The reaction p+p → p+p+π⁰ has been studied from threshold up to 500 MeV, by detecting the decay 7-rays of the π⁰ in coincidence in two large NaI crystals (TINA and MIN A). It was possible to measure the energy spectra, the differential cross sections and the asymmetry of the π⁰. The total cross sections and the angular distribution parameter b (defined by [Formula Omitted] determined in this measurement are consistent with previous measurements, but are of a much higher precision. The value obtained for b is very small indicating that most of the π⁰ mesons are isotropically distributed in the centre of mass. Assuming the energy spectra predicted by Gell-Mann, we have deduced the intensities of the Ss, Ps and Pp transitions by a global fit to all the energy spectra and the resulting cross sections. For Ss we obtained [Formula Omitted] which is smaller and more accurate than the previous measurements. A model independent [Formula Omitted] would have an uncertainty of about 6 µb. We have compared our results with those of the reaction n+p → N + N + π± and found them to be fairly similar. Any difference would demand inelasticities in the 1=0 channels, but the total cross sections indicate that σ₀₁ is small. The centre of mass pion energy spectra for pp → ppπ⁰ and np → nnπ⁺ are also similar. However a large cosΦ term is observed in the π± differential cross sections from the np reaction which is an indication of a significant value for σ₀₁. The analysing powers are fairly large and negative. This is the first measurement of this observable, although evidence from the reaction ¹³C(p, π⁻) had suggested that the asymmetry in the free pn → ppπ⁻ reaction might be positive. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

No description available.

Thesis (PhD)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: Please see full text for abstract / AFRIKAANSE OPSOMMING: Sien volteks vir opsomming

The work reported in this thesis covers the latter part of a programme undertaken at A.E.R.E. Harwell to collect data on the nucleon-nucleon scattering problem at energies accessible to the Harwell 280 cm synchrocyclotron. The experiments described belong to the second phase of data collection at these energies in that they do not of themselves determine a unique set of phase shifts in a modified phase-shift analysis, but resolve ambiguities in the earlier data available, or improve the precision to a significant degree. The first chapter contains a review of the nucleon-nucleon scattering problem, and provides a common context for the different types of experiment described. The second chapter is devoted to a description of the development and final form of a polarised proton target for use in the 70-150 Mev region for proton-proton scattering. Radiation damage resulted in a decay of the polarisation produced in this target, and a brief study of this phenomenon (described in Chapter II) was required to supplement the polarisation decay data collected in the spin correlation experiment reported in the third chapter. The third and fourth chapters contain the experimental method and analysis of experiments using the polarised target to determine the spin correlation parameter Cnn in proton-proton scattering at 90° centre of mass for three energies: 74, 98, and 143 Mev; and at 61.8° centre of mass at 143 Mev only. A typical precision of ± 0.05 was obtained for this parameter. The fifth chapter contains a description of the apparatus and methods used for measurements of polarisation in the 98 Mev region: the experiment at 98 Mev to determine P(θ) in p-p scattering is described and analysed in chapter six. Due to a recent remeasurement of the polarisation of the Harwell 142 Mev polarised proton beam, absolute polarisation values were obtained, to a typical precision of ± 2% of the peak value of the asymmetry. The 98 Mev data provide a notably more stringent restriction on phase-shift fits at this energy than previous polarisation information. The preliminary results of a measurement of the absolute differential cross section for p-p scattering at 98.8 Mev are briefly discussed, and the chapter concluded with a compilation of the N-N scattering data now available in the energy range 60-160 Mev.

We used recent phenomenological form factors to calculate the effect of on-shell two-pion exchange in nucleon-nucleon scattering below the two-pion production threshold. As expected, the contributions of partial wave amplitudes are all negligible. We also noticed that the relativistic spin-operator decomposition of the scattering amplitude is not unique at certain momenta and angles. / Graduation date: 2000

Thesis (Doctoral?)--University of Oulu, 1987. / Includes bibliographical references.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 184-188).

No description available.

No presente trabalho construímos o potencial nucleon-nucleon devido à troca de dois píons dentro do contexto relativístico da teoria de perturbação quiral, formulada por Becher e Leutwyler. No estudo do espalhamento píon-nucleon, eles desenvolveram um método que exibe a regra de contagem de potências, mantendo a invariância relativística. Os autores também chamam a atenção para um problema presente na formulação de bário pesado, de que sua série quiral não converge na região de baixa energia em torno de t=4µ2, onde µ é a massa do píon. Nós mostramos que este problema é bastante relevante para o potencial nucleon-nucleon, principalmente pelo fato dessa região de energia determinar suas características assintóticas. A dinâmica da troca de dois píons na interação nucleon-nucleon é determinada pelas sub-amplitudes píon-nucleon. Partindo da sub-amplitude de Becher e Leutwyler, obtemos diagramas classificados em três famílias, de acordo com sua topologia e constantes de acoplamento envolvidas. Na definição do potencial subtraímos, da amplitude relativéstica, a iteração da troca de um píon, seguindo a prescrição de Blankenbecler e Sugar. O nosso potencial até a ordem q4 é expresso em termos de seis funções básicas, associadas a integrais de loop, calculadas relativisticamente. Ele mantém as propriedades assintóticas corretas, desde que as integrais básicas não sejam expandidas. Forçando tal expansão, com o objetivo de comparar com os resultados de Entem e Machleidt, observamos concordância na maioria dos termos. Algumas diferenças estão associadas à discrepância na relação de Goldberger-Treiman, indicadas por GT, e dois termos, a contribuições de dois loops. As demais, muito provavelmente estão relacionadas à iteração da troca de um píon. No espaço de configuração, comparamos os nossos resultados com a parte de médio alcance de duas versões do potencial de Argonne, AV14 e AV18. Observamso uma boa concordância apenas para o potencial central isoescalar, o canal mais importante para a fenomenologia. Para as demais componentes, temos discrepâncias inclusive entre as versões AV14 e Av18. Com base na classificação da dinâmica em três famílias e analisando suas contribuições para cada componente, apresentamos uma proposta de como evitar ambiguidades desse tipo na construção de potenciais fenomenológicos. / This work is devoted to the construction of a two-pion Exchange nucleon-nucleon potential in the framework of the relativist chiral perturbation theory, formulated by Becher and Leutwyler. In their study of pion-nucleon scattering they developed a method to regain the Power counting rules while keeping Lorentz invariance. These authors also Drew attention to a problem present in the heavy baryon formulation, that is chiral serie does not converge in the low-energy region around t=4µ2, where µ is the pions mass. We have shown that this problem is rather relevant to nucleon-nucleon potential, mainly due to the fact that this range of energy determines its asymptotic properties. The dynamics of the two-pion Exchange nucleon-nucleon interaction is determined by pion-nucleon sub-amplitudes. Starting from Becher and Letwylers sub-amplitude, we obtain diagrams classified in three families, according to their topology and the coupling constants involved. In the definition of the potential we substract, from the relativist amplitude, the iteration o fone-pion Exchange, following the prescription of Blankenbecler and Sugar. Our potential up to order q4 is expressed in terms of six basic functions associated to relativistic loop integrals. It keeps the correct asymptotic properties, as long as we do not expand the basic integrals. Forcing such na expansio, in order to compare it with the results from Entem and Machleidt, we observe na agreement in the majority o terms. Some differrences are associated to the Goldberg-Treiman discrepancy, indicated by GT, and two terms come from two loop calculations. The remaining ones are probably related to the prescription adopted for the iteration o fone-pion exchange. In configuration space we compare our results with the médium-range component of two versions of the Argonne potential, AV14 and AV18. We obtain agreement only for the central isoscalar potential, the most important to phenomenology. Regarding other channels, we observe discrepancies even between AV14 and AV18. Based on the classification of the dynamics in three families and analysing their contributions to each component, we propose a way to overcome such ambiguities in the construction of phenomenological potentials.

No presente trabalho construímos o potencial nucleon-nucleon devido à troca de dois píons dentro do contexto relativístico da teoria de perturbação quiral, formulada por Becher e Leutwyler. No estudo do espalhamento píon-nucleon, eles desenvolveram um método que exibe a regra de contagem de potências, mantendo a invariância relativística. Os autores também chamam a atenção para um problema presente na formulação de bário pesado, de que sua série quiral não converge na região de baixa energia em torno de t=4µ2, onde µ é a massa do píon. Nós mostramos que este problema é bastante relevante para o potencial nucleon-nucleon, principalmente pelo fato dessa região de energia determinar suas características assintóticas. A dinâmica da troca de dois píons na interação nucleon-nucleon é determinada pelas sub-amplitudes píon-nucleon. Partindo da sub-amplitude de Becher e Leutwyler, obtemos diagramas classificados em três famílias, de acordo com sua topologia e constantes de acoplamento envolvidas. Na definição do potencial subtraímos, da amplitude relativéstica, a iteração da troca de um píon, seguindo a prescrição de Blankenbecler e Sugar. O nosso potencial até a ordem q4 é expresso em termos de seis funções básicas, associadas a integrais de loop, calculadas relativisticamente. Ele mantém as propriedades assintóticas corretas, desde que as integrais básicas não sejam expandidas. Forçando tal expansão, com o objetivo de comparar com os resultados de Entem e Machleidt, observamos concordância na maioria dos termos. Algumas diferenças estão associadas à discrepância na relação de Goldberger-Treiman, indicadas por GT, e dois termos, a contribuições de dois loops. As demais, muito provavelmente estão relacionadas à iteração da troca de um píon. No espaço de configuração, comparamos os nossos resultados com a parte de médio alcance de duas versões do potencial de Argonne, AV14 e AV18. Observamso uma boa concordância apenas para o potencial central isoescalar, o canal mais importante para a fenomenologia. Para as demais componentes, temos discrepâncias inclusive entre as versões AV14 e Av18. Com base na classificação da dinâmica em três famílias e analisando suas contribuições para cada componente, apresentamos uma proposta de como evitar ambiguidades desse tipo na construção de potenciais fenomenológicos. / This work is devoted to the construction of a two-pion Exchange nucleon-nucleon potential in the framework of the relativist chiral perturbation theory, formulated by Becher and Leutwyler. In their study of pion-nucleon scattering they developed a method to regain the Power counting rules while keeping Lorentz invariance. These authors also Drew attention to a problem present in the heavy baryon formulation, that is chiral serie does not converge in the low-energy region around t=4µ2, where µ is the pions mass. We have shown that this problem is rather relevant to nucleon-nucleon potential, mainly due to the fact that this range of energy determines its asymptotic properties. The dynamics of the two-pion Exchange nucleon-nucleon interaction is determined by pion-nucleon sub-amplitudes. Starting from Becher and Letwylers sub-amplitude, we obtain diagrams classified in three families, according to their topology and the coupling constants involved. In the definition of the potential we substract, from the relativist amplitude, the iteration o fone-pion Exchange, following the prescription of Blankenbecler and Sugar. Our potential up to order q4 is expressed in terms of six basic functions associated to relativistic loop integrals. It keeps the correct asymptotic properties, as long as we do not expand the basic integrals. Forcing such na expansio, in order to compare it with the results from Entem and Machleidt, we observe na agreement in the majority o terms. Some differrences are associated to the Goldberg-Treiman discrepancy, indicated by GT, and two terms come from two loop calculations. The remaining ones are probably related to the prescription adopted for the iteration o fone-pion exchange. In configuration space we compare our results with the médium-range component of two versions of the Argonne potential, AV14 and AV18. We obtain agreement only for the central isoscalar potential, the most important to phenomenology. Regarding other channels, we observe discrepancies even between AV14 and AV18. Based on the classification of the dynamics in three families and analysing their contributions to each component, we propose a way to overcome such ambiguities in the construction of phenomenological potentials.