In - Medium properties of the ω meson in photon induced nuclear reactions

We discuss the possibility to study the in-medium changes of the properties of the ω meson in reactions on ordinary nuclei with elementary electromagnetic probes. We present a tree-level calculation of the elementary γp → ωp process which is extended to describe also the photoproduction of medium-modified ω mesons in nuclear matter. Using a semi-classical transport approach we obtain results for e + e − and π 0 γ photoproduction off heavy nuclei in the invariant mass range of the ρ and ω mesons. Both reactions are also studied experimentally and are presently being analyzed at accelerator facilities in Bonn and at Jefferson Lab. We show that the in-medium signals expected can be as large as those obtained in heavy-ion reactions.