标题： $^{19}$B的三体结构：双中子晕核中的有限范围效应 显示英文标题

标题： Three-body structure of $^{19}$B: Finite-range effects in two-neutron halo nuclei

摘要： 研究了$B(E1)$的结构和$^{19}$B 的跃迁强度，这是基于最近的实验表明$^{19}$B 展现出明显的双中子晕结构，在一个$^{17}\text{B}+n+n$模型中进行的。 初步分析实验数据时采用了接触相互作用$n$-$n$，众所周知，这种相互作用会低估其他晕核（如$^{11}$锂）中的$s$波成分。在目前的工作中，使用了具有有限范围两体相互作用的三体超球形式来描述$^{19}$氖。特别是，将使用两种不同的有限范围$n$-$n$相互作用，以及一个中心高斯势，其范围逐渐减小。 目的是确定核的主要性质，并研究当使用类似于接触的$n$-$n$势时它们如何变化。 还特别关注了用于考虑三体效应的处方依赖性，即三体力或密度相关的$n$-$n$势。 我们发现，三体模型加上有限范围势能对$^{19}$B 的描述与实验数据一致。 结果基本上不受二体势能在短距离细节上的影响，导致约 55% 的 $(s_{1/2})^2$含量，明显大于最初的估计。 同样，三体效应所用的处方几乎没有依赖性。 计算得到的总$B(E1)$强度与实验结果一致，尽管我们在$dB(E1)/d\varepsilon$分布的低能峰附近略微高估了数据。最后，我们展示减少$n$与$n$的相互作用范围会产生显著的$s$波贡献减少，那么在使用接触相互作用的计算中应该期望这种减少。 显示英文摘要

摘要： The structure and $B(E1)$ transition strength of $^{19}$B are investigated in a $^{17}\text{B}+n+n$ model, triggered by a recent experiment showing that $^{19}$B 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 $^{11}$Li. In the present work, the three-body hyperspherical formalism with finite-range two-body interactions is used to describe $^{19}$B. 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 contact-like $n$-$n$ 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 $^{19}$B consistent with the experimental data. The results are essentially independent of the short-distance details of the two-body potentials, giving rise to an $(s_{1/2})^2$ 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 $dB(E1)/d\varepsilon$ 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.