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GlueX Experiment Document 4206-v1

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Diamond Radiator Fabrication, Characterization and Performance for the GlueX Experiment

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Richard T. Jones
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Richard T. Jones
Document Created:
03 Oct 2019, 13:51
Contents Revised:
03 Oct 2019, 13:51
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03 Oct 2019, 13:54
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The GlueX Experiment conducted in Newport News, VA requires a 9 GeV beam of linearly polarized photons to access the physics of gluonic excitations. Coherent bremsstrahlung (CB) was chosen as the radiation technique for its high intensity and degree of linear polarization. The CB radiator must be of sucient crystal quality and have appropriate material properties for operating in a 12 GeV electron beam. Diamond, due to its high Debye temperature, was chosen as the CB radiator. Due to multiple scattering of the electron through the crystal, the central region of the radiator is constrained to a thickness of 20 m. The overall crystal quality must be high in order to reduce the photon beam emittance for proper collimation of unpolarized photons. To meet this speci cation, the diamond must not have a whole-crystal rocking curve greater than the electron beam emittance, on the order of 20 rad. This work describes the development of a novel laser ablation technique for di erentially thinning single-crystal CVD diamond plate to meet the strict GlueX requirements. Transmission mode x-ray rocking curve measurements are presented which are used to characterize the diamond radiator lattice structure (mosaic spread) before and after laser ablation. Finally, an analysis of the vector meson decay channel p,gamma -> rho0 + p is discussed and used to extract the product of the beam asymmetry and polarization of the photon beam as well as spin-density matrix elements (SDMEs) in the helicity reference frame. The observables measured from this analysis are strongly correlated to the performance of the diamond radiator used to produce the linearly polarized photon beam.
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