Almost 2,400 meters below the Jinping Mountains in southwest China, the world’s deepest and largest underground laboratory has just been reopened. This vast space is home to scientists who are searching for dark matter; A hypothetical substance that is thought to make up more than 80% of the mass of the universe.
The China Jinping Underground Laboratory (CJPL) reopened in 2010, and after several years of construction, its second phase, CJPL-II, became operational in December 2023. This facility, with a huge capacity of 330,000 cubic meters, has now surpassed the Gran Sasso National Laboratory in Laquila, Italy, which previously held the record for the largest laboratory in the world in terms of depth and volume.
The additional space at the Chinese lab has enabled projects such as the Astrophysical Xenon and Particle Experiment (PandaX) and the China Dark Matter Experiment (CDEX). Juan Collar, a physicist at the University of Chicago Scientific American “It’s amazing that they were able to build such a laboratory in a decade,” he says.
Dark matter is still one of the great mysteries of science. Physicists have calculated that the gravity produced by visible matter is too weak to keep accelerating galaxies from collapsing. Therefore, they have hypothesized dark matter as the invisible glue that holds the universe together. Although dark matter must be everywhere, direct observation is difficult; Because it is thought to barely interact with ordinary matter and does not emit, reflect or absorb light.
“Scientific honor awaits those who identify dark matter for the first time”
“Scientific honor awaits those who detect dark matter for the first time, and this ongoing search is one of the biggest efforts in the world,” said Henry Tez-Qing Wong, a physicist at Sinica Academy University in Nangang, Taiwan, who is involved in China’s dark matter experiment. It is particle physics.
Discovery of science under the mountain
The best place to look for dark matter is underground; Because the rock layers shield the detectors from background “noise,” such as cosmic rays or energetic particles beamed down from space to Earth, that can mask potential dark matter signals. According to Marco Selvi, a physicist at the National Institute of Nuclear Physics in Bologna, trying to detect dark matter at Earth’s surface “is like trying to hear the faint voice of a child in a stadium full of screams.”
The CJPL-II facility is exposed to cosmic rays underground with a rate of 0.000001% of the Earth’s surface; Therefore, it is considered one of the best protected underground laboratories in the world. The walls of the laboratory are also covered with a protective shield 10 cm thick, which is a combination of rubber, concrete and other materials that block water and radioactive radon gas.
The lab’s research teams are already taking advantage of the facility’s additional space. While the second phase of the lab was under construction, the PandaX team upgraded their detector from a capacity of 120 kilograms of liquid xenon to four tons. When a potential dark matter particle collides with a xenon atom, its energy should be converted into flashes of light that can be detected by light detectors.
Although the global search for dark matter is a competitive process, researchers believe that the existence of several underground laboratories around the world conducting similar experiments will allow them to compare their results. This collaboration can promise the discovery of dark matter. However, there is still much work to be done.
