Two neutron decay from the $2_1^+$ state of $^6$He

TL;DR

This study investigates the decay modes of the $2_1^+$ resonant state of $^6$He, revealing coexistence of correlated and uncorrelated two-neutron emissions, and suggests the presence of a di-neutron configuration.

Contribution

It introduces a combined theoretical approach using continuum-discretized coupled-channels and complex-scaled Lippmann-Schwinger equations to analyze decay modes of $^6$He resonant states.

Findings

Identified two decay modes: correlated and uncorrelated two-neutron emissions.

Found evidence for a di-neutron configuration in the $2_1^+$ state.

Demonstrated coexistence of decay modes through invariant mass spectra analysis.

Abstract

Decay mode of the $2_1^+$ resonant state of $^6$He populated by the $^6$He breakup reaction by $^{12}$C at 240 MeV/nucleon is investigated. The continuum-discretized coupled-channels method is adopted to describe the formation of the $2_1^+$ state, whereas its decay is described by the complex-scaled solutions of the Lippmann-Schwinger equation. From analysis of invariant mass spectra with respect to the $\alpha$-$n$ and $n$-$n$ subsystems, coexistence of two decay modes is found. One is the simultaneous decay of two neutrons correlating with each other and the other is the emission of two neutrons to the opposite directions. The latter is found to be free from the final state interaction and suggests existence of a di-neutron in the $2_1^+$ state of $^6$He.