White Star Production by pi-Meson in Nuclear Emulsion

本研究的目的是研究核乳化液中白星的产生特征。在欧洲核子研究中心，我们利用核乳化和反混合系统进行了介子中微子和τ中微子之间的中微子振荡实验。所要得到的信号是主要衰变拓扑为极短扭结的tau粒子，它是由μ中微子振荡的tau中微子在带电电流与核乳剂相互作用中产生的。在通常的中性电流相互作用中，我们不能区分τ扭结衰变和介子产生的类扭结白星过程。因此，有必要在完成我们的中微子振荡实验后知道白扭结过程的概率。在1995 - 1996财政年度的2年时间里，“核乳剂中π介子产生白星”的研究项目获得了教育部科学、科学、体育和文化部“科研资助(B)(2)”项目的资助。本调查结果已在此报告。以下是1995财年、1996财年按时间顺序的进度项目；(1)通过制作暴露在梁上的试验模组来确定核乳液的形状、厚度和所需板的数量。(2)设计并制作了核乳化液支架，用于将乳化液板相对固定在曝光处并保持光束密度恒定。(3)将上述乳化液瓶与硅条检测器等计数器组件组装，并测量其相对位置。(4)通过连接数据采集电路对乳化液瓶总成进行了测试，同时完成了必要的软件开发。(5)乳剂计数器系统在KEK负介子上曝光。(6)曝光后，冲洗所有乳化液板，完成自动扫描仪测量的准备工作。测量的总体形势是很顺利的，但在细节上也出现了一些新的问题，即对测量仪器的操作和功能要求非常复杂。由于这些原因，在本会计年度内完成测量和分析变得不可能。但目前，已经取得了与初始目的有关的初步结果，并计划在几个月内完成测量和分析。少

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