Study of CP violation originated of mixing through FCNC decays of the B meson

本项目的目的是通过测量不同B介子衰变的CP违和参数，寻找粒子物理标准模型之外的线索。在这些衰变中，FCNC（风味变化中性电流）衰变对这一目的最敏感，因为FCNC过程是通过一个回路图发生的，其中未知的新粒子可以起作用。它的作用可以很大程度上改变CP违和参数。为了比较不同B介子衰变的CP破坏参数，通过精确测量来建立它们的标准值是很重要的。因此，我们首先集中精力测量一个重要的CP违和参数Φ2。我们研究了衰变过程，π^+π^-,(ρ π)^0,ρ^+ρ^，并成功地以10%的精度测量了它。所得值为（97±11）°，与其他间接测量值吻合较好，与标准模型中的Kobayashi-Maskawa机制一致。关于FCNC衰减通道，我们无法直接完成调查。然而，我们通过各种讨论和论文写作为他们的分析做出了很大贡献。粒子物理学的标准模型是在20世纪70年代中期建立起来的。这是一个强大而美丽的理论，描述了自然界中存在的四分之三的力。1973年，Kobayashi和Maskawa将CP违背自然地纳入了标准模型。然而，实验证明是非常困难的。KEK-B工厂加速器提供了世界上最高的亮度，使这种困难的实验成为可能。

The purpose of this project is to look for hints beyond the standard model of particle physics through measurements of CP violation parameters in various B meson decays. Among the decays, FCNC (Flavor Changing Neutral Current) decays are most sensitive for that purpose, because FCNC processes occur through a loop diagram where yet-unknown new particles can contribute. Its effect can modify CP violation parameters by a large amount. In order to compare CP violation parameters from various B meson decays, it is important to establish their standard values by measuring them accurately. Thus, we first focused our effort to measure one of the important CP violation parameters, Φ2. We have investigates the decay processes, π^+π^-,(ρ π)^0,ρ^+ρ^-and succeeded to measure it in about 10% accuracy. The obtained value is (97±11)°,which agrees well with other indirect measurements and is consistent with the Kobayashi-Maskawa mechanism in the standard model. Concerning on FCNC decay channels, we could not directly complete investigation. However, we contribute much to their analyses through various discussion and paper writing.The standard model in particle physics has been established in the middle of 1970's. It is a powerful and beautiful theory describing three out of four forces existing in nature. CP violation has been naturally incorporated into the standard model by Kobayashi and Maskawa in 1973. However, experimental proof had been very difficult. The KEK-B factory accelerator has provided world highest luminosity, which has enabled this kind of difficult experiment.