Three-body structure of 19B: Finite-range effects in two-neutron halo nuclei

Abstract

6 pags., 3 figs., 1 tab. ; The structure and B(E1) transition strength of 19B are investigated in a 17B+n+n model, triggered by a recent experiment showing that 19B exhibits a well-pronounced two-neutron halo structure. Preliminary analysis of the experimental data was performed by employing contact n¿n interactions, which are known to underestimate the s-wave content in other halo nuclei, such as 11Li. In the present Rapid Communication, the three-body hyperspherical formalism with finite-range two-body interactions is used to describe 19B. In particular, two different finite-range n¿n interactions will be used as well as a simple central Gaussian potential whose range is progressively reduced. The purpose is to determine the main properties of the nucleus and investigate how they change when using contactlike n¿n potentials. Special attention is also paid to the dependence on the prescription used to account for three-body effects, i.e., a three-body force or a density-dependent n¿n potential. We have found that the three-body model plus finite-range potentials provide a description of 19B consistent with the experimental data. The results are essentially independent of the short-distance details of the two-body potentials, giving rise to a (s1/2)2 content of about 55%, clearly larger than the initial estimates. Very little dependence has been found as well on the prescription used for the three-body effects. The total computed B(E1) strength is compatible with the experimental result, although we slightly overestimate the data around the low-energy peak of the dB(E1)/d¿ distribution. Finally, we show that a reduction of the n¿n interaction range produces a significant reduction of the s-wave contribution, which then should be expected in calculations using contact interactions. ; This work has been partially supported by SID funds 2019 (Università degli Studi di Padova, Italy) under Project No. CASA_SID19_01, by the Spanish Ministry of Science, Innovation and University MCIU/AEI/FEDER,UE (Spain) under Contract No. PGC2018-093636-B-I00, and by the European Union's Horizon 2020 Research and Innovation Program under Grant Agreement No. 654002 (ENSAR2).