by JOHN MATSON
A major dark matter experiment has taken a swipe with its technological net in the hopes of catching some of the elusive particles that make up the universe’s missing mass, and once again that net has come up empty. But in swiping and missing, the Xenon100 experiment has closed in a bit tighter on where dark matter—the invisible stuff theorized to outweigh the ordinary matter in the universe by a factor of five—might be hiding.
Xenon100, a tank of liquid xenon deep underground in Italy, has been designed to identify the rare instances when ambient dark matter particles would recoil off regular matter, a subtle collision that should generate a tiny flash of ultraviolet light and a slight electric charge from ionization effects. The detector’s 62 kilograms of cryogenic xenon are shielded from non–dark matter contamination by layers of copper, polyethylene, lead, water—and a thick slab of rock overhead that keeps out almost all cosmic rays.
Scientific American for more