A consistent dynamical model for pion photoproduction

A. MARIANO

PHYSICS LETTERS B

Elsevier

Año: 2007 vol. 647 p. 253 - 261

0370-2693

Pion-photoproduction amplitude is calculated within a consistent isobar model already used to fix the Delta++(1232 MeV) parameters in pion–nucleon scattering and bremsstrahlung. This amplitude is expressed in terms of (physical) on-shell quantities and off-shell contributions comingfrom final state interactions. These latter are isolated in principal value integrals on the non-polar part of the pion–nucleon K-matrix, being the main effect of them to dress the bare form factors present in the gammaN --> Delta vertex. First, we hide the dressing into effective form factors getting at k^2_gamma = 0, GM = 2.97 +/- 0.08 and GE = 0.055 +/- 0.010 in full consistence with recent chiral effective field theory calculations. Then, different models to regularize the mentioned integrals are analyzed. We choose those better describing the non-resonant multipoles, in order to get model independent results for the resonant ones. Finally, we try to predict the bare form factors getting G0M = 1.69 +/- 0.02 and G0E = 0.028 +/- 0.008, which are consistent with recent lattice quark calculations and other more sophisticated dynamical models.