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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超级神冈探测器
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，以及后续的超级神冈探测器。
适用于超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。东京大学教授小柴昌俊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。
相关内容：
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。
1998 年，超级神冈探测器发现了表明中微子具有质量的中微子振荡，2015 年梶田隆章教授凭借这一成就荣获诺贝尔物理学奖。
20 英寸直径 PMT
超级神冈探测器的水基切伦科夫检测器水箱容量：260,000 吨
超级神冈探测器图示
超级神冈探测器的原理图
基于多年来开发的高灵敏度中微子观测技术，超级神冈探测器在灵敏度方面实现了进一步提升。超级神冈探测器由一个圆柱形水箱构成，水深 71 米，直径 68 米。该水箱的有效探测质量约为超级神冈探测器的 10 倍。水箱壁安装了 20,000 个超高灵敏度光电传感器和 1,000 个复眼式光电传感器，用于探测水中产生的极其微弱的切伦科夫光。超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
每个光电传感器均可测量光“何时到达”以及“到达光量”。这种探测性能对水切伦科夫探测器的整体观测性能具有重大影响。例如，更精准的光到达时间测量 (光探测)，有助于更准确地估算中微子相互作用或质子衰变的起点。此外，检测到的光越多，我们就能越精准地估算相互作用中产生的粒子的能量。这些性能提升同时有助于更有效排除被称为背景噪声的干扰事件。我们专为超级神冈探测器开发了一种新型 20 英寸光电倍增管，其性能是超级神冈探测器中的光电倍增管的两倍。
© Hyper-Kamiokande Collaboration
适用于超级神冈探测器的全新 20 英寸直径 PMT
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