Does Dark Matter?

evidently it does, 

photograph Xinhua News Agency, the Deep Underground and Ultra-low Radiation BackgroundFacility for Frontier Physics Experiments (DURF) is home to the world’s deepest underground laboratory, so how deep? it is 2,400 meters under the Earth’s surface! in December 2020, Tsinghua University and Yalong River Hydropower Development Company, Ltd. began work on a daring project under Jinping Mountain in Sichuan’s Liangshan Yi Autonomous Prefecture,

the reason for the great depth was that in order to study fields, such as particle physics, nuclear astrophysics, and life sciences, the DURF reportedly provides the cleanest space on Earth to study the invisible substance known as dark matter, the extreme depth helps block most of the cosmic rays that usually interfere with the observation of dark matter, and the facility is not small, with a total room capacity of 330,000 cubic meters (about 120 Olympic-sized swimming pools), just a though if as they say dark matter is invisible, how do they know when they have found it? just curious.