Spectroscopy of $^{54}$Ti and the systematic behavior of low energy octupole states in Ca and Ti isotopes

TL;DR

This study investigates the excited states of $^{54}$Ti using proton scattering and knockout reactions, identifying a low-lying octupole state and revealing unexpected systematic behavior of octupole states in Ca and Ti isotopes.

Contribution

First identification of a low-lying octupole state in $^{54}$Ti and analysis of its systematic behavior compared to theoretical models.

Findings

Tentative identification of a low-lying octupole state in $^{54}$Ti

Systematic behavior of octupole states in Ca and Ti isotopes is unexpected

Comparison with RPA calculations highlights discrepancies

Abstract

Excited states of the $N=32$ nucleus $^{54}$Ti have been studied, via both inverse-kinematics proton scattering and one-neutron knockout from $^{55}$Ti by a liquid hydrogen target, using the GRETINA $\gamma$-ray tracking array. Inelastic proton-scattering cross sections and deformation lengths have been determined. A low-lying octupole state has been tentatively identified in $^{54}$Ti for the first time. A comparison of $(p,p')$ results on low-energy octupole states in the neutron-rich Ca and Ti isotopes with the results of Random Phase Approximation calculations demonstrates that the observed systematic behavior of these states is unexpected.