Huge Physics Anomaly Finally Put to Test, But That Just Makes it More Confusing

Ten years ago, physicists discovered an anomaly that was dubbed the “ATOMKI anomaly”. The decays of certain atomic nuclei disagreed with our current understanding of physics. Particle physicists assigned the anomaly to a new particle, X17, often described as a fifth force. The anomaly was now tested by a follow-up experiment, but this is only the latest twist in a rather confusing story.