A Measurement of the Bethe-Heitler Pair Production Asymmetries and Positronium Production Letter...
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Transcript of A Measurement of the Bethe-Heitler Pair Production Asymmetries and Positronium Production Letter...
![Page 1: A Measurement of the Bethe-Heitler Pair Production Asymmetries and Positronium Production Letter of…](https://reader036.fdocuments.in/reader036/viewer/2022062505/5a4d1be67f8b9ab0599e2379/html5/thumbnails/1.jpg)
A Measurement of the Bethe-Heitler PairProduction Asymmetries and Positronium
ProductionLetter of Intent to the HIgS PAC
June 9, 2011
Spokespeople:G. Ron (HUJI)D. Higinbotham (JLab)B. Sawatzky (JLab)B. Norum (UVa)
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Bethe-Heitler Like Processes
& Interfere with
&
Which is the T-reverse for
1st order
Born
2nd order
BornCompton
DVCS
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So WHAT?• The interference manifests itself as an asymmetry in
the e+/e- pair. Either energy (equal angle) or angle (equal energy) should work.
• For example, to 1st order, the asymmetry in energy is:
Bethe-Heitler cross section is actually suppressed for E(e+)=E(e-) Beth-Heitler
Calculation for 12C
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These Asymmetries are NOT Small
Theory300-550MeV
On Lead12C on Rho
Resonance
But not well measuredBrodsky, et al. Phys Rev 173 (1968) 1011
Brodsky, et al. Phys Rev 187 (1969) 1899
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Asymmetry Physics• Measure Real part of Compton amplitude:
• At high energy measures the J=0 fixed pole.• Corrections to forward Compton amplitude
• (which is an input to GDH sum rule).
• Related to 2g in p(e,e’p), potentially easier to measure than the asymmetry in p(e±,e±p) (OLYMPUS/JLab 2-photon exchange).
• Analogous to the QCD pomeron/odderon interference.
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Positronium Physics• Sometimes the e+/e- pair is created in a bound
state (positronium).• Test production of positronium,• Disassociation analogous to pion diffractive
dissociation (Brodsky).• Positronium is relativistic, effectively on light cone.
• Light-front wavefunctions modern method for QCD/QED calculations.
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Courtesy of S. Brodsky
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Courtesy of S. Brodsky
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Courtesy of S. Brodsky
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Courtesy of S. Brodsky
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Courtesy of S. Brodsky
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Courtesy of S. Brodsky
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Experimental Method
• Positronium atoms disassociate on thin downstream foil.
• Saskatchewan Pair-Spectrometer magnet + VDC/MWDC.
• Beam time request: 21 Calendar days
• Bethe-Heitler and Positronium production using HIgS real photon beam on different targets (p for GDH, Heavy targets for higher cross section).
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MANPOWER &Future Plans
• Lead institutes: Hebrew U., JLab, UVa.• Theory support: Budjer Institute, SLAC.• Large interested collaboration.• Most of the experimental apparatus is already available now.
• Magnet, tracking chambers, DAQ exist now.
• Plans underway to develop target ladder design and necessary support structures.
• Continued work on simulation, optics, and background studies.
• Will return with full proposal at next HIgS PAC