China’s New Dark Matter Laboratory Is the Largest and Deepest Yet

China has recently opened the world’s largest and deepest underground lab, located in southwest China, around 2,400 meters beneath the Jinping Mountains. This substantial space is now designated for scientists on a mission to study dark matter, i.e., the theoretical substance believed to account for over 80% of the material the Universe comprises. 

The China Jinping Underground Laboratory was inaugurated in 2010, and its second phase, i.e., CJPL-II, started operating in December 2023 after undergoing a construction period of three years. With a substantial capacity of 330,000 cubic centimeters, this lab has now surpassed Italy’s Gran Sasso National Laboratory, which previously held the record in terms of volume and depth. 

The added room provided by CJPL-II has enabled projects like the China Dark Matter Experiment (CDEX) and Particle and Astrophysical Xenon Experiments (PandaX) to upgrade. 

The Mystery of Dark Matter

Dark matter has long been a scientific enigma. According to physicists, the gravity created by tangible matter is not strong enough to prevent rapidly moving galaxies from drifting apart. Therefore, they proposed dark matter to be the intangible force that holds the Universe in place. Despite supposedly being present everywhere, directly observing it has been a challenge since it is believed to have minimal interactions with typical matter and does not absorb, emit, or reflect light. The detection of dark matter has long been complicated by claims that other signals might have interfered with the experiments. 

Henry Tsz-King Wong, an Academia Sinica physicist involved in the CDEX project, asserts that detecting dark matter would be a significant milestone, and the ongoing pursuit of it is among the most considerable endeavors in particle physics. 

Physicist Recommends Underground Search for Dark Matter to Avoid Cosmic Rays 

According to physicist Marco Selvi, who works at the National Institute of Nuclear Physics in Bologna, underground sites are the best places to search for dark matter since the rock layers protect detectors against background noise, including cosmic rays. 

Cosmic rays are energetic particles showered down from space and can interfere with the detection of dark matter signals. Selvi went on to compare detecting dark matter on the surface of the Earth with trying to discern a small child’s voice in a noisy stadium full of shouting people. 

CJPL-II is built to be highly shielded from cosmic rays, with exposure at only 0.000001 % of the natural cosmic radiation present on the Earth’s surface. Moreover, the laboratory’s walls are overlaid with a 10-centimeter-thick shield created from a combination of concrete, rubber, and other substances, which blocks radon gas and water that can penetrate and obstruct dark-matter experiments.