The photon beam asymmetry for KY production from the bound proton in deuterium

• Main Author: Johnstone, John Russell
• Published: University of Glasgow 2010
• Subjects: 531.16; QC Physics
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.512119

This thesis presents measurements of the photon asymmetry polarisation observable for the γd→K⁺Λ and γd→K⁺Σ⁰ reactions from the bound proton in deuterium. The data were collected in the summer of 2007 at the Thomas Jefferson National Accelerator Facility in Newport-News, Virginia, using a linearly polarised photon beam in the energy range 1.3 to 2.3 GeV. The aim of the experiment was to investigate the validity of the quasifree approximation of a bound nucleon in deuterium. This analysis focusses on the proton and by directly comparing results from this analysis to those from previous similar analyses on the free proton, this issue is addressed. Ultimately, this will allow reliable results to be extracted from analyses of channels on the bound neutron in deuterium. The photon asymmetry is found to be positive for the entire kinematic range for both channels with indications of some structure above centre-of-mass energies of 1.8 GeV. The K⁺Λ results are compared to measurements from the free proton produced with similar kinematics. Also included in the comparison are model predictions from the Kaon-MAID isobaric model which includes the established ****S₁₁(1650), ***P₁₁(1710) and ****P₁₃(1720) resonances and uses various Born terms to describe the background. Comparison to the free proton results gave good agreement with the majority of the quasifree measurements being comparable to those from the free proton. There was however seen to be some indication of a systematic overestimation of the results in one kinematic region. The model gives reasonable agreement with the data, with some evidence for a role to be played by the missing D₁₃(1900) resonance. For the K⁺Σ⁰ results, the same comparison was made with free proton results and the Kaon-MAID model, this time with the inclusion of the **S₃₁(1900) and ****P₃₁(1910) resonances. No missing states were considered in this calculation and the agreement with the results was not as good as that of the K⁺Λ channel. Comparison to measurements from the free proton produced similarly good results as were found with the K⁺Λ results but this time with no obvious indication of any systematic discrepancy. Overall, the agreement between the quasifree and the free predictions was found to be quite good and will lend weight to future analyses from the bound neutron in deuterium by allowing a quasifree approximation to be assumed prima facie.