Dynamical study of the Δ excitation in N(e,e′π) reactions -: art. no. 055201

The dynamical model developed by us [Phys. Rev. C 54, 2660 (1996)] has been applied to investigate the pion electroproduction reactions on the nucleon. It is found that the model can describe to a very large extent the recent data of p(e,e' pi (0)). reaction from Jefferson Laboratory and MIT-Bates. The extracted magnetic dipole (MI), electric dipole (E2), and Coulomb (C2) strengths of the gammaN-->Delta transition are presented. It is found that the C2/M1 ratio drops significantly with Q(2) and reaches about - 14% at Q(2) = 4 (GeV/c)(2), while the E2/M1 ratio remains close to the value similar to -3% at the Q(2) = 0 photon point. The determined M1 transition form factor drops faster than the usual dipole form factor of the proton. We also find that the nonresonant interactions can dress the gammaN --> Delta vertex to enhance strongly its strength at low Q(2), but much less at high Q(2) Predictions are presented for future experimental tests. Possible developments of the model are discussed.