Coherent photoproduction of multiple mesons off the deuteron

The coherent photoproduction of ηπ0-pairs, ωπ0-pairs, π0π0π0-triplets and ηπ0π0-triplets have been measured for the first time at a tagged photon beam of the Bonn ELSA electron accelerator with the combined Crystal Barrel - TAPS electromagnetic calorimeter for incident photon energies up to 2.5 GeV. A clear identification of the coherent signal is possible by detecting the mesons in coincidence with the recoil deuterons. This coherent productions may lead to novel approaches for the search of mesic nuclei. For example, in the reaction γd → ηπ0d, the η-mesons are emitted with very small kinetic energies, so that it can be used as a tool to study the much discussed η-nucleon, η-deuteron interaction at small relative momenta. Furthermore, the inclusive measurement (i.e. without detecting the recoil deuterons) of the coherent photoproduction of multiple mesons is also possible. This development might open a new possibility for the observation of in medium effects in heavy nuclei.