Momentum dependence of the imaginary part of the ω- and η^'-nucleus optical potential

The attenuation of ω- and η^'-mesons in cold nuclear matter has been studied in photonuclear reactions on ¹²C and ⁹³Nb for photon energies of 1.2-2.9 GeV, using the tagged photon beam at the ELSA accelerator. ω- and η^'-mesons have been identified via the ω → π⁰γ and η^' → π⁰π⁰η decays, respectively, registered with the CBELSA/TAPS detector system. The momentum dependence of the transparency ratio has been determined for both mesons. Results on the in-medium width of the ω- and η^'-meson and the corresponding meson-nucleon inelastic cross sections will be compared to previous experimental data and recent theoretical predictions. The energy dependence of the imaginary part of the ω- and η^'-nucleus optical potential has been extracted. The higher statistics and finer binning of the present data allow an extrapolation to the production threshold. Corresponding values for the imaginary part of the optical potential will be discussed in view of recent determinations of the ω and η^' scattering lengths.