M. Guidal, IPN Orsay

1. PHOTON 2011 Deep exclusive mesonelectroproduction: focus on vectormesons Discussions with/materialborrowedfrom: L. Favart, S. Kananov, P. Marage, C. Riedl, K. Park,… M. Guidal, IPN Orsay

3. ,

4. Reggetheory: Exchange of families of mesons in the t-channel

6. Reggetheory: Exchange of families of mesons in the t-channel M(s,t) ~ sa(t) wherea(t) (trajectory) is the relation between the spin and the (squared) mass of a family of particles stot~1/s x Im(M(s,t=0))->sa(0)-1 [optical theorem] M->sa(t) ds/dt~1/s2 x |M(s,t)|2->s2a(t)-2 ->[ea(t)lns(s)] stot ds/dt t s

7. ,

8. ,

9. , Q2>>

10. , Q2>> Q2>>

11. Some signatures of the (asymptotic) « hard » processes: Q2dependence: sL~1/Q6 sT~1/Q8 sL/sT~Q2 Wdependence: s~|xG(x)|2 (for gluon handbag) r/w/f/(J/Y)~9/1/2/8 (for gluon handbag) Ratioofyields: Saturationwith hard scale of aP(0), b, … SCHC : checkswithSDMEs

12. H1, ZEUS , Q2>> Q2>>

13. HERMES H1, ZEUS H1, ZEUS CLAS COMPASS , Q2>> Q2>>

14. HERMES H1, ZEUS H1, ZEUS CLAS COMPASS , + « older » data from: E665, NMC, Cornell,… Q2>> Q2>>

15. HERMES H1, ZEUS H1, ZEUS CLAS COMPASS , + « older » data from: E665, NMC, Cornell,… Q2>> Q2>>

16. W dependence SteepeningWslopeas a function of Q2 indicates« hard » regime (reflects gluon distribution in the proton)

17. W dependence SteepeningWslopeas a function of Q2 indicates« hard » regime (reflects gluon distribution in the proton) Twoways to set a « hard » scale: *large Q2 *mass of producedVM Universality : r, f at large Q2+M2similar to J/y

18. aP(0) increases from “soft” (~1.1) to “hard” (~1.3) as a function of scalem2=(Q2+MV2)/4. Hardening of W distributions withm2

19. Q2 dependence sL~1/Q6=>Fit with s~1/(Q2+MV2)n Q2 >0 GeV2=>n=2+/- 0.01 r: J/y: Q2>0 GeV2=>n=2.486 +/- 0.08 +/-0.068 Q2 >10 GeV2=>n=2.5+/- 0.02 (S. Kananov) Q2dependenceisdampedatlowQ2and steepensat large Q2 Approachinghandbagprediction of n=6 (Q2 not asymptotic, fixedW vs fixedxB, stot vs sL, Q2evolution of G(x)…)

20. t dependence b decreases from “soft” (~10 GeV-2) to “hard”(~4-5 GeV-2) as a function of scalem2=(Q2+MV2)/4

21. Ratios r/w/f/(J/Y) ~ 9/1/2/8

22. sL/sT (almost) compatible withhandbagprediction (dampingat large Q2)

23. SDMEs HERMES H1 (almost) no SCHC violation

24. At high energy (W>5 GeV), the general features of the kinematics dependences and of the SDMEs are relatively/qualitatively well understood Good indications that the “hard”/pQCD regime is dominant for m2=(Q2+MV2)/4 ~ 3-5 GeV2. Data are relatively well described by GPD/handbag approaches

25. HERMES H1, ZEUS H1, ZEUS CLAS COMPASS , Q2>> Q2>>

26. JLab& CLAS in Hall B Duty cycle 100% Emax6 GeV Pmax80%

27. Exclusive r0, w, f & r+ electroproduction on the proton @ CLAS6 } e1-b (1999) K. Lukashin et al., Phys.Rev.C63:065205,2001 (f@4.2 GeV) C. Hadjidakis et al., Phys.Lett.B605:256-264,2005 (r0@4.2 GeV) } L. Morand et al., Eur.Phys.J.A24:445-458,2005 (w@5.75GeV) e1-6 (2001-2002) J. Santoro et al., Phys.Rev.C78:025210,2008 (f@5.75GeV) S. Morrow et al., Eur.Phys.J.A39:5-31,2009(r0@5.75GeV) } e1-dvcs (2005) A. Fradi, Orsay Univ. PhD thesis (r+@5.75 GeV)

28. e1-6 experiment (Ee =5.75 GeV) (October 2001 – January 2002)

29. Mm(epp+ X) Mm(epX) ep  ep p+(p-) p+ e (p-) p

30. sr(g*p  pr0) vs W

31. r+ r0 w f C. Hadjidakis et al., Phys.Lett.B605:256-264,2005 (r0@4.2 GeV) S. Morrow et al., Eur.Phys.J.A39:5-31,2009(r0@5.75GeV) L. Morand et al., Eur.Phys.J.A24:445-458,2005 (w@5.75GeV) J. Santoro et al., Phys.Rev.C78:025210,2008 (f@5.75GeV) K. Lukashin, Phys.Rev.C63:065205,2001 (f@4.2 GeV) A. Fradi, Orsay Univ. PhD thesis, 2009 (r+@5.75GeV)

32. ep->epf ( K+[K-]) GK sL fL

33. + VGG GPD model

34. VGG GPD model GK GPD model

35. t ERBL DGLAP x +1 -1 -ξ 0 ξ Quark distribution W~1/x γ, π, ρ, ω… -2ξ x+ξ x-ξ ~ ~ H, H, E, E (x,ξ,t) “ERBL” region “DGLAP” region Antiquark distribution q q Distributionamplitude

36. DDs + “meson exchange” DDs w/o “meson exchange” (VGG) “meson exchange”

37. Comparison with r0, w, f

38. VMs (r0,w,f) the only exclusive process [with DVCS] measured over a W range of 2 orders of magnitude (sL,T, ds/dt, SDMEs,…) At high energy (W>5 GeV), transition from “soft” to “hard” (m2 scale) physics relatively well understood (further work needed for precision understanding/extractions) At low energy (W<5 GeV), large failure of “hard” approach. This is not understood. Is the GPD/handbag approach setting at much larger Q2 or is the widely used GPD parametrisation in the valence region completely wrong ? A lot of new data expected soon from JLab@11GeV, COMPASS (transv. target), HERA new analysis,…

39. GPDs/handbag ??? GPDs/handbag W~1/x

41. gN->Np

42. sr(g*p  pr0) vs W

43. Angular distribution analysis,cos qcm Relying on SCHC (exp. check to the ~25% level)

44. Longitudinal cross section sL(g*Lp prL0)

45. Interpretation “a la Regge” : Laget model g*p  pr0 g*p  pw Free parameters: *Hadronic coupling constants:gMNN *Mass scales of EM FFs:(1+Q2/L2)-2 g*p  pf

46. sL (g*Lp prL0) s,f2 Pomeron Regge/Laget

47. Exclusive r+ electroproduction

48. Channel selection g g p+ e (p-) (p) e p e’ [n]r+e’ [n]p+p0 e’ [n] p+ g g EC One event in CLAS IC

49. Invariant mass IM(p+p0) Total cross section s (Q2,xB) r+ PRELIMINARY

50. Regge “hadronic” approach r+ r+ + p+ r+ n n GPD “partonic” approach H , E r+L