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A partial wave analysis of pion photo- and electroproduction with MAID

A partial wave analysis of pion photo- and electroproduction with MAID. introduction a dynamical approach to meson electroproduction the unitary isobar model MAID comparison of multipoles between MAID and SAID resonance parameters and transition form factors summary and outlook.

preston-byrd
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A partial wave analysis of pion photo- and electroproduction with MAID

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  1. A partial wave analysisof pion photo- and electroproductionwith MAID • introduction • a dynamical approach to meson electroproduction • the unitary isobar model MAID • comparison of multipoles between MAID and SAID • resonance parameters and transition form factors • summary and outlook

  2. models and techniques of different groups

  3. why partial wave analysis • learn about nucleon resonancesin particular about their e.m. structuretransition moments, form factors GE, GM, GC • study threshold amplitudesto compare with ChPT • obtain cross sections and amplitudesover a wide range of energies for dispersive studies- sum rules: GDH, FFR, etc.- two-photon reactions: Compton, VCS, SSA, etc. • find missing or exotic resonances

  4. K-matrix approximation

  5. MAID the Mainz-Dubna Unitary Isobar Model K-matrix unitarization unitarization phase determined by the Watson theorem, below 2p threshold relaxed above 2p threshold • the Resonances in MAID are dressed resonances

  6. currently about 20 000 photoproduction points in our data base

  7. Results on photo- and electroproduction of nucleon resonances

  8. threshold p0 photoproduction simple background (non-unitarized) imag. part real part

  9. threshold p0 photoproduction unitarized background (K-matrix approx.) imag. part real part

  10. threshold p0 photoproduction phenomenological loop contribution added imag. part real part loop contribution

  11. Unitarity at Eta Threshold Data: GDH collaboration, Mainz, 2006 (PRC 74) Mainz 2006 Mainz 2006

  12. (MAID uses SAID pion nucleon analysis)

  13. comparison between MAID and SAID

  14. comparison between MAID and SAID

  15. electroproduction analysis of nucleon resonances with MAID

  16. currently about 140 000 electroproduction points in our data base

  17. Delta P33(1232) and D13(1520) resonances

  18. Roper P11(1440) and S11(1535) resonances

  19. Roper S11(1535)

  20. summary on MAID techniques • field theoretical background in tree approximation • pion loop contributions in K-matrix approximationguarantees a unitarized background • non-Born bg terms account for missing loop contributionsa) empirical terms near threshold for E0+, S0+b) PS-PV mixing at higher energies in E0+, S0+, M1-, S1- • nucleon resonance excitation in s-channel Breit-Wigner parametrization(MAID strategy: as few as necessary, in Maid07: 13 res.) • Q2 dependent transition form factorslead to superglobal energy- and Q2 dependent solutions

  21. Outlook • how can we improve the background in isobar models? • fixed-t disp. relations: changes only real parts of multipoles • parametrize p-loop effects: can also change imaginary parts of multipoles but without predictive power • apply the new Dubna-Taipei-Mainz dynamical model DMT2007 • most important candidates that need to be improved: • Real E0+ Im E0+ • Real S0+ Im S0+ • Real M1+ • Real S1+ • RealM2-

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