Humble DNA could help decipher dark matter

A few strands of DNA could help solve the mystery of dark matter. A newly proposed detector aims to use DNA to resolve the conflicting claims from current dark matter detectors.

Dark matter is thought to make up about 85 per cent of the matter in the universe. The prime suspects are so-called weakly interacting massive particles, which are immune to the electromagnetic and strong nuclear forces. In theory, WIMPs interact with normal matter only via gravity and the weak nuclear force.

Attempts to detect WIMPs on Earth have provided conflicting results. On the positive front, two experiments ? CoGeNT in Soudan, Minnesota, and DAMA/LIBRA at Gran Sasso, Italy ? have seen more putative dark matter particles hitting their detectors in June than in December. All else being equal, the excess is attributed to Earth's relative velocity through the sea of dark matter that fills our galaxy. In June, Earth is moving in the same direction as the sun and so encounters a "headwind" of dark matter, the theory goes. In December, Earth, in its orbit around the sun, is moving in the opposite direction.

But, crucially, other bigger and more sensitive experiments, such as CDMS-II and XENON1O0, have seen no such particles. One way to resolve the conflict would be to detect the directionality of dark matter particles, to see if they are indeed aligned with the direction of the sun's motion through the galaxy, as required by DAMA/LIBRA and CoGeNT.

Now Andrzej Drukier of Biotraces ? a biotech firm based in Herndon, Virginia ? and a group of cosmologists and biochemists are suggesting that DNA could help break the impasse.

Their proposed detector consists of a 1-metre-square sheet of gold foil and a "forest" of single-strand DNA molecules suspended beneath in an ordered array, like the bristles on a toothbrush. When a WIMP strikes a gold atom in the foil, it would dislodge a gold nucleus and send it careening through the array, severing the DNA strands along its path. Energetic particles like cosmic rays have been shown to collide with and break strands of DNA, though WIMPs would have much lower energy.

The broken DNA strands would be gathered, amplified and analysed to determine exactly where each strand was severed. Given that the sequence of bases that make up each DNA strand is well known, the location of the cut on each strand ? and hence the path of the gold nucleus ? could be tracked to within a nanometre in three dimensions, around 1000 times better resolution than current detectors.

"The higher resolution means that we would get more data per WIMP event," says team member George Church of Harvard University.

Such 3D resolution would allow cosmologists to infer the both the energy and the direction of a WIMP, which could in turn confirm the existence of the predicted "WIMP wind" created by the solar system's motion through the galaxy.

A DNA-based detector has other advantages too, the team claims. It can operate at room temperature, as opposed to near absolute zero for current detectors. And by changing the material of the foil, it can be tuned to look for particles of different energies, including the WIMPs apparently detected by CoGeNT and DAMA/LIBRA. The team is now testing the feasibility of the design.

CoGeNT team member Juan Collar at the University of Chicago, who is not involved with the proposal, says a DNA-based WIMP detector is intriguing. "Directional detection of dark matter is the holy grail in our field," he says.

Reference: arXiv:1206.6809v1

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