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G measurement at Ken Livingston, University of Glasgow, Scotland Slides from: Ken Livingston: Various talks at -

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Presentation on theme: "G measurement at Ken Livingston, University of Glasgow, Scotland Slides from: Ken Livingston: Various talks at -"— Presentation transcript:

1 G measurement at Ken Livingston, University of Glasgow, Scotland Slides from: Ken Livingston: Various talks at - David Howdle (ex Glasgow) - /home/davidh/docs/presentations Stuart Fegan (ex Glasgow) - /home/stuartf/Presentations/ Annika Theil (Bonn) - Also talks in this session on Baryons 2013:

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3 Missing baryon resonances

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5 Better to look at angular distributions and polarization observables.

6 Polarization observables in pseudoscalar meson production 4 Complex amplitudes: 16 real polarization observables. Complete measurement from 8 carefully chosen observables. πN has high statistics but in KY recoil is self-analysing Pseudoscalar mesons J p = 0 - Here's the nonet of uds ones:  + N →  m → Y 

7 Polarization observables in pseudoscalar meson production 4 Complex amplitudes: 16 real polarization observables. Complete measurement from 8 carefully chosen observables. πN has high statistics but in KY recoil is self-analysing I. S. Barker, A. Donnachie, J. K. Storrow, Nucl. Phys. B (1975). πNπNKY recoil targ γγ targ recoil ☻☻☻ ☻ linearly polarized photons ☻☻☻ longitudinally polarized target ☻☻☻ transversely polarized target circ polarized photons ☻☻☻ Complete, and over-determined

8 Polarization observables  + N →  m Linear Polarisation Circular polarisation Nucleon recoil polarimiter x → Y  Hyperons are “self analysing” Transverse polarized nucleon targets Longitudinally polarized nucleon targets

9 Polarization observables - a simple example, 

10 Systematics of detector acceptance cancel out. “Only” need to know P lin, the degree of linear polarization.

11 'G' is one of the beam-target double polarisation observables, arising from a linearly polarised beam with a longitudinally polarised target In this case, terms not involving linear polarisation of the beam and longitudinal polarisation of the target are zero and the above expression becomes a lot simpler:

12 The effect of G can be seen by examining the asymmetry distribution for positive and negative longitudinal target polarisations The distributions for the positive (top) and negative (bottom) target polarisations show a phase shift due to change in target polarisation By adding distributions for the two target polarisations, the G contribution can be eliminated and a measurement of can be attempted on Butanol If we take similar asymmetries of Kaon azimuthal angle distributions for the Butanol data, the amplitude of a cos(2) fit is not a pure measurement of the observable – it also contains a contribution from the G observable

13 ● The A2 Hall is a real photon experimental setup ● It uses a tagged photon beam, which stimulates a reaction within the target cell. A collection of detection systems are then used to measure the reaction products

14 ● Electrons scattering of a radiator produce bremsstrahlung photons ● Scattered electrons are bent into an electron focal plane via the Tagger dipole magnet ● The position on the focal plane is used to determine the energy of the bremsstrahlung photon incident on the experimental target

15 ● Electrons scattering of a radiator produce bremsstrahlung photons ● Scattered electrons are bent into an electron focal plane via the Tagger dipole magnet ● The position on the focal plane is used to determine the energy of the bremsstrahlung photon incident on the experimental target

16 ● Electrons scattering of a radiator produce bremsstrahlung photons ● Scattered electrons are bent into an electron focal plane via the Tagger dipole magnet ● The position on the focal plane is used to determine the energy of the bremsstrahlung photon incident on the experimental target

17 Meson photoproduction with linearly and circularly polarized photons on polarized target FROzen Spin Target (butanol = C 4 H 9 OH)

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21 ● First step in the reaction identification is to select the π 0 from two photons ● The proton can be selected from the missing mass technique, and its subsequent scattering can be measured

22 Reconstruct the invariant mass of 2 gammas to get pi (and eta) Identify proton in missing mass

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25 ~200 MeV – ~800 MeV Mainz

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27 Shift workers need to pay particular attention to this


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