【作者】 王娜；

【导师】 孙俊峰；

【作者基本信息】 河南师范大学 ， 理论物理， 2012， 硕士

【摘要】 自从1998年在CDF上首次探测到Bc介子，由于其特殊的夸克组成(由两个不同味道的重夸克组成)，一直备受实验和理论工作者的重视。然而由于过去受实验条件的限制，与Bc介子相关的数据较少。对其衰变分支比的理论计算，也多是仅考虑树图算符的贡献，应用简单因子化方法给出量级的大小。现在随着LHC的运行，每年能产生大概1010Bc事例数。这就为我们深入研究Bc介子提供了充足的实验数据。本文用QCD因子化方法(QCDF)研究B_c→B(*)cP,BV的衰变过程，计算中考虑了顶角修正图，企鹅图和弱湮灭图对衰变振幅的贡献。在衰变过程中，作为旁观者夸克的b夸克基本上是在壳的，与b夸克相连的胶子应该非常软，QCDF方法无法对这类修正进行计算。在文中我们首先介绍了几种常用的计算强子矩阵元的方法，并着重介绍了QCDF方法。其后，介绍如何将QCDF方法具体应用于计算B_c→B(*)cP,BV的衰变过程。计算结果表明，对于振幅是以a1贡献为主的过程，非因子化贡献对分之比的影响较小；而对于以a2贡献为主的色因子压低的过程，非因子化贡献对分支比影响较大。此外在湮灭图的贡献中，不存在端点发散，不需要引入唯象参数，从而提高了计算结果的准确度和可信度。本文还计算了由输入参数和标度选取引入的误差以及CP破坏的大小。深入研究Bc介子中c夸克的衰变，对于检验标准模型和探索新物理有着重要意义。更多还原

【Abstract】 In1998the CDF collaboration reported the observation of the bottom-charm Be meson at Fermilab. Because it is the lowest bound state of two heavy quarks (charm and bottom) with open flavors, the Be mesons has been paid much attention by the theoretical and experimental workers. Nevertheless, because of the limitation of the experimental conditions in the past, there is a serious lack of Be mesons data. In the previous literature, only the contributions of tree operators are considered and in the cases the order of magnitude is estimated for the branching ratio using the method of naive factoriztion. With the run of the LHC, it is estimated that around1010Be events would be produced per year. This will provide sufficient experimental data for our study of the Be meson in detail. In this paper, we use QCDF method to calculate the Be weak decays. In our calculation, the nonfactorizable contributions, such as the vertex corrections, penguin diagrams and the annihilation topologies are considered. The spectator scattering is dominated by the exchange of the soft gluon, which cannot be deal with the QCDF method. Firstly, we review several methods of calculate hadronic matrix elements, and introduce the QCDF method in detail. Then we apply the QCDF method to calculate the Be decays. The results show that the influence of the correction to the branching ratio is small for the process dominated by parameter a1, and very important for the color-suppressed process dominated by parameter a2, What should be mentioned is that the endpoint divergence is absence in the calculation of the annihilation topologies. So we don’t need to introduce the phenomenological parameters, and thus improve the accuracy and credibility of the calculation. In this paper, we also analysis the theoretical uncertainties from the input parameters, the renomoraliztion scale. It has a great significance to study the decay of c quark in Be for the test of standard model and explortion of new physics.更多还原