1 / 25

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

naomi
Download Presentation

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

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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!

More Related