理解高重子密度下核物质相图信息是当前核物理研究的前沿课题。中高能重离子碰撞(入射能量为100--400 MeV/核子)中阈能附近pion介子产生是探针高密对称能性质的最好手段之一。阈能附近pion介子主要是由Delta共振态衰变而来，其产生动力学受到核介质效应的影响。本项目将引入Delta共振态和pion介子与核子的相互作用势并考虑其同位旋相关性和产生截面的阈能修正，研究重离子碰撞中核介质效应在pion介子产生动力学和荷电pion介子比值提取高密对称能性质的影响。结合国内外大科学装置实验数据或即将进行的pion介子实验，我们将给出高密区域对称能随密度的变化关系。

Understanding the properties of nuclear matter under high baryon density is the frontier subject in the present nuclear physics research. Pions produced near the threshold energy in heavy ion collisions at incident energies from 100 to 400 MeV per nucleon are one of the best tools for extracting the information of the symmetry energy. Pions produced near the threshold energy are mainly from the decay of Delta resonances. Their production dynamics is affected by the nuclear in-medium effects. In this project, we will propose and introduce the new and isospin-dependent Delta-nucleon and pion-nucleon interaction potentials, and then consider the threshold effects of pion production. The role of the nuclear in-medium effects in pion production dynamics and extracting the information of the symmetry energy at high density by using the charged pion ratio will be investigated. Combining with the available and forthcoming experimental data of pion production, we will give the relationship between the symmetry energy and the baryon density.