Cherenkov Detector for K/π Identification and γ-ray Detection in the Rare Decay K^+→π^+vv

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We have developed a new heavy, fast-response, and radiation-hard Cherenkov radiators based on lead tungstate (PbWO4, PWO) by heavy doping with rare-earth 3+ ions (GD3+, La3+)by a concentration of 3-8 mol%. We have confirmed the performance with the 500-1000 MeV/c π+ and proton beam at KEK-PS. The radiation hardness was measured for 60Co γ-rays at JAERI (Takasaki) for the accumulated dose of 1k-100k gray (1grey = 100rad).We have also studied the effects of many other dopants in PWO and found that Th4+ ions by 〜100 mol ppm gives dramatical improvement to PWO similar to 3+ ions. A few dopants increase the light yield significantly for PET diagnosis with a time gate of a few hundred ns.Another method to efficiently discriminate between K+ and π+ is to measure dE/dx precisely. We have carried out an R＆D of fast-readout and medium-segmented Si-strip detector (92x92 mm2) and readout pitch of 0.82 mm. This Si detector can withstand high intensity charged particles at a rate of 〜10MHz. The equivalent noise charge (ENC) well less than 3000e is promising for the K+ rare decay experiment (E949) at AG