EAS Thermal Neutron Detector Array to Add into LHAASO

EN-detectors (Electron-Neutron Detector) can provide detection of both electrons and thermal neutrons generated in ground by secondary hadrons of extensive air shower (EAS). The 400 EN-detector array, so called ENDA (Electron-Neutron Detector Array), was proposed to add into the LHAASO (Large High Altitude Air Shower Observatory) project to improve its capability of EAS hybrid detection. ENDA will be located at the center of the first 1/4 of the KM2A surface scintillator array. Supported by Tibet University, Institute of High Energy Physics of Chinese Academy of Sciences (IHEP CAS) and Institute for Nuclear Research of Russian Academy of Science (INR RAS), 64 EN-detectors of so called ENDA-64 have been produced at Hebei Normal University and pulse shapes are sampled with FADCs made by Sichuan University, networked with the White Rabbit precise clock system. We expect to deploy ENDA-64 (64 EN-detectors) at LHAASO site in 2019. In this paper, we report the results of ENDA-16 (16 EN-detectors) testing run at Yangbajing (YBJ) together with YBJHA offering electrons and muons. It is the first time to obtain the high altitude hybrid detection results between neutrons, electrons and muons in EAS.