Nature News Dark-matter hunt gets deep China launches world's deepest particle-physics experiment -but it joins a crowded field. ● Eugenie Samuel Reich 20 February 2013 Corrected: 1.21 February 2013 More than 1,000 metres underground,physicists have set traps of liquid xenon to catch their prey: hypothetical particles of dark matter that might very rarely interact with ordinary matter as they drift through Earth.With construction costs on the order of US$10 million each,such experiments are a relatively cheap way to work out the composition of 85%of the matter in the Universe.But does the world really need four of them? Wolfgang Lorenzon Ongoing experiments in Italy,the United States and Japan are now being joined by a fourth in China,called PandaX (see 'Dark and deep').Nature | News Dark-matter hunt gets deep China launches world’s deepest particle-physics experiment — but it joins a crowded field.  Eugenie Samuel Reich 20 February 2013 Corrected: 1. 21 February 2013 More than 1,000 metres underground, physicists have set traps of liquid xenon to catch their prey: hypothetical particles of dark matter that might very rarely interact with ordinary matter as they drift through Earth. With construction costs on the order of US$10 million each, such experiments are a relatively cheap way to work out the composition of 85% of the matter in the Universe. But does the world really need four of them? Wolfgang Lorenzon Ongoing experiments in Italy, the United States and Japan are now being joined by a fourth in China, called PandaX (see ‘Dark and deep’)