We have determined the branching ratio for single charge exchange using stopped negative pions on $\sp{115}$In, $\sp{45}$Sc, $\sp{32}$S, $\sp{31}$P, $\sp{27}$Al, $CH\sb2$. The experiment was done at the LEP channel at LAMPF. Negative pions at $50MeV$ were slowed down in a graphite degrader and brought to rest in the target nuclei. The neutral pions that comes from single charge exchange, decays into two gamma rays, which are then detected using the LAMPF $\pi\sp0$ spectrometer. The measured branching ratios are discussed within the framework of the simple shell model. The discussion of the observed branching ratios require consideration of angular momentum, parity, and energy. These results will allow theorists to determine the strength of the isovector pion-nucleon interaction in nuclei. This information can possibly be used to determine the origin of the large repulsion of the s-wave isoscalar pion-nucleon interaction in nuclei. / Source: Dissertation Abstracts International, Volume: 51-02, Section: B, page: 0811. / Major Professor: Hans S. Plendl. / Thesis (Ph.D.)--The Florida State University, 1989.

Esta tese tem como objetivo apresentar e discutir resultados de um estudo sobre os fenômenos de polarização de híperons e de anti-híperons em processos inclusivos resultantes de interações próton-núcleo e altas energias (centenas de GeV). É proposto um modelo que acreditamos ser o principal responsável pela polarização de anti-híperons em tais processos. A polarização é resultante das interações finais entre os anti-híperons e outras partículas produzidas no processo (que na sua maioria são píons). O modelo baseia-se então em dois elementos: as interações píon-híperon a baixas energias (que estudamos através da lagrangianas efetivas) e das flutuações estatísticas do meio em expansão. O estudo deste meio baseia-se no modelo hidrodinâmico, que considera a formação de matéria hadronica quente durante tais colisões. Os resultados estão em bom acordo com os dados experimentais e conseguem explicar pela primeira vez a polarização de anti-híperons. / We present and discuss in this thesís results of a study on the hyperon and antihyperon polarization phenomena in high-energy (hundreds of GeV) proton-nudeus inclusive reactions. We propose a model that we believe is the main source of the anti-hyperon polarization in these processes. The polarization is originated by the final-state interactions between the antí-hyperons and other produced particles in these collisions (predominantly píons) and based on two elements: the low-energy pion-hyperon interaction (descriebed by effective lagrangians) and the statistical fluctuations plus expansion of the background matter. The results agree quite well wíth the experimental data and gíve for the first time a convencing explanatíon of the anti-hyperon polarization.

<p> A novel electret fabrication method has been explored using a 1.7 MV Pelletron accelerator. Also, a vibrating Kelvin probe was designed and constructed for the measurement of surface potentials. The electret formation method involved using proton beams of 2 MeV energy to both partially and completely penetrate dielectric samples with metallized back plates to create defect-induced surface potentials. These potentials would likely be more resilient than those of electrets fabricated by current popular methods because the effective charge would be deposited much deeper into the material. The potentials were monitored with a custom built Kelvin probe system. This method was worth exploring as there is currently a need for more resilient electrets in the design of energy efficient micro-electro-mechanical systems (MEMS). Currently, electrets cannot survive certain MEMS fabrication processes. Two types of samples were explored. The first were 150 um thick borosilicate glass slips with a sputter coated gold backing layer. The second were silicon substrates with a 300 nm thick SiO₂ layer deposited on one side and a silver backing layer on the other. The results of this thesis suggest that this charging method is inferior to other methods when applied to 150 um thick borosilicate glass. The borosilicate glass electrets were inferior both with respect to effective surface charge and effective surface charge retention. The effective surface charges attained with the SiO₂/Si samples were also lower than the lowest surface charges commonly achieved by other charging methods. The SiO₂/Si samples irradiated at fluences of 10¹¹ and 10¹³ ions/cm² showed decays comparable to those achieved by other methods as of this writing. This thesis is an overview of the design and construction of a Kelvin probe system, the aforementioned method, and a comparison of the results with the characteristics of electrets fabricated by other methods commonly used today.</p><p>

This thesis will present a search for sterile neutrinos using data taken with the MINOS experiment between 2005 and 2012. MINOS is a two-detector on-axis experiment based at Fermilab. The NuMI neutrino beam encounters the MINOS Near Detector 1km downstream of the neutrino-production target before travelling a further 734km through the Earth's crust, to reach the Far Detector located at the Soudan Underground Laboratory in Northern Minnesota. By searching for oscillations driven by a large mass splitting, MINOS is sensitive to the existence of sterile neutrinos through looking for any energy-dependent perturbations using a charged-current sample, as well as looking at any relative deficit in neutral current events between the Far and Near Detectors. This thesis will discuss the novel analysis that enabled a search for sterile neutrinos covering five orders of magnitude in the mass splitting and setting a limit in previously unexplored regions of the sterile neutrino parameter space, where a 3+1-flavour phenomenological model was used to extract parameter limits. The results presented in this thesis are sensitive to the sterile neutrino parameter space suggested by the LSND and MiniBooNE experiments.

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Leptogenesis is a class of scenarios where the baryon asymmetry of the Universe is produced from a lepton asymmetry generated in the decays of a heavy sterile neutrino. We explain the motivation for<br />leptogenesis. We review the basic mechanism, and describe subclasses of models. We then focus on recent developments in the understanding of leptogenesis: finite temperature effects, spectator processes, and in particular the significance of flavour physics.

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