Quantum Fluctuation Effects on Fragment Formation Processes

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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