The breakdown of the Z = 8 shell closure in the unbound 12 O and its mirror symmetry

An excited state in the proton-rich unbound nucleus 12O was identified at 1.8(4) MeV via missingmass spectroscopy with the 14O(p,t) reaction at 51 AMeV. The spin-parity of the state was determined to be 0+ or 2+ by comparing the measured differential cross sections with distorted-wave calculations. The lowered location of the excited state in 12O indicates the breakdown of the major shell closure at Z = 8 near the proton drip line. This demonstrates the persistence of mirror symmetry in the disappearance of the magic number 8 between 12O and its mirror partner 12Be. PACS numbers: 25.40.Hs, 24.10.Eq, 21.10.Hw, 27.20.+n,