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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Near-Threshold Photoproduction of £N(1520) from Protons and Deuterons at SPring-8/LEPS

Chen, Jia-ye 13 July 2009 (has links)
GeV photon beams are provided at SPring-8/LEPS facility by backward-Compton scattering (BCS) from Argon laser photon against the 8-GeV electrons inside the SPring-8 storage ring. The energy range of tagged photon by measuring the recoil electron is from 1.5 to 2.4 GeV, and enables us to study the strange meson- and baryon-photoproduction, such as £p(1020), £N(1405) and £N(1520) . In the past 30 years, other than the high-energy £N(1520) photoproduction at NINA/LAMP2 experiment, there is no further study of the £N(1520) photoproduction near the threshold. Based on this exclusive measurement at NINA/LAMP2 experiment, several theoretical calculations predict that the £N(1520) photoproduction near the threshold can be explained by t-channel K* exchange, t-channel K exchange or the contact term together with the t-channel K exchange under the gauge invariance. This experiment was performed at SPring-8/LEPS facility with liquid hydrogen and deuterium targets by a forward spectrometer from 2002 to 2003. The electroproduction experiment with similar c.m. energy region performed by JLab/CLAS is included for comparison. We study three two-track detection modes to reconstruct the £N(1520) resonance and other resonant/non-resonant backgrounds by the invariant mass and missing mass spectra. Utilizing the one-/two-step side-band subtraction methods and Monte Carlo simulation method, we measure the differential cross sections, K^- decay asymmetries in t-channel helicity frame and photon beam asymmetries to understand the production mechanism of £N(1520) . This is the first time, the differential cross sections were measured at low energies and with a deuterium target. A large asymmetry of the production cross sections from protons and neutrons was observed at backward K^{+/0} angles. It can be explained by the dominance of the contact term along with the t-channel K exchange under the satisfaction of gauge invariance. This interpretation was also compatible with the differential cross sections, K^- decay asymmetry, and the photon beam asymmetry measured in the production from protons in the forward K^+ angles. A detector upgrade for the acceptance complement is done by introducing a time projection chamber, the configuration and operation principles except for the physics results will also be discussed in this thesis.

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