北京谱仪III上Ds衰变的实验研究

Experimental study of Ds meson decays plays an important role in testing the Standard Model and searching for new physics beyond. The Ds meson decay constant can be used to test the unitarity of the CKM matrix. Study of semileptonic decays can be used to investigate the mechanism of eta-eta', omega-phi and a0(980)-f0(980) mixing, while measurement of the corresponding form factors can be used to test the Lattice QCD calculation. Measurement of the absolute branching fractions of hadronic decays can be used to test the calculations of Bs mixing in the Standard Model and light quark SU(3) symmetry in the charm meson system. And the study of rare and forbidden decays can help to search for new physics.. Currently, most of the experimental measurements of Ds meson decays are from the CLEO-c experiment, but CLEO-c results are statistical-limited and quite poor. In this research programme, we will perform precise measurements of Ds meson decays based on the the world's largest data accumulated by BESIII at Ecm=4180MeV in 2016. Since the statistical uncertainty of our measurement is better than the systematic uncertainty, we will study the consistency between MC simulation and data, so that we can publish the precise measurement by reducing the systematic uncertainty to the world's leading level, and finally provide experimental proof for precision tests of the Standard Model theory.

Ds介子衰变的实验研究对检验标准模型、寻找超出标准模型的新物理有重要意义。其中，Ds介子衰变常数的测量可以检验CKM矩阵的幺正性；半轻衰变的研究可理解eta-eta',omega-phi和a0(890)-f0(980)的混合机制，相应形状因子的测量可用来检验格点QCD计算；强子衰变绝对分支比的测量可检验Bs介子混合的计算和粲介子系统中轻夸克SU(3)对称性的计算；稀有和禁戒衰变的研究有助于寻找新物理。.目前Ds衰变的实验测量主要来自CLEO-c实验，受制于统计量的影响，测量精度较低。本项目利用北京谱仪于2016年在质心能量4180MeV所采集的世界上最大的数据样本，开展Ds介子衰变的精密实验研究。由于测量的统计误差将好于系统误差，因而我们要对MC模拟与数据一致性进行研究，使系统误差达到国际领先水平，获得高精度的测量结果，为精确检验标准模型理论提供实验依据。

Ds介子衰变是检验基于标准模型的量子色动力学与电弱统一理论、探索粲介子衰变动力学机制的理想场所。项目组利用BESIII实验在质心能量4180MeV附近采集的世界最大的数据样本，开展了Ds介子纯轻、半轻、强子和稀有衰变的精密研究。在纯轻衰变Ds->mu+nu和tau+nu的分析中，抽取了Ds介子的衰变常数fDs和CKM矩阵元|Vcs|, 提升了对CKM矩阵元幺正性检验的精度，检验了tau-mu轻子味普适性；在半轻衰变Ds->eta/eta' e+nu, K0e+nu, K*(892)e+nu 和f0(980)e+nu的分析中，抽取了半轻衰变的形状因子和CKM矩阵元|Vcs|, 测量出Ds->f0(980)e+nu的分支比,支持f0(980)为四夸克组分的描述；在强子衰变的分析中，观测到W-湮灭衰变Ds->omega pi+, p nbar, a0(980)+pi0, a0(980)0pi+, 和a0(980)0rho(770)+并测出相应的分支比，结果支持a0(980)为四夸克态；在多体强子衰变的振幅分析中，测得当今精度最高的Ds标记道Ds->K+K-pi+、K+K-pi+pi0和pi+pi0eta的分支比，测量了Ds介子衰变到两体强子末态：矢量-矢量介子、轴矢量-赝标量介子、矢量-赝标量介子和标量-赝标量介子的分支比，观测到新粒子a0(1710)，为理解高激发态K1介子的结构和混合机制提供了实验信息。在稀有衰变Ds->gamma e+nu 和 Ds->a0(980)e+nu 的寻找中，确定了相应分支比的上限，检验了标准模型的预言。以上研究成果为检验并刻度理论计算非微扰效应的参数化方法和各种唯象模型、检验SU(3)味对称性、提高理论对粲介子CP破坏的预言精度，提供了关键实验事实。