Polarization Observables in Strangeness Photoproduction with CLAS at Je erson Lab

This work presents measurements of several polarization observables for the reactions −→γ p→ KΛ and −→γ p → K+Σ0. The data were collected in the summer of 2005 at the Thomas Je erson National Accelerator Facility, using a linearly polarized photon beam in the energy range 1.66 GeV < √s < 2.24 GeV. In addition to measuring the photon asymmetry, target asymmetry and hyperon recoil polarization, rst ever measurements are made for the double polarization observables Ox and Oz. The measurements of the photon and target asymmetries vastly increase the precision of the current world dataset, as well as extending the angular coverage. The aim of the experiment was to investigate the process of strangeness production on the proton and the role played by di erent resonances in the reaction dynamics. In particular the role played by missing resonances the excited baryon states predicted by SU(6)⊗O(3) symmetric quark models but so far undetected in experiment will be studied. The photon asymmetry is found to be positive for almost the full kinematic range for both channels with some structure evident at centre of mass energies above 1.92 GeV, while the recoil polarization results reproduce the large polarizations seen in previous measurements with a much higher precision. For the Λ channel, the double polarization observables indicate that the photon polarization is preferentially transferred to the hyperon along the x̂-axis, with the Ox observable displaying a strong signal at forward angles. There is also evidence that the Λ is fully polarized at mid to forward angles, although the behaviour is not reproduced by the Σ0, where there is also a failure to de ne a preferred polarization axis. The target asymmetry results for the Λ channel display a negative polarization at backward angles with a very large positive polarization at forward production angles. The KΛ results are compared to calculations from an isobaric model and a Regge-plus-resonance approach. Both models include the established S11(1650). P11(1710) and P13(1720) resonances in their calculations, with the isobaric prescription using various Born terms to describe the background, and the Reggeplus-resonance calculation utilizing Regge trajectories. Both approaches give good agreement with the data, with some evidence for an important role to be played by the missing D13(1900) resonance and some weaker evidence for the inclusion of a missing P11(1900) state. For the KΣ results the same model