Experimental evidence of a

Data have been obtained on exclusive single neutron knockout cross sections from 12Be to study its ground state structure. Preliminary cross sections for the first (0.32 MeV, $\ensuremath{^1\!/_2 ^-}$) and second (1.78 MeV, $\ensuremath{^5\!/_2 ^+}$, unbound) excited states in 11Be have been obtained, giving evidence of significant admixtures of both $\ensuremath{\nu(1p_{^1\!/_2})^2}$ and $\ensuremath{\nu(1d_{^5\!/_2})^2}$ configurations in the ground state of 12Be