锦屏低能太阳中微子实验的关键问题研究

The region [0.8, 3.5] MeV is a unknown region of the Solar neutrino experimental detection bearing several physics interests and critically important. The pep neutrino and the low energy spectrum of B8 neutrinos still need a precision measurement, and the CNO neutrino is not discovered yet. The measurement of the neutrino spectrum in this region can be used to study the neutrino oscillation, especially the transition of neutrino vacuum oscillation to matter oscillation, which can be used to verify the matter-induced oscillation behavior or to reject sterile neutrino assumptions etc. The measurement of the Solar neutrino in this region is also helpful to study the Solar metality problem, and to judge the predictions from the Solar Standard Model and the helioseismology measurement. Jinping, as the deepest undergroud lab in the world, with an overburden of 7500 mwe, is especially good for the Solar neutrino experiment, which needs a low background environment. According to the depth and some initial ideas of the detection, the predicted background will 100 times lower than the Borexino Experiment, and its threshold will be much lower than SuperK (and HyperK). This project will study several key issues of doing solar neutrino experiments at Jinping: 1) The signal significance of detecting each type of the Solar neutrinos. 2) The significance of discovering the vacuum-matter transition of neutrino oscillation, and the significance of the Solar metality problem.

0.8至3.5 MeV区间是目前太阳中微子实验的空白区域，有多重物理意义，关系重大。这一区间的pep中微子和低能的B8中微子需要精确测量，CNO中微子仍待发现。这一段太阳中微子的能谱可以用来研究中微子振荡，尤其是振荡从真空到物质的跃迁行为，可以最终确定振荡物质效应，排除惰性中微子等假设。这一段的中微子能谱测量还能用于检查太阳的金属性问题，从实验上判断目前太阳标准模型和日震学测量的矛盾预期。锦屏- - 世界上最深的地下实验室，深度7500 mwe，特别适合需要低本底环境的太阳中微子实验。按照锦屏环境估计及初步设想的探测方案，本底将比Borexino实验低约100倍，探测阈值远低于SuperK（及HyperK）。本项目将研究在锦屏开展太阳中微子实验的几个关键问题： 1) 考察各种靶质量条件下的各太阳中微子成分的信号显著度； 2) 考察确定中微子真空到物质振荡转换问题、确定太阳金属性问题的信号显著。

a、确定在锦屏建造具有2千吨有效靶质量，并且具有500光电子/MeV光产额的中微子探测器有能力精确测量关键的几种太阳中微子的信号通量，约束太阳中微子从真空振荡到物质振荡的转化模型参数空间，约束惰性中微子和非标准相互作用模型，能够发现CNO中微子，并且精度达到10%，能够初步进行太阳金属丰度的判断。提出了建设锦屏中微子实验的提议。..b、设计建造了1吨实验原型机，成功在锦屏地下运行超过一年，有初步的宇宙线缪子通量测量，液闪本底测量。发现一种慢液闪，可以实现闪烁光和切仑科夫光的分离测量。发现一个新的量能器能量分布函数，性能超过常用的Crystal Ball函数。发明一种新型的用于光电倍增管的光收集器，适合大的接受角度（90度），并且能够实现高度密排，达到100%光阴极覆盖率。研究了一种低本底不锈钢，达到同等实验的类似水平。构建了用于快速实验研究的探测器响应模型。..c、同时发现所设计的千吨中微子探测器，可以对地球中微子有非常好的测量精度，能够排除部分冲突的地球产热模型预期，而且对超新星遗迹中微子有非常好的探测精度。