1. A Measurement of the Bethe-Heitler Pair Production Asymmetries and Positronium Production Letter of Intent to the HI  S PAC June 9, 2011 Spokespeople: G. Ron (HUJI) D. Higinbotham (JLab) B. Sawatzky (JLab) B. Norum (UVa)

2. Bethe-Heitler Like Processes &Interfere with & Which is the T-reverse for 1 st order Born 2 nd order Born Compton DVCS

3. So WHAT? The interference manifests itself as an asymmetry in the e + /e - pair. Either energy (equal angle) or angle (equal energy) should work.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 1 st order, the asymmetry in energy is:For example, to 1 st order, the asymmetry in energy is: Bethe-Heitler cross section is actually suppressed for E(e + )=E(e - ) Beth-Heitler Calculation for 12 C

4. Theory 300-550MeV On Lead 12C on Rho Resonance But not well measured Brodsky, et al. Phys Rev 173 (1968) 1011 Brodsky, et al. Phys Rev 187 (1969) 1899

5. Asymmetry Physics Measure Real part of Compton amplitude:Measure Real part of Compton amplitude: At high energy measures the J=0 fixed pole.At high energy measures the J=0 fixed pole. Corrections to forward Compton amplitudeCorrections to forward Compton amplitude (which is an input to GDH sum rule).(which is an input to GDH sum rule). Related to 2  in p(e,e’p), potentially easier to measure than the asymmetry in p(e ±,e ± p) (OLYMPUS/JLab 2-photon exchange).Related to 2  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.Analogous to the QCD pomeron/odderon interference.

6. Positronium Physics Sometimes the e+/e- pair is created in a bound state (positronium).Sometimes the e+/e- pair is created in a bound state (positronium). Test production of positronium,Test production of positronium, Disassociation analogous to pion diffractive dissociation (Brodsky).Disassociation analogous to pion diffractive dissociation (Brodsky). Positronium is relativistic, effectively on light cone.Positronium is relativistic, effectively on light cone. Light-front wavefunctions modern method for QCD/QED calculations.Light-front wavefunctions modern method for QCD/QED calculations.

7. Courtesy of S. Brodsky

13. Experimental Method Positronium atoms disassociate on thin downstream foil.Positronium atoms disassociate on thin downstream foil. Saskatchewan Pair- Spectrometer magnet + VDC/MWDC.Saskatchewan Pair- Spectrometer magnet + VDC/MWDC. Beam time request: 21 Calendar daysBeam time request: 21 Calendar days Bethe-Heitler and Positronium production using HI  S real photon beam on different targets (p for GDH, Heavy targets for higher cross section).Bethe-Heitler and Positronium production using HI  S real photon beam on different targets (p for GDH, Heavy targets for higher cross section).

14. MANPOWER & Future Plans Lead institutes: Hebrew U., JLab, UVa.Lead institutes: Hebrew U., JLab, UVa. Theory support: Budjer Institute, SLAC.Theory support: Budjer Institute, SLAC. Large interested collaboration.Large interested collaboration. Most of the experimental apparatus is already available now.Most of the experimental apparatus is already available now. Magnet, tracking chambers, DAQ exist now.Magnet, tracking chambers, DAQ exist now. Plans underway to develop target ladder design and necessary support structures.Plans underway to develop target ladder design and necessary support structures. Continued work on simulation, optics, and background studies.Continued work on simulation, optics, and background studies. Will return with full proposal at next HI  S PAC Will return with full proposal at next HI  S PAC