寻找轻型惰性中微子的物理研究

The theory of three-neutrino mixing and nonzero neutrino mass has been well established. Despite this success, the possible existence of additional sterile neutrinos beyond the known three is under active discussion in the neutrino community. Especially since the observation of anomalous short-baseline neutrino oscillation in the LSND and MiniBooNE experiments, sterile neutrino search is one of the frontiers of the neutrino physics. With several millions of reactor antineutrino interactions collected at Daya Bay experiment, we propose to search for a light sterile neutrino with the mass squared difference less than 0.3 eV^2 through the precise measurement of the Daya Bay reactor neutrino energy spectrum at multiple detectors. The expected sensitivity will be improved by at least a factor of 2 than the current upper limit of sterile neutrino mixing angle, theta14. In addition, we also propose to perform a joint sterile neutrino search analysis with the other neutrino experimental data to minimize parameter space of the possible existence of sterile neutrinos, and compare it with the LSND/MiniBooNE anomalies. In the meanwhile, based on the scientific research facilities in China，we will propose the design of the next generation short-baseline neutrino experiment to search for sterile neutrinos with the mass squared difference at the order of ～1eV^2.

大量的中微子振荡实验已证明中微子具有非零质量。通过与单态的右手中微子场（惰性中微子）的耦合来引入中微子的质量项是对粒子物理标准模型最简单的拓展。尤其在LSND和MiniBooNE实验观测到异常短基线中微子振荡信号后，寻找惰性中微子成为一个前沿热点问题。本项目提出利用大亚湾中微子实验中多个不同基线长度的探测器所积累的数百万的反应堆中微子事例来寻找轻型惰性中微子，预计在90%的高置信度下小质量范围内惰性中微子混合角sin^2_2theta_(14)的最好灵敏度将达到 2×10^(-3)；并将大亚湾实验与世界上其他的中微子实验相结合，做一个寻找惰性中微子的联合物理分析，得到其在较大参数空间内的全局图像，并检验LSND/MiniBooNE的实验结果;最后依据我国现有的和正在建设的科学装置,优化设计下一代短基线中微子实验，寻找质量平方差～1eV^2的惰性中微子。

惰性中微子对于研究中微子的质量起源有重要意义。寻找惰性中微子是中微子研究的前沿和热点领域，特别是LSND和MiniBooNE实验发现了疑似惰性中微子迹象。 本项目提出利用大亚湾实验数据，并结合其他反应堆和加速器中微子实验，来共同寻找惰性中微子，并对LSND和MiniBooNE的实验结果进行检验。按照目前的实验结果，尚未发现惰性中微子的迹象，而且基本排除了LSND和MiniBooNE在低质量段的惰性中微子信号。而且项目也研究了对江门和锦屏中微子实验进行改造的可行性研究，从而能够进一步提高对惰性中微子的探寻能力。最后项目还进一步研究了通过全球数据分析，检验中微子混合矩阵幺正性的研究。