Neutron-rich hypernuclei: Λ6H and beyond

Recent experimental evidence presented by the FINUDA Collaboration for a particle-stable H-6(Lambda) has stirred renewed interest in charting domains of particle-stable neutron-rich Lambda hypernuclei, particularly for unbound nuclear cores. We have studied within a shell-model approach several neutron-rich Lambda hypernuclei in the nuclear p shell that could be formed in (pi(-), K+) or in (K-, pi(+)) reactions on stable nuclear targets. Hypernuclear shell-model input is taken from a theoretically inspired successful fit of gamma-ray transitions in p-shell Lambda hypernuclei which includes also Lambda N <-> Sigma N coupling (Lambda Sigma coupling). The particle stability of H-6(Lambda) is discussed and predictions are made for binding energies of He-9(Lambda), Li-10(Lambda), Be-12(Lambda), B-14(Lambda). None of the large effects conjectured by some authors to arise from Lambda Sigma coupling is borne out, neither by these realistic p-shell calculations, nor by quantitative estimates outlined for heavier hypernuclei with substantial neutron excess. (C) 2013 Elsevier B.V. All rights reserved.