Reactions of the halo systems ${}^{11}\mathrm{Be}$ and ${}^{11}\mathrm{Li}$ (at 460 and 280 MeV/nucleon) with a carbon target demonstrate that ( ${n+}^9\mathrm{Li}$) has an (unbound) $l=0\mathrm{}$ ground state very close to the threshold. The neutron halo of ${}^{11}\mathrm{Li}$ has appreciable $({1s}_{1/2}{)}^2$ and $({0p}_{1/2}{)}^2$ components.

• Received 20 December 1994

DOI:https://doi.org/10.1103/PhysRevLett.75.1719