Ground-state properties ofH5from theHe6(d,He3)H5reaction

We have studied the ground state of the unbound, very neutron-rich isotope of hydrogen $^{5}\mathrm{H}$, using the $^{6}\mathrm{He}(d,^{3}\mathrm{He})^{5}\mathrm{H}$ reaction in inverse kinematics at a bombarding energy of $E(^{6}\mathrm{He})=55A$ MeV. The present results suggest a ground-state resonance energy ${E}_{R}=2.4\ifmmode\pm\else\textpm\fi{}0.3$ MeV above the $^{3}\mathrm{H}+2n$ threshold, with an intrinsic width of $\mathrm{\ensuremath{\Gamma}}=5.3\ifmmode\pm\else\textpm\fi{}0.4$ MeV in the $^{5}\mathrm{H}$ system. Both the resonance energy and width are higher than those reported in some, but not all previous studies of $^{5}\mathrm{H}$. The previously unreported $^{6}\mathrm{He}(d,t)^{5}\mathrm{He}_{\mathrm{g}.\mathrm{s}.}$ 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 $^{5}\mathrm{H}$ populated in this reaction is discussed using different calculations of the $^{6}\mathrm{He}\ensuremath{\rightarrow}^{5}\mathrm{H}+p$ spectroscopic overlaps from shell-model and ab initio nuclear-structure calculations.