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

models and techniques of different groups

why partial wave analysis learn about nucleon resonances in particular about their e.m. structure transition moments, form factors G E, G M, G C study threshold amplitudes to compare with ChPT obtain cross sections and amplitudes over 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

K-matrix approximation

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

currently about photoproduction points in our data base

Resultson photo- and electroproduction of nucleon resonances

threshold   photoproduction simple background (non-unitarized) imag. part real part

threshold   photoproduction unitarized background (K-matrix approx.) imag. part real part

threshold   photoproduction phenomenological loop contribution added imag. part real part loop contribution

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

(MAID uses SAID pion nucleon analysis)

comparison between MAID and SAID

electroproduction analysis of nucleon resonances with MAID

currently about electroproduction points in our data base

Delta P 33 (1232) and D 13 (1520) resonances

Roper P 11 (1440) and S 11 (1535) resonances

RoperS11(1535)

summary on MAID techniques  field theoretical background in tree approximation  pion loop contributions in K-matrix approximation guarantees a unitarized background  non-Born bg terms account for missing loop contributions a) empirical terms near threshold for E 0+, S 0+ b) PS-PV mixing at higher energies in E 0+, S 0+, M 1-, S 1-  nucleon resonance excitation in s-channel Breit-Wigner parametrization (MAID strategy: as few as necessary, in Maid07: 13 res.)  Q 2 dependent transition form factors lead to superglobal energy- and Q 2 dependent solutions

how can we improve the background in isobar models? 1)fixed-t disp. relations: changes only real parts of multipoles 2)parametrize  -loop effects: can also change imaginary parts of multipoles but without predictive power 3) apply the new Dubna-Taipei-Mainz dynamical model DMT2007 most important candidates that need to be improved: Real E0+Im E0+ RealS0+Im S0+ RealM1+ RealS1+ RealM2- Outlook