Scattering of vector mesons off nucleons Original Research Article

We construct a relativistic and unitary approach to ‘high’ energy pion– and photon–nucleon reactions taking the πN, πΔ, ρN, ωN, ηN, KΛ, KΣ final states into account. Our scheme dynamically generates the s- and d-wave nucleon resonances N(1535), N(1650) and N(1520) and isobar resonances Δ(1620) and Δ(1700) in terms of quasi-local interaction vertices. The description of photon-induced processes is based on a generalized vector-meson dominance assumption which directly relates the electromagnetic quasi-local four-point interaction vertices to the corresponding vertices involving the ρ and ω fields. We obtain a satisfactory description of the elastic and inelastic pion– and photon–nucleon scattering data in the channels considered. The resulting s-wave ρ– and ω–nucleon scattering amplitudes are presented. Using these amplitudes we compute the leading density modification of the ρ and ω energy distributions in nuclear matter. We find a repulsive energy shift for the ω meson at small nuclear density but predict considerable strength in resonance–hole like ω-meson modes. Compared to previous calculations our result for the ρ-meson spectral function shows a significantly smaller in-medium effect. This reflects a fairly small coupling strength of the N(1520) resonance to the ρN channel.