Chinese scientists are expanding the capacity of an underground facility designed to detect elusive dark matter particles. Scientists are still searching for evidence to conclusively prove the existence of dark matter, an invisible substance thought to account for over a quarter of the universe's mass and energy.

The Jinping Underground Laboratory, which is 2,400 meters under a mountain in Sichuan province, started operating in December 2010. It has a store of xenon, one of the few materials that interact with dark matter, and the cosmic rays that commonly interfere with attempts to observe dark matter generally cannot penetrate to such a depth underground.

Xiao Mengjiao, a researcher at the laboratory, said he and his colleagues have started the second phase of their experiments.