Thinking small: New ideas in the search for dark matter

So researchers at Caltech, led by Kathryn Zurek, a professor of theoretical physics, have gone again to the drafting board to consider new concepts. They’ve been wanting into the chance that darkish matter is made up of “hidden sector” particles, that are lighter than particles proposed beforehand, and will, in idea, be discovered utilizing small, underground table-top units. In distinction, scientists are trying to find heavier darkish matter candidates referred to as WIMPs (weakly interacting huge particles) utilizing large-scale experiments reminiscent of XENON, which is put in underground in a 70,000-gallon tank of water in Italy.

“Darkish matter is at all times flowing via us, even on this room” says Zurek, who first proposed hidden sector particles over a decade in the past. “As we transfer across the heart of the galaxy, this regular wind of darkish matter principally goes unnoticed. However we are able to nonetheless make the most of that supply of darkish matter, and design new methods to search for uncommon interactions between the darkish matter wind and the detector.”

In a brand new paper accepted for publication within the journal Bodily Overview Letters, the physicists define how the lighter-weight darkish matter particles might be detected by way of a kind of quasiparticle often called a magnon. A quasiparticle is an emergent phenomenon that happens when a stable behaves as if it accommodates weakly interacting particles. Magnons are a kind of quasiparticle wherein electron spins — which act like little magnets — are collectivity excited. Within the researchers’ thought for a table-top experiment, a magnetic crystalized materials can be used to search for indicators of excited magnons generated by darkish matter.

“If the darkish matter particles are lighter than the proton, it turns into very troublesome to detect their sign by standard means,” says research writer Zhengkang (Kevin) Zhang, a postdoctoral scholar at Caltech. “However, in keeping with many well-motivated fashions, particularly these involving hidden sectors, the darkish matter particles can couple to the spins of the electrons, such that when they strike the fabric, they are going to induce spin excitations, or magnons. If we cut back the background noise by cooling the tools and transferring it underground, we might hope to detect magnons generated solely by darkish matter and never odd matter.”

Such an experiment is just theoretical at this level however could ultimately happen utilizing small units housed underground, doubtless in a mine, the place outdoors influences from different particles, reminiscent of these in cosmic rays, will be minimized.

One telltale signal of a darkish matter detection within the table-top experiments can be adjustments to the sign that rely upon the time of day. This is because of the truth that the magnetic crystals that will be used to detect the darkish matter will be anisotropic, which means that the atoms are naturally organized in such a approach that they have an inclination to work together with the darkish matter extra strongly when the darkish matter is available in from sure instructions.

“As Earth strikes via the galactic darkish matter halo, it feels the darkish matter wind blowing from the course into which the planet is transferring. A detector mounted at a sure location on Earth rotates with the planet, so the darkish matter wind hits it from completely different instructions at completely different occasions of the day, say, generally from above, generally from the aspect,” says Zhang.

“Through the day, for instance, you could have the next detection price when the darkish matter comes from above than from the aspect. Should you noticed that, it could be fairly spectacular and a really sturdy indication that you just have been seeing darkish matter.”

The researchers produce other concepts about how darkish matter could reveal itself, along with via magnons. They’ve proposed that the lighter darkish matter particles might be detected by way of photons in addition to with one other kind of quasiparticle referred to as a phonon, which is brought on by vibrations in a crystal lattice. Preliminary experiments based mostly on photons and phonons are underway at UC Berkeley, the place the group was based mostly previous to Zurek becoming a member of the Caltech school in 2019. The researchers say that using these a number of methods to search for darkish matter is essential as a result of they complement one another and would assist verify one another’s outcomes.

“We’re wanting into new methods to search for darkish matter as a result of, given how little we find out about darkish matter, it is value contemplating all the probabilities,” says Zhang.