利用宇宙线蔟射事例对水切伦科夫探测器阵列进行时间标定

As an important part of the project LHAASO in National Twelfth Five-Year Plan, WCDA (water Cherenkov detector array) has the characteristics of wide field, full duty cycle and strong ability of background rejection, in very high energy gamma ray detection field, it is expected to greatly increase the number of radiation sources. The radiation sources shoot high-energy gamma rays into the atmosphere and making extensive air shower, the detector collects the shower secondary particles, reconstructs the original direction of the radiation source by using the arriving time and energy information. In order to control the angle deviation of the radiation sources to the minimum, the time offsets among the detector units must be calibrated strictly. The WCDA has a design of hardware calibration by using the fast LEDs and plastic optical fiber bundles, which has been verified on the 9-cell engineering array during 2011 and 2013, but it has some limitations for the future full array. The project will study the time calibration method by using GEANT4 detector simulation combined engineering array experiment data analysis, to apply the method to the whole WCDA, complement and cross check the hardware calibration, also fufills the goal of online-calibration.

作为“十二五”项目LHAASO的重要组成部分，WCDA（水切伦科夫探测器阵列）具有视场角大、全天候运行以及强大的本底排除能力等特点，在甚高能伽马射线探测领域，有望大幅度提高辐射源的样本数量。辐射源发射的高能伽马光子在大气中产生蔟射，探测器单元通过记录簇射次级粒子的到达时间来对辐射源进行方向重建。为了使辐射源的系统指向偏差控制到预期范围内，需要对探测器单元之间的相对时间延迟进行严格标定。WCDA探测器目前已经拥有一套使用快速LED+塑料光纤束的硬件标定方案，并在9单元工程样机上得到实验验证，但对于未来全阵列该方案存在一定局限性。本申请项目将通过探测器模拟以及结合工程样机的数据分析的手段，发展一套基于宇宙线簇射数据的实时时间标定方案，来应用到全阵列上，与硬件标定方案实现互补与相互校验，并实现探测器的在线时间标定。

水切伦科夫探测器阵列是LHAASO观测站的重要组成部分，1#阵列以900个8英寸直径的CR365型光电倍增管为基本探测单元，放置在900个光隔离的水切伦科夫探测单元内，目标是甚高能伽马辐射源的观测。通过探测宇宙线以及伽马光子在大气中产生的簇射次级粒子，通过探测得到的次级粒子的电荷和时间信息，对原初事例进行方向重建。本项目主要是围绕探测器的时间特性进行研究，通过利用宇宙线簇射信息来对探测器进行时间标定，结合硬件标定系统，给出标定数据，分析硬件和软件对探测器标定的差异，给出标定结果；另外对探测器探头的时间特性进行了一些实验研究，帮助更加深入理解探测器的性能参数。