Photoproduction of vector mesons off nucleons near threshold

We propose a simple meson-exchange model of the photoproduction of $\rho$- and $\omega$-mesons off protons near threshold ($E_\gamma$ less than 2 GeV). This model provides a good description of the available data and implies a large $\rho$-nucleon interaction in the scalar channel ($\sigma$-exchange). We use this phenomenological interaction to estimate the leading contribution to the self-energy of $\rho$-mesons in matter. The implications of our calculation for experimental studies of the $\rho$-meson mass in nuclei are discussed.