White Star Production by pi-Meson in Nuclear Emulsion

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In this investigation, the purpose is a study of white star production features in nuclear emulsion. We are performing the neutrino oscillation experiment between muon-neutrino and tau-neutrino by using nuclear emulsion and counter hybrid system in CERN.The signal to be obtained, is tau particle which main decay topology is very short kink and which is produced in charged current interaction with nuclear emulsion by tau neutrino oscillated from muon neutrino. In principle, we can not distiguish between tau kink decay and kink like white star process produced by pion in usual neutral current interacion. Therefore, this rises as background and it is necessitated to know the white kink process probability in completion our neutrino oscillation experiment.During the 2 year term from FY1995 through FY1996, the investigation titled as "White Star Production by pi-Meson in Nuclear Emulsion" was supported in category of "Grant-in-Aid for Scientific Research (B) (2)" by The Ministry of Educatio … More n, Science, Sports and Culture. This investigation results have been reported here.The followings are time sequential item of progress in FY1995, FY1996 ;(FY1995)(1) The nuclear emulsion shape, thickness, the number of plates needed were decided by fabricating test modules exposed on beam.(2) The nuclear emulsion holder was designed and fabricated, which is used to fix the emulsion plates relatively in a exposure and keep the beam density to be constant.(3) The emulsion holder mensioned above was assembled with Silicon Strip Detectors and other counter componets and surveyed the relative positions.(4) THe emulsion holder assembly was tested by connecting with data taking circuits and necessitating software developement was completed in same time.(FY1996)(5) The emulsion-counter system was exposed on negative pion in KEK.(6) After exposure, all amulsion plates are developped and preparation of measurement by automatic scanner was completed.The global situation of measurement is very smooth but there appeare some new probiems in detail i.e. very complicated operation and function of measuring apparatus are needed. By these reasons, the completetion of measrement and analysis in this fiscal year becomes to be impossible. But at present, the preliminary results concerned to initial purpose has been obtained and in several months the measurement and analysis is planned to be finished comletely. Less