Thirteen N* states have been well-established according to the Particle Data Group, but some relativized quark models predict that many more N* resonances exist. Diquark models predict that the N* spectrum is limited by a correlated quark-pair in the nucleon, but there is strong evidence for the existence of the [Special characters omitted.] (1900)** resonance, which is absent in diquark models. Measuring the spectrum of N* states will provide valuable information on the relevant degrees of freedom within the nucleons. Most of the experimental searches for the N* states have been conducted in the πN channel. Some models of baryon decays predict that most of the unobserved N* states couple somewhat weakly to the πN channel, and that some couple non-negligibly to the KY, K*Y , and KY* channels. Measurements of the cross sections and polarization observables of strangeness photoproduction reactions can provide additional information on the spectrum of N* states. These measurements can be used in coupled-channel partial-wave analyses that can provide simultaneous constraints on the N* resonance parameters from several channels. These analyses can also take into account hadronic rescattering, which is predicted to have a large effect on the measured cross sections. However, to determine the isospin decomposition of the photo-transition amplitudes to these channels, photoproduction measurements are necessary on both the proton and the neutron. Measurements of the differential cross sections of the γn [arrow right] K* (892) 0 Λ and γn [arrow right] K + Σ*(1385) - reactions have been performed using data from the Jefferson Lab Hall B CLAS g13 experiment. No experimental cross section data have yet been published on the γn [arrow right] K* (892) 0 Λ reaction, and the only published cross section data on the γn [arrow right] K + Σ*(1385) - reaction are limited to forward angles, where t -channel K + and K* + exchanges are predicted to dominate. These cross sections are compared against theoretical models to study the channel interactions that give rise to their distributions. These reactions also have the same final state particles ( K + π - pπ - ), so studies of their potential interference were performed as well. A measurement of the γn [arrow right] pπ - cross section was also performed, and the agreement with published results within the uncertainties validated the integrity of the data and procedures used in this analysis.
| Identifer | oai:union.ndltd.org:RICE/oai:scholarship.rice.edu:1911/70342 |
| Date | January 2011 |
| Contributors | Padley, B. Paul |
| Source Sets | Rice University |
| Language | English |
| Detected Language | English |
| Type | Thesis, Text |
| Format | 352 p., application/pdf |
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