1. High-t Exclusive Reactions With Real Photons Gerald A. Miller, UW

2. Outline Constituent counting rules- challenge and opportunity (Real) Compton scattering Transition from hadrons to quarks, gluons using nuclear targets (with M. Strikman) Exclusive reactions to test exotic nature of mesons (with M. Strikman)

3. 1973 Remarkable success –quarks are real

4. Constituent Counting Rules - Assumptions Physical mesons, baryons – s wave bound states, finite wave function at zero separation Large s, -t Disconnected Landshoff graphs unimportant Remarkable success

5. Large angle pion production Transition? at s between 3 and 6 GeV 2, t between 1 and 2.2 GeV 2 Data from 1970’s n tot -2= 1+3+2+3-2=7

6. JLab counts! (s 1/2 >2.5) Hall A, Zhu et al Phys. Rev. C 71, 044603 (2005)

7. More opportunities to check scaling JLab range of s 11 - 21 GeV 2

8. Challenges to 8 Kroll

9. Puzzle Why does constituent counting work so well for  N→ N  but NOT for  N →  N ? Kinematics are similar-another graph?   N N s -8

10. Modern Interest? AdS/CFT correspondence provides a set of solvable, non-perturbative field theories scale (conformal) invariant High momentum transfer exclusive reactions obey constituent counting rules. There are NO partons, Polchinski and Strassler Conformal dimension plays role of n H Theorists playground- learn how to calculate Renewed interest in constituent counting If constituent counting ruled out at high s,t – these insights are not valid 50 million high- energy theorists wrong

11. Summary of Constituent Counting Constituent counting is important Relates to AdS/CFT When occurring, provides a tool (see below) puzzle –pion photoproduction vs RCS

12. Real Compton Scattering RCS  p elastic scattering simplest process? many diagrams –samples below Handbag pQCD

13. RCS > reaction physics-GPDs GPD Elastic Form Factor DIS – parton dist DVCS RCS

14. RCS > reaction physics-GPDs GPD Elastic Form Factor DIS – parton dist RCS 00 Pretty much all

15. d  /dt ~1/s 8.0 +/- 0.02 constituent counting: 1/s 6 Solid Handbag –Kroll Dashed Handbag -Miller \ Danagoulian et al Hall A wave function, transverse quark momentum constituent quark mass

16. Hamilton et al Hall A CQM- Miller GPD-Huang, Kroll Morii Regge –Cano Laget ASY, COZ- pQCD- Brooks Dixon with different dist. amps

17. K LL is not A LL =A LL (Kroll) non-vanishing constituent quark mass causes K LL ≠A LL

18. Summary of RCS RCS has direct connection to DIS and elastic form factors Constituent counting not reached yet K LL ≠ A LL a new test of models

19. Constituent counting and the hadron-quark transition Remainder of talk Assume constituent counting holds at high enough s, -t (50 million high energy theorists can’t be wrong) Quark degrees of freedom dominate How to exploit

20. Hadron-Quark Transition  N πN   N N  high -t low -t   )  high -t  N N  t  =2 /m  2 Hadronic regime has long lived  How to see  go away ?

22.  N →  N Transparency vs. A, /A  10GeV  5 GeV -(t-t 0 ) GeV 2 /A  10 GeV  5 GeV

23. nuclear RCS to understand puzzle  N Nin nuclei, A dependence ? Not proportional to A 

24. Can use (A, t) - dependence of quasielastic  N →  N, to find Hadron-Quark Transition use  N →  Summary of High –t exclusive in nuclei

25. Constituent Counting and Exotics production at large s, angle Exotic meson X: n X =n  +1 (or 2) n tot = 9,10 High s, angle ratio:  N →  N, n tot =9

26. Summary of summaries Constituent counting CC is important Relates to AdS/CFT When occurring, provides a tool RCS DIS, elastic form factors Constituent counting not yet reached in RCS K LL ≠ A LL new test of models in RCS Can use (A, t) - dependence of quasielastic  N →  N, to find Hadron-Quark Transition, understand RCS Can use CC to find or verify exotics

27. Spares follow

28. Kroll 2007