Structure and decay of ${}^{21}$B resonances

Abstract

The structure of the neutron-rich nucleus ${}^{21}$B is investigated within a three-body model consisting of a ${}^{19}$B core and two neutrons. The three-body wave functions are computed using the hyperspherical adiabatic expansion method combined with the complex-scaling technique. Four potential parametrizations compatible with the available experimental information on ${}^{20}$B are considered. The calculations predict a low-lying ${\frac{3}{2}}^{-}$ state below the experimentally observed resonance at 2.47~MeV. An analysis of the dependence on the three-body interaction shows that this state cannot be shifted to the experimental resonance energy; instead, it remains either bound or becomes a near-threshold resonance with a rapidly increasing width. These results indicate that the observed resonance is more naturally interpreted as the second ${\frac{3}{2}}^{-}$ state, whereas a lower-lying ${\frac{3}{2}}^{-}$ state, dominated by an $s_{1/2}$ configuration, has so far eluded experimental observation. Momentum correlations are obtained for the experimentally observed resonance. In addition, the existence of other resonances is investigated.

Comments: Submitted to Physical Review C