P0 Photoproduction Using Linearly Polarised Photons With The Clas Detector PDF Download

The work presented in this thesis describes the first experimental measurement of the photon asymmetry of the exclusive $ ec{γ}$ → ?0p → ?+?-p reaction. The data were gathered during the summer of 2001 as a proof of principle study using a polarized beam of photons with the CLAS detector in Hall B of Jefferson Lab for the first time. The aim of the g8a set of experiments is to improve the understanding of the underlying symmetry of the quark degrees of freedom in the nucleon, the nature of the parity exchange between the incident photon and the target nucleon, the mechanism of associated strangeness production in electromagnetic reactions, and to search for evidence for the existence of the so called missing resonances. A beam of tagged and collimated linearly polarized photons (energy range 1.8-2.2 GeV) in conjunction with the large solid angle coverage of CLAS make possible the extraction of polarization observables for the photoproduction of vector mesons. For example, the azimuthal distribution of the ?0 as a function of its polar angle in the ($ ec{γ}$p) c.m. system enables the measurement of the photon asymmetry parameter, ?. This has been measured for ?c.m. ≤ 65°, the results of which are compared with the prediction of the quark model of Zhao for the ? vector meson. It has been found that the tensor coupling for the ?0 is quite different than that of the ?. The experimental technique of using a beam of linear polarized photons with the CLAS detector has been shown to be viable. By the end of the second phase of these experiments they expect to have a high quality data set which will allow the measurement of the spin density matrix elements for the ?0 and provide evidence relating to the existence of the missing resonances.