Collective-flow signatures of bubble nuclei in intermediate-energy projectile fragmentation reactions
Abstract
Characterized by central density depletion, bubble nuclei represent an important class of exotic nuclear structures. Collective flow in the 40Ca+9Be projectile fragmentation reaction at 140 MeV/u is investigated using the extended quantum molecular dynamics (EQMD) model with a parameter on of the isoscalar monopole excitation strength ε. The projectile 40Ca is initialized as a relaxed ten-α cluster configuration exhibiting a bubble-like density distribution. The results reveal that increasing ε modifies the density distribution and the size of the depleted central region of bubble, producing pronounced changes in fragment yields and collective flow around ε≈0.5. Below this value, heavy-fragment production plays a significant role, while the directed flow v1 of protons and neutrons remains predominantly negative, indicating preferential emission toward the target side. Above ε≈0.5, enhanced expansion of the central low-density region suppresses heavy residues and drives v1 toward positive values. In contrast, preformed α clusters show different responses, reflecting their origin in the initial cluster configuration rather than solely in secondary decay. At low excitation, the cluster flow exhibits a pronounced impact-parameter dependence, whereas stronger excitation weakens cluster binding and suppresses directional anisotropy, driving the flow close to zero. The rapidity slopes of the flow coefficients also vary systematically with ε, tracing changes in emission anisotropy during expansion. These findings extend traditional static descriptions by probing the dynamical evolution of exotic structures in heavy-ion reactions and the contrasting collective-flow behavior of preformed clusters and single nucleons constitutes a sensitive dynamical probe of bubble-like structures.
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BibTeX
@misc{ren2026collectiveflow,
title = {{Collective-flow signatures of bubble nuclei in intermediate-energy projectile fragmentation reactions}},
author = {Ge Ren and Chun-Wang Ma and Xi-Guang Cao and Kai-Xuan Cheng and Jie Pu},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.19632},
eprint = {2610.19632},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.19632},
}
RIS
TY - UNPB
TI - Collective-flow signatures of bubble nuclei in intermediate-energy projectile fragmentation reactions
AU - Ge Ren
AU - Chun-Wang Ma
AU - Xi-Guang Cao
AU - Kai-Xuan Cheng
AU - Jie Pu
PY - 2026
DA - 2026/10/14
PB - arXiv
DO - 10.48550/arxiv.2610.19632
UR - https://arxiv.org/abs/2610.19632
AB - Characterized by central density depletion, bubble nuclei represent an important class of exotic nuclear structures. Collective flow in the ^40Ca+^9Be projectile fragmentation reaction at 140 MeV/u is investigated using the extended quantum molecular dynamics (EQMD) model with a parameter on of the isoscalar monopole excitation strength ε. The projectile ^40Ca is initialized as a relaxed ten-α cluster configuration exhibiting a bubble-like density distribution. The results reveal that increasing ε modifies the density distribution and the size of the depleted central region of bubble, producing pronounced changes in fragment yields and collective flow around ε≈0.5. Below this value, heavy-fragment production plays a significant role, while the directed flow v_1 of protons and neutrons remains predominantly negative, indicating preferential emission toward the target side. Above ε≈0.5, enhanced expansion of the central low-density region suppresses heavy residues and drives v_1 toward positive values. In contrast, preformed α clusters show different responses, reflecting their origin in the initial cluster configuration rather than solely in secondary decay. At low excitation, the cluster flow exhibits a pronounced impact-parameter dependence, whereas stronger excitation weakens cluster binding and suppresses directional anisotropy, driving the flow close to zero. The rapidity slopes of the flow coefficients also vary systematically with ε, tracing changes in emission anisotropy during expansion. These findings extend traditional static descriptions by probing the dynamical evolution of exotic structures in heavy-ion reactions and the contrasting collective-flow behavior of preformed clusters and single nucleons constitutes a sensitive dynamical probe of bubble-like structures.
ER -