The Sciences

No Dark Matter Seen by XENON

Cosmic VarianceBy Sean CarrollApr 14, 2011 1:11 PM

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Here in the Era of (Attempted) Dark Matter Detection, new results just keep coming in. Some are tantalizing, some simply deflating. Count this one in the latter camp. The XENON100 experiment is a detector underneath the Gran Sasso mountain in Italy (NYT article). It's a very promising experiment, and they've just released results from their most recent run. Unlike some other recent announcement, this one is pretty straightforward: they don't see anything.

Here we see the usual 2-dimensional dark matter parameter space: mass of the particle is along the horizontal axis, while its cross-section with ordinary matter is along the vertical axis. Anything above the blue lines is now excluded. This improves upon previous experimental limits, and calls into question the possible claimed detections from DAMA and CoGeNT. (You can try to invent models that fit these experiments while not giving any signal at XENON, but only at the cost of invoking theoretical imagination.) See Résonaances or Tommaso Dorigo for more details. No need to hit the panic button yet -- there's plenty of parameter space yet to be explored. That grey blob in the bottom right is a set of predictions from a restricted class of supersymmetric models (taking into account recent LHC limits). So it's not like we're finished yet. But it is too bad. This run of XENON had a realistic shot of actually finding the dark matter. It could be harder to detect than we had hoped, or it could very well be something with an extremely small cross-section, like an axion. The universe decides what's out there, we just have to dig in and look for it.

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