The study of the interaction of hadrons, produced by elementary probes in a nucleus, with the surrounding nuclear medium can give insight into two important questions. First, at high energies, the production process, the time-scales connected with it and the prehadronic interactions can be studied by using the nuclear radius as a length-scale. We do this here by analyzing data from the EMC and HERMES experiements on nuclear attenuation. Second, at low energies the spectral function, and thus the selfenergy of the produced hadron, can be studied. Specifically, we analyze the CBELSA/TAPS data on $ω$ production in nuclei and discuss the importance of understanding in-medium effects both on the primary production cross section and the final state branching ratio. In both of these studies an excellent control of the final state interactions is essential.

Lecture given by U. Mosel at International School of Nuclear Physics: 29th Course: Quarks in Hadrons and Nuclei, Erice, Sicily, Italy, 16-24 Sep 2007