Hadron spectroscopy of pseudoscalar and vector meson photoproduction using linearly polarised photons at CLAS

Clark, Louise (2022) Hadron spectroscopy of pseudoscalar and vector meson photoproduction using linearly polarised photons at CLAS. PhD thesis, University of Glasgow.

Abstract

The field of hadron spectroscopy is informed by experiments which study excited states of the nucleon by detecting the decay products following excitation with a hadronic, leptonic or electromagnetic probe. Experiments using a polarised beam of photons provide an important contribution to the world data. This thesis describes the analysis of data from one such experiment, the CEBAF Large Acceptance Spectrometer at Jefferson Laboratory, Virginia, USA. In the experiment, an incident beam of electrons passes through a diamond radiator producing a linearly polarised photon beam of energy from 1.1 to 2.1 GeV on a liquid hydrogen target.

The analysis method and results for two reaction channels are presented. In the first analysis, the polarisation observables {Σ,P,T,Ox,Oz} for the reaction −→γ p → K 0 S Σ + are extracted simultaneously using likelihood sampling with Markov-Chain Monte-Carlo. The results are presented as angular distributions (cosθK 0 S ) for bins in photon energy Eγ for a total of 21 bins. The values extracted for T, Ox and Oz are a first measurement of these quantities for this reaction and the beam asymmetry (Σ) measurement supplements the one previous measurement for this quantity and extends the energy range over which it has been extracted. The measurement of the recoil polarisation, P, is consistent with previous measurements.

In a second analysis, the spin density matrix elements (SDMEs) for γ p → p φ are extracted using similar analysis techniques. The results are presented as angular distributions (cosθφ ) for bins in photon energy Eγ for a total of 24 bins. This work is the first to extract all nine SDMEs for the full angular range of the φ meson production. A comparison is made to the predictions of the Vector Meson Dominance (VMD) model and the results provide evidence for contributing processes other than VMD, particularly at more backward angles of the φ meson production. The data also indicate non-helicity conserving process in both the s-channel and the t-channel.

The results from the first analysis have been passed to the Juelich-Bonn theory group and the effect of including the new data within their dynamical coupled channel model is described. Several nucleon resonances are affected and the impact on the pole positions, widths and photon decay amplitudes of the affected resonances is described.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: Q Science > QB Astronomy; Q Science > QC Physics
• Colleges/Schools: College of Science and Engineering > School of Physics and Astronomy
• Supervisor's Name: Ireland, Professor David and McKinnon, Dr. Bryan
• Date of Award: 2022
• Depositing User: Theses Team
• Unique ID: glathesis:2022-83236
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 27 Oct 2022 09:05
• Last Modified: 27 Oct 2022 09:08
• Thesis DOI: 10.5525/gla.thesis.83236
• URI: https://theses.gla.ac.uk/id/eprint/83236