Excitation-energy spectra of 11 C nuclei near the η -meson production threshold have been measured by missing-mass spectroscopy using the 12 C(p,d) reaction. A carbon target has been irradiated with a 2.5 GeV proton beam supplied by the synchrotron SIS-18 at GSI to produce η meson bound states in 11 C nuclei. Deuterons emitted at 0 • in the reaction have been momentum-analyzed by the fragment separator (FRS) used as a high-resolution spectrometer. No distinct structure due to the formation of η -mesic states is observed although a high statistical sensitivity is achieved in the experimental spectra. Upper limits on the formation cross sections of η -mesic states are determined, and thereby a constraint imposed on the η -nucleus interaction is discussed.

We are going to perform an inclusive spectroscopy experiment of η ′ mesic nuclei with the 12 C(p,d) reaction to study in-medium properties of the η ′ meson. In nuclear medium, the η ′ meson mass may be reduced due to partial restoration of chiral symmetry. In case of sufficiently large mass reduction and small absorption width of η ′ at normal nuclear density, peak structures of η ′ mesic states in 11 C will be observed near the η ′ emission threshold even in an inclusive spectrum. The experiment will be carried out at GSI with proton beam supplied by SIS using FRS as a spectrometer. The detail of the experiment is described.