Excitation on the nucleon resonances in pion photo- and electroproduction

por Dr. Sabit S. Kamalov (Laboratory of Theoretical Physics, JINR, Dubna, Russia)

jueves 21 sept. 2000 11:30 → 12:30 Europe/Madrid

Sala Seminarios IFIC (Edf. Institutos de Investigación)

Using recently developed Unitary Isobar and Dynamical models nucleon resonances in the first, second and third resonance regions are analysed. Within Dynamical Model we find that the bare $\Delta(1232)$ resonance is almost spherical and the electric E2 and Coulomb C2 quadrupole excitations are nearly saturated by pion cloud contribution. From the recent $p(e,e'p)\pi^0$ at $Q^2=$ 2.8 and 4.0 (GeV/c)$^2$ we demonstrate that contribution from the electric E2 excitations, starting from a small and negative value at real photon point, shows a clear tendency to cross zero, and change sign with increasing $Q^2$. This is a possible indication of a slow approach toward the pQCD region.