Real-time decay dynamics of the low-lying 1/2+ state in 9Be: Signatures of virtual-state behavior
Abstract
The low-lying 1/2+ state of 9Be has been interpreted either as a near-threshold resonance or as an 8Be+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 9Be 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 8Be+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 8Be+n-like asymptotic configuration while retaining a localized p3/2 αn component suggestive of a 5He+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.
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BibTeX
@misc{kikuchi2026realtime,
title = {{Real-time decay dynamics of the low-lying $1/2^+$ state in $^9$Be: Signatures of virtual-state behavior}},
author = {Yuma Kikuchi and Kiyoshi Katō and Takayuki Myo},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.02646},
eprint = {2610.02646},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.02646},
}
RIS
TY - UNPB
TI - Real-time decay dynamics of the low-lying 1/2^+ state in ^9Be: Signatures of virtual-state behavior
AU - Yuma Kikuchi
AU - Kiyoshi Katō
AU - Takayuki Myo
PY - 2026
DA - 2026/10/02
PB - arXiv
DO - 10.48550/arxiv.2610.02646
UR - https://arxiv.org/abs/2610.02646
AB - The low-lying 1/2^+ state of ^9Be has been interpreted either as a near-threshold resonance or as an ^8Be+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 ^9Be 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 ^8Be+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 ^8Be+n-like asymptotic configuration while retaining a localized p_3/2 αn component suggestive of a ^5He+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.
ER -