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

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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