Detecting Dark Matter

Dark matter was discovered 80 years ago when astronomer Fritz Zwicky spied a galaxy cluster whirling so fast, the galaxies were bound to fly apart unless something — something less luminous than ordinary stars or gas — held them together.

Decades later, the scientific community concedes the existence of dark matter, after many different kinds of experiments and simulations, but physicists still don't know what it is.

But confidence is growing. The last 15 years have seen the construction of several exotic detectors buried deep underground, and those detectors may be giving us our first view of what dark matter is made of. In January's cover story, Dan Hooper discusses these experiments, their results, and their most recent find: a seasonal variation in detections that indicate Earth might be moving through a WIMP wind as it orbits the Sun.

We summarize the underground experiments below. All of these experiments are continually increasing their detector mass, so the masses listed here are not fixed.

Guide to Dark Matter Experiments
Experiment	Location	Detector	Start Date	Results
DAMA/ LIBRA	Gran Sasso, Italy	250 kg sodium iodide crystals	1998	Thousands of events with annual variations
CDMS-II/ SuperCDMS	Soudan, Minnesota	CDMS-II: 4.5 kg germanium crystals SuperCDMS: 9 kg germanium crystals	2003	No claimed WIMP detections yet
CoGeNT	Soudan, Minnesota	500 g germanium crystal	2004	Hundreds of events with possible annual variations
CRESST	Gran Sasso, Italy	2.4 kg calcium-tungstate crystals	2006	Tens of events, possible WIMP signal
XENON-100	Gran Sasso, Italy	161 kg liquid xenon	2009	No claimed WIMP detections yet
LUX	Homestake, South Dakota	350 kg liquid xenon	2011	No science results yet
XMASS	Kamioka, Japan	800 kg liquid xenon	2011	No science results yet