重离子物理的中心问题是研究强相互作用物质的相结构。重离子碰撞产生高重子密度物质，是研究核物质状态方程的重要手段。通过选择合适的实验观测量，可以了解状态方程对称能随核物质密度的依赖性，对诸如重核素性质、致密天体演化以及重离子碰撞体系演化等研究领域有重要意义。兰州重离子加速器是我国唯一的此类装置，其上冷却储存环（CSR）的建成，为我国相关研究的开展提供了机遇。计划在CSR外靶上进行重离子碰撞发射带电pi介子产额的测量，针对非对称核物质在高重子密度区对称能的演化开展物理研究。为获得可靠的物理结果，需要充分的实验准备。根据CSR外靶已有的实验装置条件，通过理论模型、软件框架、探测器和读出电子学系统等方面的建设，为计划开展的实验打好基础。

Exploiting the phase structure of strongly interacting material is the central question of heavy-ion physics research. It is an important method to study the equation of state (EOS) of the nuclear matter by colliding heavy nuclei into each other and creating hot matter with high baryon density. The EOS of this strongly coupled matter, especially its dependence on density, can be studied via properly chosen physical observables, among which the pi-/pi+ production ratio probes the symmetry energy, Esym(\rho), of the asymmetrical nuclear matter. It is believed to be crucial in many research fields such as the heavy nuclus property, the evolution of dense star and heavy-ion collision system. The Cooling Storage Ring (CSR) at Lanzhou, China is a heavy-ion facility that can accelerate nuclei up to 238U with a kinetic projectile energy of several hundred MeV to GeV. An External Target Experiment (ETE) is currently proposed for this study based on first-stage simulation and experimental work. To provide precise measurements and solid constraint to theory and models, experiment design and systematic requirements must be carefully studied.