First measurement of the E double-polarisation observable for γn → K+Ʃ - with CLAS & a new forward tagging hodoscope for CLAS12.
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Date
29/11/2016Author
Fleming, Jamie Alan
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Abstract
Establishing the excitation spectrum of the nucleon would be a key advance to
further our understanding of nucleon structure and Quantum Chromodynamics
(QCD). Recent theoretical advances allow predictions of the excitation spectrum
of the nucleon and other nucleon properties directly from QCD in the non-perturbative
regime, via numerical methods (such as Lattice QCD), complementing
existing constituent quark models. There is an ongoing world programme in
meson photoproduction from the nucleon, which has already led to a number of
nucleon resonances being discovered and established. This advance has largely
been made possible by the first accurate measurement of polarisation observables.
Available data has been obtained for proton targets, whereas for a complete
picture of meson photoproduction, data from the neutron must also be obtained.
This is important, as nucleon resonances can have very different photo-couplings
to the proton and neutron.
This thesis presents the first measurement of the E double-polarisation
observable for the exclusive γn → K+Ʃ- reaction using a polarised hydrogen-deuterium
target from the g14 run period at CLAS. Circularly polarised photons
of energies between 1:1 and 2:3 GeV were used, with results shown in 200 MeV
bins in Eγ and bins of 0:4 in cos θC.M./K+.
Further to this, CLAS has undergone a detector upgrade in order to facilitate
electrons of up to 12 GeV from Jefferson Lab's upgraded accelerator. Essential
to this, is a new system for tagging quasi-real photons by detecting electrons
scattered at very small angles. My work includes significant contributions to
the design, realisation and construction of a hodoscope for this forward photon
tagging apparatus. Presented in this thesis is a comprehensive overview of my
work in developing and constructing the scintillating hodoscope for the CLAS12
Forward Tagger.