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G measurement at CB@MAMIKen Livingston, University of Glasgow, Scotland
Slides from:
Ken Livingston: Various talks at - http://nuclear.gla.ac.uk/~kl/talks/David Howdle (ex Glasgow) - /home/davidh/docs/presentationsStuart Fegan (ex Glasgow) - /home/stuartf/Presentations/Annika Theil (Bonn) - http://nuclear.gla.ac.uk/~baryons2013/Talks/Thiel.pdf
Also talks in this session on Baryons 2013:
http://nuclear.gla.ac.uk/Baryons2013/HadSpect1.html
Missing baryon resonances
Better to look at angular distributions and polarization observables.
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 Jp = 0-
Here's the nonet of uds ones:
+ N → m→ Y
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. B95 347 (1975).I. S. Barker, A. Donnachie, J. K. Storrow, Nucl. Phys. B95 347 (1975).
πN KY
recoil targ γ
γ targ recoil
☻☻☻
☻
linearly polarized photons
☻☻☻☻☻☻
longitudinally polarized target
☻☻☻☻☻☻
☻☻☻☻☻☻
transversely polarized target
circ polarized photons
☻☻☻☻☻☻
Complete, andover-determined
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
Polarization observables - a simple example,
Polarization observables - a simple example,
• Systematics of detector acceptance cancel out.
• “Only” need to know Plin, the degree of linear polarization.
dσdΩ
=σ0 {1−Plincos2ϕ+Pz (P linGsin2ϕ )}
d σdΩ
=σ0 {1−Plin cos2ϕ+P x (Pcirc F+PlinHsin 2ϕ )
+P y (T−PlinPcos2ϕ )+Pz (P circE+P linGsin2ϕ)+σ x
' [ PcircC x+PlinO xsin 2ϕ +P x (T x−Plin L z cos2ϕ)+P y (PlinC z sin 2ϕ−P circO z)+P z(Lx+PlinT z cos2ϕ )]
+σ y' [P+PlinTcos 2ϕ +P x (PcircG−PlinEsin 2ϕ)
+P y (−Plincos2ϕ )+P z(P linFsin 2ϕ+P circH ) ]+σ z
' [P circC z+PlinO z sin 2ϕ+P x (T z+PlinLxcos 2ϕ )+P y (−PlinC x sin 2ϕ−P circOz)+P z(Lz+PlinT xcos2ϕ )]}
'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:
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
dσdΩ
=σ0 {1−Plincos 2ϕ+Pz(PlinGsin2ϕ )}
● 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
● 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
E =E 0−E e
● 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
E =E 0−E e
● 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
E =E 0−E e
Meson photoproduction with linearly and circularly polarized photons on polarized target
FROzen Spin Target (butanol = C4H9OH)
γp→π 0 p
● First step in the reaction identification is to select the π0 from two photons
● The proton can be selected from the missing mass technique, and its subsequent scattering can be measured
Reconstruct the invariant mass of 2 gammas to get pi (and eta)
precon=p tagged+ ptarget− pπIdentify proton in missing mass
~200 MeV – ~800 MeV Mainz
Shift workers need to pay particular attention to this