R＆D on Experimental Search Methods on Strange B-Meson Decoys

本研究的目的是优化适合于测量B介子和奇异B介子稀有衰变的探测器设计，并阐明优化的效果。特别是，这项研究试图知道顶点分辨率可以提高多少，以及我们可以利用电子-正电子碰撞的改进来开发什么样的物理。为此，我们首先对KEK B工厂现有的顶点检测器的性能进行了详细的研究。研究结果在一次国际会议上公布。然后，作为升级，我们考虑了一种配置，带有半径为1厘米的光束管，带有两个像素型传感器和四层硅条探测器。在这种配置下，分辨率可以大约是现值的三分之一。我们还证实，从背景和辐射损伤的角度来看，这种配置是一种可行的解决方案。利用蒙特卡罗模拟，我们估计了各种可观测值的改进。对于奇异B介子，我们发现与强子束实验相比，正负电子冷凝器并没有明显的优势。另一方面，改进的顶点分辨率大大减少了稀有B介子衰变的背景。我们还有一个非常重要的发现来自于这项研究，我们找到了一种新的方法，利用B→ΦΦXs衰变来寻找新的违反CP的相位。这一想法是在2001年秋季日本物理学会会议上提出的。由于这一原理同样适用于奇异B介子和Lambda-B重子的衰变，我们还需要在以后的工作中进行系统的研究

The goal of this study is to optimize the detector design that is suitable for the measurements of rare decays of B mesons and strange B mesons, and clarify the effect of the optimization. In particular, the study tries to know how much the vertex resolution can be improved, and what kind of physics we can exploit with the improvement in electron-positron collisions. To this end, we first made a detailed study on the performance of the existing vertex detector at the KEK B-factory. The results were presented at an international conference. Then, as an upgrade, we considered a configuration with a beampipe with a radius of 1 cm, with two pixel-type sensors and wrth four layers of silicon strip detectors. With this configuration, the resolution can approximately be 1/3 of the present value. We have also confirmed that this configuration is a workable solution in terms of the background and the radiation damage. Using Monte Carlo simulation, we estimated improvements on various observables. As for strange B mesons, we find that there is no clear advantage of electron-positron coliders over the experiments with hadron beams. On the other hand, the improved vertex resolution reduces backgrounds in rare B meson decays drastically.We also had a very important discovery that was derived from this study ; we find a new method that uses B →ΦΦXs decays to search for a new CP-violating phase. This idea was presented at the Japan Physics Society meeting m Autumn 2001. Since the principle can also be applied to decays of strange B mesons and Lambda-B baryons, we need a systematic study in the future