重离子碰撞中阈能附近粒子产生机制和高密对称能研究

Particle dynamics (meson, hyperon, etc) produced in heavy-ion collisions near threshold energies is related to the particle-nucleon potential, elementary cross sections, production and decay of resonances, symmetry energy etc. With the establishment of new-generation science facilities in the world, such as high-intensity heavy-ion accelerator facility (HIAF) in China, facility for antiproton and ion research (FAIR) in Germany, heavy-ion accelerator facility in Russia (NICA) etc, the particle production and symmetry energy at supra-saturation densities in heavy-ion collisions will be concentrated on experimentally. In this project, the Lanzhou quantum molecular dynamics (LQMD) model will be further improved and is used to investigate the in-medium properties of particles near threshold energies in heavy-ion collisions at energies between 100 MeV/nucleon and 10 GeV/nucleon. Some promising observables will be explored, e.g., rapidity, transverse momentum and kinetic energy distributions, transverse flows, elliptic flows. Isospin particles as probing the high-density symmetry energy are to be concentrated on. The formation mechanism of hypernuclei in heavy-ion collisions and in hadron (antiproton, proton, pion and kaon) induced reactions will be investigated, in particular the charge and mass distributions of production cross sections, rapidity, kinetic energy, momentum, azimuthal emission etc.

重离子碰撞中阈能附近产生的粒子(介子、超子等)动力学分布依赖于粒子与核子相互作用势、粒子产生截面、共振态产生和衰变、对称能等。随着新一代大科学装置的建设或投入运行如我国的强流重离子加速器(HIAF)，德国的反质子-离子研究装置(FAIR)，俄罗斯的强流重离子装置(NICA)等，必将在实验上研究重离子碰撞中粒子产生机制和高重子密度区域对称能性质。本项目中拟采用兰州量子分子动力学(LQMD)模型，研究入射能量为100 MeV/核子-10 GeV/核子区域重离子碰撞粒子产生核介质效应，特别是阈下区域，分析粒子与核子相互作用势即粒子光学势敏感实验观测量，如粒子的快度、横向动量和动能分布，平面流，椭圆流等；分析同位旋粒子产生机制，给出探针高重子密度区域对称能信息的实验观测量；研究超核产生动力学机制，给出超核产生截面的电荷或质量数分布，快度、动能(动量)、发射极角等相空间分布，为实验探测超核提供参考。

本项目基于介子交换模型和Delta-Hole模型研究了核介质中pion介子、eta介子、奇异粒子性质，结合强子输运模型系统分析了中高能重离子碰撞中粒子产生机制。以反应系统112,124Sn+112,124Sn和197Au+197Au为例，计算了100 MeV/核子－2 GeV/核子重离子碰撞中粒子产生项空间分布，即快度、动能、横动量谱；与实验数据比较发现，介质效应对eta介子产生影响比较明显，而对称能软硬对其产额影响不大；重离子碰撞中一部分pion介子在高密区域(大于饱和密度)产生，也有一定产额在亚饱和密度区域，因此荷电pion介子比值提取对称能不敏感，而高动能区域pion介子主要是在核－核碰撞压缩阶段产生，可以提取高密区域对称能信息。此外，我们研究了反质子、质子、pion介子、K介子轰击原子核引起的散裂反应，分析了电荷交换和超子产生机理，给出了超核形成截面，为正在惠州建设的强流重离子加速器HIAF提供了理论预先研究。