Direct Experimental Evidence for Strong Admixture of Different Parity States in11Li

Peripheral fragmentation of a 287 MeV/nucleon beam of the halo nucleus ${}^{11}\mathrm{Li}$ incident on a carbon target has been studied in a fragment-neutron coincidence experiment. The momentum distribution of the ${}^{10}\mathrm{Li}$ fragments gives access to the momentum distribution of the removed neutron in ${}^{11}\mathrm{Li}$. From the shape of the distribution, the $({1s}_{1/2}{)}^2$ contribution to the mixture of $({1s}_{1/2}{)}^2$ and $({0p}_{1/2}{)}^2$ components in the ground-state wave function was determined to be $(45\pm 10)\%$. The angular correlation between the knocked out neutron and the one from the decay of ${}^{10}\mathrm{Li}$ shows a skew distribution signaling interference of these two different parity states.