1. Ralf W. Gothe Nucleon Transition Form Factors Beijing 2007 1 Transition Form Factors at JLab: The Evolution of Baryonic Degrees of Freedom Ralf W. Gothe University of South Carolina Workshop on Partial Wave Analysis and Dalitz Plot Analysis January 25-26, 2007 Beijing, China  Introduction  N  N Roper, and N N* Transitions  1  and 2  Production

2. Ralf W. Gothe Nucleon Transition Form Factors Beijing 2007 2 Physics Goals  Understand QCD in the full strong coupling regime  transition form factors to nucleon excited states allow us to study  relevant degrees-of-freedom  wave function and interaction of the constituents ? ! ? ! ? ? ! ! Models Quarks and Gluons as Quasiparticles ChPT Nucleon and Mesons pQCD q, g, qq 1.0 fm <

3. Ralf W. Gothe Nucleon Transition Form Factors Beijing 2007 3  Lattice QCD indicates a small oblate deformation of the  (1232) and that the pion cloud makes E 1+ /M 1+ more negative at small Q 2.  Data at low Q 2 needed to study effects of the pion cloud. Need data at low Q 2 N  (1232) Transition Form Factors

4. Ralf W. Gothe Nucleon Transition Form Factors Beijing 2007 4 C. Alexandrou et al., PRL, 94, 021601 (2005) R EM (%) R SM (%)  Quenched LQCD describes R EM within error bars, but shows discrepancies with R SM at low Q 2. Pion cloud effects? Low-Q 2 Mutipole Ratios for R EM, R SM Need data at low Q 2

5. Ralf W. Gothe Nucleon Transition Form Factors Beijing 2007 5 Low-Q 2 Mutipole Ratios for R EM, R SM C. Alexandrou et al., PRL, 94, 021601 (2005) preliminary  Quenched LQCD describes R EM within error bars, but shows discrepancies with R SM at low Q 2. Pion cloud effects?  Significant discrepancy between CLAS and Bates/MAMI results for R SM. C. Smith

6. Ralf W. Gothe Nucleon Transition Form Factors Beijing 2007 6  Data at even lower Q 2 are needed to investigate the pion cloud further.  Data at high Q 2 are needed to study the transition to pQCD. Preliminary Multipole Ratios R EM, R SM preliminary Need data at low Q 2

7. Ralf W. Gothe Nucleon Transition Form Factors Beijing 2007 7 Constituent Counting Rule  A 1/2  1/Q 3  A 3/2  1/Q 5  G M  1/Q 4 * S 11 Q 3 A 1/2 F 15 Q 5 A 3/2 P 11 Q 3 A 1/2 D 13 Q 5 A 3/2 F 15 Q 3 A 1/2 D 13 Q 3 A 1/2 Quark mass extrapolated to the chiral limit, where q is the momentum variable of the tree-level quark propagator using the Asquat action. Bowman et al. (LQCD) (GeV )

8. Ralf W. Gothe Nucleon Transition Form Factors Beijing 2007 8 N →  Multipole Ratios R EM, R SM  New trend towards pQCD behavior does not show up.  CLAS12 can measure R EM and R SM up to Q²~12 GeV².  R EM +1 M. Ungaro  G M 1/Q 4 *

9. Ralf W. Gothe Nucleon Transition Form Factors Beijing 2007 9  electro-production (UIM, DR) PDG estimation , 2  combined analysis  electro-production (UIM, DR) PDG estimation , 2  combined analysis K. Park (Data) I. Aznauryan (UIM) preliminary Roper Electro-Coupling Amplitudes A 1/2, S 1/2 nr |q 3  |q 3 +g  LF |q 3  |q 3 +qq  LF |q 3  nr |q 3  |q 3 +qq  |q 3 +g  LF |q 3  nr |q 3  |q 3 +g  LF |q 3  |q 3 +qq  nr |q 3  |q 3 +qq  |q 3 +g 

10. Ralf W. Gothe Nucleon Transition Form Factors Beijing 2007 10 preliminary S 11 (1535) Electro-Coupling Amplitudes A 1/2, S 1/2  electro-production (UIM, DR) PDG estimation S 11, D 13 combined analysis (SQTM) K. Park (Data) I. Aznauryan (UIM)   production (UIM, DR) nr |q 3  LF |q 3  nr |q 3  LF |q 3  nr |q 3 

11. Ralf W. Gothe Nucleon Transition Form Factors Beijing 2007 11 Energy-Dependence of  + Multipoles for P 11, S 11 imaginary partreal part Q 2 = 0 GeV 2 The study of some baryon resonances becomes easier at higher Q 2. Q 2 = 2.05 GeV 2 preliminary I. Aznauryan (UIM)

12. Ralf W. Gothe Nucleon Transition Form Factors Beijing 2007 12 Legendre Moments of Structure Functions Q 2 =2.05GeV 2 M 1- = 0 I. Aznauryan UIM fit The dominating final state multipole amplitude M 1- of the P 11 (1440) resonance is at high Q 2 are much more prominent than at small Q 2. K. Park preliminary CLAS

13. Ralf W. Gothe Nucleon Transition Form Factors Beijing 2007 13  invariant mass / MC phase space BES/BEPC, Phys. Rev. Lett. 97 (2006) BESBing-Song Zou and                   

14. Ralf W. Gothe Nucleon Transition Form Factors Beijing 2007 14 Fermion Helicity Conservation Helicity Conservation  ´ for q M >> Quark mass extrapolated to the chiral limit, where q is the momentum variable of the tree-level quark propagator using the Asquat action. Bowman et al. (LQCD) (GeV )

15. Ralf W. Gothe Nucleon Transition Form Factors Beijing 2007 15 preliminary D 13 (1520) Helicity Asymmetry A hel = A 1/2 2 – A 3/2 2 A 1/2 2 + A 3/2 2 A 1/2 A 3/2

16. Ralf W. Gothe Nucleon Transition Form Factors Beijing 2007 16 Nucleon Resonances in 2  Electroproduction p(e,e’)X p(e,e’p)   p(e,e’  + )n p(e,e’p  + )    2  channel is sensitive to N*’s heavier than 1.4 GeV  Provides complementary information to the 1  channel  Many higher lying N*’s decay preferably to  N final states Q 2 < 4.0 GeV 2 Trigger W in GeV

17. Ralf W. Gothe Nucleon Transition Form Factors Beijing 2007 17 direct 2  production Full calculations  p  -  ++ p+0p+0 pppp  p  - P ++ 33 (1600)  p  + F 0 15 (1685)  p  + D 13 (1520)  Combined fit of various single differential cross sections allowed to establish all significant mechanisms Isobar Model JM05 Contributing Mechanisms to     p → p  +  - JM05

18. Ralf W. Gothe Nucleon Transition Form Factors Beijing 2007 18 CLAS photo-production W(GeV) Background Resonances Full calculation no 3/2 +  N* contributions are much smaller than non-resonant mechanisms electro-production W(GeV) M. Ripani 3/2 + (1720) P ?3 (1720)  Full JM05 calculation with and without the 3/2 + (1720) state Resonances in     p → p  +  -

19. Ralf W. Gothe Nucleon Transition Form Factors Beijing 2007 19 Resonances CLAS Background Full JM05 no 3/2 + 3/2 + (1720) P ?3 (1720) Resonances and Background in     p → p  +   electro-production photo-production JM05

20. Ralf W. Gothe Nucleon Transition Form Factors Beijing 2007 20 Combined 1  -2  Analysis of CLAS Data  PDG at Q 2 =0  Previous world data  2  analysis  1  -2  combined at //// Q 2 =0.65 GeV 2  Many more examples: //// P 11 (1440), D 13 (1520), S 31 (1650), //// S 11 (1650), F 15 (1685), D 13 (1700), //// …  EBAC at JLab: //// Full coupled channel analysis D33(1700) P13(1720) preliminary JM05

21. Ralf W. Gothe Nucleon Transition Form Factors Beijing 2007 21 Combined 1  -2  Analysis of CLAS Data  PDG at Q 2 =0  2  analysis  1  -2  combined at Q 2 =0.65 GeV 2  Previous world data

22. Ralf W. Gothe Nucleon Transition Form Factors Beijing 2007 22  v p →  0 p 1  Data Description by N * Electro-Couplings of the Combined Analysis W=1.52 GeV Q 2 =0.65 GeV 2 W=1.68 GeV Q 2 =0.65 GeV 2 JM05CLAS

23. Ralf W. Gothe Nucleon Transition Form Factors Beijing 2007 23 W=1.54 GeV Q 2 =0.65 GeV 2 W=1.66 GeV Q 2 =0.65 GeV 2 The successful description of all 1  and 2  observables measured with CLAS at Q 2 =0.65 GeV 2 demonstrates the credibility of the N * background separation. 2  Data Description by N * Electro-Couplings of the Combined Analysis JM05CLAS

24. Ralf W. Gothe Nucleon Transition Form Factors Beijing 2007 24 preliminary Roper Electro-Coupling Amplitudes A 1/2, S 1/2  PDG at Q 2 =0  1  analysis (UIM)  1  -2  combined at ////Q 2 =0.65 GeV 2  Newest 2  analysis ////at low Q 2 (JM 06) CLAS

25. Ralf W. Gothe Nucleon Transition Form Factors Beijing 2007 25 Conclusion: Do Exclusive Electron Scattering Q 2 = 2.05 GeV 2 D 13 (1520)... to Learn QCD!