Dark-matter test faces obstacles

From Nature:

News.2009 A group of scientists is hoping to replicate a controversial Italian experiment that claims to have detected dark matter. But they might have to do so without the help, or the equipment, of the original group. Dark matter is thought to make up around 85% of the matter in the Universe, but it rarely interacts with regular matter except through the force of gravity. Researchers working on the DAMA experiment at the Gran Sasso National Laboratory near L'Aquila, Italy, claim they have spotted direct signs of it.

The detector used by the DAMA team consists of 250 kilograms of ultrapure sodium iodide crystals placed 1,400 metres beneath Gran Sasso mountain. Over the past decade, the researchers have collected data showing that nuclei in the crystals periodically release flashes of light, which could be caused by interactions with dark matter. Crucially, the number of flashes varies with the seasons, which would be consistent with Earth's motion through a galactic dark-matter stream (R. Bernabei et al. Eur. Phys. J. C 56, 333–355; 2008). But other detectors have so far failed to see an effect, leading some to conclude that DAMA's signal is the result of radioactive contamination inside the sodium iodide crystals. “There are very good reasons to disbelieve the signal,” says Adam Falkowski, a theoretical physicist at Rutgers University in Piscataway, New Jersey. Still, Frank Calaprice at Princeton University in New Jersey says that the signal is significant enough to be followed up. “It could be right — they're careful people,” he says of the DAMA team. “I think it deserves to be checked.”

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