  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.

Nuclear Experiment