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The origin of cosmic rays can be deciphered by accurately measuring the components and energy spectrum in the knee region. Study of Extensive air shower (EAS) relies on information provided by secondary high energy hadrons, which generate evaporation neutrons when they interact with matter in the environment. In the early 21st century, the electron–neutron detector (EN-detector) was developed at the Institute for Nuclear Research of the Russian Academy of Science (INR RAS). The PRImary Spectrum Measurement Array (PRISMA) project was introduced to enhance the array capabilities of cosmic ray composition separation and improve measurement accuracy. Within the framework of Chinese–Russian cooperation, at the Large High Altitude Air Shower Observatory (LHAASO) at Mt. Haizi (4400 m a.s.l.) in Daocheng, Sichuan province, China, a proposal was launched to establish the EN-Detector Array (ENDA) composed of 400 detectors in area of 10000 m to measure cosmic rays up to 300 PeV. In China, in 2018, a cluster, having 16 EN-detectors, was built at Tibet University (TU, 3700 m a.s.l.) in Lhasa, Tibet, to test specification of the array, and later it was moved to the Yangbajing (YBJ) Cosmic Ray Observatory (4300 m a.s.l.) in Tibet. Since 2019, another cluster so called ENDA-16 has started running at LHAASO, and here we give the first result of thermal neutron distribution. After gaining experience from these previous works, in April 2023, we successfully extended ENDA to ENDA-64 composed of 64 EN-detectors in area of 1000 m at LHAASO to measure cosmic rays from 400 TeV to 20 PeV. Here we describe installation and running status of ENDA-64 and present first results of thermal neutron distributions at different locations and hybrid detection of cosmic ray by using ENDA and LHAASO. [ABSTRACT FROM AUTHOR]

By accurate measurement of components and energy spectrum in the knee region, problem of origin of cosmic ray can be solved. In one extensive air shower (EAS), high energy hadrons, which constitute the EAS skeleton as G.T. Zatsepin called it, carry important information for multi-parameter correlation studies. The nuclear reaction between hadrons and matter in the surrounding environment produces a large number of evaporation neutrons, moderating to thermal neutrons. At the beginning of the 21th century, a new technology, electron–neutron detector (EN-detector) was designed at Institute for Nuclear Research of Russian Academy of Science (INR RAS), and the PRImary Spectrum Measurement Array (PRISMA) project was proposed to reinforce array capability of cosmic ray composition separation and then improve measurement accuracy of cosmic ray components and energy spectrum. Besides, EN-detectors can be used for continuous environmental thermal neutron flux monitoring and its variation study is needed not only for EAS experiment background estimation but also for geophysical applications (e.g., earthquakes, thunderstorms, radioactive aerosol control, etc.) and solar activity study (e.g., solar flares, Forbush effects, etc.). Under the Chinese–Russian cooperation, we put forward to build so called EN-Detector Array (ENDA) at high altitude in China. At YangBaJing Hybrid Array (YBJHA, 4300 m a.s.l.) and at Large High Altitude Air Shower Observatory (LHAASO, 4410 m a.s.l.), two clusters of ENDA were built individually and all have obtained coincident events with the local arrays. In the near future, we plan to extend ENDA to ENDA-64 with array area of 1000 m inside LHAASO to study the knee region of the light components (H and He). After it, ENDA will be extended up to 400 detectors with array area of 10 000 m to extend the energy range up to 300 PeV. [ABSTRACT FROM AUTHOR]