Suppressed Electric Quadrupole Collectivity in ⁴⁹Ti

Single-step Coulomb excitation of 46,48,49,50Ti is presented. A complete set of $E2$ matrix elements for the quintuplet of states in ⁴⁹Ti, centered on the 2⁺ core excitation, was measured for the first time. A total of nine $E2$ matrix elements are reported, four of which were previously unknown. ⁴⁹₂₂Ti₂₇ shows a $20%$ quenching in electric quadrupole transition strength as compared to its semi-magic ⁵⁰₂₂Ti₂₈ neighbour. This $20%$ quenching, while empirically unprecedented, can be explained with a remarkably simple two-state mixing model, which is also consistent with other ground-state properties such as the magnetic dipole moment and electric quadrupole moment. A connection to nucleon transfer data and the quenching of single-particle strength is also demonstrated. The simplicity of the ⁴⁹Ti-⁵⁰Ti pair (i.e., approximate single-j 0f7/2 valence space and isolation of yrast states from non-yrast states) provides a unique opportunity to disentangle otherwise competing effects in the ground-state properties of atomic nuclei, the emergence of collectivity, and the role of proton-neutron interactions.