Observation of the near-threshold intruder $0^-$ resonance in $^{12}$Be

TL;DR

This paper reports the first observation of a near-threshold $0^-$ resonance in $^{12}$Be, highlighting the role of continuum coupling and exotic structures in its low-lying states.

Contribution

The study provides the first experimental evidence of a $0^-$ resonance in $^{12}$Be and demonstrates the significance of continuum effects via advanced theoretical models.

Findings

Identification of a $3.21$ MeV $0^-$ state in $^{12}$Be.

Continuum coupling significantly affects state energies and ordering.

Exotic cross-shell configurations are relevant in $^{12}$Be and $^{11}$Li.

Abstract

A resonant state at $3.21^{+0.12}_{-0.04}$\,MeV, located just above the one-neutron separation threshold, was observed for the first time in $^{12}$Be from the $^{11}$Be\,$(d,p)^{12}$Be one-neutron transfer reaction in inverse kinematics. This state is assigned a spin-parity of $0^-$, according to the distorted-wave Born approximation (DWBA) and decay-width analysis. Gamow coupled-channel (GCC) and Gamow shell-model (GSM) calculations show the importance of the continuum-coupling, which dramatically influences the excitation energy and ordering of low-lying states. Various exotic structures associated with cross-shell intruding configurations in $^{12}$Be and in its isotonic nucleus $^{11}$Li are comparably discussed.