大亚湾反应堆中微子实验物理分析2013年度报告

王贻芳++曹俊++陈少敏++衡月昆++王萌

摘 要：中微子是研究超出标准模型新物理的关键与突破口之一。中微子振荡是目前实验中直接观测到的新物理现象，可以使用PMNS矩阵描述，矩阵中2011年以前未知的参数有θ13、m232的符号以及CP破坏相角δCP。其中θ13不仅是混合矩阵的基本参数之一，其大小也直接决定了目前实验技术手段对后两个参数的测量能力，即决定了中微子理论与实验下一步发展的方向。大亚湾反应堆中微子实验的物理目标是精确测量，设计灵敏度为在90%置信区间上确定至0.01或更好。大亚湾实验使用8个全同的中微子探测器在山体覆盖下做远近相对测量，降低本底，抵消反应堆及探测器的关联误差，以达到设计精度。探测器系统和電子学系统得到良好的维护，运行稳定。大亚湾实验的系统误差可分为关联误差与非关联误差。最大的探测器非关联误差贡献为慢信号能量cut的效率误差，由探测器之间的相对能标误差决定，上述0.5%的能标误差带来0.12%的效率误差，优于设计目标0.24%。最大的关联系统误差为spill-in误差，通过研究刻度数据给出降低该误差的可行性。除了利用钆俘获方法测量θ13以外，还实现了利用氢俘获方法独立精确测量θ13。完成了超新星触发系统设计，并加入国际超新星预警系统。在物理分析平台方面，针对不断增大的数据量，扩大了CPU和硬盘资源，建立了计算环境监控管理系统、设计了新的软件框架，实现了满足分析需求的事例缓存机制。在能量刻度研究方面，完成了对2012年度刻度数据的分析，使正电子能量重建的精度达到了1.5%的精度。

关键词：大亚湾中微子实验 中微子振荡 刻度 重建 本底 超新星

2013 Annual Report of Physical Analysis for Daya Bay Reactor Neutrino Experiment

Wang Yifang1 Cao Jun1 Chen Shaomin2 Heng Yuekun1 Wang Meng3

（1.Institute of High Energy Physics， Chinese Academy of Sciences； 2.Tsinghua University； 3.Shandong University）

Abstract： Neutrino has been the one of the keys to sutdy the new physics beyond the Standard Model， since neutrino oscillation is the directly observed new physics phenomena. PMNS matrix is utilized to describe the neutrino oscillation， and before 2011， unknown parameters in the matrix are： θ13、sign of m232 and δCP.θ13 determines the future of neutrino theory and experiment， because its value determines with current technology， whether the other two parameters can be measured. The detectors and electronics systems have been maintained well and working in good condition. The Daya Bay reactor neutrino experiment is designed to precisely measure to 0.01 or better at 90% C.L.. Eight ”functional” identical detectors are layed underground at two near sites and one far site for the near/far relative measurement， which fully cancels correlated uncertainty. Systematic uncertainty can be divided to correlated， which is fully canceled in the near/far relative measurement， and uncorrelated， which has a designed baseline 0.38% and designed goal 0.18%. The largest uncorrelated uncertainty contribution 0.12% is induced by relative energy scale uncertainty with a designed goal 0.24%. The improvement is mainly contributed to the excellent calibration and reconstruction. With hydrogen neutron capture method， an independent precision measurement of theta13 is implemented. The study and implement of the supernova trigger at Daya Bay is finished. The Daya Bay Experiment has joined SNEWS （SuperNova Early Warning System）. The computing resources and hard disks have been increased. A computing resource monitoring system and a computing environment management system were developed. A new lightweight analysis framework was proposed and the data model was defined as well as the event buffer mechanism. As for the calibration system， we completed the detailed analysis using the calibration data taken in 2012， and the precision of positron energy reconstruction can reach 1.5%.

Key Words：Daya Bay neutrino experiment； Neutrino oscillation； Calibration； Reconstruction； Backgrounds； Supernova