Photoproduction of mesons off nuclei

Photoproduction of mesons off nuclei, in particular the deuteron, helium-, and lithium-isotopes, but also heavier ones up to lead, has been studied at the tagged photon beams of the electron accelerators ELSA in Bonn and MAMI in Mainz with the Crystal Barrel/TAPS and Crystal Ball/TAPS experiments. The aim of these measurements was twofold: the study of meson production reactions off quasi-free neutrons and the study of meson-nucleus interactions. The measurements of quasi-free reactions off the neutron include the observation of a narrow structure, of as yet unknown nature, in the excitation function of eta production off the neutron. These experiments continue now with the measurement of single and double polarization observables. The main topics for the meson-nucleus interactions were the search for eta-mesic nuclei and the investigation of nuclear double-pion production reactions in view of possible in-medium modifications of the sigma-meson. (C) 2012 Elsevier B.V. All rights reserved.