Dark reader dark
The team hypothesized that the high probability of the decay could be explained if a state in boron-11 existed as a doorway to another decay, to beryllium-10 and a proton. It looked like the beryllium-11's loosely bound neutron was ejecting an electron like normal beta decay, yet the beryllium wasn't following the known decay path to boron. And they did find a decay with unexpectedly high probability, but it wasn't a dark decay. In 2019, the researchers launched an experiment at Canada's national particle accelerator facility, TRIUMF, looking for that very hypothetical decay. This transforms the nucleus into a stable form of the element boron with five protons and six neutrons, boron-11.īut according to that very hypothetical theory, if the neutron that decays is the one in the halo, beryllium-11 could go an entirely different route: It could undergo a dark decay. One of its neutrons ejects an electron and becomes a proton. After a lifetime of about 13.8 seconds, it falls apart by what's known as beta decay. But one neutron floats far away from that core, loosely bound to the rest of the nucleus, kind of like the moon ringing around the Earth, Ayyad said.īeryllium-11 is also unstable.
It keeps 10 of those 11 nuclear particles in a tight central cluster. It's a form, or isotope, of the element beryllium that has four protons and seven neutrons in its nucleus.
But nuclei can take on strange shapes, including what are known as halo nuclei.īeryllium-11 is an example of a halo nuclei. When people imagine a nucleus, many may think of a lumpy ball made up of protons and neutrons, Ayyad said. The researchers had a good chance of discovering something new. But the gamble wasn't as big as it sounds because probing exotic decays also lets researchers better understand the rules and structures of the nuclear and quantum worlds. So Ayyad, Mittig and their team designed an experiment that could look for a dark decay, knowing the odds were against them. It posited that certain unstable nuclei, nuclei that naturally fall apart, could jettison dark matter as they crumbled. This theory centered on what it calls a dark decay. "But there was a theory, a very hypothetical idea, that you could observe dark matter with a very particular type of nucleus," said Ayyad, who was previously a detector systems physicist at NSCL. "None of them has succeeded after 20, 30, 40 years of research," he said. Speaking in round numbers, scientists have launched about 100 experiments to try to illuminate what exactly dark matter is, Mittig said. In doing so, they also revealed interesting physics that's afoot in the ultra-small quantum realm of subatomic particles. Working at NSCL, the team found a new path to their unexpected destination, which they detailed June 28 in the journal Physical Review Letters. Mittig, Ayyad and their colleagues bolstered their case at the National Superconducting Cyclotron Laboratory, or NSCL, at Michigan State University. So the team got back to work, doing more experiments, gathering more evidence to make their discovery make sense. "Instead, we found other things that have been challenging for theory to explain." "We started out looking for dark matter and we didn't find it," he said. "It's been something like a detective story," said Mittig, a Hannah Distinguished Professor in Michigan State University's Department of Physics and Astronomy and a faculty member at the Facility for Rare Isotope Beams, or FRIB. Well, at least an explanation that everyone could agree on. Their expedition didn't lead them to dark matter, but they still found something that had never been seen before, something that defied explanation.