On August 14, 2018, researchers installed observation instruments on Haizi Mountain.
In mid-October, when the temperature of Haizi Mountain in Daocheng County, Ganzi Prefecture, at an altitude of 4,410 meters, had dropped to around 0 degrees Celsius, Hou Chao, an associate researcher at the Institute of High Energy of the Chinese Academy of Sciences, and his team members were shuttling through the wasteland covered with granite drift gravel of different sizes and glacial rock basins of different shapes these days, inspecting electromagnetic particle detectors covered with green coverings. They began construction in this wasteland four years ago and have now installed more than 5,000 electromagnetic particle detectors.
This 1.36 square kilometer snowy wasteland is built with a major national scientific and technological infrastructure, equipped with advanced and sensitive detector arrays, just to explore a century of problems - the origin of high-energy cosmic rays. Its name is "LHAASO" (LHAASO), and its full name is the high-altitude cosmic ray observatory. The observatory detection array consists of three parts: a ground-based clustered particle array consisting of 5,195 electromagnetic particle detectors and 1,188 muse detectors; a 78,000-square-meter water Cherenkov detector, divided into 3,120 detection units; and 18 wide-angle Cherenkov telescopes. The main project of "cable" started in November 2017, the construction of the whole array was completed and put into operation in July 2021, and the process acceptance was passed on October 17, 2021.
On May 15, 2020, researchers crawled on boulders to install electromagnetic particle detectors.
Cosmic rays are a general term for streams of high-energy particles from outer space. These alien visitors, invisible to the naked eye, are also known as "cosmic messengers", and they carry important scientific information such as the origin of the universe, the evolution of celestial bodies, solar activity and the earth's space environment. Studying cosmic rays and their origins is an important way for humans to explore the universe. Cao Zhen, chief scientist of the "Lasso" project and a researcher at the Institute of High Energy Physics of the Chinese Academy of Sciences, said that since the discovery of cosmic rays in 1912, efforts to study cosmic rays have never been interrupted. Since 1954, Chinese researchers have officially opened the study of cosmic rays. Since the higher the cosmic ray energy, the rarer it is, and the larger the probe needs to make it possible to "capture" it, which has led scientists to turn their attention to alpine experiments. Alpine experiments can make full use of the atmosphere as a detection medium for observations on the ground, and this is currently the only means for ultra-high-energy cosmic ray observations. The "lasso" built in Haizi Mountain is the third generation of alpine cosmic ray laboratory in China.
On October 16, researchers installed photomultiplier tubes in the water Cherenkov detector pool, which were fixed "suspended" underwater to receive cosmic rays that "scattered" in the water and produced Cherenkov light.
Cosmic rays sound mysterious, but they're all around us. "There are hundreds of cosmic rays passing through the human body every second, but humans can't see or touch it." Hou Chao said that "Lasso" is an artifact that captures cosmic rays. This artifact, which is composed of a staggered arrangement of various detectors, has been built and put into scientific operation, and they have become a unique scenery on Haizi Mountain.
On the evening of October 11, researchers were debugging the Muzi detector instrument.
The construction of the plateau is extremely arduous, and under extreme conditions such as high cold and lack of oxygen, harsh climate, and lack of materials, engineering construction personnel and scientific researchers have faced difficulties. In the construction, installation and commissioning of these detectors at an altitude of 4410 meters above sea level, the difficulty of construction can be imagined, and each work is a major test of the builder's psychology and physical fitness. As a researcher of the water Cherenkov detector array, Liu Cheng has a deep understanding of this. The array for detecting cosmic rays and gamma rays consists of three pools of 350,000 tons of purified water. The installation and testing work is mainly carried out in the pool, and in addition to the challenges caused by the lack of oxygen at high altitude, the work of pulling water pipes, lifting pumps, draining and arranging cables day after day is a challenge to perseverance. In winter, the average temperature in the pool is minus 3 degrees Celsius, in such an environment to debug the equipment in the water, the degree of acidity can only be known after trying.
On October 11, a bird's eye view of the high-altitude cosmic ray observatory of Daocheng Haizi Mountain from the air.
Installing and debugging more than 5,000 electromagnetic particle detectors in a 1.36-square-kilometer wasteland is the work hou and her team have to accomplish. When she first arrived at Haizishan, she was very uncomfortable, and her strong high reflex made her often have headaches and insomnia. In order to ensure that the detectors are installed and operating properly, researchers need to test and GPS locate each detector, and hike more than 10,000 steps in the complex terrain every day. The climate of the plateau is changeable, with rainy summers and snowy winters, often accompanied by extreme weather such as high winds and hail, which increase the difficulty of field work. Hou Chao's mobile phone still has many work photos of the team members, wearing water pants, lying in the snow, lying on boulders, "Some memories, I will never forget." ”
On October 11, the drone aerial photograph of the Water Cherenkov Detector Array, with a total area of 78,000 square meters, consists of two 150-meter × 150-meter pools and a 300-meter × 110-meter pool.
In May this year, researchers discovered a large number of ultra-high-energy cosmic accelerators in the Milky Way through the "cable", and recorded a maximum of 1.4 beats of electron voltamma photons (beats = quadrillion), which is the highest energy photon observed by human beings, changing the traditional understanding of the Milky Way and opening the era of "ultra-high-energy gamma astronomy".
On October 17, "Lasso" passed the process acceptance of the acceptance expert group. The expert group believes that the observatory makes full use of the high-altitude geographical advantages of the roof of the world to become the world's largest and most sensitive ultra-high energy gamma-ray survey telescope and the world's leading international leading cosmic line observatory with the widest energy coverage.
On October 11, looking around, there were spectacular mounds evenly distributed around the observation base, which was the Muzi probe. Each mound is about 36 square meters in size, and under the mound is a 6.8 m diameter and 1.2 m high concrete tank with a high reflectivity water bag filled with ultrapure water.
From October 21st to 27th, the National "13th Five-Year Plan" Scientific and Technological Innovation Achievement Exhibition was held in Beijing, and "Lasso" showed the audience the innovative achievements in exploring the universe in the basic research exhibition area.
Qiu Li Sichuan Daily all-media reporter He Haiyang photo report
Some of the pictures were provided by the Institute of High Energy of the Chinese Academy of Sciences
Original title: Looking up at the starry sky "Lasso" waiting for the "cosmic messenger"