

Accurately collimated monoenergetic fast neutron beams of small angular width were produced by bombarding heavy ice targets with deuterons, and operating the neutron detector in coincidence with a semiconductor detector detecting the He³ recoil nuclei. Using a bombarding energy of E[subscript d] 50 keV a neutron beam of energy 2.55 MeV and known absolute intensity was produced. The measured beam profile agreed with the theoretically calculated profile. The beam was used to measure the absolute neutron detection efficiency and the pulse spectrum of a plastic scintillation counter bombarded by 2.55 MeV neutrons. Using a bombarding energy of E[subscript d] = 2 MeV a neutron beam of energy 5.08 MeV was produced and the bearers profile was measured. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The purpose of this thesis is to examine the gravitational scattering of massless scalar particles, photons, four component neutrinos, and two component neutrinos by one another. A modification of the quantum theory of the weak gravitational field developed by Gupta is used as a basis for the considerations. Cross-sections are given for the gravitational scattering of scalar particles by: scalar particles, photons, four component neutrinos, and two component neutrinos; of photons by: photons, four component neutrinos, and two component neutrinos; of four component neutrinos by four component neutrinos, and of two component neutrinos by two component neutrinos. The cross-section given by Barker et al and by Boccaletti et al for the scattering of photons by photons is confirmed. The cross-section for the scattering of massive scalar particles by massive scalar particles quoted by DeWitt and the cross-section for the scattering of photons by massive scalar particles given by Boccaletti et al are found to be in error and are corrected. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The properties of muonium(μ⁺e⁻) and positronium(e⁺e⁻) are altered significantly in the presence of matter. The study of these exotic H-like atoms provides a unique perspective on atomic interactions with atoms, surfaces, and solids. This theme is explored in a variety of hosts. The cross section for spin 1 positronium to be converted to spin 0 positronium during collisions with O₂ molecules has been measured from 120 °K to 630 °K in an SiO₂ powder moderator using a positron lifetime technique. The results indicate that positronium does not thermalize in the powder below 450 °K. The spin conversion cross section increases slightly with temperature above 450 °K. A theory for spin conversion of positronium by a spin 1 molecule is developed and used to interpret the data. Muon Spin Rotation measurements, in SiO₂, Al₂O₃, and MgO powders at low temperature in an atmosphere of He indicate that muonium emerges from the surfaces regardless of the ambient temperature of the powder. The muonium spin relaxation rate in Al203 in a He(or Ne) atmosphere is found to be a linear function of the fraction of surface area not covered by adsorbed He(or Ne). The cross sections for muonium to scatter elastically off adsorbed He and Ne atoms have been measured to be 11.0±0.2 Ų and 8.9±0.2 Ų, respectively. The first observations of muonium in the condensed phases of Ar, Kr, and Xe are presented. The data indicate that there is a high probability of muonium formation in all cases. The spin relaxation rate of muonium in solid Xe is ten times that in the liquid, where the random local fields from the nuclear moments of ¹³⁹Xe and ¹⁴¹e are averaged by additional translational motion. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The Standard Model (SM) of particle physics offers the most complete quantum description of the known universe to date, however is unable to address some still unanswered questions. Supersymmetry (SUSY) is a theory which proposes partner particles for all SM particles and offers explanations for many of these questions. Many SUSY searches performed rely on signatures of high missing transverse energy due to a heavy SUSY particle escaping the detector, however these searches have not yet yielded positive results and therefore new search strategies must be employed. In this analysis, a search for new physics is performed at the CERN LHC which targets signatures of SUSY. Specifically, a search for Stealth SUSY is performed, based on a sample of proton-proton collisions at √s = 8 TeV corresponding to 19.7 fb⁻¹ of integrated luminosity collected with the CMS detector in 2012. Stealth SUSY is a unique brand of SUSY which conserves R-Parity and naturally produces a low amount of missing transverse energy. The search strategy utilized is sen- sitive to a wide variety of new physics models including compressed spectra and long decay chains. The Stealth SUSY final state topology considered in this analysis consists of two photons, many jets and low missing transverse energy. The results of this data-driven search for new physics are reported, and good agreement is observed with the background expectation. The data are thus used to determine limits on squark/gaugino masses in the Stealth SUSY framework. / A Dissertation submitted to the Department of Physics in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester, 2015. / April 3, 2015. / CMS, High Energy Physics, LHC, Particles, Stealth SUSY, Supersymmetry / Includes bibliographical references. / Andrew Askew, Professor Directing Thesis; P. Bryant Chase, University Representative; Todd Adams, Committee Member; Joseph Owens, Committee Member; Vladimir Dobrosavljevic, Committee Member.

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In this dissertation, a theory of vibration-rotation (V-R) energy transfer in atom-vibrating-rotor collisions is formulated by a simple extension of the Arthurs and Dalgarno atom-rigid-rotor theory, and V-R transition probabilities, cross sections and rate constants are found from solutions to a set of coupled differential equations. The theory is tested on two near-resonant V-R energy transfer processes. First, the rate constant for the (υ=0, j=20 <– υ=1, j=15) transition in Ar-OH(A^2 Σ^+) is calculated in the infinite-order sudden approximation and in the distorted-wave approximation at 360°K. The results agree with experiment and indicate that the transition is direct and first-order. Second, cross sections for the (υ=1, j=7 <– υ=0, j=11) excitation in Li^+ -H_2(X^1 Σ_g^+) are obtained in the exponential distorted-wave approximation at 14,000°K. The calculated cross sections are larger than those of neighboring off-resonant V-R and non-V-R transitions. It is concluded that near-resonant V-R energy transfer is an important process in atom-diatom collisions.

In the standard model the rare kaon decay 𝙆_𝐿 → 𝜇⁺𝜇⁻ is a highly suppressed, ``strangeness changing neutral current process'' that requires the exchange of two weak bosons with an accurately measured branching fraction 𝐵(𝙆_𝐿 → 𝜇⁺𝜇⁻) = (6.84 ∓ 0.11 ) ✕ 10⁻⁹ [1]. For this measurement to become an important short-distance test of the standard model, the competing 𝑂(𝛼²_𝙴𝙼𝐺_𝙵) two-photon contribution must be computed and removed from the total decay amplitude. While the imaginary part of this contribution can be obtained from the 𝙆_𝐿 → 𝜇⁺𝜇⁻ decay rate and the optical theorem, the real part must be computed in QCD [2]. Depending on a relative sign, a 10% calculation of the real part of the 𝑂(𝛼²_𝙴𝙼𝐺_𝙵) two-photon contribution would lead to a 6% or 17% test of the standard model. As a first step in developing a strategy for computing the two-photon contribution to the 𝙆_𝐿 → 𝜇⁺𝜇⁻ decay, we examine a simpler process 𝜋⁰ → 𝓮⁺𝓮⁻. Here no weak interaction vertex is involved and, more importantly, there is no intermediate hadronic state with a mass smaller than that of the initial pion. The sole complication arises from the presence of the two-photon intermediate state, only one of the difficulties offered by the 𝙆_𝐿 → 𝜇⁺𝜇⁻ decay. We show that the 𝜋⁰ → 𝓮⁺𝓮⁻ amplitude can be calculated with an analytic continuation method where the entire decay amplitude including the imaginary part is preserved. The real part involves non-perturbative QCD contribution and is of substantial interest, while the imaginary part of calculated amplitude can be compared with the prediction of optical theorem to demonstrate the effectiveness of this method. We obtain Re𝓐 = 18.60(1.19)(1.04) eV, Im𝓐 = 32.59(1.50)(1.65) e𝐕 and a more precise value for their ratio Re𝓐/Im𝓐 = 0.571(10)(4) from continuum extrapolation of two lattice ensembles, where 𝓐 is the decay amplitude, the error in the first parenthesis is statistical and the error in the second parenthesis is systematic. Next, we develop a computational strategy to determine the 𝙆_𝐿 → 𝛾 𝛾 decay amplitude. It involves the same hadronic matrix element as the 𝙆_𝐿 → 𝜇⁺𝜇⁻ decay as well as all the intermediate states whose energies are lower than or close to the initial kaon sate except for the |𝜋𝜋𝜇〉that is difficult to deal with. While the lattice QCD calculation is carried out in finite volume, the emitted photons are treated in infinite volume and the resulting finite-volume errors decrease exponentially in the linear size of the lattice volume. Only the 𝑪𝑷-conserving contribution to the decay is computed and we must subtract unphysical contamination resulting from single pion and eta intermediate states which grow exponentially (or fall slowly) as the time separation between the initial and final lattice operators is increased. Results from a calculation without disconnected diagrams on a 24³ ✕ 64 lattice volume with 1/𝛼 =1 Ge𝐕 and physical quark masses are presented.