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