consideration is given in relation with a recent experiment.

Since $\eta$ is isoscalar, the $\pi N$ pairs produced in the subprocess (\[etaNpiN\]) have isospin $\frac12$ and hence the following isotopic contents \[for $\eta$-mesic nuclei with $A\gg 1$\]: (N) ={

[lll]{} 1/3 & [for]{} & \^+n,\
1/6 & [for]{} & \^0p,\
1/6 & [for]{} & \^0n,\
1/3 & [for]{} & \^-p.

. \[piN-modes\] From these, the channel $\pi^+n$ was chosen for detection in our experiment.

Previous searches for $\eta$-mesic nuclei {#previous-searches-for-eta-mesic-nuclei .unnumbered}
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Searches for $\eta$-mesic nuclei began very soon after their predictions [@haider86] followed by suggestions [@liu86; @kohno89; @lebedev89; @lebedev91; @kohno90] to seek these novel high-energy nuclear excitations in missing-mass experiments using the inclusive reactions $(\pi^+,p)$ and $(\gamma,p)$.

The first two experiments have been done along this line in 1988 at Brookhaven [@chrien88] and Los Alamos [@lieb88a; @lieb88b]. In both experiments, a $\pi^+$ beam was used and several targets (Li, C, O and Al) were examined. The inclusive $(\pi^+,p)$ reaction \^+ + A  \_(A-1) + p was studied in [@chrien88] with a magnetic spectrometer, whereas the Los Alamos experiment had also an additional $4\pi$ BGO crystal ball for detecting charged paticles ejected in the subprocess (\[etaNpiN\]) of $\eta$-mesic nuclei decays 