First observation of a nuclear <i>s</i>-state of a Ξ hypernucleus,15ΞC

Abstract

Bound systems of Xi(-)-N-14 are studied via Xi(-) capture at rest followed by emission of a twin single- Lambda hypernucleus in the emulsion detectors. Two events forming extremely deep Xi(-) bound states were obtained by analysis of a hybrid method in the E07 experiment at J-PARC and reanalysis of the E373 experiment at KEK-PS. The decay mode of one event was assigned as Xi(-) +N-14 -> He-5(Lambda) + He-5(Lambda) + He-4 + n. Since there are no excited states for daughter particles, the binding energy of the Xi(-) hyperon, B Xi(-), in the N-14 nucleus was uniquely determined to be 6.27 +/- 0.27MeV. Another Xi(-)-N-14 system via the decay Be-9(Lambda) +He-5(Lambda) + n brings a B Xi- value, 8.00 +/- 0.77MeV or 4.96 +/- 0.77MeV, where the two possible values of B Xi- correspond to the ground and the excited states of the daughter Be-9(Lambda) nucleus, respectively. Because the B(Xi-)values are larger than those of the previously reported events (KISO and IBUKI), which are both interpreted as the nuclear 1p state of the Xi(-)-N-14 system, these newevents give the first indication of the nuclear 1s state of the Xi hypernucleus, C-15(Xi).