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

Abstract

A resonant state at $3.21_{-0.04}^{+0.12}$\,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.