Axion Gone: New tests find no sign of anomalous particle

Last year, physicists reported seeing tantalizing experimental traces of the axion, a hypothetical subatomic particle that’s been mentioned as a possible constituent of cosmic dark matter. But the axion was showing up where theory said it shouldn’t be. It now looks as if it wasn’t there after all.

The axion sprang from an attempt to explain certain differences between the strong and weak nuclear forces.