An understanding of the spectrum and structure of the excited nucleon (N*) states is a fundamental challenge in the hadron physics. However, the N* states couple strongly to the meson-baryon continuum states and appear only as resonance states in π N and γ N reactions. Such strong couplings cannot be neglected in extracting information on the N* states from the data and giving physical interpretations. To address this issue, an extensive research program of extracting the N* information from world data of πN, γN, N(e,e') reactions is being conducted at the Excited Baryon Analysis Center (EBAC) of Jefferson Lab. The analysis is based on a dynamical coupled-channels (DCC) model developed in [1], within which the couplings among relevant meson-baryon channels are fully taken into account. In this seminar, I will review the EBAC-DCC analysis and present new aspects of the dynamical origin of the P11 nucleon resonances recently extracted from the analysis.

[1] A. Matsuyama, T. Sato, T.-S. H. Lee, Phys. Rep. 439, 193 (2007).

ANL Physics Division Seminar Schedule