粲偶素到D(s)介子和轻子末态的半轻衰变是标准模型预言可能存在的一类稀有衰变，但目前在实验上尚未观测到。通过对该类反应的测量可以精确检验标准模型，同时也提供了寻找超出标准模型新物理的机会。北京正负电子对撞机上的北京谱仪BESIII实验已在τ-粲能区稳定运行10年，并于2019年2月完成了100亿J/Psi事例的获取。这是世界上在阈值处获取的最高统计量J/Psi事例。申请人计划通过分析这批J/Psi样本，对J/Psi->D(s)(*)-e+υ_e等反应道的衰变分支比进行测量，预计能将现有上限测量的精度提高1~2个数量级，接近标准模型预言的上限区间。同时结合申请人在BESIII缪子径迹重建软件开发和粒子鉴别中的经验，采用多变量分析方法提高缪子的重建和鉴别效率，预计对粲偶素到D(s)介子和缪子半轻衰变的分支比实现首次测量，同时也对BESIII上其他缪子相关的测量提供帮助。

The Standard Model (SM) is the most successful theoretical model on particle physics and has been widely verified by experimental data. The semi-leptonic decay from Charmonium to D(s) meson and lepton is one kind of rare decays that is predicted by the SM, but has never been found experimentally. The measurement of these processes is not only a method of precision test of the SM, but also provides the possibility to search for the new physics beyond the SM. The BESIII experiment is a large scientific apparatus on BEPC and has been running at the tau-charm energy region for 10 years. In Feb 2019, BESIII has accumulated 10 Billion J/Psi events, which is the highest statistics J/Psi data sample produced near J/Psi threshold. With the large statistics and high quality J/Psi data, we propose to analyze the branching factor of the semi-leptonic decay from J/Psi to a D(s) meson and leptons, such as J/Psi->D(s)(*)-e+υ_e. Based on the statistics of the new J/Psi data sample, we expect to improve the current upper-limit measurement of these processes by about two orders of magnitude, to a precision close to the branching factor predicted by the SM. The applicants have developed the Muon-Counter track reconstruction and particle discrimination method during the construction stage of BESIII. With the experience, we expect to improve the efficiency of muon tracking and identification on BESIII, to measure the decay from Charmonium to D(s) meson and muon for the first time, and benefit other muon related analyses on BESIII.