This “disc” is called “Lasso”, and its full name is “High Altitude Cosmic Ray Observatory” (LHAASO), which is supported by the National Development and Reform Commission. It took 7 years for Chinese scientists to build it.
This unique observatory in the world connects mankind and the universe.
“Can we achieve international leadership?“
In the seemingly empty interstellar space, there are many particles invisible to the naked eye flying at a speed close to the speed of light, and many of them will “hit” the earth.
In 1912, when the Austrian physicist Hess flew to an altitude of 5,000 meters in a balloon, he confirmed these uninvited guests from the universe. Since then, mankind has a new clue to explore the mysteries of the universe-cosmic rays.
China’s cosmic ray research is almost the same age as New China. In the early days of the founding of New China, scientists such as Wang Ganchang, Zhang Wenyu, He Zehui, Xiao Jian returned to China and started research on cosmic ray observation in China.
They built China’s first cosmic ray laboratory-Luoxue Station on a 3200-meter peak in Dongchuan, Kunming.
After the reform and opening up, Tan Youheng, a researcher at the Institute of High Energy Physics, Chinese Academy of Sciences, went to Japan to study.
Japan’s advanced comprehensive air shower array gave him the idea of doing similar experiments in China.
After returning to China, he actively applied for funding, hoping to build a world-class cosmic ray observation base in China.
“In order to make China’s production and technology have the vitality of sustainable development, it must have its own basic scientific research as a background.” In a material, Tan Youheng wrote.
In 1989, Tan Youheng and others proposed to establish the first-generation gamma astronomy detector in Tibet, the Yangbajing Cosmic Ray International Observatory.
In 1992, as a student of Tan Youheng, Cao Zhen became the first duty officer of the Yangbajing Cosmic Line International Observatory.
“After that, we have basically been in the first echelon internationally, but we are still not leading, so we are thinking, if we say that the country gives us more support again, can we reach the international lead?” Cao Zhen recall.
The result of this thinking is the birth of “Lasso”. As the third-generation cosmic ray researcher in China, Cao Zhen, who is now the chief scientist of “Lasso”, remembers that during the formation of the “Lasso” program, they repeatedly balanced and traded between scientific goals and the ability to achieve engineering technology.
On December 31, 2015, the “Lasso” program stood out after being selected by the Chinese Academy of Sciences and at the national level, and was approved by the National Development and Reform Commission.
“Building while operating”
It took Cao Zhen and the site selection team five years before the project was established to build the “cable” on Haizi Mountain.
Cosmic rays are easily affected by the atmosphere. Therefore, cosmic ray observatories need to be built in high-altitude areas where the air is thin.
In the past five years, in order to find a suitable place for the “cable”, Cao Zhen and others ran all over Tibet, Qinghai, Yunnan, Sichuan and other areas with high altitude characteristics, and finally found that only Haizi Mountain can satisfy the “time and place”. And” all conditions.
Wu Chaoyong, a member of the site selection team and the overall person in charge of “Lasso” Jianan Branch, remembers that the site where “Lasso” is located is full of rivers. Go forward.
The climatic conditions here are also challenging for construction. “When it is too cold, concrete construction cannot be carried out here. The construction time is probably from May to the end of October each year, a total of less than 6 months.” Wu Chaoyong said.
Even so, in the eyes of Cao Zhen, this place is still a “treasure land”: “The high altitude of Haizi Mountain can reduce the influence of the atmosphere on cosmic ray particles; the terrain is flat and there are sufficient water resources to meet a large number of ultra-pureClean waterLocal governments at all levels also attach great importance to and provide strong support. “
In 2017, the main construction of the “cable” was started. In order to overcome the impact of the environment on the project, Cao Zhen and others put forward the idea of ”building while operating”.
According to the design, the “pull cable” project includes an electromagnetic particle detector array of 1 square kilometer and a muzi detector array with an effective area of 42,000 square meters. The 78,000 detection technology uses Cherenkov light generated by shower particles in the water as the detection technology. Square meter detector array, 18 wide-angle Cherenkov telescope arrays. “In the first year, we first build 1/4, run for half a year, then build 1/4, make up 1/2, and run for half a year…” Cao Zhen said.
“Authenticbreakthrough”
In January 2020, just as they had just completed half of the array, high-energy particles that “surpassed people’s imagination” and “lucky” came together on this “disc” that has not yet been fully formed.
Through the “pull cable”, researchers discovered that ultra-high-energy cosmic ray accelerators capable of accelerating particle energy by more than 1 pet volt are widespread in the Milky Way. This discovery exceeded the expectations of astrophysicists. On May 17, the results were published in Nature and were evaluated by the associate editor of the journal as a “real breakthrough” and “beginning of a new era.”
More than a month later, on July 9th, “Science” appeared again from the “cable” research results: the scientific researchers used “cable” to accurately measure the brightness of the high-energy astronomy standard candlelight-the Crab Nebula, A new standard has been determined for the ultra-high energy gamma light source in a wider energy range, and it has been determined that in the core area of the nebula, which is only about 1/10 the size of the solar system, there is a super-capable particle accelerator, which is close to classical electrodynamics. And the acceleration limit allowed by the ideal magnetohydrodynamic theory.
“This is our luck! These observations have shown the powerful scientific discovery power of’Lasso’.” Because of excitement, Cao Zhen’s face turned red.
“Follow this path”
What makes Cao Zhen so excited is not only the two results of “Lasso”, but also the proof that “the direction of “Lasso” is right.”“In the next ten years, our research content and research direction will be clear from this.If you follow this path, you will surely produce more significant scientific and technological achievements.“Cao Zhen said.
On October 17 this year, the “cable” passed the process acceptance and entered the stage of scientific operation. “International scientists have set their sights on the’Lasso’, and many international scientific research teams have expressed the hope to join our scientific research cooperation group.” Cao Zhen said.
Recently, the National Academy of Sciences, the Academy of Engineering, and the School of Medicine released their latest 10-year survey results, outlining the scientific goals of the astronomy community in the next 10 years. Among them, “Lasso” is mentioned many times as a leading project in this field, which will determine the current situation. The future development direction of the field.
Because of the 3 projects of this level mentioned in the report, only the “cable” has entered the working state, therefore, the “cable” has also been called by the astrophysicist Felix Aharonian as “the running’future probe'”. .
“Lasso” has been built and put into operation, but Cao Zhen and his team did not stop there. Facing the future, the “Lasso” team also has new ideas for improving spatial resolution capabilities. “We plan to build an array of 32 telescopes on the’cable’. After this array is built, the’cable’ is equivalent to adding a pair of’fire eyes’, which will have the ability to identify the location of ultra-high energy cosmic rays. , To further approach the final answer.” Cao Zhen said.
When it comes to the scientific goal of cosmic ray detection, Cao Zhen always has endless words. Today, while relying on the “Lasso” to carry out cosmic ray research, he also takes the fourth and fifth generation of Chinese cosmic ray researchers to the world to participate in the brewing work of the Southern Wide Gamma Ray Observatory (SWGO).
“We still have many ideas, which may be realized through international cooperation in the future.” Cao Zhen said. And this international cooperation is considered to be “expected to help scientists all over the world continue to explore the origin of cosmic rays, and further understand the Milky Way itself.”
“China Science News” (2021-11-11, 1st edition. News. The original title is “Seven Years of “Lasso”: Towards the Forefront of Cosmic Ray Research”)
Author | Ni Sijie