Nondiffractive feature of $γN\to ρ^\pm N$ with $ρ$-meson electromagnetic multipole moments

Abstract

We investigate photoproduction of charged $ρ$ off the nucleon using $ρ(770)+π(140)$ Regge pole exchanges by considering the $ρ$-meson electromagnetic multipole moments. The significance of the Ward identity at the $γρρ$ vertex is emphasized for current conservation in the process. Given $π$ exchange with the well-known coupling constants for $γπρ$ and $πNN$, we analyze the role of the $ρ$ exchange in the $γp\to ρ^+n$ and $γn\toρ^-p$ processes without model-dependences except for the magnetic moment $μ_{ρ^\pm}=\pm2.01$ and electric quadrupole moment ${\cal Q}_{ρ^\pm}=\pm0.027$ 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 $π$ exchange over the $ρ$\,. % 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 $ρ$-meson electromagnetic multipole moments.