Dark matter is one of the biggest mysteries in science. We don’t know what it is or if it even exists, but it's the best theory we have. So far, it has eluded detection, but a new tech could be crucial in looking for the lighter potential dark matter particles.
The new detector design was proposed by the US Department of Energy's Lawrence Berkeley National Laboratory (Berkely Lab) and uses crystals of gallium arsenide that contain silicon and boron. The system is designed to emit a flash of light when one of its electrons is knocked away by a particle of dark matter. The approach is described in the Journal of Applied Physics.
The experiment will look for dark matter particles that are lighter than protons. These particles would be thousands of times lighter than the ones that could be seen by current detectors.
"It's hard to imagine a better material for searching in this particular mass range," lead author Stephen Derenzo, from the Berkely Lab, said in a statement. "It ticks all of the boxes. We are always worried about a 'Gotcha!' or showstopper. But I have tried to think of some way this detector material can fail and I can't."
The material is nothing new, but scientists had no idea just how useful it could be for this kind of task. The gallium arsenide crystals can be grown in a way that makes them large in size and extremely pure, and adding silicon and boron, two standard "dopants", makes their scintillation a lot brighter. Dopants are used to change the electrical characteristics of semiconductors and other technologies.
Derenzo was given the sample by Edith Bourret, a senior scientist at Berkley. "If she hadn't handed me this sample from more than 20 years ago, I don't think I would have pursued it," he said. "When this material is doped with silicon and boron, this turns out to be very important and, accidentally, a very good choice of dopants."
Dark Matter detectors tend to focus on WIMPs, weakly interacting massive particles, the heavier end of the spectrum for potential dark matter particles. These experiments, such as LUX-ZEPLIN, focus on spotting potential interactions between dark matter and atomic nuclei, rather than electrons. We don’t yet know whether dark matter interacts more with nuclei or electrons, so using both approaches is very important.
"These would be complementary experiments," said Derenzo, referring to the many approaches. "We need to look at all of the possible mass ranges. You don't want to be fooled. You can't exclude a mass range if you don't look there."
Dark matter forms up to 85 percent of all matter in the universe and has helped to explain several of its observed features.