A preliminary simulation study of influence of backsplash on the plastic scintillator detector design in HERD experiment

The plastic scintillator detector (PSD) is one of the detectors in the high energy cosmic radiation detection (HERD) facility, which is designed for gamma-ray detection and a redundant charge measurement. Backsplash will lead to a decrease in PSD’s performance of gamma-ray detection and charge measurement, which should be carefully considered. Two preliminary segmentation schemes of the PSD and two veto strategies have been proposed to suppress the backsplash effect. In this paper, we focus on the influence of the backsplash caused by gamma rays. The gamma-ray trigger efficiency and identification efficiency were studied in the case of different cell sizes and veto strategies, which can provide guidance on the PSD design. A Monte Carlo simulation based on Geant4 has been performed. To simplify the simulation, the PSD is segmented into 1 cm3 cubes which can be easily aggregated into cells with different sizes during analysis. Side_Veto can be used as a baseline design of veto strategy, whereas Smart_Veto can be selected as an upgraded design. Both the PSD bar cell with a width of less than 11 cm and the PSD tile cell with a width of less than 20 cm can achieve a sufficiently high gamma-ray trigger efficiency (> 80%), which realizes the primary goal of the PSD. Meanwhile, both the PSD bar cell with a width of less than 3 cm and the PSD tile cell with a width of less than 20 cm can ensure a sufficiently high gamma-ray identification efficiency (> 80%) for photons up to 800 GeV.