China Unveils World's Deepest and Largest Underground Lab: A New Frontier in Dark Matter Research

In a significant scientific milestone, the China Jinping Underground Laboratory (CJPL), nestled 2,400 meters below the Jinping Mountains in southwest China, has become the world’s deepest and largest underground laboratory. After its second phase of construction, CJPL-II, completed in December 2023, the lab now surpasses Italy’s Gran Sasso National Laboratory in both depth and volume, offering a new frontier in the hunt for dark matter.

The expansion to a vast 330,000 cubic meters has enabled major upgrades for key experiments like the Particle and Astrophysical Xenon Experiments (PandaX) and the China Dark Matter Experiment (CDEX). Scientists globally, including Juan Collar from the University of Chicago, marvel at the rapid developments made in just over a decade.

Dark matter, making up more than 80% of the universe's mass, remains elusive due to its weak interaction with ordinary matter and light. Detecting it requires shielding from cosmic rays and other background noises, which is why underground laboratories like CJPL-II are crucial. The lab's unique location allows for cosmic ray exposure at just 0.000001% of the Earth’s surface rate, and its walls are coated with a protective shield to block water and radon gas.

Significant advancements have been made at CJPL-II. The PandaX team upgraded their detector to hold 4 tonnes of liquid xenon, moving closer to experiments like LNGS’s XENONnT and the LUX-ZEPLIN Experiment in the United States. This detector, housed in a 900-cubic-metre water tank, aims to capture light flashes from xenon atom collisions with potential dark matter particles.

Similarly, the CDEX team has enhanced its germanium detector, targeting lower mass dark matter particles. The upgrade from 1 kilogram to 10 kilograms of germanium, with plans for a one-tonne detector array, demonstrates China's commitment to leading in this field.

Despite the competitive nature of dark matter research, global collaboration remains key. In 2022, PandaX confirmed results from LNGS’s XENON experiment, emphasizing the importance of different laboratories validating each other's findings.

Looking forward, CJPL-II aims to continue improving detector sensitivity and fostering international collaboration. Qian Yue from Tsinghua University hopes to expand CDEX’s global research team. While larger and more sensitive detectors are a focus, experts like Collar suggest that innovation in research approaches could be equally beneficial.

The CJPL-II not only signifies China's growing prominence in particle physics but also strengthens the global quest to unravel the mysteries of dark matter. With its unmatched depth and capacity, CJPL-II stands as a beacon of hope for new discoveries in understanding the universe's most elusive substance.