Exploring the neutron dripline two neutrons at a time: The first observations of the 26O and 16Be ground state resonances

TL;DR

This paper reports the first observations of the ground state resonances of unbound neutron-rich isotopes $^{26}$O and $^{16}$Be, using knockout reactions and three-body decay correlations to explore neutron dripline phenomena.

Contribution

It provides the first experimental evidence of dineutron-like decay in $^{16}$Be and measures the unbound states of $^{26}$O and $^{16}$Be with high precision.

Findings

First observation of $^{26}$O ground state resonance at <200 keV

Detection of $^{16}$Be ground state resonance at 1.35 MeV

Experimental evidence supporting dineutron decay mechanism

Abstract

The two-neutron unbound ground state resonances of $^{26}$O and $^{16}$Be were populated using one-proton knockout reactions from $^{27}$F and $^{17}$B beams. A coincidence measurement of 3-body system (fragment + n + n) allowed for the decay energy of the unbound nuclei to be reconstructed. A low energy resonance, $<$ 200 keV, was observed for the first time in the $^{24}$O + n + n system and assigned to the ground state of $^{26}$O. The $^{16}$Be ground state resonance was observed at 1.35 MeV. The 3-body correlations of the $^{14}$Be + n + n system were compared to simulations of a phase-space, sequential, and dineutron decay. The strong correlations in the n-n system from the experimental data could only be reproduced by the dineutron decay simulation providing the first evidence for a dineutron-like decay.