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探索中微子
从神冈探测器和超级神冈探测器，到探索中微子和质子衰变的顶级神冈探测器
1987 年 2 月 23 日，神冈探测器实现了史上首次成功观测超新星爆炸中微子的巨大成就。这千载难逢的机会由 160,000 光年外的超新星触发，由滨松光子学株式会社的 PMT 捕捉。我们的技术一直在不断发展，并且首先传递给目前经过升级的超级神冈探测器，以及后续的顶级神冈探测器。
适用于顶级神冈探测器的全新 20 英寸传感器
重要人物访谈
什么是中微子？
组成物质的最小粒子称为基本粒子。就目前所知，基本粒子包括构成质子和中子的六种夸克，以及包括电子的六种轻子。
其中有三种轻子不带电荷，被称为中微子。中微子是在太空飞行的第二常见物质，常见度仅次于光。它们起源于太阳等星体中心的核聚变反应、重星死亡时的超新星爆炸、被宇宙射线轰击的地球大气、核反应堆和地球内部。它们能够穿过任何类型的物质。此时此刻，它们正在流过我们的身体。
原子和基本粒子
夸克和轻子
在 13 秒内检测到 11 颗中微子
从 1987 年 2 月 23 日 07:35:35 (UTC) 开始，在大约 13 秒的时间内，在大麦哲伦星云中的超新星爆炸产生的 1058 颗中微子中，有 11 颗被神冈探测器检测到了。这些中微子在 160,000 年前的超新星爆炸中释放。他们穿过地球的概率是：
$$\frac{13\ sec.}{5\cdot10^{12}sec.}=2.6\cdot\ 10^{-12}=\frac{2.6}{1\ trillion}$$
神冈探测器抓住了这个远道而来的机遇。东京大学教授 Masatoshi Koshiba 计划了神冈探测器并指导开展了实验，他于 2002 年因在观测宇宙中微子方面的成就而荣获诺贝尔物理学奖。
神冈探测器使用鱼眼镜头从底部拍摄
（图像由东京大学宇宙射线研究所神冈观测站友情提供）
超级神冈探测器超纯水罐装量：50,000 吨
超级神冈探测器概念图
（图像由东京大学宇宙射线研究所神冈观测站友情提供）
超级神冈探测器是一个将神冈探测器的能力提升 20 倍的项目，在距离神冈探测器约 300 m 的神冈矿山地下 1000 m 处建造而成。其巨大的水箱直径为 39.3 m，高度为 41.4 m，可容纳 50,000 吨水，容量约为神冈探测器的 16 倍。实验的目的是通过观测太阳中微子、大气中微子、人造中微子等来明确关于中微子的所有信息，并证明质子的寿命。
超级神冈探测器中 20 英寸直径 PMT 的数量：11,200
在超级神冈探测器的水箱中，大约有 11,200 个面朝内部的光电传感器，称为光电倍增管 (PMT)。这些传感器捕获水中带电粒子发出的切伦科夫辐射光。根据切伦科夫辐射光的量和捕获光的时间，确定带电粒子的能量、指向性等。所用的光电倍增管的光电表面直径约为 50 cm（20 英寸），是世界上最大的光电表面。
相关内容：
20 英寸 PMT 的开发
20 英寸直径 PMT
顶级神冈探测器的水基切伦科夫检测器水箱容量：260,000 吨
顶级神冈探测器探测器图示
顶级神冈探测器探测器的原理图
顶级神冈探测器旨在通过质子衰减和 CP 破坏（中微子和反中微子之间的差异）调查，以及观测超新星爆炸产生的中微子，阐明大统一理论和宇宙进化史。顶级神冈探测器的巨大水箱仅需 10 年的时间即可获得相当于超级神冈探测器在 100 年的时间内收集的数据量，从而能够支持观测先前未能揭示的罕见现象和微小的 CP 破坏效应。
© Hyper-Kamiokande Collaboration
水基切伦科夫探测器中的光电传感器
水基切伦科夫探测器中的每个光电传感器都在测量在“何时”，有“多少”光照射了传感器。水基切伦科夫探测器的性能在很大程度上取决于其光电传感器的性能。例如，通过使用更精确地测量光的到达时间的光电传感器，可以更精确地估计探测器中的中微子相互作用或质子衰减的时间点。光电传感器时序性能的改进还有助于更好地区分信号事件和被称为背景的假事件。通过使用更精确地测量光量的光电传感器，可以估计由中微子相互作用产生的基本粒子的能量。我们专为顶级神冈探测器开发了一种新型 20 英寸光电倍增管，其性能比超级神冈探测器中的光电倍增管更高。
© Hyper-Kamiokande Collaboration
适用于顶级神冈探测器的全新 20 英寸直径 PMT
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