Polarimeter 11 01 2010
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Contents
Preliminary evaluation of the options for polarimetry with nuclear pair production
References
- A photon beam polarimeter based on nuclear e+e- pair production in an amorphous target
- Experimental study of photon beam polarimeter based on nuclear e+e- pair production in an amorphous target
Considered Options
- Put a an e+e- detector in the beamline before the PS magnet allowing for ~2.5 m lever arm.
- Pros
- No magnetic field distortions.
- Cons
- Short lever arm.
- Detector is exposed to the photon beam.
- Pros
- Put a an e+e- detector in the beamline after the PS magnet allowing for ~4.5 m lever arm, no B-field.
- Pros
- Relatively longer lever arm.
- Cons
- Detector is exposed to the photon beam.
- Small distortion effects due to incomplete degaussing of the PS magnet.
- Pros
- Put separate e+ and e- detectors off the beamline after the PS magnet allowing for ~4.5 m lever arm, small T m.
- Pros
- Relatively longer lever arm.
- Detector not exposed to the beam
- Cons
- Magnetic field mixes different momenta and angles at the same position of the detector.
- Distortion due to the fringe fields.
- Pros
Simulations
- Use GEANT4 based program to simulate the basic features. The geometry may have conflicts with the current Hall D beamline configuration.
- Symmetric Pairs are simulated with GeV, and θ=6 x 10-5 rad in the lab.
- All pairs pass through a converter which is 6μm thick, positioned at z=0.
- 0.3 T constant dipole magnetic field in vertical direction starting at z=2.3 m with the magnetic length of 40 cm
- Vacuum window 100μm at z=4.45 m (5cm before the detector)
- Some sort of detector made of silicon, 300μm thick. Consists of two pieces, left and right, for positrons and electrons.
- The positions of the hit e+ or e- hits are calculated as the energy-weighed average of individually hits within certain window.
- Simulated 40K symmetric pairs with the fixed θ-angle and momentum in the lab, and uniformly distributed in φ.