Study of neutrino oscillations using solar neutrinos

本研究利用1996年4月开始使用的超级神冈探测器对中微子的振荡进行了研究。超级神冈探测器利用中微子电子散射来观测太阳中微子。超级神冈探测器的基准体积为2.2万吨，能够探测到世界上最多的太阳中微子事件（每天10-20个事件）。因此，可以研究太阳中微子通量的昼夜差异和能谱畸变。它们纯粹是由于中微子的性质，它们不受太阳模型的任何模糊性的影响。在这项研究中最关键的是探测器的能量校准。我们使用电子直线加速器（LINAC）对探测器进行了校准。我们在绝对能量尺度上取得了优于1%的精度。以1996年和1997年的日期计算，我们已经处理了374天的日期。从数据样本得到的通量是标准太阳模型期望的35.8%。结果以前所未有的统计数据再次证实了“太阳中微子问题”。然而，目前在白天和夜间的通量之间没有观察到显著差异。能谱的形状与此时的期望在统计上是一致的。如果我们有更多几年的数据，我们可以用昼夜差异和能谱来讨论中微子振荡。

In this research, the neutrino oscillations were studied using the Super-Kamiokande which was start from April 1996. The Super-Kamiokande detector observes solar neutrinos using neutrino-electron scatterings. The Super-Kamiokande detector has a fiducial volume of 22,000 tons and it is able to detect world largest number of solar neutrino events (10-20 events per day). Hence, it is able to study day/night difference of the solar neutrino flux and distortion of energy spectrum. They are purely due to the property of neutrinos and they are free from any ambiguities of solar models. The most crucial thing in this research was the energy calibration of the detector. We have calibrated the detector using an electron linear accelerator (LINAC). We have achieved an accuracy of better than 1 % in the absolute energy scale. Using the date taken in 1996 and 1997, we have processed 374 days' date. The flux obtained from the data sample is 35.8 % of the expectation from the standard solar model. The results reconfirmed the "solar neutrino problem" with an unprecedented statistics. At the moment, however, no significant difference between fluxes between dattime and nighttime is observed. And the shape of the energy spectrum is statistically consistent with the expectation at the moment. If we have few more years of data, we can discuss neutrino oscillations using day/night difference and the energy spectrum.