大型地面粒子探测器阵列触发判选的研究

As the new generation of ground-based experiment, LHAASO-KM2A is aimed at unlocking the mystery of the century—the origin of high energy cosmic ray in the galaxy by probing the ultra-high energy gamma ray. The “triggerless” data acquisition system that KM2A uses will provide a solid platform for trigger selection research of the ground particle array experiment. The project proposes to reduce the gamma ray detection threshold energy of LHAASO-KM2A experiment by optimizing trigger selection algorithm and aims to improve the sensitivity of gamma ray observation. The projects first focuses on studying the different parameters including transverse distribution and particle density of the cascade process of gamma and nucleon in the air shower with the purpose of optimizing trigger selection algorithm and improving the gamma ray detector’s sensitivity. Second, the project is designed to reduce the detector’s threshold energy by better designing the trigger selection algorithm based on the different distribution of cosmic ray and noise signal in time and space. Third, the project plans to test the trigger selection algorithm optimized from simulation with the existing KM2A prototype array.

LHAASO-KM2A实验作为新一代地面粒子阵列实验，旨在通过高能伽马射线测量来揭开银河系内高能宇宙线起源这一“世纪之谜”。KM2A将采用的“无触发”数据获取机制为地面粒子阵列实验的触发判选研究提供了非常好的平台。本项目拟通过触发判选算法的优化来降低LHAASO-KM2A实验对伽马射线探测阈能，提高其在伽马射线观测的灵敏度。本项目将重点研究利用大气簇射中伽马与核子在级联过程中的横向分、粒子数密度等参数的差异来设计优化触发判选算法，提高伽马射线的探测器灵敏度；另一方面利用宇宙线与噪声信号在时空间分布上的差异来设计触发判选算法，从而降低探测器阈能；并且利用已有的KM2A定型阵列对在模拟中优化设计得到的触发判选算法做出实验检验。

随着时钟技术的快速发展，给高能物理实验带来的新的设计方案与架构。LHAASO-KM2A实验作为一个宇宙线地面观测实验首次采用了CERN在2009年提出的基于White Rabbit技术的时钟系统，在KM2A阵列的触发判选上实现了“Triggerless”的技术方案，即完全没有硬件触发判选系统，有软件进行触发判选。这给KM2A实验的触发逻辑带来的灵活和方便。本项目基于“Triggerless”方案带来的优势特点，按计划完成了KM2A阵列触发判选条件的研究工作，取得了多个成果：1）利用宇宙线事例在空间与时间上的特点，研究了KM2A新型触发模式；2）利用电磁粒子探测器电量信息，来区分质子与伽马，从而优化触发模式；3）利用缪子探测器电量与时间信息，参与阵列触发，研究多缪子事例的触发模式；项目成员以通讯作者或者第一作者发表Asroparticle Physics文章一篇、Nuclear Inst. And Methods in Physics Research,A文章一篇，会议文章3篇，相关研究成果在LHAASO-KM2A实验已经开始采纳并且验证。本项目为LHAASO-KM2A实验的触发模式做了前沿性的研究，为其后期取得突破性的物理结果奠定了基础。