Study of background from accidental coincidence signalsin the PandaX-II experiment* *Supported in part by a grant from the Ministry of Science and Technology of China (2016YFA0400301), National Science Foundation of China (12090060, 12005131, 11905128, 11925502, 11775141), and Office of Science and Technology, Shanghai Municipal Government (18JC1410200)

Abstract

The PandaX-II experiment employed a 580kg liquid xenon detector to search for the interactions between dark matter particles and the target xenon atoms. The accidental coincidences of isolated signals result in a dangerous background which mimic the signature of the dark matter. We performed a detailed study on the accidental coincidence background in PandaX-II, including the possible origin of the isolated signals, the background level and corresponding background suppression method. With a boosted-decision-tree algorithm, the accidental coincidence background is reduced by 70% in the dark matter signal region, thus the sensitivity of dark matter search at PandaX-II is improved.