Measurement of CP violation parameter phi-2

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The B factory accelerator KEKB is the world highest luminosity machine, achieving the design luminosity of 10^<34>cm^<-2>s^<-1> in May 2003, and still improving is luminosity record. The Belle experiment has upgraded the silicon vertex detector in summer 2003, and accumulates data in a good condition.About the research topic phi-2 measurement, we have analyzed and published the results on the π+ π- decay mode based on the data of integrated luminosity 253fb-14 four times larger than that of the previous publication. The parameter A and S are obtained as follows. A=+0.56±0.12(stat.)±0.06(syst.), S=-0.67±0.16(stat.)±0.06(syst.). Thus, we have established the existence of CP violation in this channel, too, following the discovery of CP violation in the J/ΨK decay mode in 2001. This result also strongly indicates that there is direct CP violation for the first time in B meson decay, because A is nonzero by more than 4 sigma significance. We also limit the arrowed range of phi2 by using the isospin relations. The result strongly supports the framework of the Kobayashi-Maskawa mechanism in the standard model, agreeing with other indirect determination.We have also looked at a1πdecay modes toward the aim of increasing the statistics in measuring the angle phi2 and established the existence of this decay mode determining the branching fraction for the first time. As the other contributions to the Belle experiment, we generated large amount of Monte Carlo simulation data using the purchased computer farm. Furthermore e also contributed in developing analysis tools : one gives high tagging efficiency in distinguishing the B meson from the anti-B meson, one to suppress the contribution of continuum events, etc. On the hardware side, we have developed the trigger system for the newly installed silicon vertex detector (SVD-2) and contributed much in improving the performance of the SVD-2.