Trigger and noise filtering algorithms for the LHAASO water Cherenkov detector array

Introduction The Large High Altitude Air Shower Observatory (LHAASO) will be constructed at Mt. Haizishan, Sichuan Province, China. Among several detector components of the LHAASO, the Water Cherenkov Detector Array (WCDA) is of great importance for gamma-ray astronomy from 100 GeV to 30 TeV. The single-channel counting rate of a photo- multiplier tube can reach as high as 30 -35 kHz, most of them are background noise hits from the low energy cosmic ray showers, bringing a big challenge on data transferring, data storage and event reconstruction. Methods In this paper, a dedicated trigger scheme and a fast noise filtering method aiming to deal with these high rate background noise hits are introduced. These methods are tested with some Monte Carlo simulation data, showing a fair efficiency in filtering background noise hits, while most of the real shower signals are kept. Conclusion This method is proposed to be applied in a stage of the online processing just after the data are acquired in LHAASO-WCDA.