2,400 meters underground, the country's most important equipment is put into operation! Why is the world's deepest and largest deep underground laboratory in Jinping?

On December 7, the civil engineering and public works of the second phase of the Jinping Underground Laboratory in China, the ultra-deep underground ultra-low radiation background frontier physics experimental facility (referred to as the Jinping Large Facility), were completed and ready for experiment. This marks that the world's deepest and largest ultra-deep underground laboratory has officially been put into scientific operation.

The first batch of 10 experimental project teams from universities and research institutes such as Tsinghua University, Shanghai Jiaotong University, Beijing Normal University, China Institute of Atomic Energy, and Wuhan Institute of Rock and Soil Mechanics of the Chinese Academy of Sciences moved in to carry out scientific experiments.

Screenshot of Xinhua News Agency video

Why do scientists try every possible means to "catch" dark matter?

Dark matter - although it has never been "seen", various astronomical observation data have shown its existence. Since the 1930s, scientists have discovered through conjecture and continuous observation that dark matter is widely distributed in every corner of the universe, accounting for about 85% of the mass of the entire universe, and plays a very important role in the origin of matter and the evolution of the universe.

Astrophysical research has found that in the vast universe, the mass of the luminous stars we can observe (including those that emit X-rays and gamma rays) is only a small part of the total mass of matter in the universe. Studies on the expansion of the universe have shown that the density of the universe is composed of about 4.9% ordinary matter, 26.8% dark matter and 68.3% dark energy . What exactly is this invisible but real thing? Scientists call it dark matter and dark energy.

More strictly speaking, it is invisible matter that does not participate in electromagnetic interaction and strong interaction, but participates in gravitational interaction.

Although people have long speculated that dark matter may exist, dark matter particles have never been clearly detected. Therefore, the problems brought by dark matter are considered to be "a dark cloud hanging over the sky of current physics."

Since dark matter neither emits light nor participates in electromagnetic interactions, people can currently only feel the existence of dark matter through the effects of gravity. For this reason, China has established the first extremely deep underground laboratory - the "China Jinping Underground Laboratory."

According to Yue Qian, professor of engineering physics at Tsinghua University and director of the Physical Science Division of China Jinping Underground Laboratory, dark matter research is a major frontier subject, and the main experimental research methods include indirect detection of dark matter annihilation products (in the sky), direct detection of direct scattering of dark matter and matter (underground), and colliders that produce dark matter (artificial). Jinping Underground Laboratory is an "underground" research method.

This is a photo taken on July 4 of the waterproof radon suppression layer on the wall of the C Hall of the second phase of the Jinping Underground Laboratory in China. The waterproof radon suppression layer is 10 centimeters thick and can effectively prevent the penetration of groundwater in the cave and inhibit the spread of harmful radon gas in the rock formation. Xinhua News Agency reporter Jin Liwang

2,400 meters underground, chasing the "phantom" of the universe

Jinping Mountain is a mountain located in the Yalong River Basin, the largest tributary of the Jinsha River. Its peak is 4,410 meters above sea level. The China Jinping Underground Laboratory is located in the middle of the Jinping Mountain Tunnel, which is about 17.5 kilometers long. The rock is buried 2,400 meters deep .

On December 12, 2010, the "China Jinping Underground Laboratory" was officially unveiled. As my country's first dark matter laboratory, it is also the world's deepest, largest, and best-equipped underground laboratory. Its space is equivalent to the displacement of eight medium-sized aircraft carriers, and its burial depth is equivalent to nearly five Shanghai World Trade Center buildings. The cosmic ray flux inside the laboratory is about one billionth of that on the ground. In such a very special environment, the Jinping Underground Laboratory uses the thick rock layers of the mountain to block the interference of cosmic rays, providing a very "clean" test environment for dark matter experiments.

This is a photo taken on July 4 of the entrance to the Jinping Mountain Traffic Tunnel where China's Jinping Underground Laboratory is located, and the Yalong River next to it (drone photo)

In 2012, the CDEX experimental group led by Tsinghua University obtained the first batch of valuable data in Jinping Underground Laboratory and carried out data analysis. In 2013, the first research result of the experimental group was published in Physical Review D, an internationally authoritative physics journal. This was the first physical result of China's independent dark matter experimental research . What is more gratifying is that the detection sensitivity of the experimental results for low-mass dark matter particles has reached the world's first-class level, establishing the CDEX experimental group's position in the first camp in the field of international dark matter detection , which has greatly enhanced China's research level and international influence in the major basic frontier research field of dark matter.

At present, the underground laboratory has the advantages of "extremely low environmental radiation", "ultra-low cosmic ray flux" and "ultra-clean space". In addition to the dark matter detection experiment, Jinping Large Facility will also carry out research in the fields of neutrino physics, nuclear astrophysics, rock mechanics , etc. In the future, it will develop into a world-class deep earth science research center covering multidisciplinary cross-disciplinary fields such as cosmology, life sciences, and rock mechanics, and help the national science and technology innovation platform to "leapfrog upgrade" .

Dark matter detection, nuclear astrophysics, neutrino experiments... these cutting-edge basic scientific research will bring revolutionary breakthroughs to human understanding of the universe and the progress of civilization. We look forward to the cave in this mountain opening up more possibilities in the future.

Comprehensive sources: Xinhua News Agency, People's Daily, China Jinping Underground Laboratory official website, Guotou Online, etc.