Howdle, David A.
(2012)
Measurement of polarisation observables using linearly polarised photons with the crystal ball at MAMI.
PhD thesis, University of Glasgow.
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Abstract
In order to further study and expand the kinematic coverage of polarisation observables in pseudoscalar meson
photoproduction, a measurement of polarisation observables has been performed at the MAMI facility in Mainz,
Germany. The measurement used a beam of linearly polarised photons using the coherent bremsstrahlung method and
the Glasgow Tagged Photon Spectrometer. The photon beam was incident on an $lH_{2}$ target in order to produce
the meson photoproduction reaction $\gamma p \to \pi^{0} p$. This target was housed in the centre of the Crystal
Ball detector which was used to detect the reaction products. A carbon polarimeter was used to measure the
polarisation of the recoiling proton through secondary scattering. The polarisation observables for pseudoscalar
meson photoproduction which were measured included: $\Sigma$, the modulation induced in the reaction products by
the linearly polarised photon beam; $O_{x}$, the transfer of linear polarisation from the beam to the recoiling
proton; and $T$, the polarisation inherent in the target proton. These measurements were performed over a wide
kinematic range in both photon energy and polar angle in the centre of mass system, and were compared to three
partial wave analyses, SAID, MAID and Bonn-Gatchina. The results contribute to the ongoing search for a complete
understanding of the nucleon's excitation spectrum, and significantly enhance the world dataset for these
polarisation observables.
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