Three-body properties of low-lying $^{12}$Be resonances

TL;DR

This paper models the three-body resonances of low-lying states in $^{12}$Be as two neutrons around an inert $^{10}$Be core, extending bound state calculations into the continuum to analyze structure and decay modes.

Contribution

It introduces a three-body model for $^{12}$Be resonances, predicting their structures, decay channels, and spin-parity assignments, aligning with experimental data.

Findings

All considered resonances are naturally occurring in the three-body model.

$0^{+}$ and $2^{+}$ states have $^{10}$Be-neutron d-wave structure.

Decay modes include one-neutron emission, three-body direct, and sequential decays.

Abstract

We compute the three-body structure of the lowest resonances of $^{12}$Be considered as two neutrons around an inert $^{10}$Be core. This is an extension of the bound state calculations of $^{12}$Be into the continuum spectrum. We investigate the lowest resonances of angular momenta and parities, $0^{\pm}$, $1^{-}$ and $2^{+}$. Surprisingly enough, they all are naturally occurring in the three-body model. We calculate bulk structure dominated by small distance properties as well as decays determined by the asymptotic large-distance structure. Both $0^{+}$ and $2^{+}$ have two-body $^{10}$Be-neutron d-wave structure, while $1^{-}$ has an even mixture of $p$ and d-waves. The corresponding relative neutron-neutron partial waves are distributed among $s$, $p$, and d-waves. The branching ratios show different mixtures of one-neutron emission, three-body direct, and sequential decays. We argue for spin and parities, $0^{+}$, $1^{-}$ and $2^{+}$, to the resonances at 0.89, 2.03, 5.13, respectively. The computed structures are in agreement with existing reaction measurements.