Quantum Fluctuation Effects on Fragment Formation Processes

核反应研究的主要目标之一是探索核物质的不同阶段，并了解相关的相变。由于核相的实验探索必须依赖于核碰撞，因此有必要对核碰撞动力学有深入的了解，包括核系统的非平衡特性以及量子统计性质。在本研究项目中，我们首先发展了一种描述波包量子统计力学的简便方法。然后我们构造了一个动力学模型，量子朗之万模型，在该模型中，我们将一个具有量子力学起源的随机项引入波包分子动力学。有了这个随机项，就可以确保系统通过运动方程本身的形式自动弛豫到适当的量子统计平衡。我们已经成功地将该模型应用于各种碎片过程：多碎片…更多的重离子碰撞，原子团形成，以及由静止的Ξ^-吸收形成的双、双和单超碎片的形成。通过这些研究，我们阐明了量子涨落在碎片形成过程中的以下重要作用。(1)量子涨落的引入极大地改善了核系统的统计性质。(2)有了量子涨落，就有可能描述冷碎片的动态形成，这些冷碎片足够稳定，足以在以后的统计衰变中幸存下来。(3)这种动力学碎片的形成比通常的分子动力学中的无涨落要快得多。这种快速碎裂可能是在高能质子诱导的反应中观察到的反常IMF角分布(侧峰)的来源。我们利用核内级联模型和非平衡渗流模型的组合框架验证了这一观点。基于这些成果和其他关于奇异性核物理和相对论重离子碰撞的工作，我们在这四年中发表了12篇原创论文(包括一篇提交的论文)和FIFTEEEN会议论文集。较少

One of the main goals of nuclear reaction study is to explore various phases of nuclear matter and achieve an understanding of the associated phase transitions. Since the the experimental exploration of nuclear phases must rely on nuclear collisions, it is necessary to have deep knowledges of nuclear collision dynamics, including the non-equilibrium character as well as the quantal statistical nature of the nuclear system.In this research project, first we have developed a tractable method to describe the quantum statistical mechanics of wave-packets. Then we have constructed a dynamical model, the Quantum Langevin model, in which we implement a stochastic term having a quantum mechanical origin into wave-packet molecular dynamics. With this stochastic term, it is ensured that the system relaxes to proper quantum statistical equilibrium automatically, by the form of the equations of motion itself. We have successfully applied this model to various fragmentation processes : multifragmen … More tation in heavy-ion collisions, atomic cluster formation, and double, twin, and single-hyperfragment formation from Ξ^- absorption at rest. From these studies, we have clarified the following important roles of quantum fluctuations in fragment formation processes. (1) Inclusion of quantum fluctuation drastically improves the statistical properties of nuclear systems. (2) With quantum fluctuations, it becomes possible to describe dynamical formation of cold fragments, which are stable enough to survive later statistical decays. (3) This dynamical fragment formation is much faster than that in usual molecular dynamics without fluctuations. This fast fragmentation would be the origin of anomalous IMF angular distribution (side peaked) observed in high-energy proton induced reactions. We have verified this idea by using a combined framework of a intranuclear cascade model with a non-equilibrium percolation model.Based on these achievements and other works on strangeness nuclear physics and relativistic heavy-ion collisions, we have published twelve original papers (incl.one submitted paper), and fifteeen conference proceedings during these four years. Less