Ground-state properties of H 5 from the He 6 ( d , He 3 ) H 5 reaction

We have studied the ground state of the unbound, very neutron-rich isotope of hydrogen H-5, using the He-6(d, He-3)H-5 reaction in inverse kinematics at a bombarding energy of E(He-6) = 55A MeV. The present results suggest a ground-state resonance energy E-R = 2.4 +/- 0.3 MeV above the H-3 + 2n threshold, with an intrinsic width of Gamma = 5.3 +/- 0.4 MeV in the H-5 system. Both the resonance energy and width are higher than those reported in some, but not all previous studies of H-5. The previously unreported He-6(d, t)He-5(g.s). reaction is observed in the same measurement, providing a check on the understanding of the response of the apparatus. The data are compared to expectations from direct two-neutron and dineutron decay. The possibility of excited states of H-5 populated in this reaction is discussed using different calculations of the He-6 -> H-5 + p spectroscopic overlaps from shell-model and ab initio nuclear-structure calculations.