Single Arm Pair Production Cross Section at PrimEx

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(Single Arm) Pair Production Cross Section at
PrimEx

• Aram Teymurazyan
• University of Kentucky
• December 16, 2006
• PrimEx Collaboration Meeting

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Outline

• Event pre-selection
• Applied cuts
• Theoretical calculations
• Experimental results
• Summary
• And some more

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Pair Production in PrimEx

• Measured Quantities
• Energy of the incident photon
• Energies of each lepton
• Positions of each lepton

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Event Sample Selection

• Trigger HyCal_Total_Sum.Tagger_MOR
• Production phase only
• Miscellaneous checks
• At least 1 reconstructed photon
• 1 or more clusters in HyCal
• EVENTID bank present
• At least 1 photon associated with trigger

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Pair Production Events
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General Cuts

• 1)
• 2)
• 3)
• 4)
• 5)

Energy - Momentum conservation is not used in
current analysis
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General Cuts Efficiencies
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Pair Production Events
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State of the Art Calculation of ee-
CrossSection Considering PrimEx Resolutions

• Calculation by Alexandr Korchin
• Bethe-Heitler mechanism of pair production on the
  nucleus with screening effects due to atomic
  electrons and Coulomb distortion
• Pair production on atomic electrons considering
  excitation of all atomic states and correlation
  effects due to presence of other electrons and
  the nucleus
• Radiative corrections (of order ???) i)
  virtual-photon loops and ii) real-photon process
  like ? ??e e- ? ?
• Nuclear incoherent contribution ? p ?e e-
  p
• Nuclear coherent contribution (VCS) ? ???
  ??e e- ?

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State of the Art Calculation of ee-
CrossSection Considering PrimEx Resolutions
Calculation by Alexandr Korchin
12C
NIST values for stotal 351.8 mb _at_ 5.0 GeV and
352.0 mb _at_ 5.5 GeV
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Experimental Results
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Summary

• Measurement of pair production absolute cross
  section is a check of the absolute photon flux
  normalization.
• Analysis is ongoing.
• Agreement with theory at the level of 4.5 - 5
• Work in progress to reduce the systematic errors
  to 1 2 level

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p0 gains
Snake gains
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p0 gains
Snake gains
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p0 gains
Snake gains
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p0 gains
Snake gains
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