The measurement of a tau-neutorino mass

CHALUS是利用欧洲核子研究中心(CERN)的超质子同步加速器(SPS)产生的中微子束的国际项目。本项目的目的是通过从Mu中微子到Tau中微子的振荡的方法来观测tau中微子的质量。通过观察照相核乳剂中从产生点到衰变点的tau的轨迹，可以对tau-中微子进行识别。探测器由靶谱仪、量热计和µ子谱仪组成。我们正在为这个实验中最重要的目标--目标做出贡献。该靶采用乳胶片和光纤跟踪器的夹层结构，中微子曝光已于1995年11月完成。乳化液分析是本项目中最困难的工作，是利用名古屋大学药学研究所开发的自动乳化液分析系统进行的。通过4个月的扫描，分析了乳状液中中微子相互作用的个数，超过7700个中微子相互作用。这个数字约占所有合唱团的15%，但这个数字已经是1978年进行的最敏感的模拟实验E531的两倍。本实验对质量为1 eV的中微子和混合质量为1%的中微子敏感，要完成所有的分析，需要两年多的时间。

CHORUS is the international project using the neutrino beam from super proton synchrotrn (SPS) of CERN (Center of Europ organization for Research of Nuclus). The object of this project is to observe the mass of tau-neutrino by the method of the oscillation from mu-neutrino to tau-neutrino. The identification of tau-neutrino could be done by detecting the produced tau by observing the trace of tau from produced point to the decay point in the photographic nucler emulsion.The detecter have many parts, target spectrometer calorimeter and muon spectrometer. We are contributing on the target the most important target of this experiment. This target has the sandwich structure of emulsion sheets and fiber trackers.The neutrino exposure has been finished on Novenber in 1995. The emulsion analysis, the most difficult job in this project, has been done by using Automatic emulsion analysis system originally developed by physists of Nagoya university. The number of analyzed neutrino interaction in the emulsion is more than 7700 neutorino interactions by 4 month scanning. This number is about 15% of all CHORUS, but already this number is 2 times higher than the most sensitive similler experiment, named E531 done in 1978. This experiment is sensitive to 1 eV in tauneutrino mass and 1% in mixing tau-neutrino to mu-neutrino.To finish all of the analysis, it take more two years.