By Ron Cowen
A sensitive Italian experiment has found no sign of dark matter in 100 days of searching for the invisible material that is believed to account for 80 percent of the mass of the cosmos. But even in the absence of a discovery, data collected by the XENON100 experiment may shed light on fundamental physics, team leader Elena Aprile of Columbia University and her collaborators say.
The negative result, announced online April 13, doesn’t mean that dark matter doesn’t exist. It’s just harder to detect than some researchers had imagined.
XENON100 is a tank filled with 161 kilograms of chilled liquid xenon buried beneath 1,400 meters of rock in the Gran Sasso Underground Laboratory in Italy. Cosmic rays, which can mimic the action of dark matter particles, can’t easily penetrate to that depth (SN: 8/28/10, p. 22). A dark matter particle striking a xenon nucleus causes it to recoil, prompting the emission of light and ionization. The ratio of the amount of light emitted to the amount of ionization indicates whether a particle of dark matter has been found.