Creation and decay of η-mesic nuclei

First experimental results on photoproduction of η-mesic nuclei are analyzed. In an experiment performed at the 1 GeV electron synchrotron of the Lebedev Physical Institute, correlated π+n pairs arising from the reaction γ+12C→N+η(A−1)→N+π++n+(A−2) and flying transversely to the photon beam have been observed. When the photon energy exceeds the η-meson production threshold, a distribution of the π+n pairs over their total energy is found to have a peak in the subthreshold region of the internal-conversion process ηp→π+n which signals about formation of η-mesic nuclei.