Evidence of a new state in $^{11}$Be observed in the $^{11}$Li $β$-decay
Coincidences between charged particles emitted in the $β$-decay of $^{11}$Li were observed using highly segmented detectors. The breakup channels involving three particles were studied in full kinematics allowing for the reconstruction of the excitation energy of the $^{11}$Be states participating in the decay. In particular, the contribution of a previously unobserved state at 16.3 MeV in $^{11}$Be has been identified selecting the $α$ + $^7$He$\toα$ + $^6$He+n channel. The angular correlations between the $α$ particle and the center of mass of the $^6$He+n system favors spin and parity assignment of 3/2$^-$ for this state as well as for the previously known state at 18 MeV.
nucl-ex↗