1. BINP '06 1 Nucleon Form Factors Strike Back R. Baldini Ferroli, Centro Fermi/INFN-LNF 2 e + e - collisions from  to  BINP 27 feb. 2006

2. BINP '06 2 Outline Space-like Q 2 (<0) :G E /G M measurement at JLAB Time-like Q 2 (>0) : main features and previous data BaBar e + e -  p p: cross section and Form Factors The e + e -  n n puzzle Conclusions

3. BINP '06 3 space-like time-like

4. BINP '06 4 Space-like G E /G M JLab measurement

5. BINP '06 5 Renewed interest in nucleon FFRenewed interest in nucleon FF by space-like G E /G M JLab measurement of recoil polarization Crossing zero at |Q2| ~ 10 GeV2 ? Rosenbluth Polarization

6. BINP '06 6 T.Massam, A.Zichichi (1966)

7. BINP '06 7 F.Iachello, A.D.Jackson, A.Lande (1973)

8. BINP '06 8 Two photons exchange contribution Blunden-Melnitchouk-Tjon - PRL 91,142304 (2003)

9. BINP '06 9 The explanation of this discrepancy should be in the radiative corrections not properly taken into account,  exchange contribution invalidating Born approximation in the angular distribution, while recoil polarizations ratio is less affected. Minimal time-like expectations: – |G E /G M |  1 asymptotically –  EM   asymptotically – G E /G M >>1 just above threshold – Substantial N polarization and asymmetry

10. BINP '06 10 Nucleon Time-like Form Factors

11. BINP '06 11 Cross section e + e -  p p

12. BINP '06 12 “C” : correction to Born approximation for Coulomb interaction at threshold. Important in understanding threshold behaviour. Distorted wave approximation in final state interaction (Landau-Lifchitz book): C ~ 1/  at threshold   0 finite

13. BINP '06 13 G E,G M features due to crossing + analyticity:G E,G M features due to crossing + analyticity: –In principle continuity from ep  ep to (space-like) (time-like) –Cuts above inelastic thresh: space  time-like real  complex –A(hel tot =0): analytical continuation of space-like spin flip G M A(hel tot =1): analytical continuation of “ non spin flip G E – G M = F 1 +F 2, G E = F 1 +  F 2 F 1,F 2 analyticity  at threshold S wave only  Relative phase measurement needed to get F 1, F 2 (from p polarization measurement/polarized beams) G M (2m p ) = G E (2m p )

14. BINP '06 14 Previous dataPrevious data Poor statistics/angular acceptance  |G M |=|G E | Steep at threshold from (p spin alignement at rest?)

15. BINP '06 15 Space-like  |G M | 2 +  |G E | 2  |G M | dominant at high w Space-likeSpace-like Early PQCD scaling: F 1 ~ G M ~  2 (w)/w 4 |G time-like (w 2 )| ~ |G space-like (-w 2 )| (but within a factor of 2)

16. BINP '06 16 BaBar e + e -  p p new results by means of Initial State Radiation

17. BINP '06 17 Analyzed 232 fb -1 I.S.R. simulation: –20° <   * < 160 ° (H.Czyz et al, Eur. Phys. J. C 35(2004)527) –Soft photons (M.Caffo et al, N. C. 110A(1997)515) Event selection: –Tracks within DCH and DIRC acceptance –Very tight proton selector (~ 30% good events loss) –pp  kinematical fit E  resolution not reproduced  3C fit  ~ 18 ±1 % 4025 selected events

18. BINP '06 18 G E (Q 2 )/G M (Q 2 ) in the Time-like region

19. BINP '06 19 BaBar |G E /G M | measurements vs previous ones and dispersion relation prediction (yellow) based on JLab space-like G E /G M and analyticity only Hep:-ph/0507085

20. BINP '06 20 Cross section and Form Factors

21. BINP '06 21 “Dressed” cross section“Dressed” cross section Negative stepat w ~ 2.2 GeV (!?) Negative step at w ~ 2.2 GeV (!?) Speculations: Strong resonances interference ? A new (inelastic) amplitude: opening of baryonic excitations?

22. BINP '06 22 Negative step Negative step at w ~ 2.9 GeV (!?) More difficult to interpretate !

23. BINP '06 23 Near threshold dressed cross section Reasonable agreement with previous measurements

24. BINP '06 24 Very near threshold Form FactorVery near threshold Form Factor Steep behaviour at threshold confirmed Steep behaviour at threshold also seen in other processes

25. BINP '06 25 Steep behaviour at threshold also seen in other processes, with different quantum numbers BES BaBar Corrected for phase space

26. BINP '06 26 Possible interpretationsPossible interpretations : 1.Tail of a narrow resonance below threshold (Baryonium ?) 2.Dominance of  exchange in pp final state int. 3.Underestimation of the Coulomb correction factor Possible tests for “baryonium”: –Narrow vector meson, with vanishing e + e - coupling, on top of a large  recurrence: dip in some cross section - e + e -  nn (no Coulomb correction)

27. BINP '06 27 Dips have indeed been seen in diffractive photoproduction of 6  by E687:

28. BINP '06 28

29. BINP '06 29 e + e -  Hadrons

30. BINP '06 30 The e + e -  n n puzzle

31. BINP '06 31 Present Neutron Time-like Data One measurement only: FENICE at ADONE ~ 100 events at 1.9 < Q < 2.55 GeV R n =  (e+e-  n n) /  (e + e -  p p) > 1 Hints for G E << G M (sharp thresh. behavior ?)

32. BINP '06 32 Some expectations for  (e+e-  n n) /  (e + e -  p p):Some expectations for  (e+e-  n n) /  (e + e -  p p): –pQCD0.25 –pQCD ~ (q d /q u ) 2 = 0.25 –Soliton models  1 Future perspectivesFuture perspectives –Very difficult, if not impossible, by means of ISR –p p  n n, n D  e + e - (p) at GSI ? –Diffractive Photoproduction  A  (n n)/(p p) A ? –VEPP2000, BEPC2, DAFNE2 ?

33. BINP '06 33 Cross sections: nn versus pp

34. BINP '06 34 Slight evidence for |G E n | << |G M n |

35. BINP '06 35 Neutron magnetic time-like FF

36. BINP '06 36 Conclusions and perspectives Space-like FF: unexpected G E behavior –Looking for a zero @ Q 2 ~ -10 GeV 2 –Compare e - p  e - p vs e + p  e + p Time-like p FF: – G E /G M >1 just above threshold – steep behavior at threshold – steps @ Q 2 ~ 5 and 8 GeV 2 Looking for p polarization and asymmetry New measurement of Neutron FF VEPP2000, DAFNE2,  /Charm, SuperB

37. BINP '06 37 Early successfull predictions T.Massam, A.Zichichi, NC 43(’66)1137: (J.Ellis, M.Karliner NewJP 4(’02)4) VDM + SU 3 + extended source R ~ 1/M N + first time-like experimental constraint F i N ~ 1/(1-Q 2 /M N 2 )  V g V f V /(1- Q 2 /m v 2 ) F i N ~ 1/(1-Q 2 /M N 2 )  V g V f V /(1- Q 2 /m v 2 ) ~ Skyrme model F.Iachello, A.D.Jackson,A.Lande, PL 43B(’73)191, F.Iachello, A.D.Jackson,A.Lande, PL 43B(’73)191, (M.Gari, W.Krumpelmann, PL 173B(’86)10) VDM + extended source R ~ 1/M N + Hard core (~pQCD) Both models predict  (e + e -  n n)  (e + e -  p p)

38. BINP '06 38 I.S.R. Main Features

39. BINP '06 39 I.S.R. versus c.m. Advantages: All energies at the same time  less systematics c.m. boost   ≠ 0 +  w ~ 1 MeV at threshold Drawbacks: L  invariant mass bin  w More background

40. BINP '06 40 Histograms show contribution from G M (dashed) G E (dash-dotted) Transition from sin 2  G E dominant) to 1+cos 2  (G M “ ) cos  p distributions from threshold up to 3 GeV 1.877-1.950 2.4-3.0

41. BINP '06 41 1.92 GeV 1.4 ± 0.5 APPLE: (LEAR) 2.05 0.7 ± 0.3 FENICE + DM2: 2.1 5.4 ± 4.1 (Adone) (DCI) E835: 3.5 0.7 ± 0.6 (FNAL)

42. BINP '06 42 B +  K + p p B o  D o p p

43. BINP '06 43 FENICE n n typical event

44. BINP '06 44 Space+Time-like data: it might be possible to solve the dispersion relation equations to get the FF in between (unphysical region) A model-independent attempt to solve the integral equation by means of a regularization procedure Testing the method by means of F , assumed like pp: astonishing agreement Application to G M N (previous data, BaBar ignored): –  (770),  ‘(1600) and threshold : OK –Simplest VDM: G M P (   pp) ~  P F(    ) : OK –But   ~ 350 MeV : (?)