在CSR外靶终端开展非对称核物质性质实验研究

In this project, the charged particle tracking and some other detector systems at the external target experiment facility on HIRFL-CSR will be improved, and the corresponding front end electronics, the data acquisition and analyze systems will be upgraded. Based on this upgraded facility, the heavy ion collision experiments will be performed at beam energies ranging from 250 to 400 Mev/u to measure the charged pionic ratio. Theoretically we will improve the transport model with incorporating the medium effect of resonance production and the optic potential of pions. The model dependence of the conclusion on the stiffness of the symmetry energy above saturation point will be analyzed carefully. With all the elaborate improvements both experimentally and theoretically, it is intended to set a new constraint on the density dependence of the nuclear symmetry energy at supra-saturation region and to resolve the controversial view on the density behavior of symmetry energy. The project will activate the experimental researches in the intermediate and high energy heavy ion physics with the facility on HIRFL-CSR and bring the researches in this field to a world-wide scope.

为改善HIRFL-CSR上中高能核物理实验研究相对滞后的局面，推进HIRFL-CSR在核物质状态方程领域的研究进展并在国际上占据一席之地，我们提出本课题，拟完善HIRFL-CSR外靶实验终端的带电粒子径迹探测器系统及其它探测器，改进升级相应的读出电子学和数据获取及分析系统，并在此基础上开展250 至 400MeV/u的重离子碰撞实验，提取这一能区的pion-/pion+产额比的物理数据。同时对理论模型进一步优化，考虑介质效应和pion介子光学势，仔细分析目前有关对称能结论的模型相关原因，在综合比较分析的基础上得到高密区对称能的约束范围，澄清人们对对称能高密行为的相互不一致的认识。

为改善HIRFL-CSR上中高能核物理实验研究相对滞后的局面，推进HIRFL-CSR在核物质状态方程领域的研究进展，本课题拟完善HIRFL-CSR外靶实验终端的带电粒子径迹探测器系统及其它探测器，改进升级相应的读出电子学和数据获取及分析系统，并在此基础上开展250 至 400MeV/u的重离子碰撞实验，提取这一能区的pion-/pion+产额比的物理数据，并结合理论模型的优化，得到高密区对称能的约束范围。项目成功研制了外靶终端靶区的起始时间、带电粒子多重性等探测器，通过测试比较选择了MWDC的信号处理电路方案并实现了与探测器的实际结合。开发了新的模块化数据获取系统，研制了专用的触发和时钟模块。改造更新了终端TOF探测器及配气、配电等设施，极大改善了实验环境。开展了350AMeV的40Ar+Pb/C反应实验研究工作，并从实验结果中清楚的分离和鉴别了pi+/pi-介子。研究了30AMeV的40Ar+197Au反应，约束了对称能在饱和密度附近的密度斜率参数。

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