Dynamical study of the D excitation in N „ e , e 8 p ... reactions

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 ,e8p) reaction from Jefferson Laboratory and MIT-Bates. The extracted magnetic dipole (M1), electric dipole (E2), and Coulomb (C2) strengths of the gN→D transition are presented. It is found that the C2/M1 ratio drops significantly with Q and reaches about 214% at Q54 (GeV/c), while the E2/M1 ratio remains close to the value ;23% at the Q50 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 gN→D vertex to enhance strongly its strength at low Q, but much less at high Q. Predictions are presented for future experimental tests. Possible developments of the model are discussed.