Some 2,400 meters below the Jinping Mountains in southwestern China, the world's deepest and largest underground laboratory recently opened. The huge space is home to scientists who are "hunting" for dark matter, a hypothetical substance believed to make up more than 80% of the mass of the universe, writes UNN citing Nature.
Details
The China Jinping Underground Laboratory (CJPL) opened in 2010 and its second phase, CJPL-II, after three years of construction, was commissioned in December 2023. With an extensive 330,000 cubic meter capacity, it now surpasses the Gran Sasso National Laboratory (LNGS) in L'Acquila, Italy, the previous record holder in both depth and size.
The extra space allowed for upgrades to experiments such as the Particle and Astrophysical Xenon Experiment (PandaX) and the Chinese Dark Matter Experiment (CDEX).
The best place to look for dark matter is underground because layers of rock detectors protect against background "noise" such as cosmic rays, which can drown out potential dark matter signals, says Marco Selvi, a physicist at the National Institute of Nuclear Physics in Bologna.
Research teams at the facility are already utilizing the extra space. While CJPL-II was under construction, the PandaX team upgraded its detector from 120 kilograms of liquid xenon to 4 tons. When a potential dark matter particle collides with a xenon atom, its energy must be converted into flashes of light that can be detected by photosensors. The PandaX-4T detector is located inside a 900-cubic-meter water tank to further protect it from random particles, said team member Ning Zhao, a physicist at Shanghai Jiao Tong University in China.
Meanwhile, the CDEX team has also deployed a germanium detector that targets potential dark matter particles with even lower masses than those sought in xenon experiments, says CDEX team member Qian Yue, a physicist at Tsinghua University in Beijing. The CDEX detector has been upgraded from a 1 kilogram capacity to 10 kilograms of germanium, with plans to create a detector array containing one ton. If a dark matter particle crashes into this detector, the interaction should result in charges that are converted into electrical signals.
Scientific glory awaits those who first discover dark matter, and this ongoing search is one of the biggest efforts in particle physics, says Henry Tsz-King Wong, a physicist at Academia Sinica in Nangang, Taiwan, who is working on CDEX.