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

1994年进行了束流实验，研究了电子和μ子的分离效率，并研究了与大气中微子通量中nu_<mu>-亏缺有关的各种探测器效应。实验结果表明，电子和介子的分离效率达到了98%，与我们的蒙特卡罗模拟结果一致。这一结果表明，大气nu_<mu>-赤字可能与中微子振荡等真实物理现象有关。在这一研究期间，大气中微子事件的总数几乎翻了一番。观测到的（nu_<mu>/nu_e）比值相对于预期值（nu_<mu>/nu_e） _<Data>/ (nu_<mu>/nu_e) _<MC>，在亚gev能量范围内为0.60<正负>0.055 (stat.)<正负>0.05 （syst.）。nu_<mu>-赤字的统计学意义约为5 σ。我们还研究了多gev能量范围内的大气中微子通量。我们在这个能量范围内也观察到nu_<mu>-亏损。观测到的nu_<mu>/nu_e比值在该能量范围内的天顶角依赖性不均匀，与中微子振荡的期望一致。从这些研究中，我们得出结论，中微子振荡可能是大气中微子数据的原因。nu_<mu bb_0 mu或nutau的质量都可能在0.1 eV左右。

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.