Development of Neutron-Tagging Techniques and Application to Atmospheric Neutrino Oscillation Analysis in Super-Kamiokande
Development of Neutron-Tagging Techniques and Application to Atmospheric Neutrino Oscillation Analysis in Super-Kamiokande
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中子标记技术的发展及其在超级神冈探测器大气中微子振荡分析中的应用
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发表时间：
2014
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通讯作者：
T. Irvine
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作者：
T. Irvine
中微子振荡理论现在已经建立起来了。中微子混合角和质量平方分裂已经通过各种实验精确测量。然而，我们对这个领域的理解仍然是不完整的，中微子质量等级和CP破坏阶段继续躲避我们。切伦科夫探测器Super-Kamiokande对水中中微子质量层次的灵敏度取决于它区分反中微子和中微子相互作用的能力。这在水切伦科夫探测器中本质上是一项艰巨的任务，但一种可能的方法是通过中子的探测。在一个典型的带电反中微子相互作用中，即ν ε e+p→ n+ e+，一个中子会被射出，但在相应的中微子相互作用中却不是这样。在水中，这些中子然后热化并被氢捕获。发射出2.2 MeV的γ射线，可以用来标记中子，从而推断先前的相互作用是反中微子的相互作用。本文介绍了中子示踪方法的发展及其在Super-Kamiokande大气中微子样品中的应用。然后，这些信息被用来帮助区分中微子和反中微子的相互作用，从而提高我们对中微子质量层次的敏感性。中子标记效率为20.5%，与1.8%的背景每个大气中微子事件。构造了浓集中微子和反中微子样品，使探测器对中微子质量分级的灵敏度提高了0.06。利用SK-1到IV（4581.5天）的所有数据进行了三味中微子振荡分析。正态层次更受青睐，显著性为x 2（NH-IH）= −0.9。
Neutrino oscillation theory is now well established. The neutrino mixing angles and mass-squared splittings have been precisely measured, by a variety of experiments. However our understanding of this field is still not complete the neutrino mass hierarchy and CP violating phase continue to elude us. Sensitivity to neutrino mass hierarchy in the water Cherenkov detector Super-Kamiokande is dependent on its ability to distinguish anti-neutrino and neutrino interactions. This is inherently a difficult task in water Cherenkov detectors, but one possible method is through the detection of neutrons. In a typical charged-current anti-neutrino interaction, ν̄e+p→ n+ e+, a neutron is ejected, however this is not true of the corresponding neutrino interaction. In water, these neutrons then thermalize and are captured by hydrogen. A 2.2 MeV γ-ray is emitted, which can be used to tag the neutrons, and thus infer that the preceding interaction was that of an anti-neutrino. This thesis describes the development of neutron tagging methods and application to the Super-Kamiokande atmospheric neutrino sample. This information is then used to help distinguish between neutrino and anti-neutrino interactions, thus increasing our sensitivity to the neutrino mass hierarchy. A neutron-tagging efficiency of 20.5% is achieved, with a background of 1.8% per atmospheric neutrino event. Enriched neutrino and anti-neutrino samples are constructed, improving the sensitivity of the detector to neutrino mass hierarchy by ∆χ2 = 0.06. Three-flavour neutrino oscillation analysis is performed using all data from SK-I to IV (4581.5 days). The normal hierarchy is favoured, with a significance of ∆χ2(NH-IH) = −0.9.