发表机构
National Institute of Technology, Tokuyama College; RIKEN Nishina Center; Nuclear Reaction Data Centre, Faculty of Science, Hokkaido University; General Education, Faculty of Engineering, Osaka Institute of Technology; Research Center for Nuclear Physics (RCNP), Osaka University（国立技术大学山口学院; 理化学研究所仁科加速器中心; 北海道大学理学部核反应数据中心; 大阪工业大学工学部通识教育; 大阪大学核物理研究中心）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
通过实时衰变动量比较$^9$Be低位$1/2^+$态与$5/2^+$共振，发现前者有效宽度随时间减小且无稳定值，符合虚态行为，并揭示内部与渐近构型差异。
AI 中文摘要
$^9$Be 的低位 $1/2^+$ 态曾被解释为近阈值共振或 $^8$Be+$n$ 虚态。由于这两种图像都能产生显著的阈值增强，仅凭能量域观测量难以确定其本质。我们通过实时衰变动量研究低位 $1/2^+$ 态，并将其行为与公认的 $5/2^+$ 共振进行比较。由 $^9$Be 基态电偶极激发产生的波包在 $\alpha+\alpha+n$ 三体模型中传播。我们分析了存活概率、有效衰变宽度的拟合窗口依赖性以及不同 Jacobi 坐标表示中的时间相关密度。$1/2^+$ 存活动力学进一步与 $s$ 波有效程描述进行比较，该描述基于我们先前三体研究中发现的主要 $^8$Be+$n$ 分量。$5/2^+$ 通道显示出近似指数晚期衰变，有效宽度为 $0.264$ MeV，接近复标度极点宽度 $0.285$ MeV。相比之下，$1/2^+$ 有效宽度随着拟合区间移至更晚时间而减小，且未获得稳定衰变宽度。其晚期存活概率由有效程谱分布很好地描述。密度演化形成 $^8$Be+$n$ 类渐近构型，同时保留局域 $p_{3/2}$ $\alpha n$ 分量，暗示内部区域存在 $^5$He+$\alpha$ 类构型。$1/2^+$ 衰变在性质上不同于共振类指数衰变，与近阈值虚态动力学一致。时间相关密度揭示的独特内部和渐近构型提供了超越单一衰变宽度的补充结构信息。
英文摘要
The low-lying $1/2^+$ state of $^9$Be has been interpreted either as a near-threshold resonance or as an $^8$Be+$n$ virtual state. Because both pictures can produce a pronounced threshold enhancement, its nature is difficult to determine from energy-domain observables alone. We investigate the low-lying $1/2^+$ state through its real-time decay dynamics and compare its behavior with that of the well-established $5/2^+$ resonance. A wave packet produced by electric-dipole excitation of the $^9$Be ground state is propagated in an $α+α+n$ three-body model. We analyze the survival probability, the fit-window dependence of the effective decay width, and time-dependent densities in different Jacobi-coordinate representations. The $1/2^+$ survival dynamics are further compared with an $s$-wave effective-range description motivated by the dominant $^8$Be+$n$ component found in our previous three-body studies. The $5/2^+$ channel shows approximately exponential late-time decay, with an effective width of $0.264$ MeV, close to the complex-scaled pole width of $0.285$ MeV. In contrast, the $1/2^+$ effective width decreases as the fitting interval is shifted to later times, and no stationary decay width is obtained. Its late-time survival probability is well described by the effective-range spectral distribution. The density evolution develops an $^8$Be+$n$-like asymptotic configuration while retaining a localized $p_{3/2}$ $αn$ component suggestive of a $^5$He+$α$-like configuration in the internal region. The $1/2^+$ decay differs qualitatively from resonance-like exponential decay and is consistent with near-threshold virtual-state dynamics. The distinct internal and asymptotic configurations revealed by the time-dependent densities provide complementary structural information beyond that contained in a single decay width.
Comments8 pages, 6 figures
