Three types of rare radiative meson decays are studied. The first type is the weak kaon decay [special characters omitted] The interest here is this decay's sensitivity to the loop-level and hence quantum structure of the standard model. Both short-distance and long-distance effects are considered, as well as possible contributions from horizontal gauge bosons. The second decay type studied is electromagnetic η decays into neutral pions, specifically [special characters omitted] and [special characters omitted] The main interest here is possible signals for electromagnetic charge-conjugation violation. The modelling method used is vector meson dominance. The third type studied is electromagnetic η decays into charged pions, specifically [special characters omitted] and [special characters omitted] The interest here is chiral perturbation theories that incorporate vector mesons. / Graduate

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The optical interaction of low energy( ≤30 MeV) pions with nuclei is discussed. In particular, it is shown that, since the nuclear density enters the low energy pion-nucleus interaction in a very direct manner, this interaction provides a sensitive means of investigating such properties of the nuclear density.as the diffuseness of the nuclear surface. A geometric discussion of the structure of the low energy pion-nucleus interaction is given which emphasizes the analogy between adding the scattered pion waves in the nuclear medium and adding electric potentials in a classical dielectric. The parameters of the optical potential which represents the interaction are taken to be those calculated by earlier authors who have used a multiple-scattering formalism to deduce the details of the-optical interaction from a microscopic point of view. The interaction is strongly momentum-dependent and the local part of the interaction is repulsive. It is shown that in optical scattering and absorption, the resonance aspects of the problem depend mainly only upon the height of the local potential barrier (~15 MeV) because of the long wavelength of the pion inside the nucleus. The optical absorption of low energy pions is shown to be sensitive to the diffuseness of the nuclear surface through the strong suppression of momentum-dependent absorption near the top of the potential barrier. It is argued that low energy pions can therefore be used to resolve the conflicts which presently exist in the information available from several experiments concerning the distribution of neutrons in the nuclear surface. The ideas developed in discussing the optical absorption of pions are extended to the excitation by pions of rotational states in strongly deformed nuclei. It is shown that, unlike the excitation cross sections obtained with more conventional interactions (such as the Coulomb interaction) , the excitation cross sections obtained from the pion-nucleus optical interaction depend strongly upon such characteristics of the nuclear density as its surface thickness. The rotational model of strongly deformed nuclei is assumed and an analysis of the excitation cross sections is made in the Distorted Wave Born Approximation. It is shown that the sensitivity to the nuclear surface thickness in the excitation cross sections arises from the suppression of the excitation processes due to the momentum-dependent interaction near the top of the potential barrier. It is suggested that the excitation of rotational levels in strongly deformed nuclei by pions can therefore be used to carefully examine the distribution of neutrons in the surfaces of strongly deformed nuclei. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

An expression for the differential cross-section of pion production by protons on nuclei is built up using the impulse approximation. It assumes the knowledge of free nucleon-nucleon pion production and takes account of the internal nucleon momentum distribution, the Coulomb potential, and the absorption effects of the incoming protons and outgoing pions. Calculation for the special case of 450 MeV incident protons is carried out to demonstrate the success of our model and the A-dependence of the cross-section is found to agree rather well with experiment. It turns out that the pion production process is dominated by the pion absorption and the relative proportion of protons and neutrons inside the nucleus is a significant factor. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

We construct a model to explain the production of pions in the bombardment by protons of various nuclei and we use the model to calculate relative cross-sections for the process. The model assumes that the incident proton interacts with the target nucleons individually and that the proton-nucleon cross-section can be used as a free parameter. The model accounts for many important nuclear effects, some for the first time in explaining the A-dependence of the pion yield. The effects included are those due to proton and pion absorption, to the background nuclear potentials and to the struck-nucleon momentum and density distributions. We compute differential cross-sections in several special cases and compare them with experimental data at 450 MeV. Agreement is only moderate, but it is as good as any previously obtained and, unlike the earlier results, it does not depend on the assumption of an absorbing neutron blanket. Our agreement depends instead on the use of a modern nuclear radius and a reasonable treatment of pion absorption. In this respect our results confirm what earlier workers had assumed, that absorption is the dominant factor controlling the proton-nucleus production of pions. Also important is the proton-nucleon production rate, a reasonable value of which we assume. Potential effects are important because the basic production rate and pion absorption are both very energy dependent. The effects of struck-nucleon momentum and density distribution, as we calculate them, are small at the energy considered. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The differential cross sections for the production of definite lambda hypernuclear states, within the single scattering, impulse approximation, are calculated from the reaction n(K⁻,π⁻)Λ° on nuclear targets of helium, carbon and oxygen at various K-meson incident momentum. It is shown that these predictions are very sensitive to the three momentum transfer and to the wave function of the bound lambda in the hypernucleus. From the calculations, it is shown that it is possible to observe their production by studying the missing mass spectrum of the emitted pion. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The pion-nucleon total cross section is reproduced in the pion kinetic energy range of zero to 250 MeV by a simple Yukawa potential with the depth.and width as free parameters. This potential is then averaged over a nuclear matter distribution in an attempt to produce a pion-nucleus potential for pion-¹²C scattering. The model is explored by varying several parameters in the potential and observing their effect on the differential cross section for pion-12C scattering with the pion kinetic energy equal to 50 MeV. No completely satisfactory fit to the data is found. It is suggested that treating this system as a pion-nucleon system interacting in the average field of the residual nucleus may give better results and some ideas are presented as to how this might be done. Applications of such a treatment of pion-nucleus interactions to the description of pion-nucleus "doorway" states (so far, apart from the N*, unobserved) are discussed. / Science, Faculty of / Physics and Astronomy, Department of / Graduate