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Could Particle X Explain Dark Matter? Scientists Have a Plan

Scientists from Britain and Germany say a surprisingly light subatomic particle could account for the part of the universe's mass that we can't see.

What is dark matter? Scientists from Britain and Germany say an as-yet-undetected subatomic particle could help account for the 80 percent of the universe's mass that we can't see. This theoretical particle X (actually, the Greek letter "chi") would have a mass in the range of 100 electron volts, which is about 0.02 percent of an electron's mass. In an open-access paper published by Scientific Reports, the researchers say particle X "would have been missed by all experiments so far," but might be detectable in space.

If the particle exists, the scientists say an matter-wave interferometry experiment proposed by the Macroscopic Quantum Resonators Consortium, or MAQRO, could find it. The experiment involves suspending an observable particle in space, exposing it somehow to the flow of dark matter, and then using optical equipment to track whether collisions with the unseen X particles change its position in a predictable way.

"Our candidate particle sounds crazy, but currently there seem to be no experiments or observations which could rule it out," University of Southampton astrophysicist James Bateman said in a news release.

Particle X would be a dark horse in the race to find dark matter: Other physicists have suggested other scenarios, involving types of exotic stuff ranging from axions to neutralinos.



— Alan Boyle

In addition to Bateman, the authors of "On the Existence of Low-Mass Dark Matter and Its Direct Detection" include Ian McHardy, Alexander Merle, Tim Morris and Hendrik Ulbricht.