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Transition Form Factors at JLab: The Evolution of Baryonic Degrees of Freedom

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 D, N Roper, and N N* Transitions

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Transition Form Factors at JLab: The Evolution of Baryonic Degrees of Freedom

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  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 D, N Roper, and N N* Transitions 1p and 2p Production

  2. Physics Goals < 0.1fm 0.1 – 1.0 fm > 1.0 fm < • 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 ? ? ! ! pQCD ChPT Nucleon and Mesons Models Quarks and Gluons as Quasiparticles ! ! ? ? q, g, qq

  3. N D(1232) Transition Form Factors Need data at low Q2 • Lattice QCD indicates a small oblate deformation of the D(1232) and that the pion cloud makes E1+ /M1+ more negative at small Q2. • Data at low Q2 needed to study effects of the pion cloud.

  4. Need data at low Q2 Low-Q2 Mutipole Ratios for REM, RSM C. Alexandrou et al., PRL, 94, 021601 (2005) REM (%) RSM (%) • Quenched LQCD describes REMwithin error bars, but shows discrepancies with RSM at low Q2 . Pion cloud effects?

  5. Low-Q2 Mutipole Ratios for REM, RSM C. Smith C. Alexandrou et al., PRL, 94, 021601 (2005) preliminary • Quenched LQCD describes REMwithin error bars, but shows discrepancies with RSM at low Q2 . Pion cloud effects? • Significant discrepancy between CLAS and Bates/MAMI results for RSM.

  6. Need data at low Q2 Preliminary Multipole RatiosREM, RSM preliminary • Data at even lower Q2 are needed to investigate the pion cloud further. • Data at high Q2 are needed to study the transition to pQCD.

  7. S11 Q3A1/2 (GeV) Bowman et al. (LQCD) F15 Q5A3/2 P11 Q3A1/2 D13 Q5A3/2 F15 Q3A1/2 • GMa 1/Q4 * D13 Q3A1/2 Quark mass extrapolated to the chiral limit, where q is the momentum variable of the tree-level quark propagator using the Asquat action. Constituent Counting Rule • A1/2a 1/Q3 • A3/2a 1/Q5

  8. N → D Multipole RatiosREM ,RSM • New trend towards pQCD behavior does not show up. • CLAS12 can measure REM and RSM up to Q²~12 GeV². • REM +1 • GM 1/Q4 M. Ungaro *

  9. nr |q3> nr |q3> LF |q3> LF |q3> |q3+qq> |q3+qq> |q3+qq> |q3+qq> LF |q3> |q3+g> |q3+g> LF |q3> |q3+g> |q3+g> nr |q3> nr |q3> nr |q3> nr |q3> PDG estimation pelectro-production (UIM, DR) K. Park (Data) I. Aznauryan (UIM) PDG estimation p,2pcombined analysis pelectro-production (UIM, DR) p,2pcombined analysis Roper Electro-Coupling Amplitudes A1/2, S1/2 preliminary

  10. LF |q3> LF |q3> nr |q3> LF |q3> nr |q3> LF |q3> nr |q3> nr |q3> hproduction (UIM, DR) PDG estimation pelectro-production (UIM, DR) K. Park (Data) I. Aznauryan (UIM) S11, D13 combined analysis (SQTM) S11(1535) Electro-Coupling Amplitudes A1/2, S1/2 preliminary

  11. Energy-Dependence of p+ Multipoles for P11, S11 Q2 = 2.05 GeV2 The study of some baryon resonances becomes easier at higher Q2. preliminary I. Aznauryan (UIM) Q2 = 0 GeV2 real part imaginary part

  12. M1- = 0 I. Aznauryan UIM fit M1- = 0 Legendre Moments of Structure Functions CLAS K. Park Q2=2.05GeV2 preliminary The dominating final state multipole amplitude M1- of the P11(1440) resonance is at high Q2 are much more prominent than at small Q2.

  13. and BES Bing-Song Zou • N*(1440): M = 1358 m 17 • G= 179 m 56 N*(2050): M = 2068 +15-40 • G= 165 m 42 pN invariant mass / MC phase space BES/BEPC, Phys. Rev. Lett. 97 (2006)

  14. > > Bowman et al. (LQCD) (GeV) Quark mass extrapolated to the chiral limit, where q is the momentum variable of the tree-level quark propagator using the Asquat action. Fermion Helicity Conservation Helicity Conservation l=l´ for qM

  15. A1/2 preliminary A3/2 A1/22 – A3/22 Ahel = A1/22 + A3/22 D13(1520) Helicity Asymmetry

  16. Nucleon Resonances in 2p Electroproduction Q2 < 4.0GeV2 Trigger p(e,e’)X • 2p channel is sensitive to N*’s heavier than 1.4 GeV • Provides complementary information to the 1p channel • Many higher lying N*’s decay preferably to ppN final states p(e,e’p)p0 p(e,e’p+)n p(e,e’pp+)p- W in GeV

  17. Full calculations gpp-D++ gpp+D0 gpp+D13(1520) gprp gpp-P++33(1600) gpp+F015(1685) direct2p production Contributing Mechanisms tog(*)p → pp+p- JM05 Isobar Model JM05 • Combined fit of various single differential cross sections allowed to establish all significant mechanisms

  18. M. Ripani electro-production 3/2+(1720) P?3(1720) W(GeV) • Full JM05 calculation with and without the 3/2+(1720) state Resonances ing(*)p → pp+p- CLAS photo-production Full calculation no 3/2+ Background Resonances W(GeV) • N* contributions are much smaller than non-resonant mechanisms

  19. Resonances and Background ing(*)p → pp+p- no 3/2+ electro-production photo-production CLAS JM05 Background Resonances Full JM05 3/2+(1720) P?3(1720)

  20. D33(1700) D33(1700) P13(1720) P13(1720) Combined 1p-2p Analysis of CLAS Data JM05 • PDG at Q2=0 • Previous world data • 2p analysis • 1p-2p combined at ////Q2=0.65 GeV2 • Many more examples:////P11(1440), D13(1520), S31(1650), ////S11(1650), F15(1685), D13(1700),////… • EBAC at JLab:////Full coupled channel analysis preliminary

  21. Combined 1p-2p Analysis of CLAS Data • PDG at Q2=0 • 2p analysis • 1p-2p combined at Q2=0.65 GeV2 • Previous world data

  22. 1p Data Description by N* Electro-Couplings of the Combined Analysis W=1.52 GeV Q2=0.65 GeV2 CLAS W=1.68 GeV Q2=0.65 GeV2 JM05 gvp → p0p

  23. 2p Data Description by N* Electro-Couplings of the Combined Analysis W=1.54 GeV Q2=0.65 GeV2 CLAS W=1.66 GeV Q2=0.65 GeV2 JM05 The successful description of all 1p and 2p observables measured with CLAS at Q2=0.65 GeV2 demonstrates the credibility of the N* background separation.

  24. Roper Electro-Coupling Amplitudes A1/2, S1/2 CLAS • PDG at Q2=0 • 1p analysis (UIM) • 1p-2p combined at////Q2=0.65 GeV2 • Newest 2p analysis ////at low Q2(JM 06) preliminary

  25. D13(1520) Q2 = 2.05 GeV2 D13(1520) Conclusion: Do Exclusive Electron Scattering ... to Learn QCD!

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