An Improved Evaluation of the Neutron Background in the PandaX-II Experiment

Qiuhong Wang, Abdusalam Abdukerim, Wei Chen, Xun Chen, Yunhua Chen, Xiangyi Cui, Yingjie Fan, Deqing Fang, Changbo Fu, Lisheng Geng, Karl Giboni, Franco Giuliani, Linhui Gu, Xuyuan Guo, Ke Han, Changda He, Di Huang, Yan Huang, Yanlin Huang, Zhou Huang, Peng Ji, Xiangdong Ji, Yonglin Ju, Yihui Lai, Kun Liang, Huaxuan Liu, Jianglai Liu, Wenbo Ma, Yugang Ma, Yajun Mao, Yue Meng, Parinya Namwongsa, Kaixiang Ni, Jinhua Ning, Xuyang Ning, Xiangxiang Ren, Changsong Shang, Lin Si, Andi Tan, Anqing Wang, Hongwei Wang, Meng Wang, Siguang Wang, Xiuli Wang, Zhou Wang, Mengmeng Wu, Shiyong Wu, Jingkai Xia, Mengjiao Xiao, Pengwei Xie, Binbin Yan, Jijun Yang, Yong Yang, Chunxu Yu, Jumin Yuan, Dan Zhang, Hongguang Zhang, Tao Zhang, Li Zhao, Qibin Zheng, Jifang Zhou, Ning Zhou, Xiaopeng Zhou

Published 2019-07-01Version 1

In dark matter direct detection experiments, neutron is a serious source of background, which can mimic the dark matter-nucleus scattering signals. In this paper, we present an improved evaluation of the neutron background in the PandaX-II dark matter experiment by a novel approach. Instead of fully relying on the Monte Carlo simulation, the overall neutron background is determined from the neutron-induced high energy signals in the data. In addition, the probability of producing a dark-matter-like background per neutron is evaluated with a complete Monte Carlo generator, where the correlated emission of neutron(s) and $\gamma$(s) in the ($\alpha$, n) reactions and spontaneous fissions is taken into consideration. With this method, the neutron backgrounds in the Run 9 (26-ton-day) and Run 10 (28-ton-day) data sets of PandaX-II are estimated to be 0.66$\pm$0.24 and 0.47$\pm$0.25 events, respectively.