Level structures of 56,58Ca cast doubt on a doubly magic 60Ca

Gamma decays were observed in 56Ca and 58Ca following quasi-free one-proton knockout reactions from 57,59Sc beams at ≈200 MeV/nucleon. For 56Ca, a γ ray transition was measured to be 1456(12) keV, while for an indication 1115(34) keV. Both transitions tentatively assigned as the 21+→0gs+ decays, compared results ab initio conventional shell-model approaches. A calculation wide model space with marginally modified effective nucleon-nucleon interaction depicts excellent agreement experiment 21+ level energies, two-neutron separation reaction cross sections, corroborating formation of new nuclear shell above N = 34 shell. Its constituents, 0f5/2 0g9/2 orbitals, are almost degenerate. This degeneracy precludes possibility doubly magic 60Ca potentially drives dripline Ca isotopes 70Ca or even beyond.