ParityViolating Photoproduction of on the Delta Resonance

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Parity-Violating Photoproductionof ?- on the
Delta Resonance

• Jeff Martin
• Caltech

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Premise

• From a well-motivated model, the parity-violating
  asymmetry for pion photoproduction (Q2 0) might
  be as large as
• A? 5 ppm.

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Effects for G0

• Backgrounds
• Inelastic background at Forward Angles.
• Negative Pion Background at Backward Angles.
• Physics
• Inelastic Electron Scattering at Backward Angles.
• Photoproduction of Pions on the Delta Resonance.

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Negative Pion Background at Backward Angles

• At 799 MeV on LD2, expect a 10 background due to
  ?- misidentified by the Cerenkov counters as e-.
• Might the asymmetry of this background be large
  as well?
• For A? 5 ppm, get 0.5 ppm uncertainty.
• Quasi-elastic asymmetry is -72 ppm so who cares,
  right?
• No data for A?, just a model.
• (Indication of sign change with W2 from fwd angle
  data.)

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Physics

• Parity-violating Electro- and photo-excitation of
  resonances. For example, the ?-resonance.
• For Electro-excitation (finite Q2), goal is to
  extract axial structure of resonance.
• However, additional measurements will be required
  to relate those data to structure, because there
  are potentially large electroweak radiative
  corrections (Zhu et al, Phys. Rev. D).

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Physics for ?- at Backward Angles

• Electroweak radiative corrections generate a
  non-zero asymmetry at Q2 0. (Siegerts
  theorem)
• Can access this from inclusive ?- asymmetries at
  ? kinematics. (Zhu et al, Phys. Rev. Lett.)
• A? 5 ppm
• Related to physically motivated model which works
  very well for hyperon decay.
• Interpretable as d?- for 424 MeV only.
• Get a 12 g? extraction (theory range 100 g?)
• parasitic

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backward angle electronics schematic one octant
MT
CED
coincidence logic
scalers
BPO
MT
FPD
C
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mod for self-trigger
MT
CED
coincidence logic
scalers
MT
FPD
C
master trigger
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mod for pion asymmetries
MT
CED
coincidence logic
scalers
MT
FPD
C
master trigger
analog split, duplicate the whole thing.
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mod for pion asymmetries more realistic
possibility
MT
CED
coincidence logic
scalers
MT
FPD
C
master trigger
coincidence logic
scalers
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mod for pion asymmetries my favorite possibility
MT
CED
C coinc
coincidence logic
scalers
MT
FPD
C
master trigger
C coinc
scalers
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mod for pion asymmetries my really favorite
possibility
MT
CED
scalers
coincidence logic
MT
scalers
FPD
C
master trigger
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Electronics

• Duplicate of FPD-CED coincidence logic.
• Logic Fan out.
• Scalers.
• Extra French electronics.
• 200k? likely an overestimate.
• manpower requirements?
• scaler count (Paul) 57 modules installed now
• NA needs (Steve W.) 5.5/oct 4 22.