The Search for Missing Resonances in gp to K+L Using Circularly Polarized Photons on a Longitudinally Polarized Frozen Spin Target

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The Search for Missing Resonances in gp to K+L Using Circularly Polarized Photons on a Longitudinally Polarized Frozen Spin Target

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Title: The Search for Missing Resonances in gp to K+L Using Circularly Polarized Photons on a Longitudinally Polarized Frozen Spin Target
Author: Casey, Liam Robert
Abstract: This works presents the first measurements of three double-polarization observables for the &gamma p &rarr K<super>+</super> &Lambda reaction: E (beam-target asymmetry), L<sub>x'</sub> and L<sub>z'</sub> (target-recoil asymmetries). Each of these measurements required the longitudinal polarization of target protons. To that end, a longitudinally polarized frozen-spin butanol target was constructed for use in the Thomas Jefferson National Accelerator Facility's Hall B. The data presented in this analysis were taken during the g9a run period from November 2007 - February 2008 using the aforementioned target and a circularly polarized photon beam in the energy range of 0.5 - 2.4 GeV . The motivation for this experiment was to extend the set of measured observables describing the reaction channel in order to aid in the search for missing baryon resonances. The complete set of polarization observables can be used to perform a model-independent partial wave analysis (PWA) of the reaction channel and extract resonant contributions to the cross section. Consistency checks with previously measured polarization observables were also performed by extracting the &Lambda recoil polarization and the beam-recoil asymmetries C<sub>x' </sub>and C<sub>z'</sub> . The recoil polarization P extracted from g9a data is in good agreement with previous data. On the other hand, some major discrepancies are found between the g9a results and previous data for the beam-recoil transfer C<sub>x'</sub> and C<sub>z'</sub>. The statistics generated for K<super>+</super> &Lambda were insufficient to adequately resolve between models, although better agreement with the Mart-Bennhold model which includes the missing D<sub>13</sub>(1960) resonance was evident in much of the data. Nonetheless, little evidence of resonant structure appears in the smoothly varying measurements of E and the target-recoil tranfer L<sub>x'</sub> and L<sub>z'</sub> are frequently consistent with a flat asymmetry or none at all. Identification of missing resonances from individual observable measurements is unlikely. Instead, these new measurements will serve to further constrain parameters for the full PWA of &gamma p &rar K<super>+</super> &Lambda.
Description: Degree awarded: Ph.D. Physics. The Catholic University of America
URI: http://hdl.handle.net/1961/9714
Date: 2011-06-24


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