Codling, Richard F.B.
Photon asymmetry of the g p -> pi+ n reaction in the region of the D(1232) resonance.
MSc(R) thesis, University of Glasgow.
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The photon asymmetry, Sigma, of the g p -> pi+ n reaction was measured for incident linearly polarised photons with coherent peak energies of 400 and 440 MeV, corresponding to the upper region of the Delta(1232) resonance. The measurements show the energy and angular dependence of Sigma over the range 30 degrees < theta(pi+) < 170 degrees in the Centre of Mass frame in five bins of varying width. Each of these theta bins is subdivided into five photon energy bins over the 100 MeV range up to the coherent peak energy, each energy bin having a width of 20 MeV. This gave some overlap between the two experimental data sets which thus allowed for comparisons to be made between them for the expected internal consistency of the experiment.
The measurements were made as part of the A2 collaboration's photo-nuclear research programme using the Glasgow tagged photon spectrometer in conjunction with the CB and TAPS detectors at the MAMI-B electron beam facility. Data was collected between July and October 2004 and yielded approximately 130 hours of data for the 400 MeV data set and 460 hours for the 440 MeV data set.
The presented experimental results for Sigma will eventually provide additional data points for the MAID and SAID databases used to test and consolidate current photo-production models and fits in a currently sparsely populated experimental data region. In addition, this first round of experiments with the CB and TAPS detectors represents the first use of the CB for the detection of charged pions. This has applications for future experiments at MAMI involving the measurement of polarisation observables relying on charged-meson final states. The output of the newly upgraded GEANT-4 simulation of the apparatus setup in A2 was also compared to the experimental results for consistency.
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