Single photo and electroproduction of pions at EBAC@JLAB

Abstract

Within the Excited Baryon Analysis Center we have performed a dynamical coupled-channels analysis of the available $p(e,e^{\prime }\pi )N$ data in the region of $W\le$ 1.6 GeV and $Q^2\le$ 1.45 (GeV/c)${}^2$. The channels included are ${\gamma }^{\ast }N$, $\pi N$, $\eta N$, and $\pi \pi N$ which has $\pi \Delta$, $\rho N$, and $\sigma N$ components. With the hadronic parameters of the model determined in our previous investigations of $\pi N\to \pi N$ reaction, we have found that the available data in the considered $W\le$ 1.6 GeV region can be fitted well by only adjusting the bare ${\gamma }^{\ast }N\to N^{\ast }$ helicity amplitudes for the lowest $N^{\ast }$ states in $P_{33}$, $P_{11}$, $S_{11}$ and $D_{13}$ partial waves. The meson cloud effect, as required by the unitarity conditions, on the ${\gamma }^{\ast }N\to N^{\ast }$ form factors are examined.

Comments: 6 pages, invited talk at NSTAR 2009, Beijing (China), 2009, to appear in the proceedings