# Presentation: 469963

## The EDDA Experiment at COSY

- Polarized Elastic Proton Proton Scattering
- at TLab < 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.

## Proton Proton Scattering

- 0 GeV

- 0.3 GeV

- 1 GeV

- 10 GeV

- Total cross section
- Vector mesons

- TLab

- Regge Theory

- Nuclear models

- QCD

- NN potentials:
- One meson exchange
- Bonn, Paris, Nijmegenand others

- meson exchange, phenomenological, QCD inspired

- good results from meson exchange models

- EDDA data: 0.35-2.5 MeV

## Observables

-   44=256 possible Observables

- Pauli principleParity conservationTime invariance
-   25 independent Observables
- Parametrization of **M**

- Helicity amplitudesdescribed by nine independent amplitudes

## Observables

- Scattering frame

- Laboratory frame

*x*

*y*

*z*

- scattering plane

**

## COSY seen from Space?

**J****ülich**

**Aachen**

**Cologne**

## Cooler Synchrotron COSY

- quadrupoles

- polarimeter

- COSY11

- cavity

- electron cooling

- ANKE

- stochastic cooling

- polarimeter

- COSY11

- EDDA

- exctraction

- injection

- 5·1010 unpolarized or 1.5·1010 polarized Protons and DeuteronsTLab < 2500 MeV

## Depolarizing Resonances

- Momentum (MeV/c)

- Momentum (MeV/c)

- working point qy

- Intrinsic resonances

- beam polarization

- Imperfection resonances

- Polarization at 3300 MeV/cP ≈ 75%

- Resonance stregth

## EDDA

- Kinematic Correlation of Elastic Scattering

- 32 scintillator bars (parallel to beam)2∙20 scintillator half-rings + 4∙64 scintillating fibers
- 4∙160 scintillating fibers

- two different target systems

## Light Splitting

- scintillator bars

- scintillator half-rings

- compare light yield in adjacent scintillators
- resolution: five times better than granularity

## EDDA

## Atomic Beam Target

- Target holding field B < 1 mT (±Qx, ± Qy, and ±Qz)
- Effective Polarization Q ≈ 70%
- Effective Target thickness 1.8·1011 cm-2

## ABT

## Measurement

- Excitation functions: measurement during acceleration
***MultiPass Technique***:  thousands of cycles
- Change polarization between cycles ...+Py...–Py...+Py...–Py...
- Low cross section at high momenta: longer storage at flattop several flattop momenta above 2300 MeV/c

## Event Selection

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

## Asymmetries

_**Asymmetries**_
- left-right  AN or Py

- top-bottom  Qx

- diagonal strain  ASS – ANN

- Yield:

## Asymmetries

- +Py+Qx

- +Py–Qx

- –Py+Qx

- –Py–Qx

## 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)

## Systematic Uncertainties

- Simulation:
- False Asymmetries
- Direction of Polarization Vectors
- Differences in +P and –P, +Q and –Q
- Inelastic Background

## Excitation functions ANN

- Momentum (MeV/c)

- Momentum (MeV/c)

## Excitation functions ASS

- Momentum (MeV/c)

- Momentum (MeV/c)

## Excitation functions ASL

- Momentum (MeV/c)

- Momentum (MeV/c)

## 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

## Summary

- Five observables of elastic p+p 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