The first evidence of a deeply bound state of Xi--14N system

We have observed a deeply bound state of the --14 N system that decayed into twin singlehypernuclei in nuclear emulsion exposed in the E373 experiment at KEK-PS. The process is uniquely identified as -+ 14 N 10 Be + 5 He. We have measured the binding energy of the --14 N system, B -, to be 4.38 0.25 MeV, which is significantly larger than that of the --14 N 3D atomic state (0.17 MeV), if both single-hypernuclei are emitted in the ground state from at-rest capture of a -hyperon. If the 10 Be nucleus is produced in an excited state, the B -value mentioned above decreases by the excitation energy. Model calculations based on known values for 9 Be excited states have predicted two excited states in the bound region. Even in the case of 10 Be production in the highest excited state, the B -value is far from the 3D atomic level of the --14 N system by more than 3.7 standard deviations. The event provides the first clear evidence of a deeply bound state of the --14 N system by an attractive N interaction. . . . . .