Nondiffractive feature of $\gamma N\to \rho^\pm N$ with $\rho$-meson electromagnetic multipole moments

Abstract

We investigate photoproduction of charged $\rho$ off the nucleon using $\rho(770)+\pi(140)$ Regge pole exchanges by considering the $\rho$-meson electromagnetic multipole moments. The significance of the Ward identity at the $\gamma\rho\rho$ vertex is emphasized for current conservation in the process. Given $\pi$ exchange with the well-known coupling constants for $\gamma\pi\rho$ and $\pi NN$, we analyze the role of the $\rho$ exchange in the $\gamma p\to \rho^+n$ and $\gamma n\to\rho^-p$ processes without model-dependences except for the magnetic moment $\mu_{\rho^\pm}=\pm2.01$ and electric quadrupole moment ${\cal Q}_{\rho^\pm}=\pm0.027$ fm$^2$ taken from theoretical estimates. The nondiffractive feature of both cross sections is reproduced with a rapid decrease beyond the resonance region by the dominance of $\pi$ exchange over the $\rho$\,. % Cross sections for differential and density matrix elements are presented to compare with existing data. The parity and photon polarization asymmetries are predicted to demonstrate the apparent roles of the $\rho$-meson electromagnetic multipole moments.