Invariant-Mass Spectroscopy of $^{14}\mathrm{Be}$ with a Carbon Target at 68.1~{\textit A}MeV

We have studied the nuclear structure of $^{14}\mathrm{Be}$ using nuclear-breakup reaction with a carbon target at 68.1~\textit{A}MeV. In the neighboring beryllium isotope $^{12}\mathrm{Be}$, the disappearance of $N=8$ magic number was suggested, which was shown by observations of the low-lying first $2^+$ and the intruder $1^- $ state. On the other hand, no excited state has been observed for $^{14} \mathrm{Be}$. It is thus interesting to study such low excited state in $^{14} \mathrm{Be}$, in discussing the change of shell structure and the effect of neutron halo. The experiment was performed at the RIKEN Accelerator Research Facility. The secondary $^{14}\mathrm{Be}$ beam was produced and identified using RIPS beam line. The $^{14}\mathrm{Be}$ was broken up into $^{12}\mathrm{Be}$ and two neutrons by the carbon target. These decay particles were measured and identified using magnetic spectrometer and neutron detectors. The relative-energy spectrum of $^{12}\mathrm{Be}+2n$ system was extracted using invariant-mass method. In the spectrum we found a narrow peak in the unbound region of $^{14}\mathrm{Be}$. We also show the angular distribution of this transition in order to determine the spin/parity of the state.