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In-medium Properties of Hadrons - an Overview

An overview is given over recent results on in-medium properties of hadrons, obtained in experiments with photon, proton and deuteron beams at ANKE, CBELSA/TAPS, Crystal Ball, HADES, and BigRIPS. These experiments focus on identifying spectral in-medium modifications of hadrons, frequently discussed in the context of a partial restoration of chiral symmetry at finite nuclear densities. Three experimental approaches are presented: the measurement of the transparency ratio, the meson line shape analysis, and the search for meson-nucleus bound states. Results for $ω,ϕ, $ and $ η^\prime$ mesons indicate a broadening in the nuclear medium. Corresponding inelastic in-medium meson-nucleon cross sections have been extracted. Evidence for an in-medium mass shift has not been reported. Further information on the meson-nucleus interaction is derived from a spectroscopy of meson-nucleus bound states. A critical comparison of the results with theoretical predictions is presented.