The Yangpajing Experiment in Tibet was a meritorious service. How much do you know about this experiment?

Event review: On April 2, reporters learned from a press conference held by the Institute of High Energy Physics of the Chinese Academy of Sciences that using the AS? experimental array in Yangbajing, Tibet, China, researchers from my country and Japan observed The highest energy diffuse gamma ray radiation ever produced has a maximum energy of 957 trillion electron volts, which is close to 1 peta electron volt (1000 trillion electron volts). The direction of these ultra-high-energy gamma rays is not directed at known low-energy gamma ray sources, but is diffusely distributed on the galactic disk. This is the first time in the world that evidence of the existence of a PeVatron in the Milky Way has been discovered. The research results were commented by the American Physical Society as a milestone in the study of the origin of high-energy cosmic rays, the mystery of the century.

The Yangpajing Cosmic Ray Observatory in Tibet is located at the foot of the Nyenchen Tanglha Mountain in Tibet. It is the best mountain station site currently known in the world. It now includes two large-scale international cooperation projects: the Sino-Japanese Air Shower (AS?) cosmic ray experiment and the Sino-Italian Astrophysics Research on Ground Observations (ARGO) experiment, which can simultaneously carry out research on climate, space weather and other aspects. The station was listed as one of China's 25 scientific research bases by the American "Science" magazine in 1995. In 2002, it was listed as one of the first 25 field pilot stations by the Ministry of Science and Technology. Sino-Japanese cooperation began in Yangbajing in 1988. In 1990, the highest (4300m) Yangbajing cosmic ray observatory in the northern hemisphere and the Sino-Japanese cooperative Yangbajing Phase 1 Array were built in 1990. The first-class results of the Yangbajing Phase 1 experiment were announced to the Chinese and the world. Showing the scientific value and huge physical potential of the Yangbajing site, experts have focused their research on three of the four major topics of ground-based cosmic ray experiments (namely, knee zone physics, astronomy, and the use of cosmic rays to monitor solar activity and Monitoring research on the sun-terrestrial environment), come to grasp the second phase of experiments and future development of Yangbajing.

According to Huang Jing, researcher at the center and leader of the Tibet AS? experiment, most of the cosmic rays are charged particles, but magnetic fields exist everywhere in the universe, such as the Milky Way magnetic field, the solar magnetic field, and the earth's magnetic field. , the charged particles reach the earth through the magnetic field, the direction information disappears, and it is not known where it came from. However, there is a type of cosmic rays that are neutral particles and are not affected by magnetic fields, such as gamma rays. As long as scientific researchers observe gamma rays on the earth and infer their original direction, they can study the origin of cosmic rays. Huang Jing also introduced that the intensity of ultra-high-energy gamma rays is too low, less than 1% of cosmic rays, and they are submerged in the background of cosmic rays. Finding them is like "looking for a needle in a haystack". In this work, the AS? experimental team comprehensively used data from ground and underground detector arrays to reduce the cosmic ray background noise above 100TeV (1TeV is 10 to the 12th power of electron volts) to one part per million, thus extremely Earth increases the sensitivity of gamma ray detection. This is the key technical basis for the AS? experiment to achieve a series of major discoveries in recent years.

?The AS? experiment discovered ultra-high-energy diffuse gamma rays on the galactic disk. Its energy spectrum characteristics are consistent with the model predictions of gamma rays produced by the collision of PeV energy cosmic rays and the Milky Way molecular cloud, just like It is the series of "footprints" left by "PeVatron" in the Milky Way, and it is important evidence that "PeVatron" exists in the Milky Way.