Shell evolution of N = 40 isotones towards ⁶⁰Ca: First spectroscopy of ⁶²Ti

Excited states in the N=40 isotone ⁶²Ti were populated via the ⁶³V(p,2p)⁶²Ti reaction at ∼200 MeV/nucleon at the Radioactive Isotope Beam Factory and studied using γ-ray spectroscopy. The energies of the 2₁ ⁺→0_gs ⁺ and 4₁ ⁺→2₁ ⁺ transitions, observed here for the first time, indicate a deformed ⁶²Ti ground state. These energies are increased compared to the neighboring ⁶⁴Cr and ⁶⁶Fe isotones, suggesting a small decrease of quadrupole collectivity. The present measurement is well reproduced by large-scale shell-model calculations based on effective interactions, while ab initio and beyond mean-field calculations do not yet reproduce our findings. The shell-model calculations for ⁶²Ti show a dominant configuration with four neutrons excited across the N=40 gap. Likewise, they indicate that the N=40 island of inversion extends down to Z=20, disfavoring a possible doubly magic character of the elusive ⁶⁰Ca.