The New York Times has a story today about the very first results from XENON 100, a powerful dark matter detector at Italy’s Gran Sasso National Laboratory underneath the Gran Sasso mountain near Rome. It’s only 11 days’ worth of accumulated data, and there’s no hint of dark matter, but given the recent to-ing and fro-ing between different groups, and XENON 100’s power as a detector, the results are noteworthy.

First, a recap on dark matter. Physicists believe that dark matter is heavy stuff that makes up to around 85% of the matter in the Universe. It interacts weakly (if at all) with regular matter except through the force of gravity. To date, it has mostly been inferred via measurements of galaxy rotations and the cosmic microwave background, the radiation leftover from the Big Bang.

But there’s a hope that if the dark stuff does interact, then physicists will be able to see it, at least occasionally, through its collisions with other, more conventional sorts of matter. To find it, they’ve set up a slew of detectors around the world. Some detectors (and in particular another experiment located in Gran Sasso) have claimed to see it, but to date there has been nothing definitive.

XENON 100 is in a class all its own. It uses around 50 kilograms of a liquid xenon compound that is supposed to emit a flash of light if it gets knocked by a passing dark matter particle. It’s the size of the detector that really makes it stand out from the crowd: most dark matter experiments to date measure the size of their detectors in grams rather than kilos. More mass makes an interaction more likely and so even after just 11 days of running XENON 100 has something to say about dark matter.

The result, now on the preprint server arXiv.org, undercuts previous claims of dark matter detection. Basically, if earlier experiments really have seen something, then XENON 100 would be likely to see it too. The fact that it hasn’t leaves many in doubt as to the veracity of those earlier detections (see plot).

But stay tuned! XENON 100 will be gathering lots more data in the coming months, and there’s no reason to think that it won’t turn up something interesting…

UPDATE: The experiments that XENON 100 claims to rule out are striking back. In an online posting to arxiv.org a rival experiment named CoGeNT says that XENON 100 may not be sensitive at lower energies where CoGeNT operates. “These results cannot be defended,” CoGeNT physicist Juan Collar of the University of Chicago told physicsworld.com. DAMA, a second experiment that claims to have seen dark matter, is also criticizing the new results. They have now been submitted to Physical Review Letters for publication.