大亞灣反應堆中微子實驗物理分析2013年度報告

王貽芳++曹俊++陳少敏++衡月昆++王萌

摘 要：中微子是研究超出標準模型新物理的關鍵與突破口之一。中微子振蕩是目前實驗中直接觀測到的新物理現象，可以使用PMNS矩陣描述，矩陣中2011年以前未知的參數有θ13、m232的符號以及CP破壞相角δCP。其中θ13不僅是混合矩陣的基本參數之一，其大小也直接決定了目前實驗技術手段對后兩個參數的測量能力，即決定了中微子理論與實驗下一步發展的方向。大亞灣反應堆中微子實驗的物理目標是精確測量，設計靈敏度為在90%置信區間上確定至0.01或更好。大亞灣實驗使用8個全同的中微子探測器在山體覆蓋下做遠近相對測量，降低本底，抵消反應堆及探測器的關聯誤差，以達到設計精度。探測器系統和電子學系統得到良好的維護，運行穩定。大亞灣實驗的系統誤差可分為關聯誤差與非關聯誤差。最大的探測器非關聯誤差貢獻為慢信號能量cut的效率誤差，由探測器之間的相對能標誤差決定，上述0.5%的能標誤差帶來0.12%的效率誤差，優于設計目標0.24%。最大的關聯系統誤差為spill-in誤差，通過研究刻度數據給出降低該誤差的可行性。除了利用釓俘獲方法測量θ13以外，還實現了利用氫俘獲方法獨立精確測量θ13。完成了超新星觸發系統設計，并加入國際超新星預警系統。在物理分析平臺方面，針對不斷增大的數據量，擴大了CPU和硬盤資源，建立了計算環境監控管理系統、設計了新的軟件框架，實現了滿足分析需求的事例緩存機制。在能量刻度研究方面，完成了對2012年度刻度數據的分析，使正電子能量重建的精度達到了1.5%的精度。

關鍵詞：大亞灣中微子實驗 中微子振蕩 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