Optimization of Charge Measurement for LHAASO Muon Detector

The Large High Altitude Air Shower Observatory (LHAASO) is mainly used for exploring the origin of high-energy cosmic rays, the evolution of high-energy celestial bodies and the research of new frontiers of physics. The large area Muon Detector (MD) array has high identification ability of primary gamma rays and can detect ultra-high energy gamma rays with high sensitivity. MD achieves a large dynamic range detection of 1-10 000 muons through the common readout of the anode and the seventh dynode. In order to reduce the error of directly converting the anode signal into the dynode signal in the saturated area, an optimization scheme of charge measurement was proposed by combining the anode (the unsaturated part of the anode) and the dynode (the saturated part of the anode) signals. The connection mode between the anode and the dynode is obtained by numerical simulation, and the relationship between the anode and dynode calibrated in the laboratory could be used for connection. Numerical simulation results show that the proposed scheme can effectively reduce the measurement error in the large dynamic range of 1-10 000 muons, the error is less than 1%, and the muons spectrum structure is obviously improved. The results of data analysis with full waveform signal are in good agreement with the simulation results, which verifies the effectiveness of the scheme.