波包分子动力学中动量涨落的激发：对类弹核碎片动量分布的影响
Activation of momentum fluctuations in wave packet molecular dynamics: Impacts on momentum distributions of projectilelike fragments
AI总结：
本文提出一种在AMD模型中基于孤立度一致激发动量涨落的改进方法，应用于100 meV/核子下的核反应，显著改善了类弹核碎片的动量分布，并揭示了分布的双分量结构及团簇关联的作用。
摘要：
分子动力学方法使用波包作为核子波函数来模拟核反应的时间演化。激发每个波包固有的动量涨落至关重要，以便其能正确影响时间演化。在反对称化分子动力学（AMD）模型中，传统上通过分裂波包来实现这一点，即对每个粒子的波包中心引入随机涨落。本研究提出了一种改进方法，基于由用于零点能扣除的碎片数函数导出的孤立度（degree of isolation）的渐进或突变变化，在单体平均场传播和两核子碰撞过程中一致地激发涨落。该新方法被应用于约 100 meV/核子的 12C + 12C 和 12C + p 反应，重点关注由从 12C 弹核中移除一个质子所产生的 11B 碎片的动量分布。结果表明，在适当激发动量涨落后，该方法能正确考虑被移除核子对余核的反冲，11B 动量分布得到显著改善；而若不激发涨落，分布相比实验数据则过窄。此外，AMD 结果表明该动量分布由两个分量组成：一个是高 $P_z$ 分量，其相对于束流速度偏移较小，由与靶粒子发生高能碰撞后简单移除一个质子产生；另一个是低 $P_z$ 分量，具有较大的峰位偏移，由受激发的 12C 核在较长时间尺度内衰变产生。动量涨落的激发主要作用于高 $P_z$ 分量使其展宽。本文还研究了团簇关联在该问题中的作用。
英文摘要：
Molecular dynamics approaches use wave packets as nucleon wave functions to simulate the time evolution of nuclear reactions. It is crucial to activate the momentum fluctuation inherent in each wave packet so that it properly affects the time evolution. In the antisymmetrized molecular dynamics (AMD) model, this has traditionally been done by splitting the wave packets, i.e., by introducing a random fluctuation to the wave packet center of each particle. The present work proposes an improved approach to activate the fluctuation in both the one-body mean-field propagation and the two-nucleon collision processes, consistently based on the gradual or sudden change of the degree of isolation, which is derived from the fragment number function used for the zero-point energy subtraction. This new method is applied to the 12C + 12C and 12C + p reactions at about 100 MeV/nucleon, focusing on the momentum distribution of the 11B fragments produced by one-proton removal from the 12C projectile. The results show that, with the momentum fluctuation suitably activated, the method correctly accounts for the recoil from the removed nucleon to the residue and the 11B momentum distribution is significantly improved, while without activating the fluctuation the distribution is too narrow compared to the experimental data. Furthermore, the AMD results indicate that the momentum distribution consists of two components; one is the high $P_z$ component with a small shift from the beam velocity, resulting from the simple removal of a proton after an energetic collision with a target particle; the other is the low $P_z$ component with a larger peak shift resulting from the decay of an excited 12C nucleus in a longer time scale. The activation of momentum fluctuation mainly affects the high $P_z$ component to broaden it. The role of cluster correlations in this problem is also investigated.
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