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Dark matter: Good news, everyone! We've found ... NOTHING AT ALL

But that too is knowledge, grasshopper

The most sensitive dark-matter detector ever built has failed to detect any dark matter.

It's not yet a problem for the instrument, the LUX Dark Matter Collaboration that The Register described here and here. What it might mean is, in an echo of the kind of iterative narrowing-down that characterised the hunt for the Higgs-boson, a re-drawing of the boundaries around where to seek the stuff.

Over at Nature, the scientists explain that after running the LUX experiment for 110 days, no statistically significants were detected. The 160 events that were spotted are well within the level that would be generated by background radiation not screened out by the rock and water that surrounds the detector.

LUX's 300 kg of liquid Xenon is supposed to detect hypothesised WIMPs – weakly interacting massive particles – using 122 photmultiplier tubes to spot the tiny flashes of light that theory predicts would be given off if a WIMP strikes a Xenon nucleus.

So far, however, that just hasn't happened. However, according to Brown University physics professor and LUX co-founder Rick Gaitskell: “This first run demonstrates a sensitivity that is better than any previous experiment looking to detect dark matter particles directly”.

The first run gives the LUX operators a baseline from which they can adjust the instrument for a 300-day detection run due to start in 2014. The no-show also suggests that WIMPs might have lower mass than predicted, or might interact even more weakly than expected.

As noted at “In the upcoming 300-day run, the LUX researchers hope either to detect dark matter definitively or to rule out a vast swath of parameter space where it might be found.”

The experiment's paper suggests that the LUX data eliminates low-mass WIMP models in the 33 GeV range.

Gaitskell says new models of dark matter need to be probed (and if necessary ruled out), “because we don't yet understand the universe well enough to know which of the models is actually the correct one. LUX is helping to pin that down.”

The researchers also hope that their work to date will help them secure further Department of Energy funding to scale up LUX from its current 300 kg of Xenon to seven tonnes of the stuff. ®

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