基于暗物质粒子探测卫星的硼碳比率精确测量的研究

As the first astroobservation satellite of China, Dark Matter Particles Explorer (DAMPE), which concentrated on indirect detection of dark matter particles, the research about gamma ray astronomy and the precision measurement of energy spectrum of nuclear species in cosmic rays, had been launched on Dec.17th, 2015. And the Institute of Modern Physics, Chinese Academy of Science (IMPCAS) was responsible for developing the Plastic Scintillator Detector (PSD) and participating in analyzing on-orbit data. Among cosmic rays nuclei measurements, boron-to-carbon ratio is the most key observable for restricting parameters of cosmic ray propagation modeling. Based on the precision calibration of all sub-detectors of DAMPE, this project will mainly carry out seven aspects of researches for the target of boron-to-carbon ratio measurement as follows: 1) On the basis of enhancing the charge resolution of sub-detectors, plastic scintillator detector (PSD) and silicon-tungsten tracker (STK) especially, selecting good, pure boron and carbon events as reliable sample; 2) Using reliable sample as signal template and combining with the Monte Carlo method, to estimate the background and the fragmentation probability in PSD and STK of boron and carbon; 3) Detailed study the conditions of using subdetectors to select and match boron and carbon events, further improve and match the efficiency of selecting boron and carbon; 4) Calculating the effective acceptance which is multiplication of geometry acceptance, trigger efficiency and event reconstruction efficiency. The geometry acceptance is obtained by simulating the process of detecting boron and carbon events with Geant4 open source package; 5) Calculating the exposure time; 6) Energy reconstruction; 7) Unfolding study.

作为我国首颗天文观测卫星，暗物质粒子探测卫星（DAMPE）于2015年12月17日发射成功，其致力于暗物质粒子的间接探测、伽马天文学的研究以及宇宙射线核素能谱的精确测量，其中近代物理研究所承担了子探测器塑闪阵列探测器（PSD）的研制工作，并参与了后续的数据分析工作，积累了相应的工作经验。在宇宙射线核素能谱测量方面，硼碳比率是限制宇宙线传播模型参数最关键的测量。本项目在暗物质粒子探测卫星各子探测器精细标定的基础上，以硼碳比率测量为主线，主要开展以下七个方面的研究：1）选择良好的干净的硼、碳事例作为可信赖的样本；2）以可信赖的样本为信号模板，结合蒙特卡罗方法估算硼、碳事例的本底及其碎裂的概率；3）详细研究得到较高的、一致的硼、碳事例选择效率；4）有效接受度的计算。有效接受度为几何接受度、探测器触发效率和事例重建效率的乘积；5）曝光时间的计算；6）能量重建；7）unfolding研究。

宇宙线物理时代的开启始于Hess首次观测到地外辐射，至今100年有余。关于宇宙线基本的物理问题起源、加速以及传播至今未有清晰的答案，实验物理学家不断升级观测设备以确保观测到更为精确的数据以供理论物理学家发展并不断完善理论模型以便更好地描述整个宇宙线物理图像。其中DAMPE就是这样一款优秀的宇宙线望远镜，基于这一平台，科学家们可以分析各类核素的能谱，如硼碳比率的测量，这可以为宇宙线的传播提供关键参数。在本项目支持下，我们基于DAMPE开展了一些基础性工作，如PSD分系统在轨工作寿命评估、PSD模拟程序构建、PSD在轨标定和电荷重建，并进一步开展了碳流量的初步分析。