Abstract
Different experimental approaches to determine the meson-nucleus optical potential are discussed. The experiments have been performed with the Crystal Barrel/TAPS detector system at the ELSA accelerator in Bonn and the Crystal Ball/TAPS at the MAMI accelerator in Mainz. Experimental results about the real and imaginary part of the η′- and ω-nucleus optical potential are presented. The imaginary part of the meson-nucleus optical potential is determined from the in-medium width of the meson by the measurement of the transparency ratio. Information on the real part of the optical potential is deduced from measurements of the excitation function and momentum distribution which are sensitive to the sign and depth of the potential. The results are discussed and compared to theoretical predictions. The data for both mesons are consistent with a weakly attractive potential. The formation and population of ω-nucleus and η′-nucleus bound states is additionally discussed.
Highlights
The meson-nucleus interaction can be described by an optical potential U = V + iW, comprising a real and an imaginary part
The experiments have been performed at the ELSA facility in Bonn using the Crystal Barrel (CB) and the TAPS detector system and Crystall Ball and the TAPS detector systems at the MAMI-C accelerator in Mainz
The transparency ratio for ω and η mesons has been measured in photo production experiments for several nuclei in a series of measurements with the CBELSA/TAPS detector system in Bonn
Summary
Nambu-Jona-Lasinio-model which expect almost no change in the η mass as a function of nuclear density [11]. Further model calculations claim mass shift of the η of -80, -40 MeV at normal nuclear density [12, 13]. It is obvious that these contradictory theoretical predictions call for an experimental clarification
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