【作者】 李海燕；

【导师】 孙俊峰； 杨悦玲；

【作者基本信息】 河南师范大学 ， 物理学、粒子物理与原子核物理， 2017， 硕士

【摘要】 在过去几十年中,B介子物理一直是高能物理研究的热点和前沿。它在确定模型参数,检验标准模型,探索CP破坏以及寻找可能潜在的新物理等方面发挥着重要的作用。美国和日本的两个B介子工厂BaBar和Belle收集了大量的B介子事例,测量了一系列B介子稀有衰变道的分支比,给出了 sin（2β）的实验测量值,确认了 B介子系统的CP破坏。与B介子相比,关于B*介子的研究相对较少,这主要是因为相关的实验数据太少。不过,随着大型强子对撞机LHC和超级B工厂SuperKEKB的运行,未来将会收集到大量的B*介子事例,这为B*介子衰变的研究提供了一个很好的机会。B*介子和B介子有相同的夸克组分。从夸克层次上讲,B*和B介子的衰变主要是b夸克衰变引起的,因而研究B介子弱衰变的模型和方法可以推广应用到B*介子弱衰变的研究,B介子弱衰变过程中提取出来的参数同样可以推广运用到B*介子的弱衰变过程,进而可以对这些模型及参数做进一步的限制和约束。在本文中,我们将采用PQCD方法来研究B*介子的两体弱衰变过程。由于b夸克是第三代夸克,根据CKM矩阵中各个矩阵元的大小关系可知,b夸克最易衰变成第二代的c夸克,因此我们选取B*介子到两个D介子这一类的衰变过程作为研究对象。在计算中,我们考虑了树图算符、企鹅图算符对发射图和湮灭图的贡献。结果表明:（1）、CKM因子和威尔逊系数对分支比的结果影响比较大;（2）、树图算符对衰变分支比的贡献比企鹅图算符的贡献要大;（3）、发射图对分支比的贡献要比湮灭图的大;（4）、轻夸克对产生湮灭图对分支比的贡献要比c夸克对产生湮灭图要大;（5）、在湮灭图中,因子化的两个图贡献相长,非因子化的两个图贡献是相消的;（6）、B_s^*0→D_s^-D_s⁺、B_d^*0→D_d^-D_s⁺和B_u^*+→（?）_u⁰D_s⁺等过程具有较大的分支比,可以达到10-9量级以上,这些衰变过程在将来的高能物理实验中有可能被观测到。更多还原

【Abstract】 B meson physics has been being one of the hot topics in high energy physics during the past few decades. It plays an important role in determining the flavour parameters, testing Standard Model,exploring the mechanism of CP violation and searching for potential new physics. With the running of the B meson factories , Belle and BaBar had collected a large amount of B meson data samples. Based on these B meson events, many B meson rare decays have been investigated. The value of sin（2β） has been measured, and the CP violation in B meson systerm has been well studied. Compared with B mesons, the study on the B* meson decay is few subject to the relatively inadequate statistics. Fortunately, with the running of LHC and forthcoming SuperKEKB, there will be a large amount of B* meson data samples,which provide a good opportunity to study B* mesons decay in the future.The B* and B mesons have the same quark components. At the quark level, the weak decay of B* and B mesons are mainly induced by the b quark decay. So the phenomenological models for the B meson decays can be applied to the study of B meson decays, and parameters extracted from B meson decays could be constrained with the B* meson decays.In this paper, we study the two-body weak decay ofB* mesons with perturbative QCD approach.According to magnitude of the CKM matrix elements, the b quark is apt to decay to the charm quark. So we focus on the B* meson decay into two D mesons. In the calculation, we consider the contributions of tree operators and penguin operators to the emission and annihilation diagrams. It is found that （1） the CKM factors and Wilson coefficients have much influence on the branching ratio; （2） the contributions of the tree operators to the branching ratio dominate over these of the penguin operators; （3） the contributions of emission diagrams to the branching ratio are much larger than those of annihilation diagrams; （4） the contributions of light-quark-pair-production annihilation diagram to the branching ratio is larger than c-quark-pair-production annihilation diagrams; （5） the interference between factorizable annihilation diagrams are constructive, and those between the nonfactorizable annihilation diagrams are destructive; （6）it is found that the B_s^*0→D_s^-D_s⁺、B_d^*0→D_d^-D_s⁺和B_u^*+→（?）_u⁰D_s⁺ decays have relatively large branching ratios, which might be detectable in the future experiments.更多还原