"", a -meson nuclear bound state, observed in He( reactions

Hashimoto, Tadashi   ; Tanida, Kiyoshi   ; 67 of others*

We observed a distinct peak in the invariant mass spectrum of , well below , , the mass threshold of the to be bound to two protons. By selecting a relatively large momentum-transfer region MeV/, one can clearly separate the peak from the quasi-free process, followed by the non-resonant absorption by the non-resonant absorption by the two spectator-nucleons . We found that the simplest fit to the observed peak gives us a Breit-Wignerpole position at MeV having a width MeV, and the -wave Gaussian reaction form-factor parameter MeV/, as a new form of the nuclear bound system with strangeness -"".