Study of the nu_<mu>-deficit in the atmospheric neutriono fluxes. (Study of the origin of neutrino mass.)

1994年，为了研究分离电子和µ子的效率，以及研究与大气中微子通量中的nu；u；u&gt；-亏损有关的各种探测器效应，进行了束流实验。实验结果表明，电子与介子的分离效率达到了我们蒙特卡罗模拟所预期的98%。这一结果表明，大气中微子的亏损可能与中微子振荡等真实物理现象有关。在本研究期间，大气中微子事件的总数几乎翻了一番。观察到的(nu_&lt；u&>；/nu_e)比率与预期比率(nu_&lt；u&>；/nu_e)_&lt；/(nu_&lt；u&>；/nu_e)_&lt；MC&>；比率为0.6；正->0.055(统计)&lt；正->0.05(系统)。在亚GeV能量范围内。我们还研究了多GeV能量范围内的大气中微子通量。在这个能量范围内，我们也观察到了nu&lt；u；u；-亏缺。在该能量范围内观测到的nu&lt；u&gt；/nu_e比值与天顶角的关系并不均匀，与中微子振荡的预期一致。Nu-Mu->Mu；Mu或Nu-Tau的质量可能约为0.1 eV。

In 1994, a beam experiment was carried out to study the efficiency of separating electrons and muons, and to study various detector effects related to the nu_<mu>-deficit in the atmospheric neutrino fluxes. The result from this experiment showed that the efficiency of separating electrons and muons was 98% as expected by our Monte Carlo simulation. This result suggests that the atmospheric nu_<mu>-deficit is probably related to a real physics such as neutrino oscillations.The total number of atmospheric neutrino events was nearly doubled during this research period. The observed (nu_<mu>/nu_e) ratio relative to the expected one, (nu_<mu>/nu_e) _<Data>/ (nu_<mu>/nu_e) _<MC>, was 0.60<plus-minus>0.055 (stat.)<plus-minus>0.05 (syst.) at the sub-Gev energy range. The statistical significance of the nu_<mu>-deficit was about 5sigma.We also studied the atmospheric neutrino fluxes in the multi-GeV energy range. We observed nu_<mu>-deficit in this energy range too. The observed zenith-angle dependence of the nu_<mu>/nu_e ratio in this energy range was not uniform and was consistent with the expectation from neutrino oscillations.From those studies, we concluded that neutrino oscillations might account for the atmospheric netrino data. The mass of either nu_<mu>mu or nutau might be about 0.1 eV.