Tübingen, Univ., Diss., 2003.

Tübingen, Univ., Diss., 2002.

Thesis supervisor: Onel Yasar. Includes bibliographic references (p. 73-74).

Universiẗat, Diss., 2000--Bonn.

University, Diss., 2002--Tübingen.

Th.--Sci. phys.--Clermont-Ferrand 2, 1977. N°: 238.

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

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The composite structure of the nucleon leads to a spectrum of excited states, or resonances, which contain important constraints on the dynamics and interactions of its constituents. A major world programme measuring meson photoproduction from the nucleon is currently under way to improve our knowledge of this fundamental spectrum. These new generation of measurements exploit polarisation degrees of freedom of the incident photon along with spin degrees of freedom in the target and recoiling nucleons. The meson photoproduction process can be described by 16 independent experimental observables. To fully constrain the four underlying complex photoproduction amplitudes requires the measurement of a least 8 of these. Measurements of double polarisation observables, where the photon beam and nucleon target are polarised are crucial to achieve this requirement. This thesis will present the analysis and extraction of the first preliminary measurement of the double polarisation observable. F in the single pion photoproduction reaction γ→ + p →n + π+ was undertaken to measure both F and T. The resulting measurement of polarisation observables from this reaction in conjunction with with those from the Pπ0 channel will provide stringent constraints on partial wave analyses aiming to extract precision information on the properties of the low lying nucleon resonances.