Suppressed Electric Quadrupole Collectivity in $^{49}$Ti

TL;DR

This paper reports the first complete measurement of $E2$ matrix elements in $^{49}$Ti, revealing a 20% quenching in quadrupole strength compared to $^{50}$Ti, explained by a simple two-state mixing model.

Contribution

It provides the first complete set of $E2$ matrix elements for $^{49}$Ti and demonstrates a simple model explaining the observed quadrupole quenching.

Findings

20% quenching in $^{49}$Ti compared to $^{50}$Ti

First complete $E2$ matrix element set for $^{49}$Ti

Two-state mixing model explains quadrupole quenching

Abstract

Single-step Coulomb excitation of $^{46,48,49,50}$Ti is presented. A complete set of $E2$ matrix elements for the quintuplet of states in $^{49}$Ti, 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. $^{49}_{22}$Ti$_{27}$ shows a $20\%$ quenching in electric quadrupole transition strength as compared to its semi-magic $^{50}_{22}$Ti$_{28}$ 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 $^{49}$Ti-$^{50}$Ti pair (i.e., approximate single-$j$ $0f_{7/2}$ 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.