The EDDA Experiment at COSY

1
The EDDA Experiment at COSY

• Polarized Elastic Proton Proton Scattering
• at TLab lt 2.5 GeV
• Why?
• What?
• Where?
• How?
• So?
• And now?

K. Oleg EyserUniversity of California,
Riverside The EDDA experiment was a small
collaboration between University of
Bonn,University of Hamburg, and
Forschungszentrum Jülich.
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Proton Proton Scattering
meson exchange, phenomenological, QCD inspired
Nuclear models
QCD
0 GeV
0.3 GeV
1 GeV
10 GeV
TLab
EDDA data 0.35-2.5 MeV
Total cross section Vector mesons
NN potentials One meson exchange Bonn, Paris,
Nijmegenand others
Regge Theory
good results from meson exchange models
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Observables

• Pauli principleParity conservationTime
  invariance
• 25 independent Observables
• Parametrization of M

Helicity amplitudesdescribed by nine independent
amplitudes
? 44256 possible Observables
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Observables
Scattering frame
Laboratory frame
y
?
z
x
scattering plane
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COSY seen from Space?
Jülich
Aachen
Cologne
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Cooler Synchrotron COSY
cavity
electron cooling
polarimeter
ANKE
COSY11
stochastic cooling
quadrupoles
polarimeter
COSY11
EDDA
exctraction
51010 unpolarized or 1.51010 polarized Protons
and DeuteronsTLab lt 2500 MeV
injection
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Depolarizing Resonances
Intrinsic resonances
working point qy
Imperfection resonances
Momentum (MeV/c)
Resonance stregth
beam polarization
Polarization at 3300 MeV/cP 75
Momentum (MeV/c)
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EDDA
Kinematic Correlation of Elastic Scattering
two different target systems
32 scintillator bars (parallel to beam)220
scintillator half-rings 464 scintillating
fibers 4160 scintillating fibers
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Light Splitting
scintillator bars
scintillator half-rings
compare light yield in adjacent
scintillators resolution five times better than
granularity
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EDDA
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Atomic Beam Target
Target holding field B lt 1 mT (Qx, Qy, and
Qz) Effective Polarization Q 70 Effective
Target thickness 1.81011 cm-2
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ABT
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Measurement
Excitation functions measurement during
acceleration MultiPass Technique thousands of
cycles Change polarization between cycles
PyPyPyPy Low cross section at high
momenta longer storage at flattop several
flattop momenta above 2300 MeV/c
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Event Selection

• Kinematic CorrelationVertex ReconstructionHit
  Pattern Outer/Inner Layers
• Detector Acceptance
• Vertex Cut
• Kinematic DeficitCompare CH2 / C fiber targets

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Asymmetries
Asymmetries left-right ? AN or Py
top-bottom ? Qx
diagonal strain ? ASS ANN
Yield
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Asymmetries
PyQx
PyQx
PyQx
PyQx
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Analyzing Power AN
Measured as in M. Almeier et al., Phys. Rev.
Lett. 85 (2000), 1819. Normalized with M.W.
McNaughton et al., Phys. Rev. C 41 (1990),
2809. Different momentum bins(Depolarizing
resonances)? Legendre-Polynomials Normalization
ofANN, ASS, and ASL Consistency in
doublepolarized measurement
Momentum (MeV/c)
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Systematic Uncertainties
Simulation False Asymmetries Direction of
Polarization Vectors Differences in P and P, Q
and Q Inelastic Background
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Excitation functions ANN
Momentum (MeV/c)
Momentum (MeV/c)
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Excitation functions ASS
Momentum (MeV/c)
Momentum (MeV/c)
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Excitation functions ASL
Momentum (MeV/c)
Momentum (MeV/c)
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Direct Reconstruction of Scattering Amplitude
Usually needs more than nine Observables Only few
energies 1300 MeV 16 1600 MeV 16 1800 MeV
21 2100 MeV 19 2400 MeV 17
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Summary

• Five observables of elastic pp scattering
• Statistical accuracy
• Excitation functions for unpolarized and single
  polarized scattering
• Excitation functions and fixed momentum for
  double polarized scattering
• 3 (343 120) data points
• F. Bauer et al.Phys. Rev. C 71 (2005), 045002.
• Internal consistency
• First data for ASS above 800 MeV
• Direct reconstruction of scattering amplitude
  for five energies
• Impact on new phase shift analyses
• Attempts of meson exchange model
  variationsincorporating phenomenological
  Regge-effects on vector mesonsO. Eyser, R.
  Machleidt, and W. ScobelEurop. Phys. J. A 22
  (2005), 105