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 ${\mu }_{{\rho }^{\pm }}=\pm 2.01$ and electric quadrupole moment ${\mathcal{Q}}_{{\rho }^{\pm }}=\pm 0.027$ 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.

Comments: 5 pages, 8 figures