We have observed a $K^-pp$-like structure in the $d(pi^+,K^+)$ reaction at 1.69 GeV/$c$. In this reaction $Lambda(1405)$ hyperon resonance is expected to be produced as a doorway to form the $K^-pp$ through the $Lambda^*prightarrow K^-pp$ process. Ho
wever, most of the produced $Lambda(1405)$s would escape from deuteron without secondary reactions. Therefore, coincidence of high-momentum ($>$ 250~MeV/$c$) proton(s) in large emission angles ($39^circ<theta_{lab.}<122^circ$) was requested to enhance the signal-to-background ratio. A broad enhancement in the proton coincidence spectra are observed around the missing-mass of 2.27 GeV/$c^2$, which corresponds to the $K^-pp$ binding energy of 95 $^{+18}_{-17}$ (stat.) $^{+30}_{-21}$ (syst.) MeV and the width of 162 $^{+87}_{-45}$ (stat.) $^{+66}_{-78}$ (syst.) MeV.
We are going to perform an inclusive spectroscopy experiment of eta mesic nuclei with the 12C(p,d) reaction to study in-medium properties of the eta meson. In nuclear medium, the eta meson mass may be reduced due to partial restoration of chiral symm
etry. In case of sufficiently large mass reduction and small absorption width of eta at normal nuclear density, peak structures of eta mesic states in 11C will be observed near the eta 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.
A novel method is proposed to measure eta(958) meson bound states in 11C nuclei by missing mass spectroscopy of the 12C(p,d) reaction near the eta production threshold. It is shown that peak structures will be observed experimentally in an inclusive
measurement in case that the in-medium eta mass reduction is sufficiently large and that the decay width of eta mesic states is narrow enough. Such a measurement will be feasible with the intense proton beam supplied by the SIS synchrotron at GSI combined with the good energy resolution of the fragment separator FRS.
