Study And Optimization Of LHAASO-ED Array Calibration Method

Large High Altitude Air Shower Observatory(LHAASO)is currently the largest and most sensitive composite cosmic ray ground-based observatory in the world.The one square kilometer array(KM2A)is one of the main array of LHAASO.The main scientific goal is to measure the cosmic ray energy spectrum in the range of 10 TeV to 100 PeV and carry out the survey of gamma-ray above 100 TeV with the most sensitive in the world.Detector calibration is the key to ensure the performance of cosmic ray observation device.Time calibration is directly related to whether the cosmic ray acceleration source can be found in the accurate direction,and charge calibration is related to the accuracy of cosmic ray energy measurement.One square kilometer array has 5249 electromagnetic particle detectors(ED)and 1188 muon detectors(MD).There is no precedent for calibrating detectors of this scale,and it is not feasible to rely on traditional hardware calibration technology.The preliminary study of KM2A group shows that the offline calibration technique is the most ideal calibration method for LHAASO-KM2A experiment.Based on the background,this paper proposes a charge calibration method for large-scale cosmic ray experiment,which uses the characteristic single particle signal in extended air shower(EAS)as the particle source,in order to suppress the signal pollution caused by multiple particles hitting the detector in shower.This paper firstly proposes an analytical method using untriggered probability to estimate the probability of a single particle signal hitting the detector in an EAS.The advantage of the method is that it is not necessary to know the original composition model of cosmic ray and the interaction model of cosmic ray through atmosphere in advance,which reduces the influence of model uncertainty on calibration.The experimental results show the accuracy of the number of particles detected by 5249 EDs in the whole array can be less than 2%,and the calibration can be completed every 4 hours,which achieves high accuracy and efficiency.The time calibration of KM2A-ED is carried out based on the characteristic plane(CP)method.In this method,the secondary particles in EAS are used as the calibration beam to scale the time response between different EDs,and the time synchronization accuracy of more than 5,000 EDs reaches sub-nanosecond.In this paper,we optimize this method by analyzing the time walking effect caused by timing design of electronic.The time resolution of the detector is improved after the～1ns uncertainty caused by this effect is corrected in the data.The high efficiency and hardware independent calibration method not only solves the difficulties of large-scale detector calibration,but also provides an ideal monitoring method for LHAASO-KM2A experiment.The stability of the detector was analyzed using long-term data of the calibration parameters,and these results improve our understanding of scintillator detector performance.So far,LHAASO-KM2A has discovered more than ten different types of ultra-high-energy gamma-ray sources,opening of the era of "ultra-high-energy gamma astronomy".These physical results also verify the reliability of the calibration method.