Search for unbound $^{15}$Be states in the 3-neutron decay channel

The first observation of $^{15}$Be has been made recently using a (d,p) reaction from a $^{14}$Be beam. The observed resonance at 1.8(1) MeV, which decays to the ground state in $^{14}$Be, was tentatively assigned to have a spin and parity of 5/2$^{+}$. Prior to this result, a two-proton knockout reaction from $^{17}$C, which was expected to populate the 3/2$^{+}$ state, did not produce a significant number of one-neutron decay events from $^{15}$Be. It was suggested that any states populated in this way should then decay through the first excited unbound state of $^{14}$Be [2]. Both experiments used the Modular Neutron Array (MoNA) together with the Sweeper dipole magnet and charged particle detectors to make measurements of the neutron-fragment coincidences from the decay of the neutron-unbound systems. The two-proton knockout data were recently analyzed to search for the predicted, yet unobserved, 3/2$^{+}$ state in the 3-neutron decay channel to $^{12}$Be. Through simultaneous fitting of the reconstructed decay energy spectra and other experimental observables, limits on the potential 3/2$^+$ state will be presented.\\[4pt] [1] J. Snyder et al., Phys. Rev. C 88, 031303(R) (2013).\\[0pt] [2] A. Spyrou et al., Phys. Rev. C 84, 044309 (2011).