| Cosmic rays are high-energy particles originating from outer space.Understanding their origin,acceleration,and propagation is crucial for the study of high-energy astrophysics.The large radio array is essential in ground-based cosmic ray experiments.By detecting the radio signals generated by extensive air showers,radio arrays can accurately reconstruct relevant information,such as the direction and energy of the primary cosmic rays.Moreover,radio arrays have advantages such as low cost,easy scalability,all-weather operation,and measurement of the entire shower evolution process.Therefore,they have become one of the important research directions in cosmic ray detection.However,radio detection technology faces many challenges,especially in implementing self-triggering.Persistent low-amplitude noise,such as the Galactic background noise,determines the threshold for triggering radio arrays.In addition,high-amplitude noise generated by background sources such as aircraft and substations can cause false triggering of radio arrays.These factors make the self-triggering of radio arrays difficult.At the same time,noise can also be coupled into the final observed data through antenna response,posing a significant challenge for correctly reconstructing the electric field of the radio signal.With the development of radio detection experiments and an understanding of the mechanisms behind the radio signals produced by extensive air showers,it has been discovered that background events can be identified and removed through methods such as identifying the polarization characteristics of the shower by using the different characteristics between background events and the radio radiation produced by extensive air showers.Thus,actual shower events can be distinguished from the vast background events.Based on the GRAND(Giant Radio Array for Neutrino Detection)engineering array and the actual antenna response,this paper studied the polarization characteristics of radio signals.It estimated the level of noise suppression that can be achieved using these polarization characteristics,together with the simulated radio signals produced by ZHAireS for extensive air showers.Based on the current research status at home and abroad,this paper elaborates on the basic research of cosmic rays,the physical processes of extensive air showers,and the specific mechanisms of radio radiation.The entire radio signal simulation toolchain has been developed and improved,and the fundamental theories in related fields have been carefully summarized.In order to simulate real scenarios,noise,filtering,sampling,and other processing are added to the signal.Then,the Hilbert transform and Stokes parameters are used to reconstruct the radio signal’s polarization characteristics along the shower plane.The results are consistent with the numerical analysis,showing that the polarization of the radio signal strongly points towards-v×B.In order to measure the relative strength of the geomagnetic field effect and the charge-excess effect,this work studied the basic characteristics of the polarization ratio a.ZHAireS was used to simulate a large number of proton cosmic rays with different energies,zenith angles,and azimuth angles.It was found that the polarization ratio a is strongly correlated with the zenith angle θ,weakly correlated with the energy E,and the noise and trigger settings also affect the final result when the incident angle is large(θ>70°).Next,this paper avoided the complex operation of reconstructing the electric field polarization using Stokes parameters by defining the polarization ratio aDAQ.Then,the distribution of aDAQ and Etot was studied.A trigger method based on polarization characteristics was proposed,which can be used for the level-one triggering of a single antenna,avoiding the occurrence of false triggering under high amplitude noise caused by simple threshold triggering.The corresponding antenna triggering efficiency was statistically analyzed under different cut conditions.Finally,considering the actual antenna response of the three-butterfly antenna based on the GRAND engineering array,the polarization characteristics of the radio signal were studied,and the antenna triggering efficiency was statistically analyzed under the actual response.At the same time,based on the voltage data without reconstruction,the radio signal’s polarization characteristics were also studied. |
