High Altitude Cosmic Ray Observatory (LHAASO).

On May 10, the National Major Science and Technology Infrastructure High Altitude Cosmic Ray Observatory (LHAASO) successfully passed the national acceptance.

The acceptance committee believes that the Chengdu Branch of the Chinese Academy of Sciences, the project legal entity, and the Institute of High Energy Physics, the Chinese Academy of Sciences, the co-construction unit, have completed the construction tasks approved by the National Development and Reform Commission on schedule, comprehensively, and with high quality, and all indicators have reached or exceeded the approved acceptance indicators. LHAASO's 1/4-scale detection device was put into trial operation in April 2019, and the full-scale detection device was put into trial operation in July 2021. The overall performance is reliable and it has long-term and stable scientific operation capabilities. LHAASO has made full use of the superior high-altitude conditions of 4410 meters in a specific area and advanced technological advantages to become the most sensitive ultra-high-energy gamma-ray detection device in the world, the most sensitive very-high-energy gamma-ray source survey telescope in the world, and energy coverage The widest range of ultra-high energy cosmic ray compound stereo measurement system. The completion and operation of LHAASO has made it one of the three major experimental facilities for particle astrophysics in the world, which is of great significance for promoting major original breakthroughs in this field, driving the development of cutting-edge cross-related disciplines and international cooperation.

LHAASO is a major national scientific and technological infrastructure with the core of cosmic ray observation and research. It was approved by the National Development and Reform Commission on December 31, 2015. The project was jointly established by the Chinese Academy of Sciences and the Sichuan Provincial People's Government. The Institute of High Energy Physics of the Academy of Sciences undertakes the construction, and the construction period is 4 years. The main project of LHAASO started in 2017 and will be completed in 2021. It has passed the inspection and acceptance of five professional groups organized by the competent department, Chinese Academy of Sciences, including technology, construction and installation, finance, equipment assets and archives.

The national acceptance meeting was entrusted by the National Development and Reform Commission and organized by the Chinese Academy of Sciences in conjunction with Sichuan Province. Nearly 20 experts from the National Development and Reform Commission, China Consulting Corporation, scientific research institutes, universities and other units attended the acceptance meeting.

LHAASO is located in Haizi Mountain, Daocheng County, Sichuan Province, with an average altitude of 4,410 meters and an area of about 1.36 square kilometers. It aims at the most important scientific frontier topic—the origin of high-energy cosmic rays. It is composed of 5216 electromagnetic particle detectors and 1188 muon detectors, a one-square-kilometer ground shower particle detector array, a 78,000-square-meter water Cherenkov detector array, and 18 wide-angle Cherenkov telescopes. Composition of large arrays.

Cao Zhen, Chief Scientist of LHAASO, introduced that the LHAASO project team has completed a number of key core technology breakthroughs through independent innovation and international cooperation. The traditional observation mode that the telescope cannot work on a moonlit night has realized the doubling of the effective observation time; developed a large-area, multi-node, high-precision clock synchronization based on the "little white rabbit" technology to adapt to high-altitude field conditions above 4,000 meters Technology, the long-distance synchronization accuracy has been increased to 0.2 nanoseconds, reaching the international leading level; the domestic 20-inch ultra-large photomultiplier tube has been adopted, the time response has been increased by 3 times, and the observation threshold has been reduced from 300 billion electron volts to 70 billion electron volts , the observation capability has reached the international leading level; significant progress has been made in massive data acquisition technology, and "no-trigger" data acquisition has been developed and realized, and "zero dead time" observation of cosmic ray events has been achieved; The data is losslessly compressed to realize real-time data transmission from Haizishan to the Institute of High Energy.

Based on its ultra-high detection sensitivity, LHAASO has achieved many breakthroughs and major scientific achievements during its initial operation. LHAASO discovered a large number of ultra-high-energy cosmic accelerator candidate celestial bodies in the Milky Way, and recorded the highest-energy photons observed by human beings, which opened the era of "ultra-high-energy gamma astronomy"; accurately measured the brightness of the ultra-high-energy segment of the standard candlelight crab nebula, Discovered 1 quadrillion electron volts of gamma radiation, challenging the theoretical limit. LHAASO carried out observations during the construction period, and scientific results continued to be produced. Up to now, about 215 journal papers and 156 conference papers have been published based on the LHAASO project.

LHAASO project construction units give full play to the advantages of the institutionalized research of the Chinese Academy of Sciences, rely on the facilities to carry out observation and theoretical research, and fully open and share it at home and abroad. At present, 28 astrophysics research institutions have become members of the international cooperation group of LHAASO. The cooperation team uses the observation data of LHAASO to carry out particle astrophysics research, and at the same time conduct basic research in many fields such as cosmology, astronomy, and particle physics. LHAASO will become an international cosmic ray research center centered on China and participated by many countries. With the advantages of high-altitude gamma ray astronomy and cosmic ray observation, it will become a unique, comprehensive and open scientific research platform.

Cao Zhen introduced that China's cosmic ray experimental research has gone through three stages. In 1954, China's first high-mountain cosmic ray laboratory was built in a mountain at an altitude of 3,180 meters in Dongchuan, Yunnan; from 1989 to 2000, it was established in Tibet at an altitude of 4,300 meters. Yangbajing has successively launched the Sino-Japanese cooperation ASγ experiment and the Sino-Italian ARGO-YBJ experiment; LHAASO is the third generation alpine cosmic ray observatory in my country, and has become one of the most important particle astrophysics pillar experimental stations in the world. Research in the field of high-energy gamma-ray astronomy has reached the international leading level. (Original title "High Altitude Cosmic Ray Observatory Passes National Acceptance")