Mesonic Decays of Spallation Hyperfragments and theΛ−NPotential-Well Depth

The short-range (≲10μ) mesonic hyperfragments produced by 1.1-BeV/c $K^{-}$ mesons and 2.3-BeV/c $K^{-}$ mesons in $K5\mathrm{}$ nuclear emulsions have been studied in order to estimate the potential-well depth of the $\Lambda -N$ interaction. Among more than 261 000 $K^{-}$ interactions examined, we have observed 70 mesonic decays, which consist of 41 heavy hyperfragments, 28 light hyperfragments, and one ${\pi }^{+}$ decay. Based on eight ${\pi }^{-}-p-r$ decays ($r$ indicates residual nucleus) in the lower region of a plot of binding energy versus mass, the upper limit of the potential-well depth of the $\Lambda -N$ interaction was estimated to be 27.7±0.6 MeV, assuming a square-well potential. A further elaboration of a more accurate estimate of the binding energy and consequently derived potential-well depth is discussed. The nonmesonic-to-${\pi }^{-}$-mesonic decay ratio of the heavy hyperfragments ($A=65\mathrm{}\pm 40$) was estimated to be 153±27. This value agrees fairly well with the theoretical ratio 130 at $A=100\mathrm{}$, estimated by Dalitz. The study of 28 light-hyperfragment events indicates that (75±22)% of the light hyperfragments originated in light nuclei (O, N, C).