Search for $\eta '$ mesic nuclei with (p,d) reaction at GSI

We report a spectroscopy experiment of the ($p$,$d$) reaction searching for $\eta '$ mesic nuclei. The large mass of the $\eta '$ meson is explained by the axial anomaly effect associated with spontaneous breaking of chiral symmetry. In nuclear medium, due to restoration of chiral symmetry, mass of the $\eta '$ meson may be reduced, and $\eta '$ meson-nucleus bound states may exist. To search for such $\eta '$ mesic nuclei, we plan an inclusive measurement of the ${}^{12}$C ($p$,$d$) reaction around the $\eta '$ emission threshold using a 2.5 GeV proton beam at GSI. For momentum analysis of the ejectile deuteron, the FRS (Fragment Separator) is used as a spectrometer. The first experiment will be carried out in July-August 2014. The status of the experiment and preliminary results will be reported.