Physics of CP Violation at the Tevatron

自1985年首次观测到质子-反质子碰撞以来，CDF合作研究了1.8 TeV质量中心能量的质子-反质子碰撞，使用的是美国巴达维亚费米国家加速器实验室（费米实验室）的Tevatron对撞机。CDF于1996年完成了上一次物理运行（run I），下一次运行（run II）计划于2001年春季开始，届时将配备升级后的探测器，并由升级后的加速器综合体提供更高的亮度。Run II中最重要的物理主题之一将是详细研究B强子系统中的CP违背现象。它将提供对基本粒子标准模型的检验，包括小林益川理论作为CP违背起源的有效性。CDF TOF计数器将在B强子的研究中发挥至关重要的作用。我们与滨松光电公司共同开发并批量生产了TOF计数器用光电倍增管。整个TOF计数器的建设是与其他研究所的研究人员密切合作完成的，包括费米实验室和美国宾夕法尼亚大学。1999年7月，原型光电倍增管在高能加速器研究组织（KEK）的1.4 T磁场中进行了性能测试。1999年7月开始批量生产，所有产品都以类似的方式进行了测试。它们已经被运送到费米实验室并安装在CDF探测器上。目前，除了读出电子设备外，TOF计数器已经完成，这些电子设备将在未来几个月内安装。随着TOF探测器的建设，我们被用于开发事件重建程序和物理分析。

The CDF collaboration has studied proton-antiproton collisions at a center-of-mass energy of 1.8 TeV, using the Tevatron collider at Fermi National Accelerator Laboratory (Fermilab) in Batavia, USA, since its first collisions observed in 1985. CDF finished its last physics run (Run I) in 1996, and the next run (Run II) is scheduled to begin spring 2001 with an upgraded detector along with a higher luminosity provided by the also upgraded accelerator complex.One of the most important physics topics in Run II will be a detailed study of CP violation phoenomena in the B hadron system. It would provide a test of the Standard Model of elementary particles, including the validity of the Kobayashi-Maskawa theory as the origin of CP violation.The CDF TOF counter will play a crucial role in the study of B hadrons. We have developed and mass-produced the photomultiplier tubes for the TOF counter together with Hamamatsu Photonics. The construction of the TOF counter as a whole has been performed with a close collaboration with researchers from other institutes, including Fermilab and the University of Pennsylbania, USA.The prototype photomultiplier tubes was tested in July 1999 for performance in a 1.4 T magnetic field at the High Energy Accelerator Research Organization, KEK.The mass production started in July 1999, and all of them have been tested in a similar fashion. They have been shipped to Fermilab and installed in the CDF detector. At this moment, the TOF counter is complete except for readout electronics, which will be installed in the coming months.Along with the TOF detector construction, we have been employed in development of event reconstruction programs and physics analyses.