Fast Simulation Of Dynamic Range Extension System In LHAASO-WCDA

The origin and spread of cosmic rays is an important issue in high energy astrophysics.Cosmic rays are a product of the evolution of various celestial bodies,and in particular,the products of various high-energy astrophysical processes carry abundant information about these processes.However,there are many difficulties in the study of the origin and propagation of cosmic rays.They can only be indirectly inferred from the radio waves,X-rays,and gamma rays emitted by cosmic rays during their movement and action.Therefore,in modern physics,ultra-high energy gamma astronomy has become one of the main branches of astrophysics.The unique Large High Altitude Air Shower Observatory(LHAASO)was constructed by conducting a full-area gamma source scan and accurately measuring the gamma spectrum,measuring the single component cosmic ray spectrum,determining the position of the “knee”,and achieving space The seamless connection between direct measurement of cosmic rays and air shower measurement on the ground completes the frontier topics of new physical research such as the continuous and consistent measurement of the cosmic ray spectrum and the development of dark matter.In order to measure the core position information of cosmic ray particles between 100 TeV and10PeV and to distinguish them,LHAASO plans to build a Water Cherenkov Detector Array(WCDA)dynamic range expansion system.This article will focus on the WCDA dynamic range expansion system,to do preparatory work for the expansion of the number of measurements of the dynamic range of the shower particle number,particle identification and the original energy reconstruction.The WCDA dynamic range expansion system requires the use of GEANT4 to simulate large statistical examples of high-energy cosmic rays.However,the full simulation based on GEANT4 is very CPU-intensive,and there are three difficulties:First,high-energy showers produce too many secondary particles;second,there is not enough memory;and third,the running time is too long.For these simulation difficulties,this paper introduces the optimization of the frame structure of the WCDA dynamicrange expansion system GEANT4.The fast simulation method is studied,mainly including two methods of photon thinning and parameterization to save memory and time.These two methods can be applied to the WCDA dynamic range expansion system to quickly and efficiently simulate the response of high-energy cosmic ray cases on the detector.