A search for deeply bound kaonic nuclear states

We have measured proton and neutron energy spectra by means of time-of-flight (TOF) from 4He(Kstopped−,p/n) reactions (KEK PS E471 experiment). In the proton spectrum, a clear mono-energetic peak was observed under semi-inclusive condition, which was assigned to the formation of a strange tribaryon S0(3115) with isospin T=1. The mass and width of the state were deduced to be 3117.7−2.0+3.8(syst.)±0.9(stat.)MeV/c2 and <21.6MeV/c2, respectively, and its main decay mode was ΣNN. In the neutron spectrum, a mono-energetic peak was found as the result of a detailed analysis, which was assigned to the formation of another kind of strange tribaryon S+(3140). The mass and width of the state were deduced to be 3140.5−0.8+3.0(syst.)±2.3(stat.)MeV/c2 and <21.6MeV/c2, respectively, and its main decay mode was Σ±NN. The isospin of the state is assigned to be 0. The results are compared with recent theoretical calculations.