Eta photoproduction study with the upgraded Glasgow tagger at MAMI

QC Physics;T Technology (General);Q Science (General)

McNicoll, Eilidh F. ; Annand, John R.M.

University:University of Glasgow

Department:School of Physics and Astronomy

关键词: nuclear, physics, differential cross-sections, differential cross sections, η, eta, photoproduction, proton, tagging, tagger, MAMI, meson;   

Others  :  http://theses.gla.ac.uk/1469/1/2010McNicollPhD.pdf

来源: University of Glasgow

【 摘 要 】

Photoproduction of mesons provides an excellent means by which to study the proton excitation spectrum. The existence and properties of some nucleon resonances are well established, but many more are still debated, meriting much theoretical and experimental attention. The proximity and widths of such excited states result in difficulties in separating contributions from individual resonances. However, the S_11(1535) is the only state in the second resonance region to couple strongly to an Nη final state. Consequently, η production provides clean selection of this S_11 intermediate state, for incident photons in the energy range 700 to 1400MeV. The S_11(1535) is a well-established resonance, but its composition is a contentious topic, requiring further experimental data to distinguish between competing theories.The MAMI electron accelerator was upgraded in 2006 to increase its maximum beam energy from 885 to 1508MeV. The A2 collaboration use tagged Bremsstrahlung to produce the necessary photons for photoproduction experiments. The upgrade granted access to the second resonance region of the proton excitation spectrum, which covers the centre-of-mass energy range 1.3 < W < 1.6GeV. This exceeds the η production threshold of W = 1485MeV (Eγ = 707MeV) and encompasses the full width of the S_11(1535). For exclusive measurements of η photoproduction, a reasonably precise knowledge of the incident photon energy is required. This isprovided for the A2 collaboration by the Glasgow Photon Tagging Spectrometer (the “tagger”). The upgrade of MAMI necessitated the corresponding upgrade of the tagger.The work of this thesis included assisting in the upgrade and calibration of the tagger before using the completed spectrometer in the measurement of differential cross-sections of η photoproduction on the proton from threshold to 1403MeV incident photon energy. The agreement of this analysis with previous experiments demonstrates the success of both upgrade and calibration.