在BESIII上通过联合拟合研究Ds+ -> tau+ nu_tau的衰变

寻找超出标准模型的新物理是当前粒子物理学最前沿的课题之一。实验上可以通过精密测量一些标准模型预言的参数来间接寻找新物理。目前，实验测量结果与标准模型预言值在精度范围内基本一致，因此，提高测量精度是实验上所追求的重要目标之一。基于此，本项目将利用BESIII实验采集的目前世界上最大统计量且高质量的总积分亮度为6.32/fb的Ds*Ds数据样本，通过双标记分析方法，联合拟合tau+的多个衰变道，精确测量Ds+衰变到tau+及相应中微子的绝对分支比，以此精确计算不同轻子味的Ds+纯轻衰变的分支比比值、Ds+的衰变常数及CKM矩阵元｜Vcs｜。与以往通过tau+的单一衰变道测量的结果相比，本项目的测量精度会有大幅度改善，这将有助于在更高精度上检验标准模型中tau-mu轻子普适性、非微扰量子色动力学计算的Ds+衰变常数及CKM矩阵元的幺正性，从而为探索超越标准模型的新物理提供实验依据。

Search for new physics beyond the standard model is the frontier of current particle physics. The precision measurements of some parameters that predicted by the standard model is an indirect way to search for new physics. So far, the experimental measurements have been consistent with the standard model predictions within uncertainties. Therefore, improving the accuracy of the experimental measurements is one of the principal goals. Using the currently largest and high-quality Ds*Ds threshold data samples of 6.32/fb collected by the BESIII experiment, we precisely measure the absolute branching fraction of Ds+ -> tau+ nu_tau decay with a simultaneous fit for some tau+ decays, based on the double tag method. And then we can precisely calculate the ratio of the branching fractions of some pure leptonic Ds+ decays, Ds+ decay constant and CKM matrix element |Vcs|. Compared with the previous measurements that only using one of tau+ decays, our results will achieve a higher precision, which will be very helpful to precisely test tau-mu lepton flavor universality in the standard model, theoretical calculations of Ds+ decay constant from non-perturbative quantum chromodynamics, and the unitarity of the CKM matrix, and then provides the experimental basis for probing new physics beyond the standard model.