How to build a dark matter detector out of DNA and gold

Dark matter makes up about 84% of the universe, which is strange, since we have no idea what it is and we've never seen any of it before. A new type of directional dark matter detector has the potential to spot the signature of dark matter coming from the center of our galaxy, and it's made out of customized strands of DNA and sheets of solid gold.

Most astrophysicists think that dark matter is made up of weakly interacting massive particles, or WIMPs. WIMPs don't absorb or emit electromagnetic radiation, and they don't carry a charge. They're actually a lot like neutrinos, able to pass straight through normal matter most of the time, except while you've got about a hundred billion neutrinos passing through your fingernail every second, dark matter WIMPs are far less common.

Theoretically, the way to go about detecting a WIMP is the same way we try to detect neutrinos: you put a bunch of atoms together into a big mass and hope you get lucky and that a neutrino will run into a nucleus, creating a detectable burst of energy. With neutrinos, we use things like giant underground caves full of water, but with dark matter, a little more finesse is required.

A team of biologists and astrophysicists from the University of Michigan and Harvard University have come up with a way of detecting dark matter particles using a combination of customized strands of DNA and gold. The detector starts off with a thin, horizontal gold sheet, from which are hung an inverted "forest" of long strands of DNA, sort of like a bunch of beaded curtains all hung next to each other. Each DNA strand is identical, except for a little tag at the bottom containing a unique code that identifies where on the sheet the strand is hanging from. Beneath the sheet and the DNA forest is a collection tray. The whole thing sort of looks like this:

wimp_dna.jpg

When a WIMP strikes a gold nucleus in the sheet on top of the detector, the nucleus will be sent flying into the forest of DNA strands below, As the gold nucleus plows through the DNA, it severs the strands, the ends of which fall down into the collection tray. When the severed DNA is later collected, researchers can read the codes on the ends of the strands to figure out where the strands were located, and by measuring how much of the strand remains, they can work out the trajectory that the gold nucleus was traveling on, and therefore figure out which direction the WIMP came from in the first place.

The final version of the detector will use a whole bunch of these sheets all stacked on top of each other (to make it more sensitive while filtering out cosmic rays and background radiation), and even though a detector the size of a brick would need about a kilogram of solid gold, it would still be much cheaper to build and operate than any other WIMP detector with similar capabilities.

So, why is it so important to get all of this detailed directional info about WIMPs? Well, the theory about WIMPs is that they're flying at us from one single location: the center of our galaxy. If this is true, the apparent direction that WIMPs arrive in should change as the Earth orbits the sun, and even throughout the day as the Earth rotates on its axis. Since the detector is highly directional, using it to measure WIMP impacts over days and months should result in a cyclical signal that would say "yes, for the first time ever, we're definitely detecting dark matter."

arXiv, via Tech Review

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