Wide - Angle Compton Scattering pi-0 photo-production in 12 GeV era

1. Wide-Angle Compton Scatteringpi-0 photo-production in 12 GeV era p -> p B. Wojtsekhowski Outline • WACS and other Hard Exclusive Reactions. • WACS physics and GPDs. Theoretical framework. • Experimental technique. How will we do these experiments?

2. WACS: Introduction Part of JLab program of Hard Exclusive Reactions • Elastic Form Factors: GMP,GEP,GMN,GEN,FF • WACS: high t in two-photon reaction • Deeply Virtual Compton Scattering (DVCS) • Deeply Virtual Meson Production Common issues: • Handbag diagram • Interplay between hard and soft processes • Threshold for onset of asymptotic regime • Role of hadron helicity flip

3. Unification of nucleon structure within GPDs DIS Form factors DVMP N -> N* GPDs WACS DVCS x t 

4. GPDs and form factors of WACS GA at w 

5. Cross section of Wide-Angle Compton Scattering • Three-quark mechanism dominates at “asymptopia” 2 hard gluon exchanges. Constituent counting rules: d/dt = f(CM)/s6 “complicated” polarization observables • Single-quark mechanism “handbag” diagram dominates. Form factors: “simple” polarization observables

6. Polarization observables of WACSin GPDs handbag calculations photon helicity and PL of the recoil proton hard soft LO: LO + RT :

7. Mixed e/gbeam –> productivity 1300 higherthan “clean” g 1013 photons/sec Two body kinematics ep events RCS events “pion” events

8. Results of 6 GeV experiment PRL 94, 242001 (2005)

9. Form factors of RCS and partonic structure of the nucleon

10. Very clean data Calibration to elastic e-p polarization data taken parallel to WACS Expected small systematic uncertainty Result is favor to CQM Polarization transfer in Wide Angle Compton Scattering ep

11. ALL- initial state polarization correlation parameter D.Day, BW ALL=KLL in QCD ALL- KLL diff. as a measure of quark spin flip ~ mq/Eg

12. RCS perspective with 12 GeV Jlab beam

13. Neutron Compton Scattering • Need to know incident photon energy -> • Limited luminosity • Post-target tagging! • For s = 7, t = 4 GeV2 120 hours beam time per data point

14. BIGCAL Calorimeter Joint Hall A + C project consists of 1744 blocks front face - 1.2 m x 2.2 m resolution ∆E ~ 6%/√E σposition ~ 1 cm Ready for experiments

15. Summary of the physics plan • Proton WACS – cross section with 11 GeV beam, ALL&KLL • Neutron WACS – cross section • Pi-0 from the proton – cross section, KLL, ALL • Pi-0 from the neutron – cross section • Strange form-factor at large Q2 ( ep->e’p, both in calorimeters)

16. Calorimeter parameters • Calorimeter size – match of Super Bigbite Spectrometer – 20 cm long target, 70 msr ( horizontal +/- 5 degree, vertical +/- 12 degree), energy resolution <10%, angular/position resolution of 1-2 mrad, two cluster resolution < 10 mrad, need at least 2-3 m between magnet and the calorimeter. Radiation hardness!! • For example: at distance 5-10 meters from the target: BigCal 1.2x 2.2 m, 6% energy resolution, 1 cm coordinate resolution, RMol ~ 3.7 cm, limit for radiation dose of 1 krad. What need to be done: a) Study of radiation hardness and resolution at high luminosity b) Budget and used equipment: PMT, DAQ, HV, crystals