MEASUREMENT OF CP VIOLATION PARAMETER USING RARE KAON DECAYS

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The decay KL→π^<0>νν is one of the best decays to measure the CP violation parameter.We prepared experiment KEK E391a to search for the decay with the best sensitivity, and started running in February 2004. The experiment will also serve as a pilot experiment for the next experiment to measure its branching ratio.We studied a new experiment for J-PARC 50GeV proton accelerator using Monte Carlo simulation. We found that the acceptance is increased by a factor 4 by utilizing the side of the decay region as a calorimeter. With the 10% of the design intensity of the accelerator, we can observe 150 signal events and measure the CP violation parameter with a 6% accuracy.We also developed a new calorimeter which can measure the incident angle of photons. This is a shashlik type detector with individual fibers reading one of the 3 different depth regions. A test experiment using 1.5-2.8GeV photons at SPring8 showed that it has an angle resolution of 9%/ Sqrt (E (GeV) ). The resolution can be improved further by increasing the light yield etc..We also developed a new type of light guide to inject the light from fibers to a phototube at a shallow incident angle. Using the light guide, the number of photoelectrons was increased by a factor 1.8.We also published results from Fermilab KTeV experiment, including the measurement of CP violation parameter, ε'/ε, establishing the direct CP violation.