利用反应堆中微子精确测量弱混合角

The weak mixing angle, one of the key parameteters in the Standard Model, has been measured to about 0.1-0.2% at the Z-pole. The renormalization group running of the weak mixing angle predicted by SM is also tested experimently. Poor precison in the low momentum transfer range and the NuTeV (a neutrino nucleon deep inelasitc scattering experiment ) 3 sigma deviation from the standard model are promoting more expermental efforts in precise measurements in the low energy range. Precision measurement of the weak mixing angle at low energy transfer allow indirect access to new physis effects at and beyond the TeV scale...As a pure leptonic process, neutrino electron scattering can provide a clean channel for a precise measurement of the weak mixing angle at low momentum transfer. Chinese experimental neutrino physics research has been focusing on studing reactor neutrinos based on liquid scintillator detection method. This includes the Daya Bay experiment, which has collected large statistics and high resolution reactor neutrino events and the Jiangmen Neutrino Observatory, which is under construction now. Given the above, this project will study the physics potential of measuring weak mixing angle at a precision better than 1% using reactor neutrino and electron scattering in a Gd-doped liquid scintillator detector.

弱混合角是粒子物理标准模型的核心参数之一，其数值随着能标不同而变化。在高能端的Z质量附近，该参数的测量精度已经达到约0.1-0.2%。但不同的实验结果相差约3.2个标准方差。在约4-5GeV的动量转移区，利用中微子与核子深度非弹性散射物理过程的NuTeV实验，测量结果与标准模型预测相差3个标准方差。在更低能区的测量精度较差，世界范围内多个在低能区精确测量弱混合角的实验被提出。.中微子与电子散射为纯的轻子弱作用过程，提供了干净的检验电弱统一理论的途径。中国中微子实验研究主要使用液体闪烁体技术来探测反应堆中微子，比如目前已获取大量高精度的反应堆中微子事例的大亚湾实验，和正在建设中的江门中微子实验。本项目研究使用反应堆中微子与电子的弹性散射来精确测量低能区的弱混合角度，研究如何实现在基于参钆液体闪烁体的探测器中好于1%的弱混合角测量精度。本研究一个应用为江门中微子近点探测器。

弱混合角是粒子物理标准模型中重要的参数。根据标准模型，其值随作用能标跑动。精确测量这种跑动，是对标准模型的精确检验。Z质量附近，该参数的测量精度已经达到~0.1%，而低能区实验测量精度仅为~10%。 中微子与电子弹性散射是纯轻子过程，为精确验证电弱统一理论提供了一个干净的途径。 项目计划分析大亚湾实验数据，选取单信号的反应堆中微子与电子弹性散射信号，针对天然放射性本底、宇宙线诱发本底等进行研究。 利用该信号与反贝塔信号的事例率比值消除关联误差，构建统计方法，尝试获得弱混合角的测量，并研究本底、探测器响应等因素对该参数测量的精度的影响。 项目分析了大亚湾1800天数据， 完成了反贝塔衰变(钆俘获和氢俘获）的信号、本底的测量，单信号信号的选取，统计方法的构建。项目还在开展中。