High-t Exclusive Reactions With Real Photons

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 ntot -2= 1+3+2+3-2=7 Transition? at s between 3 and 6 GeV2 , t between 1 and 2.2 GeV2 Data from 1970’s

6. JLab counts! (s1/2>2.5) Hall A, Zhu et alPhys. Rev. C 71, 044603 (2005)

7. More opportunities to check scaling JLab range of s 11 - 21 GeV2

8. Challenges to 8 Kroll

9.  N N Puzzle • Why does constituent counting work so well for  N→ N , but NOT for  N → N ? • Kinematics are similar-another graph?  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 nH • 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 DVCS RCS GPD DIS –parton dist Elastic Form Factor

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

15. Danagoulian et al Hall A • d/dt ~1/s8.0 +/- 0.02 constituent counting: 1/s6 Solid Handbag –Kroll Dashed Handbag -Miller \ 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. KLL is not ALL =ALL (Kroll) non-vanishing constituent quark mass causes KLL≠ALL

18. Summary of RCS • RCS has direct connection to DIS and elastic form factors • Constituent counting not reached yet • KLL≠ ALL 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 high -t low -t ()     N N high -t  t=2/m2  Hadronic regime has long lived  N N How to see  go away?

22. N → N Transparency vs. A,  =10GeV /A /A /A =10 GeV =5 GeV = 5 GeV -(t-t0) GeV2 -(t-t0) GeV2

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

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

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